Your attention is presented to the circuit, assembled on the basis of the NE 555 timer (domestic analogue of KR1006VI1).
Rice. 1 PWM voltage regulator circuit
Schematic diagram of the stabilizer is shown on fig.1. Generator on DA1 ( NE 555), similar to that described in, works according to the pulse-phase principle, because the pulse width remains unchanged and equal to hundreds of microseconds, and only the distance between two pulses (phase) changes. Due to the low current consumption of the microcircuit (5 ... 10 mA), I increased the resistance R4 by almost 5 times, which facilitated its thermal regime. The key stage on VT2, VT1 is assembled according to the “common emitter - common collector” scheme, which minimizes the voltage drop across VT1. Only 2 transistors are used in the power amplifier, because the high output current of the microcircuit (according to 200 mA) allows you to directly drive powerful transistors without an emitter follower. Resistor R5 is necessary to exclude through current through the emitter-base VT1 and collector-
Fig.2
emitter VT2, which in open transistors are connected as two diodes. Due to the relatively low speed of this circuit, it was necessary to lower the generator frequency (increasing the capacitance C1). The input voltage should be as high as possible, but not exceed 40 ... 50 V. The resistance of the resistor R8 can be calculated by the formula
So, if the input voltage is 40 V, and at the output it should vary within 0 ... 25 V, then the resistance R8 is approximately equal to 6 kOhm. The most significant drawback of switching regulators compared to linear ones is that, due to the pulsed mode of operation, a high ripple coefficient (“whistling”) is observed at the output, which is very difficult to eliminate. It can be advised to include another similar filter in series with the L1-C3 filter.
The most significant advantage of this circuit is its high efficiency, and with a load current of up to 200 mA, a radiator on VT1 is not needed. The printed circuit board drawing of the stabilizer is shown on fig.2. The board is attached to the heatsink using the VT1 transistor soldered to it, but it can be attached to the chassis and separately from the transistor. The length of the connecting wires in this case should not exceed 10 ... 15 cm. Resistor R7
Imported, variable, instead of it you can use a trimmer or variable, which is located outside the board. The length of the wires in this case is not critical. The inductor L1 is wound on a ring with an outer diameter of 10 ... 15 mm with a wire d = 0.6 ... 0.8 mm until it is filled, the inductor of the additional filter is wound with the same wire on the coil from the transformer, the number of turns should be maximum. Transistor VT2 - any average power (KT602, KT817B ... G).
Capacitor C1 is better film (with low leakage). Choke L1 is desirable to fill with paraffin, because. he whistles quite loudly.
A.KOLDUNOV
Timers also deserve attention in the construction of laboratory power supplies. Possessing versatility, good load properties and operating in a fairly wide frequency range, timers are the best suited for creating simple pulsed LBPs. Hence, apparently, the love of the creators of the most popular series of SHI controllers for "timer" master oscillators, because, as you know, the timing part of the 38XX series and many families of other manufacturers, including the legendary Viper, is made on just such a generator.
Unlike its more specific counterparts in the “pulse-power” shop, the famous one is less picky about launch conditions, operating in the voltage range of 3-18V, and no less versatile, which allows creating a self-sufficient “core” for controlling a pulsed LBP based on this simple microcircuit with no worse parameters than on specialized microcircuits.
Scheme 6
Scheme 6 shows a simple version of the impulse-linear concept on .
As you can see, almost all the same key components and adjustment circuits are used in the circuit, so it does not make much sense to describe them separately and again.
The timer switching circuit also has no secrets. I will only pay attention to how the regulation of the output voltage is organized. Conclusions 5 and 6 of the timer are inputs of the differential stage of the built-in comparator. At the direct input (pin 6) of the comparator, using R3, C4 and a discharge transistor built into the timer, a triangular voltage is formed, the level of which is compared with the voltage at the inverse input of the comparator (pin 5).
The lower the voltage level at the inverse input (which is initially formed by the built-in voltage divider), the earlier in time the timer output (pin 3) rolls over to "0", the shorter the output positive pulse, the shorter the time the VT3 power switch is in the open state, saturating the circuit L1-C6, the lower the output voltage of the LBP. By increasing the voltage at pin 5, we get the opposite picture. In this case, in relation to circuits 6 and 7, the voltage at pin 5 of the timer is controlled by optocoupler IC1.
When a certain voltage drop is reached at the input / output of DA2 (approximately 2.9-3.3V, depending on the type of optocoupler, resistor R5), the optocoupler LED lights up, provoking the unlocking of its own transistor, which, in turn, de-energizes the inverse input of the built-in timer comparator . The timer output is flipped to "0", locking the power switch VT3 (locking the driver VT1 in circuit 7).
