Educational article on LED current stabilizers and more. The circuits of linear and pulse current stabilizers are considered.

The current stabilizer for the LED is installed in many luminaire designs. LEDs, like all diodes, have a non-linear current-voltage characteristic. This means that as the voltage across the LED changes, the current changes disproportionately. As the voltage increases, at first the current rises very slowly, while the LED does not light up. Then, when the threshold voltage is reached, the LED starts to glow and the current increases very quickly. With a further increase in voltage, the current increases catastrophically and the LED burns out.

The threshold voltage is specified in the LED specifications as a forward voltage at rated current. The current rating for most low power LEDs is 20 mA. For high power lighting LEDs, the current rating can be as high as 350mA or more. By the way, high-power LEDs generate heat and should be mounted on a heat sink.

For proper operation of the LED, it must be powered through a current stabilizer. For what? The fact is that the threshold voltage of the LED has a spread. Different types of LEDs have different forward voltages, even the same type of LEDs have different forward voltages - this is indicated in the LED characteristics as the minimum and maximum values. Therefore, two LEDs connected to the same voltage source in parallel will pass different currents. This current can be so different that the LED may fail earlier or burn out immediately. In addition, the voltage regulator also has parameter drift (depending on the primary power level, on load, on temperature, just in time). Therefore, turning on LEDs without current equalization devices is undesirable. Various methods of current equalization are considered. This article discusses devices that set a well-defined, given current - current stabilizers.

Types of current stabilizers

The current stabilizer sets the specified current through the LED, regardless of the voltage applied to the circuit. When the voltage on the circuit increases above the threshold level, the current reaches the set value and then does not change. With a further increase in the total voltage, the voltage on the LED stops changing, and the voltage on the current regulator increases.

Since the voltage on the LED is determined by its parameters and is generally unchanged, the current regulator can also be called the LED power regulator. In the simplest case, the active power (heat) released by the device is distributed between the LED and the stabilizer in proportion to the voltage on them. Such a stabilizer is called linear. There are also more economical devices - current stabilizers based on a pulse converter (switch converter or converter). They are called pulsed, because they pump power inside themselves in portions - pulses as needed for the consumer. The correct pulse converter consumes power continuously, internally transfers it with pulses from the input circuit to the output circuit and outputs power to the load again continuously.

Linear Current Stabilizer

The linear current regulator heats up the more, the more voltage is applied to it. This is its main drawback. However, it has a number of advantages, for example:

• Linear stabilizer does not create electromagnetic interference
• Simple in design
• Low cost in most applications

Since a switching converter is never completely efficient, there are applications where a linear regulator has comparable or even greater efficiency - when the input voltage is only slightly higher than the LED voltage. By the way, when powered from the mains, a transformer is often used, at the output of which a linear current stabilizer is installed. That is, first the voltage is reduced to a level comparable to the voltage on the LED, and then, using a linear stabilizer, the required current is set.

In another case, you can bring the LED voltage closer to the supply voltage - connect the LEDs in a series chain. The voltage across the string will equal the sum of the voltages across each LED.

Schemes of linear current stabilizers

The simplest current stabilizer circuit is on a single transistor (circuit "a"). Since the transistor is a current amplifier, its output current (collector current) is greater than the control current (base current) by h 21 times (gain). The base current can be set using a battery and a resistor, or using a zener diode and a resistor (diagram "b"). However, such a circuit is difficult to tune, the resulting stabilizer will depend on temperature, in addition, transistors have a large spread of parameters and when replacing a transistor, the current will have to be selected again. The circuit with feedback "c" and "d" works much better. Resistor R in the circuit acts as a feedback - as the current increases, the voltage across the resistor increases, thereby locking the transistor and the current decreases. Scheme "g", when using the same type of transistors, has greater temperature stability and the ability to minimize the value of the resistor, which reduces the minimum voltage of the stabilizer and the power dissipation on the resistor R.

The current stabilizer can be made on the basis of a field-effect transistor with a p-n junction (diagram "e"). The gate-source voltage sets the drain current. At zero gate-source voltage, the current through the transistor is equal to the initial drain current specified in the documentation. The minimum operating voltage of such a current stabilizer depends on the transistor and reaches 3 volts. Some manufacturers of electronic components produce special devices - ready-made fixed current stabilizers assembled according to this scheme - CRD (Current Regulating Devices) or CCR (Constant Current Regulator). Some call it a diode stabilizer, because it works like a diode in reverse.

On Semiconductor produces a linear regulator of the NSIxxx series, for example, which has two outputs and, to increase reliability, has a negative temperature coefficient - as the temperature rises, the current through the LEDs decreases.

A current stabilizer based on a pulse converter is very similar in design to a voltage regulator based on a pulse converter, but it controls not the voltage at the load, but the current through the load. With a decrease in current in the load, it pumps up power, with an increase, it reduces. The most common circuits of pulse converters include a reactive element - a choke, which, with the help of a switch (key), is pumped up in portions of energy from the input circuit (from the input capacitance) and, in turn, transfers it to the load. In addition to the obvious advantage of saving energy, pulse converters have a number of disadvantages that have to be dealt with by various circuitry and design solutions:

• Pulse converter produces electrical and electromagnetic interference
• It usually has a complex structure
• It does not have absolute efficiency, that is, it spends energy for its own work and heats up
• It usually has a higher cost than, for example, transformer plus linear devices

Since energy savings are critical in many applications, component designers and circuit designers try to reduce the impact of these shortcomings, and often succeed.

Schemes of pulse converters

Since the current stabilizer is based on a pulse converter, let's consider the main circuits of pulse converters. Each pulse converter has a key, an element that can only be in two states - on and off. In the off state, the key does not conduct current and, accordingly, no power is generated on it. In the on state, the key conducts current, but has a very low resistance (ideally, zero), respectively, it releases power close to zero. Thus, the key can transfer portions of energy from the input circuit to the output circuit with virtually no power loss. However, instead of a stable current, which can be obtained from a linear power supply, the output of such a switch will be a pulsed voltage and current. In order to get stable voltage and current again, you can put a filter.

Using a conventional RC filter, you can get the result, however, the efficiency of such a converter will not be better than a linear one, since all the excess power will be released on the active resistance of the resistor. But if you use a filter instead of RC - LC (circuit "b"), then, due to the "specific" properties of inductance, power losses can be avoided. Inductance has a useful reactive property - the current through it increases gradually, the electrical energy supplied to it is converted into magnetic energy and accumulates in the core. After the switch is turned off, the current in the inductor does not disappear, the voltage on the inductor changes polarity and continues to charge the output capacitor, the inductance becomes a current source through the bypass diode D. Such an inductance, designed to transmit power, is called a choke. The current in the inductor of a properly operating device is constantly present - the so-called continuous mode or continuous current mode (in Western literature, this mode is called Constant Current Mode - CCM). When the load current decreases, the voltage on such a converter increases, the energy accumulated in the inductor decreases and the device can switch to discontinuous operation when the current in the inductor becomes intermittent. With this mode of operation, the level of interference created by the device increases sharply. Some converters operate in border mode, when the current through the inductor approaches zero (in Western literature, this mode is called Border Current Mode - BCM). In any case, a significant direct current flows through the inductor, which leads to the magnetization of the core, and therefore, the inductor is made of a special design - with a gap or using special magnetic materials.

The stabilizer based on a pulse converter has a device that regulates the operation of the key, depending on the load. The voltage stabilizer registers the voltage at the load and changes the operation of the key (diagram "a"). The current stabilizer measures the current through the load, for example, using a small measuring resistance Ri (circuit "b"), connected in series with the load.

The converter key, depending on the regulator signal, turns on with different duty cycles. There are two common ways to control the key - pulse width modulation (PWM) and current mode. In PWM mode, the error signal controls the pulse width while maintaining the repetition rate. In current mode, the peak current in the inductor is measured and the interval between pulses is changed.

In modern key converters, a MOSFET transistor is usually used as a key.

Buck Converter

The version of the converter considered above is called a step-down converter, since the voltage at the load is always lower than the voltage of the power source.

Since the inductor constantly flows unidirectional current, the requirement for the output capacitor can be reduced, the inductor with the output capacitor plays the role of an effective LC filter. In some circuits of current stabilizers, for example for LEDs, the output capacitor may be absent altogether. In Western literature, a buck converter is called a Buck converter.

Boost Converter

The switching regulator circuit below also works with a choke, but the choke is always connected to the output of the power supply. When the key is open, power is supplied through the inductor and diode to the load. When the key is closed, the inductor accumulates energy; when the key is opened, the EMF that occurs at its terminals is added to the EMF of the power source and the voltage at the load increases.

Unlike the previous circuit, the output capacitor is charged by an intermittent current, so the output capacitor must be large and an additional filter may be needed. In Western literature, a boost-buck converter is called a Boost converter.

inverter converter

Another circuit of the pulse converter works in a similar way - when the key closes, the inductor accumulates energy, when the key opens, the EMF that occurs at its terminals will have the opposite sign and a negative voltage will appear on the load.

