23.10.202327.05.2017

For safety and the ability to continue active activities in the dark, a person needs artificial lighting. Primitive people pushed back the darkness by setting fire to tree branches, then they came up with a torch and a kerosene stove. And only after the invention of the prototype of a modern battery by the French inventor Georges Leclanche in 1866, and the incandescent lamp in 1879 by Thomson Edison, did David Mizell have the opportunity to patent the first electric flashlight in 1896.

Since then, nothing has changed in the electrical circuit of new flashlight samples, until in 1923, Russian scientist Oleg Vladimirovich Losev found a connection between luminescence in silicon carbide and the p-n junction, and in 1990, scientists managed to create an LED with greater luminous efficiency, allowing them to replace a light bulb incandescent The use of LEDs instead of incandescent lamps, due to the low energy consumption of LEDs, has made it possible to repeatedly increase the operating time of flashlights with the same capacity of batteries and accumulators, increase the reliability of flashlights and practically remove all restrictions on the area of their use.

The LED rechargeable flashlight that you see in the photograph came to me for repair with a complaint that the Chinese Lentel GL01 flashlight I bought the other day for $3 does not light, although the battery charge indicator is on.

The external inspection of the lantern made a positive impression. High-quality casting of the case, comfortable handle and switch. The plug rods for connecting to a household network for charging the battery are made retractable, eliminating the need to store the power cord.

Attention! When disassembling and repairing the flashlight, if it is connected to the network, you should be careful. Touching unprotected parts of your body to uninsulated wires and parts may result in electric shock.

How to disassemble the Lentel GL01 LED rechargeable flashlight

Although the flashlight was subject to warranty repair, remembering my experiences during the warranty repair of a faulty electric kettle (the kettle was expensive and the heating element in it burned out, so it was not possible to repair it with my own hands), I decided to do the repair myself.

It was easy to disassemble the lantern. It is enough to turn the ring that secures the protective glass a small angle counterclockwise and pull it off, then unscrew several screws. It turned out that the ring is fixed to the body using a bayonet connection.

After removing one of the halves of the flashlight body, access to all its components appeared. On the left in the photo you can see a printed circuit board with LEDs, to which a reflector (light reflector) is attached using three screws. In the center there is a black battery with unknown parameters; there is only a marking of the polarity of the terminals. To the right of the battery there is a printed circuit board for the charger and indication. On the right is a power plug with retractable rods.

Upon closer examination of the LEDs, it turned out that there were black spots or dots on the emitting surfaces of the crystals of all LEDs. It became clear even without checking the LEDs with a multimeter that the flashlight did not light due to their burnout.

There were also blackened areas on the crystals of two LEDs installed as backlight on the battery charging indication board. In LED lamps and strips, one LED usually fails, and acting as a fuse, it protects the others from burning out. And all nine LEDs in the flashlight failed at the same time. The voltage on the battery could not increase to a value that could damage the LEDs. To find out the reason, I had to draw an electrical circuit diagram.

Finding the cause of the flashlight failure

The electrical circuit of the flashlight consists of two functionally complete parts. The part of the circuit located to the left of switch SA1 acts as a charger. And the part of the circuit shown to the right of the switch provides the glow.

The charger works as follows. The voltage from the 220 V household network is supplied to the current-limiting capacitor C1, then to a bridge rectifier assembled on diodes VD1-VD4. From the rectifier, voltage is supplied to the battery terminals. Resistor R1 serves to discharge the capacitor after removing the flashlight plug from the network. This prevents electric shock from capacitor discharge in the event of your hand accidentally touching two pins of the plug at the same time.

LED HL1, connected in series with current-limiting resistor R2 in the opposite direction with the upper right diode of the bridge, as it turns out, always lights up when the plug is inserted into the network, even if the battery is faulty or disconnected from the circuit.

The operating mode switch SA1 is used to connect separate groups of LEDs to the battery. As you can see from the diagram, it turns out that if the flashlight is connected to the network for charging and the switch slide is in position 3 or 4, then the voltage from the battery charger also goes to the LEDs.

If a person turns on the flashlight and discovers that it does not work, and, not knowing that the switch slide must be set to the “off” position, about which nothing is said in the flashlight’s operating instructions, connects the flashlight to the network for charging, then at the expense If there is a voltage surge at the output of the charger, the LEDs will receive a voltage significantly higher than the calculated one. A current that exceeds the permissible current will flow through the LEDs and they will burn out. As an acid battery ages due to sulfation of the lead plates, the battery charge voltage increases, which also leads to LED burnout.

Another circuit solution that surprised me was the parallel connection of seven LEDs, which is unacceptable, since the current-voltage characteristics of even LEDs of the same type are different and therefore the current passing through the LEDs will also not be the same. For this reason, when choosing the value of resistor R4 based on the maximum permissible current flowing through the LEDs, one of them may overload and fail, and this will lead to an overcurrent of parallel-connected LEDs, and they will also burn out.

Rework (modernization) of the electrical circuit of the flashlight

It became obvious that the failure of the flashlight was due to errors made by the developers of its electrical circuit diagram. To repair the flashlight and prevent it from breaking again, you need to redo it, replacing the LEDs and making minor changes to the electrical circuit.

In order for the battery charge indicator to actually signal that it is charging, the HL1 LED must be connected in series with the battery. To light an LED, a current of several milliamps is required, and the current supplied by the charger should be about 100 mA.

To ensure these conditions, it is enough to disconnect the HL1-R2 chain from the circuit in the places indicated by red crosses and install an additional resistor Rd with a nominal value of 47 Ohms and a power of at least 0.5 W in parallel with it. The charge current flowing through Rd will create a voltage drop of about 3 V across it, which will provide the necessary current for the HL1 indicator to light. At the same time, the connection point between HL1 and Rd must be connected to pin 1 of switch SA1. In this simple way, it will be impossible to supply voltage from the charger to the LEDs EL1-EL10 while charging the battery.

To equalize the magnitude of the currents flowing through the LEDs EL3-EL10, it is necessary to exclude resistor R4 from the circuit and connect a separate resistor with a nominal value of 47-56 Ohms in series with each LED.

Electrical diagram after modification

Minor changes made to the circuit increased the information content of the charge indicator of an inexpensive Chinese LED flashlight and greatly increased its reliability. I hope that LED flashlight manufacturers will make changes to the electrical circuits of their products after reading this article.

After modernization, the electrical circuit diagram took the form as in the drawing above. If you need to illuminate the flashlight for a long time and do not require high brightness of its glow, you can additionally install a current-limiting resistor R5, thanks to which the operating time of the flashlight without recharging will double.

LED battery flashlight repair

After disassembly, the first thing you need to do is restore the functionality of the flashlight, and then start upgrading it.

Checking the LEDs with a multimeter confirmed that they were faulty. Therefore, all the LEDs had to be desoldered and the holes freed from solder to install new diodes.

Judging by its appearance, the board was equipped with tube LEDs from the HL-508H series with a diameter of 5 mm. LEDs of type HK5H4U from a linear LED lamp with similar technical characteristics were available. They came in handy for repairing the lantern. When soldering LEDs to the board, you must remember to observe polarity; the anode must be connected to the positive terminal of the battery or battery.

After replacing the LEDs, the PCB was connected to the circuit. The brightness of some LEDs was slightly different from others due to the common current-limiting resistor. To eliminate this drawback, it is necessary to remove resistor R4 and replace it with seven resistors, connected in series with each LED.

To select a resistor that ensures optimal operation of the LED, the dependence of the current flowing through the LED on the value of the series-connected resistance was measured at a voltage of 3.6 V, equal to the voltage of the flashlight battery.

Based on the conditions for using the flashlight (in case of interruptions in the power supply to the apartment), high brightness and illumination range were not required, so the resistor was chosen with a nominal value of 56 Ohms. With such a current-limiting resistor, the LED will operate in light mode, and energy consumption will be economical. If you need to squeeze out maximum brightness from the flashlight, then you should use a resistor, as can be seen from the table, with a nominal value of 33 Ohms and make two modes of operation of the flashlight by turning on another common current-limiting resistor (in the diagram R5) with a nominal value of 5.6 Ohms.

To connect a resistor in series with each LED, you must first prepare the printed circuit board. To do this, you need to cut any one current-carrying path on it, suitable for each LED, and make additional contact pads. The current-carrying paths on the board are protected by a layer of varnish, which must be scraped off with a knife blade to the copper, as in the photograph. Then tin the bare contact pads with solder.

It is better and more convenient to prepare a printed circuit board for mounting resistors and soldering them if the board is mounted on a standard reflector. In this case, the surface of the LED lenses will not be scratched, and it will be more convenient to work.

Connecting the diode board after repair and modernization to the flashlight battery showed that the brightness of all LEDs was sufficient for illumination and the same brightness.

Before I had time to repair the previous lamp, the second one was repaired, with the same fault. I didn’t find any information about the manufacturer or technical specifications on the flashlight body, but judging by the manufacturing style and the cause of the breakdown, the manufacturer is the same, Chinese Lentel.

Based on the date on the flashlight body and on the battery, it was possible to establish that the flashlight was already four years old and, according to its owner, the flashlight worked flawlessly. It is obvious that the flashlight lasted a long time thanks to the warning sign “Do not turn on while charging!” on a hinged lid covering a compartment in which a plug is hidden for connecting the flashlight to the mains for charging the battery.