Scheme notes. For the normal functioning of this LBP, the key of which is made on a powerful field-effect transistor, one should not neglect the presence of a stabilizer on VT1, because otherwise, the quality of the control pulses may be degraded due to relatively large pulse currents at the moment of charging the FET gate.
This remark is also true for other schemes (previous and subsequent, where this stabilizer is “registered”) described in this article.
Scheme 7
Scheme 7 is a prototype of Scheme 1 and I cannot say anything new about the LBP layout shown in Scheme 7. This option was tested at the same input voltages, it is able to provide the same output parameters (under conditions limited by a breadboard assembly) as a prototype built on the 38XX microcircuit family.
Scheme 8
The simplest version of a pulsed LBP using a timer is shown in diagram 8. No features, except that a low-power field-effect transistor is used as an element that monitors the voltage at the midpoint of the P1-R8 divider KP501A, which copes with many tasks in the above schemes better than its bipolar counterparts. It is much cheaper than its foreign prototypes.
Oscillograms
Oscillograms 1-4 show SHI and relay modes depending on the output voltage adjustments at almost zero load. It can be seen that when the adjustment range is shifted towards low voltages, the SHI-regulation is combined with the relay one. This mode is typical for all schemes presented in the article.
Waveform 1
Waveform 2
Waveform 3
Waveform 4
pics
Figure 1, 2 shows a section of the breadboard, on which the LBP schemes were worked out.
Despite the installation, which is unusual for power impulse devices, the mounted circuits produced the declared results.
I needed to make a speed controller for the propeller. To blow off the smoke from the soldering iron, and ventilate the face of the face. Well, for fun, put everything at the minimum cost. The easiest way is to regulate a low-power DC motor, of course, with a variable resistor, but to find a cut for such a small denomination, and even the required power, you have to try hard, and it will obviously cost more than ten rubles. Therefore, our choice is PWM + MOSFET.
I took the key IRF630. Why this one MOSFET? Yes, I just got about ten of them from somewhere. So I use it, so you can put something less overall and low-power. Because the current here is unlikely to be more than an ampere, and IRF630 able to drag through itself under 9A. But it will be possible to make a whole cascade of fans by connecting them to one twist - enough power :)
Now it's time to think about what we'll do PWM. The thought immediately suggests itself - a microcontroller. Take some Tiny12 and do it on it. I dismissed this thought instantly.
- Spending such a valuable and expensive part on some kind of fan is disgusting to me. I will find a more interesting task for the microcontroller
- Another software for this to write, doubly zapadlo.
- The supply voltage is 12 volts there, lowering it to power the MK to 5 volts is generally already lazy
- IRF630 will not open from 5 volts, so here you would also have to install a transistor so that it supplies a high potential to the gate of the field worker. Nafig nafig.
Operational amplifiers can be discarded immediately. The fact is that for a general-purpose op-amp, after 8-10 kHz, as a rule, limit output voltage begins to collapse sharply, and we need to jerk the field worker. Yes, even at a supersonic frequency, so as not to squeak.
Op-amps devoid of such a drawback cost so much that you can buy a dozen of the coolest microcontrollers with this money. Into the fire!
Comparators remain, they do not have the ability of the opamp to smoothly change the output voltage, they can only compare two voltages and close the output transistor based on the results of the comparison, but they do it quickly and without blocking the characteristic. I rummaged through the barrels and did not find any comparators. Ambush! More precisely was LM339, but it was in a large case, and religion does not allow me to solder a microcircuit for more than 8 legs for such a simple task. It was also too much to drag into the storehouse. What to do?
And then I remembered such a wonderful thing as analog timer - NE555. It is a kind of generator, where you can set the frequency, as well as the duration of the pulse and pause, with a combination of resistors and a capacitor. How much different crap has been done on this timer, over its more than thirty-year history ... Until now, this microcircuit, despite its venerable age, is stamped in millions of copies and is available in almost every store at a price of a few rubles. With us, for example, it costs about 5 rubles. Rummaged through the bottom of the barrel and found a couple of pieces. ABOUT! Right now and stir up.
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How it works
If you do not delve deeply into the structure of the 555 timer, then it is not difficult. Roughly speaking, the timer monitors the voltage on the capacitor C1, which removes from the output THR(THRESHOLD - threshold). As soon as it reaches the maximum (the conder is charged), the internal transistor opens. which closes the output DIS(DISCHARGE - discharge) to the ground. At the same time, at the output OUT a logical zero appears. The capacitor begins to discharge after DIS and when the voltage on it becomes equal to zero (full discharge), the system will switch to the opposite state - at output 1, the transistor is closed. The capacitor starts to charge again and everything repeats again.