As in the previous circuit, the output capacitor is charged by an intermittent current, so the output capacitor must be large, and an additional filter may be needed. In Western literature, the inverting converter is called the Buck-Boost converter.

Forward and flyback converters

Most often, power supplies are made according to a scheme that uses a transformer in its composition. The transformer provides galvanic isolation of the secondary circuit from the power source, in addition, the efficiency of the power supply based on such circuits can reach 98% or more. The forward converter (circuit "a") transfers energy from the source to the load at the moment the key is on. In fact, this is a modified buck converter. The flyback converter (circuit "b") transfers energy from the source to the load during the off state.

In a forward converter, the transformer operates normally and the energy is stored in the inductor. In fact, it is a pulse generator with an LC filter at the output. The flyback converter stores energy in the transformer. That is, the transformer combines the properties of a transformer and a choke, which creates certain difficulties when choosing its design.

In Western literature, a forward converter is called a forward converter. Flyback - Flyback converter.

Application of a pulse converter as a current stabilizer

Most switching power supplies are available with output voltage stabilization. Typical circuits of such power supplies, especially powerful ones, in addition to output voltage feedback, have a key element current control circuit, for example, a low resistance resistor. Such control allows you to ensure the mode of operation of the throttle. The simplest current stabilizers use this control element to stabilize the output current. Thus, the current stabilizer is even simpler than the voltage stabilizer.

Consider a switching current stabilizer circuit for an LED based on a microcircuit from a well-known manufacturer of electronic components On Semiconductor:

The buck converter circuit operates in continuous current mode with an external switch. The circuit was chosen from many others because it shows how simple and effective a switching current regulator circuit with an external switch can be. In the above diagram, the control chip IC1 controls the operation of the MOSFET switch Q1. Since the converter operates in continuous current mode, it is not necessary to install an output capacitor. In many circuits, a current sensor is installed in the source circuit of the switch, however, this reduces the turn-on speed of the transistor. In the above diagram, the R4 current sensor is installed in the primary power circuit, as a result, the circuit turned out to be simple and effective. The key operates at a frequency of 700 kHz, which allows you to install a compact choke. With an output power of 7 watts, an input voltage of 12 volts when operating at 700 mA (3 LEDs), the efficiency of the device is more than 95%. The circuit works stably up to 15 watts of output power without the use of additional heat dissipation measures.

An even simpler circuit is obtained using key stabilizer microcircuits with a built-in key. For example, a diagram of a key LED current stabilizer based on the /CAT4201 chip:

To operate a device with a power of up to 7 watts, only 8 components are needed, including the microcircuit itself. The switching regulator operates in current limit mode and requires a small output ceramic capacitor to operate. Resistor R3 is needed when powered from 24 volts and above to reduce the slew rate of the input voltage, although this somewhat reduces the efficiency of the device. The frequency of operation exceeds 200 kHz and varies depending on the load and input voltage. This is due to the method of regulation - control of the peak current of the inductor. When the current reaches the maximum value, the key opens, when the current drops to zero, it turns on. The efficiency of the device reaches 94%.

Every time I read new blog entries, I encounter the same error - put current stabilizer where needed Voltage regulator and vice versa. I will try to explain on my fingers, without delving into the jungle of terms and formulas. It will be especially useful for those who put driver for powerful LEDs and nourishes many of the weak with it. For you - a separate paragraph at the end of the article.

Let's start with the concepts:

VOLTAGE REGULATOR
Based on the name - stabilizes the voltage. If it is written that the stabilizer is 12V and 3A, then it stabilizes precisely for a voltage of 12V! But 3A is the maximum current that the stabilizer can give. Maximum! And not "always gives 3 amps." That is, it can give out 3 milliamps, and 1 ampere, and two ... How much your circuit eats, it gives so much. But no more than three. Actually this is the main thing.

Once they were like that and connected TVs to them ...

And now I will move on to describing the types of voltage stabilizers:

Linear stabilizers (the same ROLL or LM7805/LM7809/LM7812 etc.)

Here it is - LM7812. Our Soviet analogue - KREN8B

The most common type. They cannot operate at a voltage lower than that indicated on his belly. That is, if the LM7812 stabilizes the voltage at 12 volts, then it needs to be applied to the input by at least about one and a half volts more. If it is less, it means that the output of the stabilizer will be less than 12 volts. He cannot take the missing volts out of nowhere. That's why it's a bad idea - to stabilize the voltage in the car with 12-volt rolls. As soon as the input is less than 13.5 volts, it starts to give less than 12 at the output.

Another disadvantage of linear stabilizers- strong heating at such a good load. That is, in a village language - everything that is above the same 12 volts turns into heat. And the higher the input voltage, the more heat. Up to the temperature of frying eggs. We loaded it a little more than a couple of small LEDs and that's it - we got an excellent iron.

Switching stabilizers - much cooler, but also more expensive. Usually, for an ordinary buyer, this already looks like a kind of scarf with details.

For example, here is such a handkerchief - a switching voltage stabilizer.

There are three types: lowering, increasing and omnivores. The coolest are omnivores. They do not care that the input voltage is lower or higher than desired. He automatically switches to the mode of increasing or decreasing the voltage and keeps the specified output. And if it is written that it can be input from 1 to 30 volts and the output will be stable 12, then it will be so.

But more expensive. But tougher. But more expensive...
If you don’t want an iron from a linear stabilizer and a huge cooling radiator to boot, put a pulse one.
What is the conclusion on voltage stabilizers?
SET HARD VOLTS - and the current can swim as you like(within limits of course)

CURRENT STABILIZER
When applied to LEDs, they are also called "LED driver". Which would also be true.

Here, for example, is a ready-made driver. Although the driver itself is a small black eight-legged microcircuit, the whole circuit is usually called the driver at once.

Sets the current. Stable! If it is written that the output is 350mA, then even if you crack, it will be so. But the volts at its output can vary depending on the voltage required by the LEDs. That is, you do not regulate them, the driver will do everything for you based on the number of LEDs.
If it is very simple, then I can only describe it this way. =)
What about the conclusion?
SET A HARD CURRENT - and the voltage can float.

Now - to the LEDs. After all, all the fuss is because of them.

The LED is powered by CURRENT. It does not have a VOLTAGE parameter. There is a parameter - voltage drop! That is how much is lost. If it is written on the LED 20mA 3.4V, then this means that it needs no more than 20 milliamps. And at the same time, 3.4 volts will be lost on it. Not for power, you need 3.4 volts, but simply “lost” on it!

That is, you can power it at least from 1000 volts, only if you give it no more than 20mA. It will not burn out, will not overheat and will shine as it should, but after it there will be 3.4 volts less. That's all science. Limit the current to him - and he will be full and will shine happily ever after.

Here we take the most common option for connecting LEDs(this is used in almost all tapes) - 3 LEDs and a resistor are connected in series. We feed from 12 volts. We limit the current to the LEDs with a resistor so that they do not burn out (I don’t write about the calculation, there are a lot of calculators on the Internet). After the first LED, 12-3.4= 8.6 volts remains……… We still have enough. On the second, another 3.4 volts will be lost, that is, 8.6-3.4 \u003d 5.2 volts will remain. And for the third LED is also enough. And after the third, 5.2-3.4 \u003d 1.8 volts will remain. And if you want to put the fourth, then it's not enough. Now, if you power not from 12V but from 15, then that's enough. But we must take into account that the resistor will also need to be recalculated. Well, actually, they came smoothly to ...

The simplest current limiter is a resistor. They are often placed on the same tapes and modules. But there are downsides - the lower the voltage, the lower the current on the LED. And vice versa. Therefore, if the voltage jumps in your network, that horses jump through barriers at show jumping competitions (and in cars this is usually the case), then we first stabilize the voltage, and then limit the current to the same 20mA with a resistor. And that's it. We don’t care about power surges anymore (the voltage stabilizer works), and the LED is full and shines to the delight of everyone.
That is - if we put a resistor in the car, then you need to stabilize the voltage.

You may not stabilize if you calculate the resistor for the maximum possible voltage in the car network, you have a normal on-board network (and not a Chinese-Russian tazoprom) and make a current margin of at least 10%.
Well, besides, resistors can only be set up to a certain current value. After a certain threshold, the resistors start to heat up like hell and you have to greatly increase them in size (resistors 5W, 10W, 20W, etc.). We smoothly turn into a large iron.

There is another option- put something like LM317 in the current stabilizer mode as a limiter.

LM317. Externally, like the LM7812. The body is one, the meaning is somewhat different. But they also heat up, because this is also a linear regulator (remember I wrote about ROLL in the paragraph about voltage stabilizers?). And then they created...

Switching current stabilizer (or driver).