In this flashlight model, the LEDs are included in the circuit according to the rules; a 33 Ohm resistor is installed in series with each one. The resistor value can be easily recognized by color coding using an online calculator. A check with a multimeter showed that all the LEDs were faulty, and the resistors were also broken.

An analysis of the cause of the failure of the LEDs showed that due to sulfation of the acid battery plates, its internal resistance increased and, as a result, its charging voltage increased several times. During charging, the flashlight was turned on, the current through the LEDs and resistors exceeded the limit, which led to their failure. I had to replace not only the LEDs, but also all the resistors. Based on the above-mentioned operating conditions of the flashlight, resistors with a nominal value of 47 Ohms were chosen for replacement. The resistor value for any type of LED can be calculated using an online calculator.

Redesign of the battery charging mode indication circuit

The flashlight has been repaired, and you can begin making changes to the battery charging indication circuit. To do this, it is necessary to cut the track on the printed circuit board of the charger and indication in such a way that the HL1-R2 chain on the LED side is disconnected from the circuit.

The lead-acid AGM battery was deeply discharged, and an attempt to charge it with a standard charger was unsuccessful. I had to charge the battery using a stationary power supply with a load current limiting function. A voltage of 30 V was applied to the battery, while at the first moment it consumed only a few mA of current. Over time, the current began to increase and after a few hours increased to 100 mA. After fully charging, the battery was installed in the flashlight.

Charging deeply discharged lead-acid AGM batteries with increased voltage as a result of long-term storage allows you to restore their functionality. I have tested the method on AGM batteries more than a dozen times. New batteries that do not want to be charged from standard chargers are restored to almost their original capacity when charged from a constant source at a voltage of 30 V.

The battery was discharged several times by turning on the flashlight in operating mode and charged using a standard charger. The measured charge current was 123 mA, with a voltage at the battery terminals of 6.9 V. Unfortunately, the battery was worn out and was enough to operate the flashlight for 2 hours. That is, the battery capacity was about 0.2 Ah and for long-term operation of the flashlight it is necessary to replace it.

The HL1-R2 chain on the printed circuit board was successfully placed, and it was necessary to cut only one current-carrying path at an angle, as in the photograph. The cutting width must be at least 1 mm. Calculation of the resistor value and testing in practice showed that for stable operation of the battery charging indicator, a 47 Ohm resistor with a power of at least 0.5 W is required.

The photo shows a printed circuit board with a soldered current-limiting resistor. After this modification, the battery charge indicator lights up only if the battery is actually charging.

Modernization of the operating mode switch

To complete the repair and modernization of the lights, it is necessary to resolder the wires at the switch terminals.

In models of flashlights being repaired, a four-position slide-type switch is used to turn on. The middle pin in the photo shown is general. When the switch slide is in the extreme left position, the common terminal is connected to the left terminal of the switch. When moving the switch slide from the extreme left position to one position to the right, its common pin is connected to the second pin and, with further movement of the slide, sequentially to pins 4 and 5.

To the middle common terminal (see photo above) you need to solder a wire coming from the positive terminal of the battery. Thus, it will be possible to connect the battery to a charger or LEDs. To the first pin you can solder the wire coming from the main board with LEDs, to the second you can solder a current-limiting resistor R5 of 5.6 Ohms to be able to switch the flashlight to an energy-saving operating mode. Solder the conductor coming from the charger to the rightmost pin. This will prevent you from turning on the flashlight while the battery is charging.

Repair and modernization
LED rechargeable spotlight "Foton PB-0303"

I received another copy of a series of Chinese-made LED flashlights called the Photon PB-0303 LED spotlight for repair. The flashlight did not respond when the power button was pressed; an attempt to charge the flashlight battery using a charger was unsuccessful.

The flashlight is powerful, expensive, costs about $20. According to the manufacturer, the luminous flux of the flashlight reaches 200 meters, the body is made of impact-resistant ABS plastic, and the kit includes a separate charger and a shoulder strap.

The Photon LED flashlight has good maintainability. To gain access to the electrical circuit, simply unscrew the plastic ring holding the protective glass, rotating the ring counterclockwise when looking at the LEDs.

When repairing any electrical appliances, troubleshooting always starts with the power source. Therefore, the first step was to measure the voltage at the terminals of the acid battery using a multimeter turned on in mode. It was 2.3 V, instead of the required 4.4 V. The battery was completely discharged.

When connecting the charger, the voltage at the battery terminals did not change, it became obvious that the charger was not working. The flashlight was used until the battery was completely discharged, and then it was not used for a long time, which led to a deep discharge of the battery.

It remains to check the serviceability of the LEDs and other elements. To do this, the reflector was removed, for which six screws were unscrewed. On the printed circuit board there were only three LEDs, a chip (chip) in the form of a droplet, a transistor and a diode.

Five wires went from the board and battery into the handle. In order to understand their connection, it was necessary to disassemble it. To do this, use a Phillips screwdriver to unscrew the two screws inside the flashlight, which were located next to the hole into which the wires went.

To detach the flashlight handle from its body, it must be moved away from the mounting screws. This must be done carefully so as not to tear the wires off the board.

As it turned out, there were no radio-electronic elements in the pen. Two white wires were soldered to the terminals of the flashlight on/off button, and the rest to the connector for connecting the charger. A red wire was soldered to pin 1 of the connector (the numbering is conditional), the other end of which was soldered to the positive input of the printed circuit board. A blue-white conductor was soldered to the second contact, the other end of which was soldered to the negative pad of the printed circuit board. A green wire was soldered to pin 3, the second end of which was soldered to the negative terminal of the battery.

Electrical circuit diagram

Having dealt with the wires hidden in the handle, you can draw an electrical circuit diagram of the Photon flashlight.

From the negative terminal of the battery GB1, voltage is supplied to pin 3 of connector X1 and then from its pin 2 through a blue-white conductor it is supplied to the printed circuit board.

Connector X1 is designed in such a way that when the charger plug is not inserted into it, pins 2 and 3 are connected to each other. When the plug is inserted, pins 2 and 3 are disconnected. This ensures automatic disconnection of the electronic part of the circuit from the charger, eliminating the possibility of accidentally turning on the flashlight while charging the battery.

From the positive terminal of battery GB1, voltage is supplied to D1 (microcircuit-chip) and the emitter of a bipolar transistor type S8550. The CHIP performs only the function of a trigger, allowing a button to turn on or off the glow of EL LEDs (⌀8 mm, glow color - white, power 0.5 W, current consumption 100 mA, voltage drop 3 V.). When you first press the S1 button from the D1 chip, a positive voltage is applied to the base of the transistor Q1, it opens and the supply voltage is supplied to the LEDs EL1-EL3, the flashlight turns on. When you press button S1 again, the transistor closes and the flashlight turns off.

From a technical point of view, such a circuit solution is illiterate, since it increases the cost of the flashlight, reduces its reliability, and in addition, due to the voltage drop at the junction of transistor Q1, up to 20% of the battery capacity is lost. Such a circuit solution is justified if it is possible to adjust the brightness of the light beam. In this model, instead of a button, it was enough to install a mechanical switch.

It was surprising that in the circuit, LEDs EL1-EL3 are connected in parallel to the battery like incandescent light bulbs, without current-limiting elements. As a result, when turned on, a current passes through the LEDs, the magnitude of which is limited only by the internal resistance of the battery and when it is fully charged, the current may exceed the permissible value for the LEDs, which will lead to their failure.

Checking the functionality of the electrical circuit

To check the serviceability of the microcircuit, transistor and LEDs, a 4.4 V DC voltage was applied from an external power source with a current limiting function, maintaining polarity, directly to the power pins of the printed circuit board. The current limit value was set to 0.5 A.

After pressing the power button, the LEDs lit up. After pressing again, they went out. The LEDs and the microcircuit with the transistor turned out to be serviceable. All that remains is to figure out the battery and charger.

Acid battery recovery

Since the 1.7 A acid battery was completely discharged, and the standard charger was faulty, I decided to charge it from a stationary power supply. When connecting the battery for charging to a power supply with a set voltage of 9 V, the charging current was less than 1 mA. The voltage was increased to 30 V - the current increased to 5 mA, and after an hour at this voltage it was already 44 mA. Next, the voltage was reduced to 12 V, the current dropped to 7 mA. After 12 hours of charging the battery at a voltage of 12 V, the current rose to 100 mA, and the battery was charged with this current for 15 hours.

The temperature of the battery case was within normal limits, which indicated that the charging current was not used to generate heat, but to accumulate energy. After charging the battery and finalizing the circuit, which will be discussed below, tests were carried out. The flashlight with a restored battery illuminated continuously for 16 hours, after which the brightness of the beam began to decrease and therefore it was turned off.

Using the method described above, I had to repeatedly restore the functionality of deeply discharged small-sized acid batteries. As practice has shown, only serviceable batteries that have been forgotten for some time can be restored. Acid batteries that have exhausted their service life cannot be restored.

Charger repair

Measuring the voltage value with a multimeter at the contacts of the output connector of the charger showed its absence.

Judging by the sticker pasted on the adapter body, it was a power supply that outputs an unstabilized DC voltage of 12 V with a maximum load current of 0.5 A. There were no elements in the electrical circuit that limited the amount of charging current, so the question arose, why in the quality charger, did you use a regular power supply?

When the adapter was opened, a characteristic smell of burnt electrical wiring appeared, which indicated that the transformer winding had burned out.