The charge of the capacitor C1 follows the path: " R4->upper arm R1 ->D2", and the discharge along the way: D1 -> lower arm R1 -> DIS. When we turn the variable resistor R1, then we change the ratio of the resistances of the upper and lower arms. Which, accordingly, changes the ratio of the pulse length to the pause.
The frequency is set mainly by the capacitor C1 and also depends a little on the value of the resistance R1.
Resistor R3 provides a pull-up output to a high level - so there is an open collector output. Which is not able to set a high level on its own.
Diodes can be installed completely, conders of about the same value, deviations within one order of magnitude do not particularly affect the quality of work. At 4.7 nanofarads set in C1, for example, the frequency drops to 18 kHz, but it is almost inaudible, it seems that my hearing is no longer perfect :(
I dug into the bins, which itself calculates the operating parameters of the NE555 timer and assembled the circuit from there, for an astable mode with a duty cycle of less than 50%, but instead of R1 and R2 I screwed in a variable resistor, which changed the duty cycle of the output signal. It is only necessary to pay attention to the fact that the output DIS (DISCHARGE) through the internal key of the timer connected to ground, so it was impossible to plant it directly to the potentiometer, because when the regulator is turned to the extreme position, this output would sit on Vcc. And when the transistor opens, there will be a natural short circuit and a timer with a beautiful puff will emit magic smoke, on which, as you know, all electronics work. As soon as the smoke leaves the microcircuit, it stops working. That's how it is. Therefore, we take and add another resistor per kilo-ohm. It will not make the weather in regulation, but it will protect it from burnout.
No sooner said than done. Etched the board, soldered the components:
Everything is simple below.
Here I am attaching a signet, in my dear Sprint Layout -
And this is the voltage on the engine. You can see a small transition process. It is necessary to put the conder in parallel on the floor of the microfarad and smooth it out.
As you can see, the frequency floats - it’s understandable, because our operating frequency depends on the resistors and the capacitor, and since they change, the frequency floats, but it doesn’t matter. In the entire range of regulation, it never fits into the audible range. And the whole construction cost 35 rubles, not counting the body. So - Profit!
When choosing a power source for powering LEDs, a PWM voltage regulator will be the right solution - for example, on a NE555 chip. The principle of operation of such a device is to pulse the supply of a given constant voltage to the LED with different duty cycles. So, for example, if a voltage pulse with a duration of only 0.1 second is applied to an LED per unit time (for example, one second), then, accordingly, the brightness of the LED will be 10% of its power, and if a pulse with a duration of 0.9 seconds is applied, 90%. This process is shown in graph 1.
The PWM circuit for the LED dimmer is shown in Figure 1. The circuit is assembled on an NE555 chip and is a pulse generator with adjustable duty cycle. The duty cycle of the pulses of this device depends on the rate of charge and discharge of the capacitor C1. The charge of the capacitor C1 is carried out along the circuit R2, D1, R1, C1, and the discharge - C1, R1, D2, pin 7 of the microcircuit. Thus, by changing the resistance of the resistor R1, we change the charge and discharge time of the capacitor C1 - thereby adjusting the duty cycle of the pulses at the output of the microcircuit (pin 3). At pin 3 of the microcircuit, the logical value "0" is +0.25V, and the logical value "1" is +1.7V. Thus, a voltage of +0.25V will not open transistor T1 - and at the output of the device, in a given period of time, there will be no voltage, and a voltage of +1.7V will open transistor T1 completely. Transistor T1 is represented by a CMOS field effect transistor IRFZ44N whose power reaches 150 watts. However, if you use more powerful transistors as T1, then you can achieve a greater output power of the device. As diodes D1, D2, you can use diodes 1N4148 or any of a number of diodes of the 1N4002 - 1N4007 series.
Fig.1. PWM circuit for LED dimmer on NE555
Also, this device is widely used as a DC motor speed controller. To do this, another diode is added to the circuit, installed at the output of the device (the cathode of the diode is connected to + Upit., The anode of the diode is connected to the drain of transistor T1. This diode protects the device from reverse voltage coming from the engine after turning off the power to the device.
The microcircuit of the 555th timer (the domestic analogue of KR1006VI1) is so versatile that it can be found in the most unexpected REA nodes. This article discusses switching power supply circuits that use this microcircuit.
In the home laboratory, especially in the field, a low-power source of various constant voltages is needed, which can be powered by batteries or galvanic cells, light and portable. Similar switching power supply circuits, which are commonly called DC / DC converters, can be created on the 555th timer. It so happened that we use the NE555 chip in our designs, but any of its analogues can be used in the circuits under consideration.