That's exactly what I'm talking about. In the picture we are talking about 1W LEDs, but the picture is the same with any other.
This is exactly what we see in Chinese modules and corn, which burn like matches after a week / month of work. Because LEDs have a hell of a spread, and the Chinese save more on drivers than anyone else. Why don't branded modules and lamps of Osram, Philips, etc. light up? Because they make a rather powerful rejection of LEDs and 10-15% of the wildest number of LEDs produced remains, which are almost identical in parameters and you can make such a simple look from them, which many are trying to do - one powerful driver and many identical chains of LEDs without drivers. But only in the conditions “I bought LEDs on the market and soldered it myself”, as a rule, it will not be good for them. Because even the “non-Chinese” will have a scatter. It may be lucky and work for a long time, or it may not.

Remember once and for all! I am begging you! =)
And it's easy - to do it right and to do "look how I saved, and the rest are fools" - these are somewhat different things. Even very different. Learn to do not like the notorious Chinese, learn to do it beautifully and correctly. This was said a long time ago and not by me. I just tried to explain the common truths for the hundredth and five hundredth time. Sorry if I didn't explain well =)

Here's a great illustration. Do you think I didn’t want to save money and reduce the number of drivers by 3-4 times? But this is correct, which means it will work happily ever after.

And finally, for those to whom even such a presentation was too abstruse.
Remember the following and try to follow it (here a "string" is a single LED or multiple LEDs in SERIES):

1.—- EVERY chain has its own current limiter (resistor or driver ...)
2. - Low-power circuit up to 300mA? We put a resistor and that's enough.
3. Is the voltage unstable? We put the VOLTAGE STABILIZER
4. - Is the current more than 300mA? We put on EVERY chain a DRIVER (current stabilizer) without a voltage stabilizer.

This is how it will be right and most importantly - it will work for a long time and shine brightly! Well, I hope that all of the above will save many from mistakes and help save money and nerves.

Transistor current stabilizer. Circuit Current Stabilizers

Current stabilizer circuits for LEDs on transistors and microcircuits

It is known that the brightness of the LED is very dependent on the current flowing through it. At the same time, the current of the LED is very steeply dependent on the supply voltage. This results in noticeable brightness ripples even with slight power instability.

But ripple is not terrible, what is much worse is that the slightest increase in the supply voltage can lead to such a strong increase in current through the LEDs that they simply burn out.

To prevent this, LEDs (especially powerful ones) are usually powered through special circuits - drivers, which are essentially current stabilizers. This article will consider circuits of simple current stabilizers for LEDs (on transistors or common microcircuits).

To stabilize the current through the LEDs, well-known solutions can be applied:

Figure 1 shows a circuit, the operation of which is based on the so-called. emitter follower. The transistor, connected in this way, tends to keep the voltage at the emitter exactly the same as at the base (the only difference will be the voltage drop at the base-emitter junction). Thus, by fixing the base voltage with a zener diode, we get a fixed voltage across R1.

Ordinary diodes have a very weak dependence of forward voltage on current, so they can be used instead of hard-to-reach low-voltage zener diodes. Here are two options for circuits for transistors of different conductivity, in which the zener diodes are replaced by two conventional diodes VD1, VD2:

The current through the LEDs is set by selecting the resistor R2. Resistor R1 is chosen in such a way as to reach the linear section of the CVC of the diodes (taking into account the base current of the transistor). The supply voltage of the entire circuit must be no less than the total voltage of all LEDs plus about 2-2.5 volts on top for stable operation of the transistor.

For example, if you need to get a current of 30 mA through 3 LEDs connected in series with a forward voltage of 3.1 V, then the circuit should be powered with a voltage of at least 12 Volts. In this case, the resistance of the resistor should be about 20 ohms, the dissipation power should be 18 mW. The transistor should be selected with a maximum voltage Uke not lower than the supply voltage, for example, the common S9014 (n-p-n).

The resistance R1 will depend on the coefficient. amplification of the transistor hfe and VAC of the diodes. For S9014 and 1N4148 diodes, 10 kΩ will suffice.

Let's apply the described stabilizer to improve one of the LED lamps described in this article. The improved schema would look like this:

This refinement can significantly reduce the current ripple and, consequently, the brightness of the LEDs. But the main advantage of the circuit is to normalize the mode of operation of the LEDs and protect them from voltage surges during switching on. This leads to a significant extension of the life of the LED lamp.

It can be seen from the oscillograms that by adding a current stabilizer for the LED on a transistor and a zener diode to the circuit, we immediately reduced the amplitude of the ripples several times:

With the ratings indicated on the diagram, a little more than 0.5 W of power is dissipated on the transistor, which makes it possible to do without a radiator. If the capacitance of the ballast capacitor is increased to 1.2 uF, then ~ 23 Volts will drop across the transistor, and the power will be about 1 W. In this case, you cannot do without a radiator, but the ripples will drop almost to zero.

Instead of the transistor 2CS4544 indicated on the diagram, you can take 2SC2482 or similar with a collector current of more than 100 mA and a permissible voltage Uke of at least 300 V (for example, the old Soviet KT940, KT969 are suitable).

The desired current, as usual, is set by the resistor R*. The zener diode is designed for a voltage of 5.1 V and a power of 0.5 W. As LEDs, common smd LEDs from a Chinese light bulb are used (or even better, take a finished lamp and add the missing components to it).

Now consider the circuit shown in Figure 2. Here it is separately:

The current sensor here is a resistor, the resistance of which is calculated by the formula 0.6 / Iload. With an increase in current through the LEDs, the transistor VT2 begins to open more strongly, which leads to a stronger blocking of the transistor VT1. The current is decreasing. Thus, the output current is stabilized.

The advantage of the scheme is its simplicity. The disadvantage is a rather large voltage drop (and hence power) across the transistor VT1. This is not critical at low currents (tens and hundreds of milliamps), however, a further increase in current through the LEDs will require the installation of this transistor on a radiator.

This drawback can be eliminated by using a p-channel MOSFET with low drain-to-source resistance instead of a bipolar transistor:

The desired current, as before, is set by selecting the resistor R1. VT1 - any low-power. Instead of a powerful IRL3705N, you can take, for example, IRF7210 (12A, 12V) or IRLML6402 (3.7A, 20V). See for yourself which currents you need.

The simplest current regulator circuit for FET LEDs consists of just one transistor with a shorted gate and source:

Instead of KP303E, for example, BF245C or similar with a built-in channel is suitable. The principle of operation is similar to the circuit in Figure 1, only the "ground" potential is used as a reference voltage. The value of the output current is determined solely by the initial drain current (taken from the datasheet) and practically does not depend on the drain-source voltage Us. This is clearly seen from the output characteristic graph:

In the circuit in Figure 3, a resistor R1 is added to the source circuit, which sets some reverse gate bias and thus allows you to change the drain current (and hence the load current).

An example of the simplest LED current driver is shown below:

It uses an insulated gate field effect transistor with a built-in n-type BSS229 channel. The exact value of the output current will depend on the characteristics of a particular instance and the resistance R1.

These are, in general, all ways to turn a transistor into a current stabilizer. There is also the so-called current mirror, but it is not suitable for LED lamps. So let's move on to microchips.

Current stabilizers on microcircuits

Chips can achieve much higher performance than transistors. Most often, do-it-yourself precision thermostable reference voltage sources (TL431, LM317 and others) are used to assemble a current stabilizer for LEDs.

TL431

A typical current stabilizer circuit for LEDs on the TL431 looks like this:

Since the IC behaves in such a way as to maintain a fixed voltage of 2.5 V across the resistor R2, the current through this resistor will always be 2.5/R2. And if we neglect the base current, then we can assume that IRn \u003d IR2. And the higher the transistor gain hfe, the more these currents will match.

R1 is calculated in such a way as to ensure the minimum operating current of the microcircuit is 1 mA.

And here is an example of the practical application of TL431 in an LED lamp:

The transistor drops about 20-30 V, the power dissipation is less than 1.5 W. In addition to the 2SC4544 indicated on the diagram, you can use the BD711 or the old Soviet KT940A. Transistors in the TO-220 package do not require installation on a radiator up to a power of 1.5-2 W inclusive.

Resistor R3 serves to limit the charging pulse of the capacitor when the power is turned on. The current through the load is set by resistor R2.

Here, 90 white LED2835 chip LEDs act as load Rn. The maximum power at a current of 60 mA is 0.2 W (24Lm), the voltage drop is 3.2 V.

To increase the service life, the power of the diodes is specially underestimated by 20% (0.16 W, current 45 mA), respectively, the total power of all LEDs is 14 W.

Of course, the current regulator circuit for 220 V LEDs can be converted to any required current and / or other number of LEDs available.

Given the allowable voltage spread of 220 volts (see GOST 29322-2014), the rectified voltage across capacitor C1 will be in the range from 293 to 358 V, so it must be rated for a voltage of at least 400 V.