A continuity test of the primary winding of the transformer showed that it was broken. After cutting the first layer of tape insulating the primary winding of the transformer, a thermal fuse was discovered, designed for an operating temperature of 130°C. Testing showed that both the primary winding and the thermal fuse were faulty.

Repairing the adapter was not economically feasible, since it was necessary to rewind the primary winding of the transformer and install a new thermal fuse. I replaced it with a similar one that was on hand, with a DC voltage of 9 V. The flexible cord with a connector had to be resoldered from a burnt adapter.

The photo shows a drawing of the electrical circuit of a burnt-out power supply (adapter) of the Photon LED flashlight. The replacement adapter was assembled according to the same scheme, only with an output voltage of 9 V. This voltage is quite sufficient to provide the required battery charging current with a voltage of 4.4 V.

Just for fun, I connected the flashlight to a new power supply and measured the charging current. Its value was 620 mA, and this was at a voltage of 9 V. At a voltage of 12 V, the current was about 900 mA, significantly exceeding the load capacity of the adapter and the recommended battery charging current. For this reason, the primary winding of the transformer burned out due to overheating.

Finalization of the electrical circuit diagram
LED rechargeable flashlight "Photon"

To eliminate circuit violations in order to ensure reliable and long-term operation, changes were made to the flashlight circuit and the printed circuit board was modified.

The photo shows the electrical circuit diagram of the converted Photon LED flashlight. Additional installed radio elements are shown in blue. Resistor R2 limits the battery charging current to 120 mA. To increase the charging current, you need to reduce the resistor value. Resistors R3-R5 limit and equalize the current flowing through the LEDs EL1-EL3 when the flashlight is illuminated. The EL4 LED with a series-connected current-limiting resistor R1 is installed to indicate the battery charging process, since the developers of the flashlight did not take care of this.

To install current-limiting resistors on the board, the printed traces were cut, as shown in the photo. The charge current-limiting resistor R2 was soldered at one end to the contact pad, to which the positive wire coming from the charger had previously been soldered, and the soldered wire was soldered to the second terminal of the resistor. An additional wire (yellow in the photo) was soldered to the same contact pad, intended to connect the battery charging indicator.

Resistor R1 and indicator LED EL4 were placed in the flashlight handle, next to the connector for connecting the charger X1. The LED anode pin was soldered to pin 1 of connector X1, and a current-limiting resistor R1 was soldered to the second pin, the cathode of the LED. A wire (yellow in the photo) was soldered to the second terminal of the resistor, connecting it to the terminal of resistor R2, soldered to the printed circuit board. Resistor R2, for ease of installation, could have been placed in the flashlight handle, but since it heats up when charging, I decided to place it in a freer space.

When finalizing the circuit, MLT type resistors with a power of 0.25 W were used, except for R2, which is designed for 0.5 W. The EL4 LED is suitable for any type and color of light.

This photo shows the charging indicator while the battery is charging. Installing an indicator made it possible not only to monitor the battery charging process, but also to monitor the presence of voltage in the network, the health of the power supply and the reliability of its connection.

How to replace a burnt out CHIP

If suddenly a CHIP - a specialized unmarked microcircuit in a Photon LED flashlight, or a similar one assembled according to a similar circuit - fails, then to restore the flashlight's functionality it can be successfully replaced with a mechanical switch.

To do this, you need to remove the D1 chip from the board, and instead of the Q1 transistor switch, connect an ordinary mechanical switch, as shown in the above electrical diagram. The switch on the flashlight body can be installed instead of the S1 button or in any other suitable place.

Repair and alteration of LED flashlight
14Led Smartbuy Colorado

The Smartbuy Colorado LED flashlight stopped turning on, although three new AAA batteries were installed.

The waterproof body was made of anodized aluminum alloy and had a length of 12 cm. The flashlight looked stylish and was easy to use.

How to check batteries for suitability in an LED flashlight

Repair of any electrical device begins with checking the power source, therefore, despite the fact that new batteries were installed in the flashlight, repairs should begin with checking them. In the Smartbuy flashlight, the batteries are installed in a special container, in which they are connected in series using jumpers. In order to gain access to the flashlight batteries, you need to disassemble it by rotating the back cover counterclockwise.

Batteries must be installed in the container, observing the polarity indicated on it. The polarity is also indicated on the container, so it must be inserted into the flashlight body with the side on which the “+” sign is marked.

First of all, it is necessary to visually check all contacts of the container. If there are traces of oxides on them, then the contacts must be cleaned to a shine using sandpaper or the oxide must be scraped off with a knife blade. To prevent re-oxidation of the contacts, they can be lubricated with a thin layer of any machine oil.

Next you need to check the suitability of the batteries. To do this, touching the probes of a multimeter turned on in DC voltage measurement mode, you need to measure the voltage at the contacts of the container. Three batteries are connected in series and each of them should produce a voltage of 1.5 V, therefore the voltage at the terminals of the container should be 4.5 V.

If the voltage is less than specified, then it is necessary to check the correct polarity of the batteries in the container and measure the voltage of each of them individually. Perhaps only one of them sat down.

If everything is in order with the batteries, then you need to insert the container into the flashlight body, observing the polarity, screw on the cap and check its functionality. In this case, you need to pay attention to the spring in the cover, through which the supply voltage is transmitted to the flashlight body and from it directly to the LEDs. There should be no traces of corrosion on its end.

How to check if the switch is working properly

If the batteries are good and the contacts are clean, but the LEDs do not light, then you need to check the switch.

The Smartbuy Colorado flashlight has a sealed push-button switch with two fixed positions, closing the wire coming from the positive terminal of the battery container. When you press the switch button for the first time, its contacts close, and when you press it again, they open.

Since the flashlight contains batteries, you can also check the switch using a multimeter turned on in voltmeter mode. To do this, you need to rotate it counterclockwise, if you look at the LEDs, unscrew its front part and put it aside. Next, touch the body of the flashlight with one multimeter probe, and with the second touch the contact, which is located deep in the center of the plastic part shown in the photo.

The voltmeter should show a voltage of 4.5 V. If there is no voltage, press the switch button. If it is working properly, then voltage will appear. Otherwise, the switch needs to be repaired.

Checking the health of the LEDs

If the previous search steps failed to detect a fault, then at the next stage you need to check the reliability of the contacts supplying the supply voltage to the board with LEDs, the reliability of their soldering and serviceability.

A printed circuit board with LEDs sealed into it is fixed in the head of the flashlight using a steel spring-loaded ring, through which the supply voltage from the negative terminal of the battery container is simultaneously supplied to the LEDs along the flashlight body. The photo shows the ring from the side it presses against the printed circuit board.

The retaining ring is fixed quite tightly, and it was only possible to remove it using the device shown in the photo. You can bend such a hook from a steel strip with your own hands.

After removing the retaining ring, the printed circuit board with LEDs, which is shown in the photo, was easily removed from the head of the flashlight. The absence of current-limiting resistors immediately caught my eye; all 14 LEDs were connected in parallel and directly to the batteries via a switch. Connecting LEDs directly to a battery is unacceptable, since the amount of current flowing through the LEDs is limited only by the internal resistance of the batteries and can damage the LEDs. At best, it will greatly reduce their service life.

Since all the LEDs in the flashlight were connected in parallel, it was not possible to check them with a multimeter turned on in resistance measurement mode. Therefore, the printed circuit board was supplied with a DC supply voltage from an external source of 4.5 V with a current limit of 200 mA. All LEDs lit up. It became obvious that the problem with the flashlight was poor contact between the printed circuit board and the retaining ring.

Current consumption of LED flashlight

For fun, I measured the current consumption of LEDs from batteries when they were turned on without a current-limiting resistor.

The current was more than 627 mA. The flashlight is equipped with LEDs of type HL-508H, the operating current of which should not exceed 20 mA. 14 LEDs are connected in parallel, therefore, the total current consumption should not exceed 280 mA. Thus, the current flowing through the LEDs more than doubled the rated current.

Such a forced mode of LED operation is unacceptable, as it leads to overheating of the crystal, and as a result, premature failure of the LEDs. An additional disadvantage is that the batteries drain quickly. They will be enough, if the LEDs do not burn out first, for no more than an hour of operation.

The design of the flashlight did not allow soldering current-limiting resistors in series with each LED, so we had to install one common one for all LEDs. The resistor value had to be determined experimentally. To do this, the flashlight was powered by pants batteries and an ammeter was connected to the gap in the positive wire in series with a 5.1 Ohm resistor. The current was about 200 mA. When installing an 8.2 Ohm resistor, the current consumption was 160 mA, which, as tests showed, is quite sufficient for good lighting at a distance of at least 5 meters. The resistor did not get hot to the touch, so any power will do.

Redesign of the structure

After the study, it became obvious that for reliable and durable operation of the flashlight, it is necessary to additionally install a current-limiting resistor and duplicate the connection of the printed circuit board with the LEDs and the fixing ring with an additional conductor.

If previously it was necessary for the negative bus of the printed circuit board to touch the body of the flashlight, then due to the installation of the resistor, it was necessary to eliminate the contact. To do this, a corner was ground off from the printed circuit board along its entire circumference, from the side of the current-carrying paths, using a needle file.

To prevent the clamping ring from touching the current-carrying tracks when fixing the printed circuit board, four rubber insulators about two millimeters thick were glued onto it with Moment glue, as shown in the photograph. Insulators can be made from any dielectric material, such as plastic or thick cardboard.