Based on the range of supply voltages, the parameters of the remaining elements of the circuit are calculated.

For example, a resistor that sets the operating mode of the DA1 chip must provide a current of at least 0.5 mA at a voltage of C1 = 293 V. The maximum number of LEDs should not exceed NLED< (358 - 6) / 3.2, причем, чем их больше, тем выше яркость светильника и тем меньшая мощность будет уходить в никуда (рассеиваться в виде тепла на транзисторе VT1). Максимальное напряжение Uкэ транзистора VT1 должно быть не ниже 358 - (ULED * NLED).

LM7805, LM7812...

Any integrated voltage regulator can be turned into a current regulator by adding just one resistor in accordance with the diagram:

Just keep in mind that, with this inclusion, the input voltage must be greater than the stabilization voltage of the microcircuit by a certain amount (voltage drop on the stabilizer itself). Usually it is somewhere around 2-2.5 volts. And, of course, add voltage to the load.

Here, for example, is a specific example of a current stabilizer for LEDs on the LM7812:

The circuit parameters are designed for 10 5730 smd diodes with a forward voltage of 3.3 volts on each. Current consumption (current through LEDs) - 300 mA. Luminaire power ~10 watts.

Since when the LEDs are connected in series, the total voltage will be equal to the sum of the voltages on each of the LEDs, the minimum supply voltage of the circuit should be: Upit \u003d 2.5 + 12 + (3.3 x 10) \u003d 47.5 Volts.

You can calculate the resistance and power of the resistor for other current values ​​\u200b\u200busing a simple Regulator Design program (download).

Obviously, the higher the output voltage of the stabilizer, the more heat will be generated on the current-setting resistor and, therefore, the worse the efficiency. Therefore, for our purposes, the LM7805 is better suited than the LM7812.

LM317

Equally effective is a linear current regulator for LEDs on the LM317. Typical switching circuit:

The simplest LM317 switching circuit for LEDs, which allows you to assemble a powerful lamp, consists of a rectifier with a capacitive filter, a current stabilizer and 93 SMD 5630 LEDs. MXL8-PW35-0000 (3500K, 31 Lm, 100 mA, 3.1 V, 400 mW, 5.3 x3 mm).

If such a large garland of LEDs is not needed, then a ballast resistor or capacitor will have to be added to the driver on the LM317 to power the LEDs (to extinguish the excess voltage). How to do this, we discussed in great detail in this article.

The disadvantage of such a current driver circuit for LEDs is that when the voltage in the network rises above 235 volts, the LM317 will be outside the calculated operating mode, and when it drops to ~ 208 volts and below, the microcircuit completely ceases to stabilize and the depth of the ripples will depend entirely and completely from tank C1.

Therefore, it is necessary to use such a lamp where the voltage is more or less stable. And the capacitance of this capacitor is not worth saving. The diode bridge can be taken ready-made (for example, a miniature MB6S) or assembled from suitable diodes (Uobr at least 400 V, direct current >= 100 mA).

Instead of a conclusion

The disadvantages of the schemes given in the article include low efficiency due to the useless waste of power on the regulatory elements. However, this is characteristic of all linear current stabilizers.

Low efficiency is unacceptable for devices powered by autonomous current sources (lamps, flashlights, etc.). A significant increase in efficiency (90% or more) can be achieved by using pulse current stabilizers.

electro-shema.com

When the first power supply is assembled, the simplest circuit is taken - so that everything works out for sure. When you manage to start it up and get as much as 12 regulated volts and a current under half an ampere, the radio amateur is imbued with the meaning of the phrase “And you will be happy!”. Only this happiness does not last very long and it soon becomes quite obvious that the PSU must have the ability to regulate the output current. By finalizing the existing power supply, this is achievable, but somewhat troublesome - it’s better to assemble another, more “advanced” one. There is an interesting option. To a low-power power supply, you can make an attachment to adjust the current in the range from 20 mA to the maximum that it can give, according to this scheme:

I assembled this device almost a year ago.

The current stabilizer is really a necessary thing. For example, it will help to charge any battery designed for voltage up to 9 volts inclusive, and, I note, charge it efficiently. But she clearly lacks a measuring head. I decide to upgrade and disassemble my homemade product into its components, where, perhaps, the most significant component is the variable resistor PPB-15E with a maximum resistance of 33 Ohm.

The new case is oriented exclusively to the dimensions of the indicator from the tape recorder, which will perform the functions of a milliammeter.

To do this, he “draws” a new scale (I chose a current of full deflection of the arrow of 150 mA, but you can do it to the maximum).

Then a shunt is placed on the pointer device.

The shunt was made from a nichrome heating coil with a diameter of 0.5 mm. The KT818 transistor must be placed on the cooling radiator.

Connection (articulation) of the set-top box with the power supply unit is carried out using an improvised plug integrated into the case, the pins of which are taken from a conventional power plug, at one end of which an M4 thread is cut, through which each of them is screwed to the case with two nuts.

The final image of what happened. Definitely a more perfect creation. The LED performs not only the function of indication, but partly also the illumination of the scale of the current stabilizer. Wishing you success, Babay.

el-shema.ru

Current stabilizers. Types and device. Work and application

Current stabilizers are designed to stabilize the current on the load. The voltage across the load depends on its resistance. Stabilizers are necessary for the functioning of various electronic devices, such as gas discharge lamps.

For high-quality battery charging, current stabilizers are also needed. They are used in microcircuits to adjust the current of the conversion and amplification stages. In microcircuits, they play the role of a current generator. In electrical circuits, there are always various kinds of interference. They adversely affect the operation of appliances and electrical devices. Current stabilizers can easily cope with such a problem.

A distinctive feature of current stabilizers is their significant output impedance. This makes it possible to eliminate the influence of the input voltage and load resistance on the current value at the output of the device. Current stabilizers maintain the output current within certain limits, while changing the voltage in such a way that the current flowing through the load remains constant.

Device and principle of operation

The instability of the load current is affected by the value of the resistance and voltage at the input. Consider an example where the load resistance is constant and the input voltage rises. The load current also increases.

As a result of this, the current and voltage across the resistances R1 and R2 will increase. The voltage of the zener diode will become equal to the sum of the voltages of the resistances R1, R2 and at the VT1 base-emitter junction: Uvd1=UR1+UR2+UVT1(b/e)

The voltage at VD1 does not change with the changing input voltage. As a result, the current at the base-emitter junction will decrease, and the resistance between the emitter-collector terminals will increase. The current strength at the collector-emitter junction and the load resistance will decrease, that is, go to the original value. This is how the current is equalized and maintained at the same level.

Consider an elementary circuit using a field effect transistor.

The load current passes through R1. The current in the circuit: “+” of the voltage source, drain-gate VT1, load resistance, the negative pole of the source is very small, since the drain-gate has a bias in the opposite direction.

The voltage on R1 is positive: on the left is "-", on the right, the voltage is equal to the voltage of the right arm of the resistance. Therefore, the gate voltage relative to the source is minus. As the load resistance decreases, the current increases. Therefore, the gate voltage compared to the source has an even greater difference. As a result, the transistor closes more strongly.

With a greater closing of the transistor, the load current will decrease and return to the initial value.

Types of current stabilizers

There are many different types of stabilizers, depending on their purpose and principle of operation. Let us consider in more detail the main of these devices.

resistor stabilizers

In the elementary case, the current generator can be a circuit consisting of a power supply and resistance. A similar circuit is often used to connect an LED that acts as an indicator.

Among the disadvantages of such a scheme, one can note the need to use a high-voltage source. Only under this condition can a resistor having a high resistance be used and good current stability can be obtained. The resistance dissipates power P = I 2 x R.

Transistor stabilizers

Stabilizers assembled on transistors function much better.

You can adjust the voltage drop so that it is very small. This makes it possible to reduce losses with good current stability at the output. At the output of the transistor, the resistance is very high. This circuit is used to connect LEDs or charge low-power batteries.

The voltage across the transistor is determined by the zener diode VD1. R2 plays the role of a current sensor and determines the current at the output of the stabilizer. As the current increases, the voltage drop across this resistor becomes larger. The voltage is applied to the emitter of the transistor. As a result, the voltage at the base-emitter junction, which is equal to the difference between the base voltage and the emitter voltage, decreases, and the current returns to the set value.

Schematic of the current mirror

Current generators function similarly. A popular circuit for such generators is the “current mirror”, in which a bipolar transistor, or rather, an emitter junction, is used instead of a zener diode. Instead of resistance R2, the emitter resistance is used.

Stabilizers on the field

The circuit using field effect transistors is simpler. In it, the ground potential can be used as a voltage stabilizer.

Devices on a chip

In past schemes, there are elements of comparison and adjustment. A similar circuit structure is used in the design of voltage equalization devices. The difference between devices that stabilize current and voltage is that the signal comes to the feedback circuit from the current sensor, which is connected to the load current circuit. Therefore, to create current stabilizers, popular microcircuits 142 EH 5 or LM 317 are used.

Here, the role of the current sensor is played by the resistance R1, on which the stabilizer maintains a constant voltage and load current. The resistance value of the sensor is much lower than the load resistance. Reducing the voltage on the sensor affects the output voltage of the stabilizer. A similar scheme goes well with chargers, LEDs.

Switching stabilizer

Switching stabilizers made on the basis of keys have high efficiency. They are capable of creating a high voltage at the consumer at a low input voltage. Such a circuit is assembled on a MAX 771 chip.

Resistors R1 and R2 play the role of voltage dividers at the output of the microcircuit. If the voltage at the output of the microcircuit becomes higher than the reference value, then the microcircuit reduces the output voltage, and vice versa.

If the circuit is changed in such a way that the microcircuit reacts and regulates the current at the output, then a stabilized current source will be obtained.

When the voltage across R3 drops below 1.5 V, the circuit acts as a voltage regulator. As soon as the load current rises to a certain level, then the voltage drop across the resistor R3 becomes larger, and the circuit acts as a current regulator.

The resistance R8 is connected according to the scheme when the voltage becomes higher than 16.5 V. The resistance R3 sets the current. The negative point of this circuit is a significant voltage drop across the current-measuring resistance R3. This problem can be solved by connecting an operational amplifier to amplify the signal from R3.

Current stabilizers for LEDs

You can make such a device yourself using the LM 317 chip. To do this, you just have to pick up a resistor. It is advisable to use the following power supply for the stabilizer:

• 32V printer block.
• Block from a laptop for 19 V.
• Any 12V power supply.

The advantage of such a device is low cost, simple design, increased reliability. It makes no sense to assemble a complex scheme on your own, it is easier to purchase it.

Similar topics:

electrosam.ru

Current stabilizer circuit

Content:

1. Relay current stabilizers
2. Triac stabilizer
3. High frequency current stabilizer
4. Pulse Width Devices
5. Resonant Current Stabilizer
6. AC stabilizer
7. Stabilizers for LED
8. Adjustable current stabilizer
9. DC Stabilizers
10. A simple two-transistor current regulator

In existing electrical networks, there are constantly various interferences that have a negative impact on the operation of devices and equipment. The current stabilizer circuit helps to effectively deal with this problem. Stabilizing devices differ in technical characteristics and depend on power sources. If at home current stabilization is not a priority, then when using measuring equipment, current indicators must be stable. Field-effect transistor devices are especially accurate. The absence of interference allows you to get the most reliable results after measurements.

General device and principle of operation

The main element of each stabilizer is a transformer. The simplest circuit consists of a rectifier bridge connected to capacitors and resistors. Each circuit uses elements of various types, with individual capacitance and ultimate resistance.

The principle of operation of the stabilizer is quite simple. When current enters the transformer, its limiting frequency changes. At the input, this parameter coincides with the mains frequency and is 50 Hz. After performing the current conversion, the value of the limiting frequency at the output will already be 30 Hz. During the operation of high-voltage rectifiers, the voltage polarity is determined. Current stabilization is carried out due to the operation of capacitors, and noise reduction occurs with the help of resistors. In the end, a constant voltage is again formed at the output, which enters the transformer with a frequency not exceeding 30 Hz.

Types of current stabilizers

In accordance with the intended purpose, a large number of different types of stabilizing devices have been developed.

Relay current stabilizers. Their circuit consists of typical elements, including compensation capacitors. In this case, the installation of bridge rectifiers is carried out at the beginning of the circuit. One should also take into account such a factor as the presence of two pairs of transistors in the stabilizer. The installation of the first pair is carried out in front of the condenser. This raises the limiting frequency.

In a stabilizer of this type, the output voltage will be about 5 amperes. Support for a certain level of nominal resistance is carried out using resistors. In simple models, two-channel elements are used. They are characterized by a long conversion process, but they have a small dispersion coefficient.

Triac stabilizer LM317. This model is widely used in various fields. Its main element is a triac, with the help of which the limiting voltage is significantly increased in the device. This indicator at the output has a value of about 12 V. The system is able to withstand external resistance up to 3 ohms. The increase in the smoothing factor is carried out using multichannel capacitors. Open-type transistors are used only in high-voltage devices.

Position change is controlled by changing the output current rating. The LM317 current stabilizer can handle differential resistance up to 5 ohms. In the case of using measuring instruments, this value must be at least 6 ohms. A powerful transformer provides a non-breakable choke current mode. In a conventional circuit, it is installed immediately after the rectifier. In 12 volt receivers, a ballast type of resistor is used, due to which oscillations in the circuit are reduced.

High frequency current stabilizer. Its main element is the KK20 transistor, which is characterized by an accelerated conversion process. This is facilitated by a change in polarity at the output. Capacitors that set the frequency are installed in pairs in the circuit. The pulse front in this case should not be more than 2 μs, otherwise it will lead to significant dynamic losses.

In some circuits, powerful amplifiers in an amount of at least three are used to saturate the resistors. Capacitive capacitors are used to reduce heat losses. The value of the speed characteristics of the key transistor depends entirely on the parameters of the divider.

Pulse-width stabilizers. Stabilizers of this type have a rather significant inductance of the inductor, due to the quick change of the divider. This circuit uses two-channel resistors that pass current in different directions, as well as capacitance capacitors. All these elements allow you to maintain the output value of the limiting resistance within 4 ohms. The maximum load withstood by such stabilizers is 3 A. These models are rarely used in measuring instruments. The limiting dissipation of power sources in this case should not exceed 5 volts, which allows maintaining the standard value of the dissipation factor.

In current stabilizers of this type, key transistors do not have very high speed characteristics. The reason is the low ability of the resistors to block the current coming from the rectifier. As a result, high amplitude interference causes significant heat loss. The neutralization of the transformer properties is reduced and leads to pulse drops. Current conversion is carried out only due to the operation of a ballast resistor installed directly behind the rectifier bridge. The pulse-width regulator very rarely uses semiconductor diodes, since the front of the pulses in the circuit is no more than 1 μs.

Resonant current stabilizer. It consists of small capacitors and resistors with different resistances. Transformers are an integral part of such amplifiers. The increase in the efficiency of the device is achieved through the use of a large number of fuses. This leads to an increase in the dynamic characteristics of the resistors. Installation of low-frequency transistors is carried out directly behind the rectifiers. Under the condition of good current conductivity, the operation of capacitors becomes possible at various frequencies.

AC stabilizer. As a rule, it is used in power supplies with voltage up to 15 volts and is their integral part. The maximum value of external resistance perceived by devices is 4 ohms. The average input AC voltage will be within 13 V. In this case, the level of the smoothing factor is controlled using open-type capacitors. The resistor design has a direct effect on the level of ripple generated at the output.

The maximum linear current for such stabilizers is 5 amperes. Accordingly, the differential resistance will have a value of 5 ohms. The value of the maximum allowable power dissipation is on average 2 W. This indicates serious problems with AC stabilizers with the front of the pulses. Reducing their oscillations is possible only with the help of bridge rectifiers. Fuses can significantly reduce heat loss.

Stabilizers for LED. In this case, the stabilizers should not have too much power. The main task of the current stabilizer is to minimize the dissipation threshold. To make such a stabilizer with your own hands, two main schemes are used. The first option is performed using converters. This makes it possible to achieve a maximum frequency of no more than 4 Hz at all stages, thereby significantly increasing the performance of the device.

In the second case, reinforcing elements are used. The main task is to neutralize the alternating current. It is possible to reduce dynamic losses with the help of high-voltage transistors. Excessive saturation of the elements is overcome by open-type capacitors. The speed of the transformers is provided by key resistors. Their location in the circuit is standard - directly behind the rectifier bridge.

Adjustable current stabilizer. Demanded mainly in the field of industrial production. The adjustable stabilizer makes it possible to tune instruments and equipment by changing the current and voltage. Many models can be controlled remotely using special controllers mounted inside the stabilizer. For such devices, the AC voltage limit value is approximately 12 V. In this case, the stabilization level must be at least 14 W. The threshold voltage is in direct proportion to the frequency of the device.

To change the smoothing factor, capacitive capacitors are installed in the adjustable stabilizer. These devices have good performance: maximum current 4 A, differential resistance - 6 ohms. Ensuring the continuous mode of the throttle is carried out by key-type transformers. The voltage is applied to the primary winding through the cathode, the output current is blocked depending on the type of capacitors. Fuses, most often, do not participate in process stabilization.

DC stabilizers. Their work is based on the principle of double integration. Special converters are responsible for this process. The dynamic characteristics of the stabilizers are increased with the help of two-channel transistors. The significant capacitance of the capacitors makes it possible to minimize heat losses. Rectification rates are determined by precise calculations. A DC output voltage of 12A corresponds to a maximum limit of 5 volts at a device frequency of 30 Hz.