The resistor was pre-soldered to the clamping ring, and a piece of wire was soldered to the outermost track of the printed circuit board. An insulating tube was placed over the conductor, and then the wire was soldered to the second terminal of the resistor.

After simply upgrading the flashlight with your own hands, it began to turn on stably and the light beam illuminated objects well at a distance of more than eight meters. Additionally, the battery life has more than tripled, and the reliability of the LEDs has increased many times over.

An analysis of the causes of failure of repaired Chinese LED lights showed that they all failed due to poorly designed electrical circuits. It remains only to find out whether this was done intentionally in order to save on components and shorten the life of the flashlights (so that more people would buy new ones), or as a result of the illiteracy of the developers. I am inclined to the first assumption.

Repair of LED flashlight RED 110

A flashlight with a built-in acid battery from the Chinese manufacturer RED brand was repaired. The flashlight had two emitters: one with a beam in the form of a narrow beam and one emitting diffused light.

The photo shows the appearance of the RED 110 flashlight. I immediately liked the flashlight. Convenient body shape, two operating modes, a loop for hanging around the neck, a retractable plug for connecting to the mains for charging. In the flashlight, the diffused light LED section was shining, but the narrow beam was not.

To make the repair, we first unscrewed the black ring securing the reflector, and then unscrewed one self-tapping screw in the hinge area. The case easily separated into two halves. All parts were secured with self-tapping screws and were easily removed.

The charger circuit was made according to the classical scheme. From the network, through a current-limiting capacitor with a capacity of 1 μF, voltage was supplied to a rectifier bridge of four diodes and then to the battery terminals. The voltage from the battery to the narrow beam LED was supplied through a 460 Ohm current-limiting resistor.

All parts were mounted on a single-sided printed circuit board. The wires were soldered directly to the contact pads. The appearance of the printed circuit board is shown in the photograph.

10 side light LEDs were connected in parallel. The supply voltage was supplied to them through a common current-limiting resistor 3R3 (3.3 Ohms), although according to the rules, a separate resistor must be installed for each LED.

During an external inspection of the narrow beam LED, no defects were found. When power was supplied through the flashlight switch from the battery, voltage was present at the LED terminals, and it heated up. It became obvious that the crystal was broken, and this was confirmed by a continuity test with a multimeter. The resistance was 46 ohms for any connection of the probes to the LED terminals. The LED was faulty and needed to be replaced.

For ease of operation, the wires were unsoldered from the LED board. After freeing the LED leads from the solder, it turned out that the LED was tightly held by the entire plane of the reverse side on the printed circuit board. To separate it, we had to fix the board in the desktop temples. Next, place the sharp end of the knife at the junction of the LED and the board and lightly hit the knife handle with a hammer. The LED bounced off.

As usual, there were no markings on the LED housing. Therefore, it was necessary to determine its parameters and select a suitable replacement. Based on the overall dimensions of the LED, the battery voltage and the size of the current-limiting resistor, it was determined that a 1 W LED (current 350 mA, voltage drop 3 V) would be suitable for replacement. From the “Reference Table of Parameters of Popular SMD LEDs,” a white LED6000Am1W-A120 LED was selected for repair.

The printed circuit board on which the LED is installed is made of aluminum and at the same time serves to remove heat from the LED. Therefore, when installing it, it is necessary to ensure good thermal contact due to the tight fit of the rear plane of the LED to the printed circuit board. To do this, before sealing, thermal paste was applied to the contact areas of the surfaces, which is used when installing a radiator on a computer processor.

In order to ensure a tight fit of the LED plane to the board, you must first place it on the plane and slightly bend the leads upward so that they deviate from the plane by 0.5 mm. Next, tin the terminals with solder, apply thermal paste and install the LED on the board. Next, press it to the board (it’s convenient to do this with a screwdriver with the bit removed) and warm up the leads with a soldering iron. Next, remove the screwdriver, press it with a knife at the bend of the lead to the board and heat it with a soldering iron. After the solder has hardened, remove the knife. Due to the spring properties of the leads, the LED will be pressed tightly to the board.

When installing the LED, polarity must be observed. True, in this case, if a mistake is made, it will be possible to swap the voltage supply wires. The LED is soldered and you can check its operation and measure the current consumption and voltage drop.

The current flowing through the LED was 250 mA, the voltage drop was 3.2 V. Hence the power consumption (you need to multiply the current by the voltage) was 0.8 W. It was possible to increase the operating current of the LED by decreasing the resistance to 460 Ohms, but I did not do this, since the brightness of the glow was sufficient. But the LED will operate in a lighter mode, heat up less, and the flashlight’s operating time on a single charge will increase.

Checking the heating of the LED after operating for an hour showed effective heat dissipation. It heated up to a temperature of no more than 45°C. Sea trials showed a sufficient illumination range in the dark, more than 30 meters.

Replacing a lead acid battery in an LED flashlight

A failed acid battery in an LED flashlight can be replaced with either a similar acid battery or a lithium-ion (Li-ion) or nickel-metal hydride (Ni-MH) AA or AAA battery.

The Chinese lanterns being repaired were equipped with lead-acid AGM batteries of various sizes without markings with a voltage of 3.6 V. According to calculations, the capacity of these batteries ranges from 1.2 to 2 A×hours.

On sale you can find a similar acid battery from a Russian manufacturer for the 4V 1Ah Delta DT 401 UPS, which has an output voltage of 4 V with a capacity of 1 Ah, costing a couple of dollars. To replace it, simply re-solder the two wires, observing the polarity.

When purchasing or assembling new LED flashlights, you should definitely pay attention to the LED used. If you are purchasing a lantern only to illuminate a dark street, then there is a huge choice - choose any one with a bright white LED. But if you want to buy a portable lighting device with characteristics for more complex tasks, the important point here is the choice of the appropriate luminous flux, that is, the ability of the device to illuminate a large space with a powerful beam.

Main characteristics

LEDs are responsible for the quality of light that the flashlight emits. The stability of lighting depends on many characteristics, including current consumption, light flux and color temperature. Among the trendsetters, it is worth noting the company Cree; in its assortment you can find very bright LEDs for flashlights.

Modern pocket models are created using a single LED, the power of which reaches 1, 2, or 3 W. The indicated electrical characteristics are the properties of various LED models from well-known brands. The intensity of the light rays or luminous flux is an indicator that depends on the type of LED and the manufacturer. The manufacturer also indicates the number of lumens in the characteristics.

This indicator directly correlates with the color temperature of the light. Light-emitting diodes can produce up to 200 lumens per watt and are produced today in different temperatures to glow: warm yellowish or cool white.

Lanterns with a warm white tint produce a pleasant light to the human eye, but they are less bright. Light with a neutral color temperature effectively allows the smallest elements to be seen. Cool white lighting is usually typical for models with a huge beam range, but can irritate the eyes during prolonged use.

If the temperature reaches approximately 50 °C, then the life of the crystal can be up to 200,000 hours, but this is not justified from an economic point of view. For this reason, many companies produce products that can withstand operating temperatures of up to 85 °C, while saving on cooling costs. If the temperature exceeds 150 °C, the equipment may completely fail.

The color rendering index is a qualitative indicator that characterizes the ability of an LED to illuminate a space without distorting the actual shade. LEDs for flashlights with a color rendering source characteristic of 75 CRI or more are a good option. An important element of the LED is the lens, thanks to which the angle of dispersion of the light fluxes is set, that is, the range of the beam is determined.

In any technical specification of an LED, the angle of radiation must be noted. For any of the models, this characteristic is considered individual and usually varies in the range from 20 to 240 degrees. High-power LED flashlights have an angle of approximately 120°C and generally include a reflector and an additional lens.

Although today we can see a strong leap in the production of high-power LEDs consisting of multiple crystals, global brands are still producing LEDs with lower power. They are produced in a small case that does not exceed 10 mm in width. In a comparative analysis, one can notice that one such powerful crystal has a less reliable circuit and dispersion angle than a pair of similar elements simultaneously in a single housing.

It would not be amiss to recall the four-pin “SuperFlux” LEDs, the so-called “piranha”. These flashlight LEDs have improved specifications. The piranha LED has the following main advantages:

the light flux is distributed evenly;
no need to remove heat;
lower price.

Types of LEDs

There are many flashlights with improved features available in the market today. The most popular LEDs are from Cree Inc.: XR-E, XP-E, XP-G, XM-L. Today the latest XP-E2, XP-G2, XM-L2 are also popular - they are mainly used in small flashlights. But, for example, Cree MT-G2 and MK-R LEDs from Luminus are widely used in huge models of search lights that can operate simultaneously from a pair of batteries.

In addition, LEDs are usually distinguished by brightness - there is a special code thanks to which you can sort LEDs by this parameter.

When comparing some diodes with others, it is worth paying attention to their dimensions, or rather, to the area of the light-emitting crystals. If the area of such a crystal is small, then it is easier to concentrate its light into a narrow beam. If you want to get a narrow beam from XM-L LEDs, you will need to use a very large reflector, which negatively affects the weight and dimensions of the housing. But with small reflectors on such an LED, a fairly effective pocket flashlight will come out.

Application area of LEDs

Mostly, when choosing flashlights, consumers choose models with the maximum beam of light, but in many cases they do not need this option. In many cases, such equipment is used to illuminate a nearby area or an object that is no more than 10,000 m away. A long-range flashlight shines at 100 m, although in many cases with a rather narrow beam that poorly illuminates the surrounding area. As a result, when illuminating a distant object with such lighting devices, the user will not notice those objects that are located in close proximity to him.