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cxema.org - Three circuits of simple current regulators

Three schemes of simple current regulators

There are a lot of voltage regulator circuits on the network for a variety of purposes, but things are different with current regulators. And I want to fill this gap a little, and present you with three simple DC regulator circuits that are worth taking into service, as they are universal and can be used in many homemade designs.

Current regulators, in principle, are not much different from voltage regulators. Please do not confuse current regulators with current stabilizers, unlike the first ones, they maintain a stable output current regardless of the input voltage and output load.

The current stabilizer is an integral part of any normal laboratory power supply or charger, it is designed to limit the current supplied to the load. In this article, we will look at a pair of stabilizers and one regulator for general use.

In all three versions, shunts, in fact, low-resistance resistors, are used as a current sensor. To increase the output current of any of these circuits, you will need to reduce the resistance of the shunt. The desired current value is set manually, usually by rotating a variable resistor. All three circuits operate in a linear mode, which means that the power transistor will get very hot under heavy loads.

The first scheme is characterized by maximum simplicity and availability of components. There are only two transistors, one of them is control, the second is power, through which the main current flows.

The current sensor is a low-resistance wire-wound resistor. When an output load is connected, a certain voltage drop is formed on this resistor, the more powerful the load, the greater the drop. Such a voltage drop is enough to trigger the control transistor, the larger the drop, the more the transistor is ajar. Resistor R1 sets the bias voltage for the power transistor, it is thanks to him that the main transistor is in the open state. Current limitation occurs due to the fact that the voltage at the base of the power transistor, which was formed by the resistor R1, roughly speaking, attenuates or closes to the supply ground through the open junction of a low-power transistor, this will close the power transistor, therefore, the current flowing through it decreases down to zero .

Resistor R1 is essentially a conventional voltage divider, with which we can set, as it were, the degree of opening of the control transistor, and therefore control the power transistor by limiting the current flowing through it.

The second circuit is based on an operational amplifier. It has been repeatedly used in car battery chargers. Unlike the first option, this circuit is a current stabilizer.

As in the first circuit, there is also a current sensor (shunt), the operational amplifier detects the voltage drop across this shunt, all according to the scheme already familiar to us. The op amp compares the shunt voltage to the reference voltage, which is set by the zener diode. With a variable resistor, we artificially change the reference voltage. The operational amplifier, in turn, will try to balance the voltage at the inputs by changing the output voltage.

The output of the operational amplifier drives a powerful FET. That is, the principle of operation is not much different from the first circuit, except that there is a reference voltage source made on a zener diode.

This circuit also operates in a linear mode and the power transistor will get very hot under heavy loads.

The last circuit is based on the popular LM317 stabilizer integrated circuit. This is a linear voltage regulator, but it is possible to use a microcircuit as a current regulator.

The desired current is set by a variable resistor. The disadvantage of the circuit is that the main current flows precisely through the previously indicated resistor and, of course, it needs a powerful one, it is very desirable to use wire resistors.

The maximum allowable current for the LM317 chip is 1.5 amperes, you can increase it with an additional power transistor. In this case, the microcircuit will already be as a control one, so it will not heat up, in return the transistor will heat up and you can’t get away from it.

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Current stabilizers

Content:

1. General device and principle of operation
2. Diode Current Stabilizer
3. Current stabilizer on two transistors
4. Video: Do ​​it yourself stabilizer on the LM2576

In every electrical network, interference periodically occurs that adversely affects the standard parameters of current and voltage. This problem is successfully solved with the help of various devices, among which current stabilizers are very popular and effective. They have different technical characteristics, which makes it possible to use them in conjunction with any household electrical appliances and equipment. Special requirements are placed on measuring equipment that requires a stable voltage.

General device and principle of operation of current stabilizers

Knowledge of the basic principles of operation of current stabilizers contributes to the most efficient use of these devices. Electrical networks are literally saturated with various interferences that adversely affect the operation of household appliances and electrical equipment. To overcome the negative effects, a simple voltage and current stabilizer circuit is used.

Each stabilizer has a main element - a transformer that ensures the operation of the entire system. The simplest circuit includes a rectifier bridge connected to various types of capacitors and resistors. Their main parameters are individual capacitance and ultimate resistance.

The current stabilizer itself works according to a very simple scheme. When current enters a transformer, its limiting frequency changes. At the input, it will coincide with the frequency of the electrical network and will be 50 Hz. After all current conversions have been completed, the cut-off frequency at the output will drop to 30 Hz. High-voltage rectifiers are involved in the conversion circuit, with the help of which the voltage polarity is determined. Capacitors are directly involved in current stabilization, and resistors reduce interference.

Diode Current Stabilizer

Many luminaire designs include diode regulators, better known as LED current regulators. Like all types of diodes, LEDs have a non-linear current-voltage characteristic. That is, with a changing voltage on the LED, a disproportionate change in current occurs.

As the voltage increases, a very slow increase in current is initially observed, as a result, the LED does not glow. Then, when the voltage reaches the threshold value, the emission of light begins and the current increases very rapidly. A further increase in voltage leads to a catastrophic increase in current and burnout of the LED. The value of the threshold voltage is reflected in the technical characteristics of LED light sources.

High power LEDs require a heatsink as they generate a lot of heat. In addition, they require a sufficiently powerful current stabilizer. The correct operation of the LEDs is also ensured by stabilizing devices. This is due to the strong spread of the threshold voltage even for the same type of light sources. If two such LEDs are connected in parallel to the same voltage source, a current of different magnitude will pass through them. The difference can be so significant that one of the LEDs will immediately burn out.

Thus, it is not recommended to turn on LED light sources without stabilizers. These devices set the current to a given value without regard to the voltage applied to the circuit. The most modern devices include a two-terminal LED stabilizer, which is used to create low-cost solutions for driving LEDs. It includes a field effect transistor, strapping parts and other radio elements.

Schemes of current stabilizers on ROLL

This circuit works stably using elements such as KR142EN12 or LM317. They are adjustable voltage stabilizers operating with current up to 1.5A and input voltage up to 40V. Under normal thermal conditions, these devices are capable of dissipating power up to 10W. These ICs have a low self-consumption of approximately 8mA. This indicator remains unchanged even with a changing current passing through the ROLL and a changed input voltage.

The LM317 element is able to hold a constant voltage on the main resistor, regulated within certain limits using a trimmer resistor. The main resistor with a constant resistance ensures the stability of the current passing through it, so it is also known as a current-setting resistor.

The KREN stabilizer is simple and can be used as an electronic load, battery charger and other applications.

Current stabilizer on two transistors

Due to its simple design, stabilizers on two transistors are very often used in electronic circuits. Their main disadvantage is not quite stable current in loads with varying voltages. If high current characteristics are not required, then this stabilizing device is quite suitable for solving many simple tasks.

In addition to two transistors, there is a current-setting resistor in the stabilizer circuit. When current increases on one of the transistors (VT2), the voltage across the current-setting resistor increases. Under the influence of this voltage (0.5-0.6V), another transistor (VT1) begins to open. When this transistor opens, another transistor - VT2 starts to close. Accordingly, the amount of current flowing through it also decreases.

A bipolar transistor is used as VT2, however, if necessary, it is possible to create an adjustable current stabilizer on a MOSFET field effect transistor used as a zener diode. Its choice is based on a voltage of 8-15 volts. This element is used when the power supply voltage is too high, under the influence of which the gate in the field-effect transistor can be broken. More powerful MOSFET zener diodes are rated for higher voltage - 20 volts or more. The opening of such zener diodes occurs at a minimum gate voltage of 2 volts. Accordingly, there is an increase in voltage, which ensures the normal operation of the current stabilizer circuit.

Adjustable DC Stabilizer

Sometimes there is a need for current stabilizers with the ability to adjust over a wide range. Some circuits may use a derated current-setting resistor. In this case, it is necessary to use an error amplifier, which is based on an operational amplifier.

With the help of one current-setting resistor, the voltage is amplified in the other resistor. This condition is called amplified error voltage. Using the reference amplifier, the parameters of the reference voltage and the error voltage are compared, after which the state of the field-effect transistor is adjusted.

Such a circuit requires a separate power supply, which is supplied to a separate connector. The supply voltage must ensure the normal operation of all components of the circuit and not exceed a level sufficient to breakdown the field effect transistor. Proper circuit setup requires setting the variable resistor slider to its highest position. With the help of a tuning resistor, the maximum current value is set. Thus, the variable resistor allows you to adjust the current from zero to the maximum value set during the tuning process.

Powerful switching current stabilizer

A wide range of supply currents and loads is not always the main requirement for stabilizers. In some cases, the high efficiency of the device is of decisive importance. This problem is successfully solved by a microcircuit of a pulsed current stabilizer, which replaces compensation stabilizers. Devices of this type allow you to create a high voltage on the load even in the presence of a low input voltage.

In addition, there is a pulse-type step-up current stabilizer. They are used together with loads whose supply voltage exceeds the input voltage of the stabilizing device. As output voltage dividers, two resistors are used, which are used in the microcircuit, with the help of which the input and output voltage alternately decreases or increases.

Stabilizer on LM2576

electric-220.ru

Transistor Current Stabilizer

Content:

1. Assembling a current stabilizer from two transistors

During the operation of electrical networks, there is a constant need for current stabilization. This procedure is carried out using special devices, which include a current stabilizer on a transistor. They are widely used in various electronic devices, as well as when charging batteries of all types. Stabilizers are used in integrated circuits as current generators, creating converting and amplifying stages.

Conventional current regulators have a large output impedance, thereby eliminating the influence of load resistance and input voltage on the output current. The main disadvantage of these devices is the need to use a high voltage power supply. In this case, current stability is achieved by using resistors with high resistance. Therefore, the power dissipated by the resistor (P = I2 x R) at high currents may become unacceptable for the normal operation of the system. Current stabilizers on transistors have proven themselves much better, which perform their functions, regardless of the input voltage.

A simple transistor current regulator

Diode stabilizers are considered the simplest devices. Thanks to them, electrical circuits are greatly simplified, which leads to a decrease in the overall cost of devices. The operation of circuits becomes more stable and reliable. These qualities have made diode stabilizers indispensable in providing power to LEDs. The voltage range in which they can function normally is 1.8-100 volts. Due to this, it becomes possible to overcome impulse and continuous voltage changes.

Therefore, the glow of the LEDs can be of different brightness and shades, depending on the current flowing in the circuit. Several of these lamps, connected in series, operate in normal mode with the participation of only one diode stabilizer. This circuit can be easily converted, depending on the number of LEDs and the supply voltage. The required current is set by the stabilizers connected in parallel in the LED circuit.

Such stabilizers are installed in many designs of LED lamps, including the current stabilizer on a bipolar transistor. This is due to the properties of LEDs, which have a non-linear current-voltage characteristic. That is, when the voltage on the LED changes, the change in current occurs disproportionately. With a gradual increase in voltage, at first a very slow increase in current is observed and the LED does not glow. After the voltage reaches the threshold value, light appears and at the same time a very rapid increase in current is observed.

If the voltage continues to increase, a critical increase in current occurs, which leads to the burning of the LED. Therefore, the value of the threshold voltage is always indicated among the characteristics of LED light sources. High power LEDs generate a lot of heat and must be connected to special heat sinks.

Due to the wide spread of threshold voltage, all LEDs must be connected to a power source through a regulator. Even LEDs of the same type can have different forward voltages. Therefore, when two light sources are connected in parallel, different currents will pass through them. The difference can be so great that one of the LEDs will fail prematurely or burn out immediately.

With the help of a stabilizer for the LED, the value of the specified current is set, regardless of the voltage applied to the circuit. When the voltage exceeds the threshold level, the current, having reached the desired value, no longer changes. With a further increase in voltage, it remains unchanged on the LED, and increases only on the stabilizer.

FET current stabilizer circuit

Power surges very often lead to failure of electrical appliances, devices and other equipment. In order to prevent the occurrence of such situations, various stabilizing devices are used. Among them, current stabilizers on field-effect transistors, which ensure the stable operation of electrical equipment, are very popular. In everyday life, a do-it-yourself DC stabilizer is often used, the circuit of which allows you to solve basic problems.

The main function of these devices is to compensate for voltage drops and surges in the network. Stabilizers automatically maintain exactly the specified current parameters. In addition to current surges, changes in load power and ambient temperature are compensated. For example, if the power consumed by the equipment increases, then the current consumed will increase accordingly. As a rule, this leads to a voltage drop across the resistance of the wires and the current source.

Among many stabilizing devices, the most reliable is the current stabilizer circuit on the field, in which the transistor is connected in series with the load resistance. This causes only slight changes in the load current, while the input voltage value is constantly changing.

In order to know how such stabilizers work, you need to know the device and the principle of operation of field-effect transistors. These elements are controlled by an electric field, in connection with this, their name arose. The electric field itself arises under the action of an applied voltage, therefore, all field-effect transistors are semiconductor devices that operate under the control of a voltage that opens the channels of these devices.

The field effect transistor consists of three electrodes - source, drain and gate. Charged particles enter through the source and exit through the drain. Closing or opening the flow of particles is carried out using a shutter that performs the functions of a tap. Charged particles will only flow if a voltage is applied between drain and source. If there is no voltage, then there will be no current in the channel. Therefore, the higher the applied voltage, the more the tap opens. Due to this, the current in the channel between the drain-source increases, and the channel resistance decreases. For power supplies, the operation of field-effect transistors in the key mode is provided, which ensures full opening or closing of the channel.

These properties make it possible to calculate the current stabilizer on the transistor, which ensures that the current parameters are maintained at a certain level. The use of field-effect transistors also determines the principle of operation of such a stabilizer. Everyone knows that every ideal current source has an EMF tending to infinity and also an infinitely large internal resistance. This allows you to get the current with the required parameters, regardless of the load resistance.

In such an ideal source, a current arises that remains at the same level despite changes in load resistance. Maintaining the current at a constant level requires a constant change in the value of the EMF in the range above zero and to infinity. That is, the load resistance and EMF must change in such a way that the current remains stably at the same level.

However, in practice, such an ideal current stabilizer microcircuit will not be able to provide all the necessary qualities. This is due to the fact that the voltage range at the load is very limited and does not support the required current level. In real conditions, current and voltage sources are used together. An example is a conventional network with a voltage of 220 volts, as well as other sources in the form of batteries, generators, power supplies and other devices that generate electricity. Each of them can be connected in series with current stabilizers on field-effect transistors. The outputs of these devices are essentially current sources with the desired parameters.

Do-it-yourself wiring diagrams in the house

How to test a transistor without soldering it out of the circuit with a multimeter

How to test a transistor with a multimeter without soldering it out of the circuit

Ouzo designation on the diagram

Over the past 10-20 years, the number of consumer electronics has increased many times over. A huge variety of electronic components and ready-made modules appeared. Power requirements have also increased, many require a stabilized voltage or a stable current.

The driver is most often used as a current stabilizer for LEDs and charging car batteries. Such a source is now in every LED spotlight, lamp or luminaire. Consider all options for stabilization, ranging from old and simple to the most effective and modern. They are also called led driver.

• 1. Types of stabilizers
• 2. Popular models
• 3. Stabilizer for LEDs
• 4. Driver for 220V
• 5. Current stabilizer, circuit
• 6. LM317
• 7. Adjustable current stabilizer
• 8. Prices in China

Types of stabilizers

Pulse adjustable DC

15 years ago, in my first year, I took tests in the subject "Power Sources" for electronic equipment. From then until today, the LM317 chip and its analogues, which belongs to the class of linear stabilizers, remain the most popular and popular.

At the moment, there are several types of voltage and current stabilizers:

1. linear up to 10A and input voltage up to 40V;
2. pulse with a high input voltage, lowering;
3. pulse with low input voltage, increasing.

On a pulse PWM controller, usually from 3 to 7 amperes according to the characteristics. In reality, it depends on the cooling system and efficiency in a particular mode. Boosting from a low input voltage makes a higher output voltage. This option is used for power supplies with a small number of volts. For example, in a car, when you need to make 19V or 45V out of 12V. With a buck, it's easier, the high is reduced to the desired level.

Read about all the ways to power LEDs in the article "to 12 and 220V". Connection schemes are described separately from the simplest ones for 20 rubles to full-fledged blocks with good functionality.

By functionality, they are divided into specialized and universal. Universal modules usually have 2 variable resistances to adjust Volts and Amps output. Specialized ones most often do not have building elements and the output values ​​\u200b\u200bare fixed. Among the specialized ones, current stabilizers for LEDs are common, there are a large number of circuits on the Internet.

Popular Models

Lm2596

Among the impulse ones, the LM2596 has become popular, but by modern standards it has a low efficiency. If more than 1 amp, then a heatsink is required. A small list of similar ones:

1. LM317
2. LM2576
3. LM2577
4. LM2596
5. MC34063

I will supplement with a modern Chinese assortment, which is good in terms of characteristics, but is much less common. On Aliexpress, the search for the marking helps. The list is compiled by online stores:

• MP2307DN
• XL4015
• MP1584EN
• XL6009
• XL6019
• XL4016
• XL4005
• L7986A

Also suitable for Chinese DRL daytime running lights. Due to the low cost, LEDs are connected through a resistor to a car battery or car network. But the voltage jumps up to 30 volts in pulses. Low-quality LEDs cannot withstand such surges and begin to die. Chances are you've seen flashing DRLs or running lights where some of the LEDs don't work.

Do-it-yourself circuit assembly on these elements will be simple. Mostly these are voltage stabilizers, which are switched on in the current stabilization mode.