Let's look at a comparison of the tonality of light produced by LEDs: warm, neutral and cold. When selecting the appropriate flashlight light temperature, the following important points must be taken into account: LEDs with a warm glow can minimally distort the color of the illuminated objects, but they have lower brightness than neutral-spectrum LEDs.

When choosing a powerful search or tactical flashlight, where the brightness of the device is an important point, it is recommended to select an LED with a cold spectrum of light. If a flashlight is needed for everyday life, tourism purposes, or for use in a head-mounted model, then proper color rendering is important, which means LEDs with warm light will be more advantageous. A neutral LED is the golden mean in all respects.

Not taking into account the cheapest flashlights, which only have a single button, many flashlights have a couple of operating modes, including strobe and SOS modes. The non-brand model has the following operating options: the highest power rating, medium power and “strobe”. In addition, the average power is basically equal to 50% of the highest brightness of the light, and the lowest is 10%.

Branded models have a more complex structure. Here you can control the operating mode using a button, rotating the “head”, turning the magnetic rings and a combination of all of the above.

Boruit heavy duty headlamp. For lighting during fishing, hunting and household work.

Flashlights powered by a single 1.5-volt battery typically consist of a battery, a button, and an incandescent bulb. The light bulb is a light source with a fairly low efficiency and quickly drains the battery. It's tempting to use LEDs in miniature flashlights, but the problem of powering them inevitably arises. As you know, an LED requires about 3.6 volts to operate. Therefore, LED flashlights usually run on 3 1.5V batteries. In this case, the batteries can provide enough current to operate an impressive number of LEDs. But at the same time the dimensions of the flashlight also increase. You can use small prismatic batteries, but their capacity is relatively small and clearly insufficient for a flashlight.

Is it possible to make a flashlight with at least one LED that could run on one 1.5 battery or rechargeable battery? Of course you can. The principle of powering the LED here is very simple: we use the inductor as an energy storage device from the battery. To do this, we need an elementary circuit, which includes a pulse generator, a switch and, in fact, a choke. We will tell you how to assemble such a unit yourself in the continuation of this article, but for now we will analyze a ready-made flashlight made in China.

The flashlight is quite small and convenient, but it is not without some disadvantages. First of all, it is thicker than necessary. It is about twice as thick as a battery. This space inside is not used in any way; there are only stiffening ribs there. For this flashlight this is completely unnecessary. The flashlight has a rather weak LED. But still, the undeniable advantage of this flashlight is the presence inside of a converter for powering the LED from one 1.5-volt AAA battery, which works exactly according to the principle discussed above - storing energy in the inductor and then releasing it to the LED.

In this modification, we will replace the LED with a more powerful one, and also provide the ability to replace the LED with any other without disassembling the flashlight.

First you need to disassemble the flashlight. To do this, you need to remove the back cover and remove the metal ring using a thin screwdriver. The front part of the flashlight is secured with glue; to detach it, you need to go along the seam with a thin knife.

The insides of the flashlight can then be easily removed. The metal petal extends down to the negative terminal of the battery.

The flashlight board is secured with two small bolts that need to be unscrewed.

Remove the flashlight board. The circuit is notable for the presence of a microcontroller filled with compound. The on/off button is just that, a button, without locking. A transistor marked 2100A is also installed, which could not be identified. In addition to these parts, there are: a Schottky diode, a capacitor and a choke.

We unsolder the LED and install a kind of “connector” for the new LED - two collets from the socket for microcircuits. They need to be carefully soldered to the inside of the board.

Solder the first collet:

And the second:

Top view of the board:

For testing, a 5mm diameter LED with a 20cd warm white glow was installed.

We check the functionality and continue. We install an LED with a diameter of 8mm at 20cd into the resulting connector.

We assemble the flashlight in reverse order.

The flashlight shines much brighter.

Screw on the cap with the lens.

In order to secure the front part (which was originally attached with glue), we use a small bolt.

What have radio amateurs come up with so far in order to power a bright white LED from one AA or AAA battery? Alas, the circuit solutions are quite modest. Basically, it all comes down to the blocking generator. The disadvantage of such schemes is obvious: when the battery is discharged, the brightness of the LED will decrease.

Of course, it is imperative to assemble such circuits - for training and testing their properties.

After this, you can move on to designing your own ideal flashlight.

The design of our “ideal” flashlight is very simple, technologically advanced and modern. A special ZXLD381 chip is used to power the bright white LED.

The circuit diagram for connecting the microcircuit is typical, from the datasheet. The inductance of the inductor is matched to the existing LED. In this case, you need to look in the datasheet at the inductor to see how much current it can withstand without entering saturation.

Checking the circuit. Since the LED in this circuit is the largest element, the remaining parts (ZXLD381 chip and inductor) are soldered to it.

The ZXLD381 chip is soldered directly to the inductor pads.

The parts fit into a suitable small flashlight with one battery.

To build a flashlight powered by a battery with a voltage greater than 1.5V, you can use the ZXSC400 chip, which has the ability to connect a more powerful LED.

When choosing or assembling a new LED flashlight, be sure to pay attention to the LED used. If the only task of the future flashlight is to illuminate a dark entrance, then almost any bright white LED will cope with this task. Another thing is the desire to get a portable lighting device with parameters for a more complex task. In this case, the luminous flux is of particular importance, that is, the ability of the flashlight to produce a sufficiently powerful beam and illuminate a wide area of space.

Which LED brands are in the top positions, and what characteristics do their light-emitting diodes used in flashlights have?

Main characteristics

The quality of light emitted by the flashlight is controlled by the LED, which can be called, without exaggeration, the heart of the device. The stability of a flashlight's heart rate depends on many parameters, the main ones being current consumption, luminous flux and color temperature. The trendsetter is considered to be the Cree company, which produces a wide line of super-bright and powerful LEDs, including for flashlights. Modern flashlights are designed with a single LED with a power of 1, 2, or 3 W. In the one-watt version, the forward current is about 350 mA with a voltage drop of 2.8-2.9 V.

The current and voltage of a two-watt LED is about 700 mA and 3.0 V, respectively, and a similar 3 W crystal consumes approximately 1000 mA and 3.2 V. The electrical indicators given are typical for LED models of the world's leading brands.

The radiation intensity, also called luminous flux, depends on the manufacturer and family of the LED. The rated value of the luminous flux of high-power LEDs is usually measured at the maximum permissible operating current. The manufacturer of branded flashlights, along with the type of LED installed, indicates the number of lumens produced by the product.

Unfortunately, flashlight packaging often indicates inflated characteristics, including luminous flux. The reason for this is simple - any manufacturer wants to sell as much product as possible.

Luminous flux is inextricably linked with light. Modern light-emitting diodes are capable of emitting a luminous flux of up to 200 lumens per 1 watt and can be produced with any glow temperature: from yellowish warm to cool white. Lanterns with a warm white emission color (T≤3500°K) are the most pleasing to the eye, but less bright. Lighting with a neutral color temperature (T=4000-5500°K) allows you to view fine details more effectively. Cool white beam (T≥6500°K) in powerful flashlights with a long illumination range, but irritates the eyes during prolonged use.
Due to the impossibility of making accurate calculations, the lifespan of LEDs is calculated by extrapolation. At a temperature of 25-50 °C, their crystal service life can exceed 200 thousand hours, but this is not economically justified. Therefore, manufacturers allow the operating temperature to increase to 85°C, thus saving on cooling costs. Exceeding the threshold of 150°C leads to irreversible processes of crystal burnout and loss of brightness.

Color rendering index (CRI) is a qualitative indicator characterizing the ability of an LED to illuminate objects without distorting their real color. For LED lighting sources, including flashlights, a color rendering index of 75 CRI or higher is considered good.

An important element of an LED is the lens. It sets the angle of dispersion of the light flux, and therefore determines the range of the beam. The technical characteristics of LEDs must indicate the value of the radiation angle. For each model, this parameter is individual and can vary from 20 to 240 degrees. Powerful LEDs for flashlights have an angle of 90-120° and, as a rule, are equipped with a reflector with an additional lens in the housing.

Despite the sharp leap in the development of high-power multi-chip LEDs, world leaders continue to produce less powerful LEDs. They are produced in small cases, not exceeding 10 mm in width or diameter. The typical current value of such light-emitting diodes does not exceed 70 mA, and the luminous flux is 50 lm. Powerful flashlights based on them are gradually disappearing from store shelves due to worse technical characteristics and the need for series-parallel connection to increase brightness. Compared to one powerful crystal, the reliability of the circuit and the dispersion angle of several such elements in one package are much worse.

Separately, it is worth noting the four-pin LEDs in the P4 “SuperFlux” or “Piranha” package, which have improved technical characteristics. Piranha LEDs have two important advantages that make them in demand:

distribute the light flux more evenly;
do not require heat removal;
have low cost.

5 largest manufacturers

A portable flashlight must not only be ergonomic, but also be equipped with a reliable LED source with a high working life without loss of brightness. In order not to make a mistake with your choice, preference should be given to world-class manufacturers of LED products.