Do not confuse the maximum voltage of the entire unit and the maximum voltage of the PWM controller. Low-voltage 20V capacitors can be installed on the block when the pulse chip has an input up to 35V.

LED Stabilizer

It is easiest to make a current stabilizer for LEDs with your own hands on the LM317, you only need to calculate the resistor for the LED on an online calculator. Food can be used at hand, for example:

1. 19V laptop power supply;
2. from the printer for 24V and 32V;
3. from consumer electronics at 12 volts, 9V.

The advantages of such a converter are low price, easy to buy, minimum parts, high reliability. If the current stabilizer circuit is more complicated, then it becomes not rational to assemble it with your own hands. If you are not a radio amateur, then a switching current stabilizer is easier and faster to buy. In the future, it can be modified to the required parameters. You can find out more in the section "Ready-made modules".

Driver for 220 V

..

If you are interested in a driver for a 220v LED, then it is better to order or buy it. They are of medium difficulty to manufacture, but setup will take more time and setup experience will be required.

The 220 LED driver can be removed from faulty LED lamps, fixtures and spotlights that have a faulty LED circuit. In addition, almost any existing driver can be modified. To do this, find out the model of the PWM controller on which the converter is assembled. Typically, the output parameters are set by a resistor or several. Look at the datasheet to see what resistance should be in order to get the required amps.

If you put an adjustable resistor of the calculated value, then the number of amperes at the output will be configurable. Just do not exceed the rated power that was indicated.

Current stabilizer, circuit

I often have to look through the assortment on Aliexpress in search of inexpensive but high-quality modules. The difference in cost can be 2-3 times, it takes time to find the minimum price. But thanks to this I make an order for 2-3 pieces for tests. I buy for reviews and consultations of manufacturers who buy components in China.

In June 2016, the universal module on the XL4015 became the best choice, the price of which is 110 rubles with free delivery. Its characteristics are suitable for connecting powerful LEDs up to 100 watts.

Schematic in driver mode.

In the standard version, the XL4015 case is soldered to the board, which serves as a heatsink. To improve cooling on the XL4015 case, you need to put a radiator. Most put it on top, but the effectiveness of such an installation is low. It is better to put the cooling system on the bottom of the board, opposite the place where the microcircuit is soldered. Ideally, it is better to unsolder it and put it on a full-fledged radiator through thermal paste. The legs will most likely need to be lengthened with wires. If such serious cooling is required for the controller, then the Schottky diode will also need it. It will also have to be put on a radiator. Such a refinement will significantly increase the reliability of the entire circuit.

In general, the modules do not have protection against incorrect power supply. This instantly disables them, be careful.

LM317

Application (roll) does not even require any skills and knowledge of electronics. The number of external elements in the circuits is minimal, so this is an affordable option for anyone. Its price is very low, its possibilities and application have been repeatedly tested and verified. Only it requires good cooling, this is its main drawback. The only thing to be wary of is low-quality Chinese LM317 microcircuits, which have worse parameters.

Due to the absence of unnecessary noise at the output, linear stabilization microcircuits were used to power high-quality Hi-Fi and Hi-End DACs. For DACs, power cleanliness plays a huge role, so some use batteries for this.

The maximum power for the LM317 is 1.5 Amps. To increase the number of amperes, you can add a field effect transistor or a regular one to the circuit. It will be possible to get up to 10A at the output, it is set by low-resistance. In this scheme, the KT825 transistor takes on the main load.

Another way is to put an analog with higher specifications on a larger cooling system.

Adjustable current stabilizer

As a radio amateur with 20 years of experience, I am pleased with the range of ready-made blocks and modules for sale. Now you can assemble any device from ready-made blocks in a minimum time.

I began to lose confidence in Chinese products after I saw in the "Tank Biathlon" how the best Chinese tank had a wheel fall off.

Chinese online stores have become the leader in the range of power supplies, DC-DC current converters, drivers. In their free sale, you can find almost any modules, if you look better, then very highly specialized ones. For example, for 10,000 thousand rubles, you can assemble a spectrometer worth 100,000 rubles. Where 90% of the price is a markup for a brand and slightly modified Chinese software.

The price starts from 35 rubles. for a DC-DC voltage converter, the driver is more expensive and has two three trimming resistors instead of one.

For more versatile use, an adjustable driver is better. The main difference is the installation of a variable resistor in the circuit that sets the output amperes. These characteristics can be indicated in typical switching circuits in the specifications for the microcircuit, datasheet, datasheet.

The weak points of such drivers are the heating of the inductor and the Schottky diode. Depending on the PWM controller model, they can withstand 1A to 3A without additional cooling of the microcircuit. If above 3A, then cooling of the PWM and a powerful Schottky diode is required. The inductor is rewound with a thicker wire or replaced with a suitable one.

The efficiency depends on the operating mode, the voltage difference between the input and output. The higher the efficiency, the lower the heating of the stabilizer.

Prices in China

The cost is very low considering that shipping is included in the price. I used to think that because of the goods for 30-50 rubles, the Chinese will not even get dirty, a lot of work with a low income. But as practice has shown, I was wrong. Any penny nonsense they pack and send. It comes in 98% of cases, and I have been buying on Aliexpress for more than 7 years and for large amounts, probably already about 1 million rubles.

Therefore, I place an order in advance, usually 2-3 pieces of the same name. Unnecessary sell on a local forum or Avito, everything sells like hot cakes.

It is known that the brightness of the LED is very dependent on the current flowing through it. At the same time, the current of the LED is very steeply dependent on the supply voltage. This results in noticeable brightness ripples even with slight power instability.

But ripple is not terrible, what is much worse is that the slightest increase in the supply voltage can lead to such a strong increase in current through the LEDs that they simply burn out.

To prevent this, LEDs (especially powerful ones) are usually powered through special circuits - drivers, which are essentially current stabilizers. This article will consider circuits of simple current stabilizers for LEDs (on transistors or common microcircuits).

There are also very similar LEDs - SMD 5730 (without a unit in the name). They have a power of only 0.5 W and a maximum current of 0.18 A. So do not confuse.

Since when the LEDs are connected in series, the total voltage will be equal to the sum of the voltages on each of the LEDs, the minimum supply voltage of the circuit should be: Upit \u003d 2.5 + 12 + (3.3 x 10) \u003d 47.5 Volts.

You can calculate the resistance and power of the resistor for other current values ​​\u200b\u200busing a simple Regulator Design program (download).

Obviously, the higher the output voltage of the stabilizer, the more heat will be generated on the current-setting resistor and, therefore, the worse the efficiency. Therefore, for our purposes, the LM7805 is better suited than the LM7812.

LM317

Equally effective is a linear current regulator for LEDs on the LM317. Typical switching circuit:

The simplest LM317 switching circuit for LEDs, which allows you to assemble a powerful lamp, consists of a rectifier with a capacitive filter, a current stabilizer and 93 LEDs SMD 5630. MXL8-PW35-0000 (3500K, 31 Lm, 100 mA, 3.1 V, 400 mW, 5.3x3 mm) are used here.

If such a large garland of LEDs is not needed, then a ballast resistor or capacitor will have to be added to the driver on the LM317 to power the LEDs (to extinguish the excess voltage). How to do this, we considered in great detail in.

The disadvantage of such a current driver circuit for LEDs is that when the voltage in the network rises above 235 volts, the LM317 will be outside the calculated operating mode, and when it drops to ~ 208 volts and below, the microcircuit completely ceases to stabilize and the depth of the ripples will depend entirely and completely from tank C1.

Therefore, it is necessary to use such a lamp where the voltage is more or less stable. And the capacitance of this capacitor is not worth saving. The diode bridge can be taken ready-made (for example, a miniature MB6S) or assembled from suitable diodes (U arr at least 400 V, forward current >= 100 mA). Perfect for the ones mentioned above. 1N4007.

As you can see, the circuit is simple and does not contain any expensive components. Here are the current prices (and they are likely to drop further):

Name	characteristics	price
SMD 5630	LED, 3.3V, 0.15A, 0.5W	240 rub. / 1000pcs
LM317	1.25-37V, >1.5A	112 rub. / 10 pieces.
MB6S	600V, 0.5A	67 rub. / 20pcs
120µF, 400V	18x30mm	560 rub. / 10 pieces.

Thus, spending a total of 1000 rubles, you can collect a dozen 30-watt (!!!) non-flickering (!!!) light bulbs. And since the LEDs do not operate at full capacity, and the only electrolyte does not overheat, these lamps will be almost eternal.

Instead of a conclusion

The disadvantages of the schemes given in the article include low efficiency due to the useless waste of power on the regulatory elements. However, this is characteristic of all linear current stabilizers.

Low efficiency is unacceptable for devices powered by autonomous current sources (lamps, flashlights, etc.). A significant increase in efficiency (90% or more) can be achieved by using.