A division of the Japanese company Nichia has long held a leading position in the production of LEDs of all types. Due to the high cost of products and increasing competition from China and Taiwan, today it is becoming increasingly rare to find their LEDs in flashlights on the European market. However, the world needs Nichia as an engine of progress. After all, the developments of Japanese companies are taken as a basis by their Chinese and Taiwanese colleagues.
Powerful LEDs for flashlights from the world-famous company Cree hold the lead not only on the American continent. Standing out due to their lower cost and high quality, LEDs from Cree are available to everyone on the European continent. A rechargeable flashlight with a powerful crystal from an American brand is a reliable friend on a hike, night fishing, etc.
Philips Lumileds is a European manufacturer of wide-spectrum light-emitting diodes. The company has achieved certain progress in the construction of outdoor lighting systems of functional and architectural significance. Philips Lumileds developers take an integrated approach to building LED systems, taking into account their design, degree of protection and ease of use.
The South Korean corporation Samsung, well known in Russia, promptly financed its division to search for new LED solutions and now has a full production cycle of emitting diodes. Samsung is not limited to producing LED backlights for its own displays. Their successes have spread to other market segments: high-power LEDs (including for flashlights), ultra-bright flash elements, as well as indoor and outdoor lighting modules.
Osram Opto Semiconductors has become famous for the excellent characteristics of LEDs from the Duris series, which are distinguished by their high luminous efficiency and color rendering index. The German company has relied on the introduction of LED technologies into industrial sectors, focusing on the production of ready-made specialized lamps and fixtures. Osram laboratories improve the performance of light-emitting diodes not only in the visible spectrum, but also make discoveries in the IR, UV and laser directions.

Scientific reports coupled with news about the development of artificial lighting indicate continued healthy competition between large corporations. We see positive trends in the development of LED technology in the constantly updated range of flashlights, surprising with their long-range beam, high degree of protection, ability to charge from solar energy and other know-how.

Making a modern flashlight

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Rice. 1. Schematic diagram of a current stabilizer

Using the pulse current stabilizer circuit (Fig. 1), long known in amateur radio circles, using modern affordable radio components, you can assemble a very good LED flashlight.

For modification and alteration, the author purchased a mongrel flashlight with a 6 V 4 Ah battery, a “spotlight” on a 4.8 V 0.75 A lamp and a diffused light source on a 4 W LDS. The “original” incandescent light bulb almost immediately turned black due to operation at too high a voltage and failed after several hours of operation. A full battery charge was enough for 4-4.5 hours of operation. Turning on the LDS generally loaded the battery with a current of about 2.5 A, which led to its discharge after 1-1.5 hours.

To improve the flashlight, white LEDs of an unknown brand were purchased on the radio market: one with a beam divergence of 30o and an operating current of 100 mA for the “spotlight”, as well as a dozen matte LEDs with an operating current of 20 mA to replace the LDS. According to the scheme (Fig. 1), a stable current generator was assembled with an efficiency of about 90%. The circuitry of the stabilizer made it possible to use a standard switch to switch the LEDs. The LED2 indicated in the diagram is a battery of 10 parallel connected identical white LEDs, each rated for a current of 20 mA. Parallel connection of LEDs does not seem entirely advisable due to the nonlinearity and steepness of their current-voltage characteristics, but experience has shown that the spread of LED parameters is so small that even with such a connection their operating currents are almost the same. What is important is the complete identity of the LEDs; if possible, they should be purchased “from the same factory packaging.”

After modification, the “spotlight” of course became a little weaker, but it was quite sufficient, the diffused light mode did not visually change. But now, thanks to the high efficiency of the current stabilizer, when using the directional mode, a current of 70 mA is consumed from the battery, and in the diffuse mode, mA, that is, the flashlight can work without recharging for about 50 or 25 hours, respectively. Brightness does not depend on the degree of discharge of the battery due to current stabilization.

The current stabilizer circuit works as follows: When power is applied to the circuit, transistors T1 and T2 are locked, T3 is open, because an unlocking voltage is applied to its gate through resistor R3. Due to the presence of inductor L1 in the LED circuit, the current increases smoothly. As the current in the LED circuit increases, the voltage drop across the R5-R4 chain increases; as soon as it reaches approximately 0.4 V, transistor T2 will open, followed by T1, which in turn will close the current switch T3. The increase in current stops, a self-induction current appears in the inductor, which begins to flow through diode D1 through the LED and a chain of resistors R5-R4. As soon as the current decreases below a certain threshold, transistors T1 and T2 will close, T3 will open, which will lead to a new cycle of energy accumulation in the inductor. In normal mode, the oscillatory process occurs at a frequency of the order of tens of kilohertz.

About the details: there are no special requirements for the parts; you can use any small-sized resistors and capacitors. Instead of the IRF510 transistor, you can use the IRF530, or any n-channel field-effect switching transistor with a current of more than 3 A and a voltage of more than 30 V. Diode D1 must be equipped with a Schottky barrier for a current of more than 1 A; if you install even a regular high-frequency type KD212, the efficiency will decrease up to 75-80%. The inductor can be homemade; it is wound with a wire no thinner than 0.6 mm, or better - a bundle of several thinner wires. About 20-30 turns of wire per armor core B16-B18 are required with a non-magnetic gap of 0.1-0.2 mm or close from 2000NM ferrite. If possible, the thickness of the non-magnetic gap is selected experimentally according to the maximum efficiency of the device. Good results can be obtained with ferrites from imported inductors installed in switching power supplies and also in energy-saving lamps. Such cores have the appearance of a spool of thread and do not require a frame or a non-magnetic gap. Coils on toroidal cores made of pressed iron powder, which can be found in computer power supplies (the output filter inductors are wound on them), work very well. The non-magnetic gap in such cores is evenly distributed throughout the volume due to the production technology.

The same stabilizer circuit can be used in conjunction with other batteries and galvanic cell batteries with a voltage of 9 or 12 volts without any change in the circuit or cell ratings. The higher the supply voltage, the less current the flashlight will consume from the source, its efficiency will remain unchanged. The operating stabilization current is set by resistors R4 and R5. If necessary, the current can be increased to 1 A without the use of heat sinks on the parts, only by selecting the resistance of the setting resistors.

The battery charger can be left “original” or assembled according to any of the known schemes, or even used externally to reduce the weight of the flashlight.

The device is assembled by hanging installation in the free cavities of the flashlight body and filled with hot-melt adhesive for sealing.

It’s also a good idea to add a new device to the flashlight: a battery charge indicator (Fig. 2).

Rice. 2. Schematic diagram of the battery charge level indicator.

The device is essentially a voltmeter with a discrete LED scale. This voltmeter has two operating modes: in the first, it estimates the voltage on the battery being discharged, and in the second, the voltage on the battery being charged. Therefore, in order to correctly assess the degree of charge, different voltage ranges were selected for these operating modes. In the discharge mode, the battery can be considered fully charged when the voltage on it is 6.3 V, when it is completely discharged, the voltage will drop to 5.9 V. In the process of charging the voltages are different, a battery is considered fully charged if the voltage at the terminals is 7, 4 V. In connection with this, an algorithm for the operation of the indicator has been developed: if the charger is not connected, that is, at the “+ Charge” terminal there is no voltage, the “orange” crystals of the two-color LEDs are de-energized and transistor T1 is locked. DA1 generates the reference voltage determined by resistor R8. The reference voltage is supplied to a line of comparators OP1.1 - OP1.4, on which the voltmeter itself is implemented. To see how much charge is left in the battery, you need to press the S1 button. In this case, supply voltage will be supplied to the entire circuit and, depending on the voltage on the battery, a certain number of green LEDs will light up. When fully charged, the entire column of 5 green LEDs will light up; when completely discharged, only one, the lowest LED, will light up. If necessary, the voltage is adjusted by selecting the resistance of resistor R8. If the charger is turned on, through the “+ Charge” terminal and diode D1 supplies voltage to the circuit, including the “orange” parts of the LEDs. In addition, T1 opens and connects resistor R9 in parallel with resistor R8, as a result of which the reference voltage generated by DA1 increases, which leads to a change in the operating thresholds of the comparators - the voltmeter is adjusted to a higher voltage. In this mode, all the time the battery is charging, the indicator displays the charging process also with a column of glowing LEDs, only this time the column is orange.

Homemade LED flashlight

The article is dedicated to radio amateur tourists, and to everyone who has in one way or another encountered the problem of an economical lighting source (for example, a tent at night). Although LED flashlights have not surprised anyone lately, I will still share my experience in creating such a device, and will also try to answer questions from those who want to repeat the design.

Note: The article is intended for “advanced” radio amateurs who are well aware of Ohm’s law and have held a soldering iron in their hands.

The basis was a purchased flashlight "VARTA" powered by two AA batteries:

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Here's what the assembled diagram looks like:

The reference points are the legs of the DIP chip.

A few explanations to the diagram: Electrolytic capacitors - tantalum CHIP. They have low series resistance, which slightly improves efficiency. Schottky diode - SM5818. The chokes had to be connected in parallel, because there was no suitable rating. Capacitor C2 - K10-17b. LEDs - super bright white L-53PWC "Kingbright". As can be seen in the figure, the entire circuit easily fits into the empty space of the light-emitting unit.
The output voltage of the stabilizer in this connection circuit is 3.3V. Since the voltage drop across the diodes in the nominal current range (15-30mA) is about 3.1V, the extra 200mV had to be sown on a resistor connected in series with the output. In addition, a small series resistor improves load linearity and circuit stability. This is due to the fact that the diode has a negative TCR, and when warmed up, its forward voltage drop decreases, which leads to a sharp increase in the current through the diode when it is powered from a voltage source. There was no need to equalize the currents through parallel-connected diodes - no differences in brightness were observed by eye. Moreover, the diodes were of the same type and taken from the same box.
Now about the design of the light emitter. Perhaps this is the most interesting detail. As can be seen in the photographs, the LEDs in the circuit are not tightly sealed, but are a removable part of the structure. I decided to do this in order not to screw up the flashlight, and if necessary, I could insert an ordinary light bulb into it. As a result of much thought about killing two birds with one stone, this design was born:

I think that no special explanation is required here. The original light bulb from the same flashlight is gutted, 4 cuts are made in the flange on 4 sides (one was already there). 4 LEDs are arranged symmetrically in a circle with some splay for a larger coverage angle (I had to file them a little at the base). The positive terminals (as it turned out according to the diagram) are soldered onto the base near the cuts, and the negative terminals are inserted from the inside into the central hole of the base, cut off and also soldered. The result is such a “lampodiode”, which takes the place of an ordinary incandescent light bulb.

And finally, about the test results. Half-dead batteries were taken for testing in order to quickly bring them to the finish line and understand what the newly made flashlight is capable of. The battery voltage, load voltage, and load current were measured. The run started with a battery voltage of 2.5V, at which the LEDs no longer light up directly. Stabilization of the output voltage (3.3V) continued until the supply voltage was reduced to ~1.2V. The load current was about 100mA (~ 25mA per diode). Then the output voltage began to decrease smoothly. The circuit has switched to a different operating mode, in which it no longer stabilizes, but outputs everything it can. In this mode, it worked up to a supply voltage of 0.5V! The output voltage dropped to 2.7V, and the current from 100mA to 8mA. The diodes were still on, but their brightness was only enough to illuminate the keyhole in the dark entrance. After this, the batteries practically stopped discharging, because the circuit stopped consuming current. After running the circuit in this mode for another 10 minutes, I became bored and turned it off, because further running was of no interest.

The brightness of the glow was compared with a conventional incandescent light bulb at the same power consumption. A 1V 0.068A light bulb was inserted into the flashlight, which at a voltage of 3.1V consumed approximately the same current as the LEDs (about 100mA). The result is clearly in favor of LEDs.

Part II. A little about efficiency or “There is no limit to perfection.”

More than a month has passed since I assembled my first circuit to power an LED flashlight and wrote about it in the above article. To my surprise, the topic turned out to be very popular, judging by the number of reviews and site visits. Since then I have gained some understanding of the subject :), and I considered it my duty to take the topic more seriously and conduct more thorough research. This idea was also brought to me by communication with people who solved similar problems. I would like to tell you about some new results.

Firstly, I should have immediately measured the efficiency of the circuit, which turned out to be suspiciously low (about 63% with fresh batteries). Secondly, I understood the main reason for such low efficiency. The fact is that those miniature chokes that I used in the circuit have an extremely high ohmic resistance - about 1.5 ohms. There could be no talk of saving electricity with such losses. Thirdly, I discovered that the amount of inductance and output capacitance also affects the efficiency, although not as noticeably.

I somehow didn’t want to use a rod choke of the DM type because of its large size, so I decided to make the choke myself. The idea is simple - you need a low-turn choke, wound with a relatively thick wire, and at the same time quite compact. The ideal solution turned out to be a ring made of µ-permalloy with a permeability of about 50. There are ready-made chokes on sale on such rings, widely used in all kinds of switching power supplies. I had at my disposal such a 10 μG choke, which has 15 turns on the K10x4x5 ring. There was no problem rewinding it. The inductance had to be selected based on the efficiency measurement. In the range of 40-90 µG the changes were very insignificant, less than 40 - more noticeable, and at 10 µG it became very bad. I did not raise it above 90 μH, because the ohmic resistance increased, and the thicker wire “inflated” the dimensions. In the end, more for aesthetic reasons, I settled on 40 turns of PEV-0.25 wire, since they lay evenly in one layer and the result was about 80 μG. The active resistance turned out to be about 0.2 ohms, and the saturation current, according to calculations, was more than 3A, which is enough for the eyes... I replaced the output (and at the same time the input) electrolyte with 100 μF, although without compromising the efficiency it can be reduced to 47 μF. As a result, the design has undergone some changes, which, however, did not prevent it from maintaining its compactness:

Laboratory work" href="/text/category/laboratornie_raboti/" rel="bookmark">laboratory work and took down the main characteristics of the scheme:

	1. Dependence of the output voltage measured on capacitor C3 on the input. I have taken this characteristic before and I can say that replacing the throttle with a better one gave a more horizontal plateau and a sharp break.
	2. It was also interesting to track the change in current consumption as the batteries discharged. The “negativity” of the input resistance, typical of key stabilizers, is clearly visible. The peak consumption occurred at a point close to the reference voltage of the microcircuit. A further drop in voltage led to a decrease in the support, and hence the output voltage. The sharp drop in current consumption on the left side of the graph is caused by the nonlinearity of the I-V characteristics of the diodes.
	3. And finally, the promised efficiency. Here it was measured by the final effect, i.e. by the power dissipation on the LEDs. (5 percent is lost on the ballast resistance). The chip manufacturers did not lie - with the correct design it gives the required 87%. True, this is only with fresh batteries. As the current consumption increases, the efficiency naturally decreases. At an extreme point, it generally drops to the level of a steam locomotive. An increase in efficiency with a further decrease in voltage is of no practical value, since the flashlight is already “on its last legs” and shines very weakly.

Looking at all these characteristics, we can say that the flashlight shines confidently when the supply voltage drops to 1V without a noticeable decrease in brightness, i.e. the circuit actually handles a three-fold voltage drop. An ordinary incandescent light bulb with such a discharge of batteries is unlikely to be suitable for lighting.

If something remains unclear to someone, write. I will respond by letter and/or add to this article.

Vladimir Rashchenko, E-mail: rashenko (at) inp. nsk. su

May, 2003.

Velofara - what's next?

So, first headlight built, tested and tested. What are the future promising directions for LED headlight manufacturing? The first stage will probably be a further increase in capacity. I am planning to build a 10-diode headlight with a switchable 5/10 operating mode. Well, further improvement of quality requires the use of complex microelectronic components. For example, it seems to me that it would be nice to get rid of quenching/equalizing resistors - after all, 30-40% of the energy is lost on them. And I would like to have current stabilization through LEDs, regardless of the discharge level of the source. The best option would be to sequentially switch on the entire chain of LEDs with current stabilization. And in order not to increase the number of series batteries, this circuit also needs to increase the voltage from 3 or 4.5 V to 20-25 V. These are, so to speak, specifications for the development of an “ideal headlight”.
It turned out that specialized ICs are produced specifically to solve such problems. Their area of application is controlling the backlight LEDs of LCD monitors for mobile devices - laptops. cell phones, etc. Dima brought me to this information gdt (at) *****- THANK YOU!

In particular, a line of ICs for various purposes for controlling LEDs is produced by Maxim (Maxim Integrated Products, Inc), on whose website ( http://www.) the article "Solutions for Driving White LEDs" (Apr 23, 2002) was found. Some of these "solutions" are great for bicycle lights:

https://pandia.ru/text/78/440/images/image015_32.gif" width="391" height="331 src=">

Option 1. MAX1848 chip, controlling a chain of 3 LEDs.

https://pandia.ru/text/78/440/images/image017_27.gif" width="477" height="342 src=">

Option 3: Another scheme for switching on feedback is possible - from a voltage divider.

https://pandia.ru/text/78/440/images/image019_21.gif" width="534" height="260 src=">

Option 5. Maximum power, multiple LED strings, MAX1698 chip

current mirror", chip MAX1916.

https://pandia.ru/text/78/440/images/image022_17.gif" width="464" height="184 src=">

Option 8. Chip MAX1759.

https://pandia.ru/text/78/440/images/image024_12.gif" width="496" height="194 src=">

Option 10. MAX619 chip - perhaps. the simplest connection scheme. Operation when the input voltage drops to 2 V. Load 50 mA at Uin>3 V.

https://pandia.ru/text/78/440/images/image026_15.gif" width="499" height="233 src=">

Option 12. The ADP1110 chip is rumored to be more common than MAXs, it works starting from Uin = 1.15 V ( !!! only one battery!!!) Uout. up to 12 V

https://pandia.ru/text/78/440/images/image028_15.gif" width="446" height="187 src=">

Option 14. Microcircuit LTC1044 - a very simple connection diagram, Uin = from 1.5 to 9 V; Uout = up to 9 V; load up to 200mA (but, however, typical 60 mA)

As you can see, all this looks very tempting :-) All that remains is to find these microcircuits inexpensively somewhere....

Hooray! Found ADP1rub. with VAT) We are building a new powerful headlight!

10 LEDs, switchable 6\10, five chains of two.

MAX1848 White LED Step-Up Converter to SOT23

MAX1916 Low-Dropout, Constant-Current Triple White LED Bias Supply

Display Drivers and Display Power Application Notes and Tutorials

Charge Pump Versus Inductor Boost Converter for White LED Backlights

Buck/Boost Charge-Pump Regulator Powers White LEDs from a Wide 1.6V to 5.5V Input

Analog ICs for 3V Systems

On the Rainbow Tech website: Maxim: DC-DC conversion devices(pivot table)

On the Premier Electric website: Pulse regulators and controllers for power supply without galvanics. interchanges(pivot table)

On the Averon website - microcircuits for power supplies(Analog Devices) - summary table

Powering LEDs with ZXSC300

Davidenko Yuri. Lugansk
Email address -
david_ukr (at) ***** (replace (at) with @)

The feasibility of using LEDs in flashlights, bicycle lights, and local and emergency lighting devices today is beyond doubt. The light output and power of LEDs is growing, and their prices are falling. There are more and more light sources that use white LEDs instead of the usual incandescent lamp and it is not difficult to buy them. Shops and markets are filled with LED products made in China. But the quality of these products leaves much to be desired. Therefore, there is a need to modernize affordable (primarily priced) LED light sources. Yes, and replacing incandescent lamps with LEDs in high-quality Soviet-made flashlights also makes sense. I hope that the following information will not be superfluous.

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As is known, an LED has a nonlinear current-voltage characteristic with a characteristic “heel” in the initial section.

Rice. 1 Volt-ampere characteristics of a white LED.

As we can see, the LED begins to glow if a voltage of more than 2.7 V is applied to it. When powered by a galvanic or rechargeable battery, the voltage of which gradually decreases during operation, the brightness of the radiation will vary widely. To avoid this, it is necessary to power the LED with a stabilized current. And the current must be rated for this type of LED. Typically for standard 5 mm LEDs it averages 20 mA.

For this reason, it is necessary to use electronic current stabilizers, which limit and stabilize the current flowing through the LED. It is often necessary to power an LED from one or two batteries with a voltage of 1.2 - 2.5 V. For this, step-up voltage converters are used. Since any LED is essentially a current device, from an energy efficiency standpoint it is advantageous to provide direct control of the current flowing through it. This eliminates losses that occur on the ballast (current-limiting) resistor.

One of the optimal options for powering various LEDs from autonomous current sources of low voltage 1-5 volts is to use a specialized ZXSC300 microcircuit from ZETEX. ZXSC300 is a pulsed (inductive) DC-DC boost converter with pulse frequency modulation.

Let's look at the operating principle of the ZXSC300.

On the image Fig.2 shows one of the typical schemes for powering a white LED with pulsed current using the ZXSC300. The pulsed power supply mode of the LED allows you to make the most efficient use of the energy available in the battery or accumulator.

In addition to the ZXSC300 microcircuit itself, the converter contains: a 1.5 V battery, a storage choke L1, a power switch - transistor VT1, a current sensor - R1.

The converter works in its traditional way. For some time, due to the pulse coming from generator G (via the driver), transistor VT1 is open and the current through inductor L1 increases linearly. The process lasts until the voltage drop across the current sensor - low-resistance resistor R1 reaches 19 mV. This voltage is enough to switch the comparator (the second input of which is supplied with a small reference voltage from the divider). The output voltage from the comparator is supplied to the generator, as a result of which the power switch VT1 closes and the energy accumulated in the inductor L1 enters the LED VD1. Then the process is repeated. Thus, fixed portions of energy are supplied to the LED from the primary power source, which it converts into light.

Energy management occurs using pulse-frequency modulation PFM (PFM Pulse Frequency Modulation). The principle of PFM is that the frequency changes, but the duration of the pulse or pause, respectively, the open (On-Time) and closed (Off-Time) state of the key remains constant. In our case, the Off-Time remains unchanged, i.e. the pulse duration at which the external transistor VT1 is in the closed state. For the ZXSC300 controller, Toff is 1.7 µs.

This time is enough to transfer the accumulated energy from the inductor to the LED. The duration of the pulse Ton, during which VT1 is open, is determined by the value of the current-measuring resistor R1, the input voltage, and the difference between the input and output voltage, and the energy that accumulates in the inductor L1 will depend on its value. It is considered optimal when the total period T is 5 µs (Toff + Ton). The corresponding operating frequency is F=1/5μs =200 kHz.

With the element ratings indicated in the diagram in Fig. 2, the oscillogram of the voltage pulses on the LED looks like

Fig.3 type of voltage pulses on the LED. (grid 1V/div, 1μs/div)

A little more detail about the parts used.

Transistor VT1 - FMMT617, n-p-n transistor with a guaranteed collector-emitter saturation voltage of no more than 100 mV at a collector current of 1 A. Capable of withstanding pulsed collector current up to 12 A (constant 3 A), collector-emitter voltage 18 V, coefficient current transmission 150...240. Dynamic characteristics of the transistor: on/off time 120/160 ns, f = 120 MHz, output capacitance 30 pF.

FMMT617 is the best switching device that can be used with ZXSC300. It allows you to obtain high conversion efficiency with an input voltage of less than one volt.

Storage choke L1.

Both industrial SMD Power Inductor and homemade ones can be used as a storage choke. Choke L1 must withstand the maximum current of power switch VT1 without saturating the magnetic circuit. The active resistance of the inductor winding should not exceed 0.1 Ohm, otherwise the efficiency of the converter will noticeably decrease. Ring magnetic cores (K10x4x5) from power filter chokes used in old computer motherboards are well suited as a core for self-winding. Today, used computer hardware can be purchased at bargain prices on any radio market. And hardware is an inexhaustible source of various parts for radio amateurs. When winding yourself, you will need an inductance meter for control.

Current measuring resistor R1. Low-resistance resistor R1 47 mOhm is obtained by parallel connection of two SMD resistors of standard size 1206, 0.1 Ohm each.

LED VD1.

White LED VD1 with a rated operating current of 150 mA. The author's design uses two four-crystal LEDs connected in parallel. The rated current of one of them is 100 mA, the other 60 mA. The operating current of the LED is determined by passing a stabilized direct current through it and monitoring the temperature of the cathode (negative) terminal, which is a radiator and removes heat from the crystal.

At the rated operating current, the temperature of the heat sink should not exceed degrees. Instead of one VD1 LED, you can also use eight standard 5 mm LEDs connected in parallel with a current of 20 mA.

Appearance of the device

Rice. 4a.

Rice. 4b.

Shown in Fig. 5

Rice. 5(size 14 by 17 mm).

When developing boards for such devices, it is necessary to strive for the minimum values of capacitance and inductance of the conductor connecting K VT1 with the storage choke and LED, as well as for the minimum inductance and active resistance of the input and output circuits and the common wire. The resistance of the contacts and wires through which the supply voltage is supplied should also be minimal.

In the following diagrams Fig. 6 and Fig. Figure 7 shows a method for powering high-power Luxeon type LEDs with a rated operating current of 350 mA

Rice. 6 Power supply method for high-power Luxeon LEDs

Rice. 7 The method of powering high-power LEDs of the Luxeon type - ZXSC300 is powered from the output voltage.

Unlike the previously discussed circuit, here the LED is powered not pulsed, but direct current. This makes it easy to control the operating current of the LED and the efficiency of the entire device. Feature of the converter in Fig. 7 is that ZXSC300 is powered by output voltage. This allows the ZXSC300 to operate (after startup) when the input voltage drops down to 0.5 V. The VD1 diode is a Schottky diode designed for a current of 2A. Capacitors C1 and C3 are ceramic SMD, C2 and C3 are tantalum SMD. Number of LEDs connected in series.

Resistance of the current measuring resistor, mOhm.

Inductance of storage choke, μH.

Today, powerful 3 - 5 W LEDs from various manufacturers (both famous and not so famous) have become available for use.

And in this case, the use of ZXSC300 makes it possible to easily solve the problem of efficiently powering LEDs with an operating current of 1 A or more.

It is convenient to use an n-channel (operating from 3 V) Power MOSFET as a power switch in this circuit; you can also use an assembly of the FETKY MOSFET series (with a Schottky diode in one SO-8 package).

With the ZXSC300 and a few LEDs, you can easily breathe new life into your old flashlight. The FAR-3 battery flashlight was modernized.

Fig.11

LEDs were used 4-crystal with a rated current of 100 mA - 6 pcs. Connected in series by 3. To control the light flux, two converters on the ZXSC300 are used, with independent on/off. Each converter operates on its own triple LED.

Fig.12

The converter boards are made on double-sided fiberglass, the second side is connected to the power supply minus.

Fig.13

Fig.14

The FAR-3 flashlight uses three sealed batteries NKGK-11D (KCSL 11) as batteries. The nominal voltage of this battery is 3.6 V. The final voltage of a discharged battery is 3 V (1 V per cell). Further discharge is undesirable because it will shorten the battery life. And further discharge is possible - the converters on the ZXSC300 operate, as we remember, down to 0.9 V.

Therefore, to control the voltage on the battery, a device was designed, the circuit of which is shown in Fig. 15.

Fig.15

This device uses inexpensive, readily available components. DA1 - LM393 is a well-known dual comparator. A reference voltage of 2.5 V is obtained using TL431 (analogue of KR142EN19). The response voltage of the comparator DA1.1, about 3 V, is set by the divider R2 - R3 (selection of these elements may be required for accurate operation). When the voltage on battery GB1 drops to 3 V, the red LED HL1 lights up, if the voltage is more than 3 V, then HL1 goes out and the green LED HL2 lights up. Resistor R4 determines the hysteresis of the comparator.

The control circuit board is shown in Rice. 16 ( size 34 by 20 mm).

If you have any difficulties purchasing the ZXSC300 microcircuit, FMMT617 transistor or low-resistance SMD resistors 0.1 Ohm, you can contact the author by e-mail david_ukr (at) *****

You can purchase the following components (delivery by mail)

Elements	Quantity	Price, $	Price, UAH
Chip ZXSC 300 + transistor FMMT 617
Resistor 0.1 Ohm SMD size 0805
Printed circuit board Fig. 8

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