Bipolar voltage switching power supply circuit
It is assembled on a single NE555 chip (Fig. 1), which serves as a master square-wave generator. The generator is assembled according to the classical scheme. The repetition rate of the output pulses of the generator is 6.474 ... 6.37 kHz. It varies depending on the supply voltage, which can be 3.6 V (3 batteries in the power cassette) and 4.8 V (with 4 batteries in the cassette). ENERGIZER AA batteries with a capacity of 2500 mAh were used in the switching power supply circuit.
Rectangular pulses from the output 3 MS 555 through the limiting resistor R5 are fed to the base of the transistor switch VT1, the load of which is the inductor L1 with an inductance of 3 mH. With a sharp locking of this transistor, a large EMF of self-induction is induced in the inductor L1. The high-voltage pulses obtained in this way are fed to two parallel rectifiers with voltage doubling, the outputs of which will have two different polarity voltages of ± 4.5 ... 15 V.
These voltages can be adjusted by changing the duty cycle of the output pulses using the potentiometer R1. The constant voltage from the R1 engine enters pin 5 of the MC555 and changes the duty cycle, and hence the output voltage of both rectifiers. The output voltages of this source will be ideally equal only when the duty cycle of the generator pulses is equal to 2 (the duration of the pulses is equal to the pause between them). With a different duty cycle of the pulses, the output voltages of the source at points A and B will differ somewhat (up to 1 ... 2 V). Such a small difference is ensured by the use of doubling rectifiers in the switching power supply circuit, the capacitors of which are charged by both positive and negative pulses. This disadvantage is compensated by the simplicity and low cost of the scheme.
In this switching power supply circuit, chokes from electronic ballasts of unusable economical fluorescent lamps can be used. When disassembling these lamps, be careful not to damage the helical or U-shaped glass tubes, as they contain mercury. It is best to do this outdoors.
On some chokes, especially imported ones, the inductance value is marked in mH (2.8, 2.2, 3.0, 3.6, etc.).
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 1 are shown in Table 1.
Switching power supply circuit on two NE555
Figure 2 shows a diagram of a switching power supply with two NE555 timers. The first of these microcircuits (DD1) is connected according to the multivibrator circuit, at the output of which short rectangular pulses appear, taken from leg 3. The repetition rate of these pulses is changed using the potentiometer R3.
By this, the pulses are fed to the differentiating circuit C3R5 and the VD1 diode connected in parallel to the resistor R5. Since the cathode of the diode is connected to the power bus, short positive bursts of differentiated pulses (fronts) are shunted by the low direct resistance of the diode and have an insignificant value, and negative bursts (slumps), falling on the locked diode VD1, freely pass to the input of the waiting multivibrator MS DD2 (leg 2 ) and run it. Although VD1 is indicated on the diagram as D9I, in this position it is desirable to use a low-power Schottky diode, and, in extreme cases, you can use a KD 522 silicon diode.
Resistor R6 and capacitor C6 determine the duration of the output pulse of the waiting multivibrator (single vibrator) DD2, which controls the key VT1.
As in the previous switching power supply circuit, the current through the transistor VT1 is regulated by resistor R7, and the load is a choke from a ballast of 3 mH economical fluorescent lamps.
Since the MS generation frequency is lower than in the first circuit, the voltage doubling rectifier capacitor C7 has a capacitance of 10 μF, and a ceramic SMD capacitor was used in this position to reduce the size, but other types of capacitors can be used: K73, KBGI, MBGCH, MBM or electrolytic for a suitable voltage.
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 2 are shown in Table 2.
Switching power supply circuit on the NE555 timer and operational amplifier
The switching power supply circuit shown in Fig. 3 is similar, but an operational amplifier (op-amp) of the K140 UD12 or KR140 UD 1208 type is used as a master square-wave generator. This op-amp is very economical, can operate from a unipolar supply voltage from 3 to 30 V or from bipolar ± 1.5 ... 15 V.
The generation frequency is regulated by the potentiometer R3. To increase the bandwidth, conclusions 1,4,5 are combined and grounded to a common wire. Resistor R6, which regulates the control current, is reduced to the minimum possible value of 100 kOhm. The current consumption of the op-amp is within 1.5 ... 2 mA. Between the output of the op amp and the differentiating circuit C3R10VD1, from which the single vibrator DD1 is started, a buffer amplifier is connected on a transistor VT1 of the BC237 type, which serves to increase the steepness of the front and the decay of the output pulse of the MS DA1. 
In the load of the VT2 key, the L1 choke is used from the same ballasts from economical lamps. This inductor is protected from overvoltage by the R13VD2 chain. Its inductance is 1.65 mH, but it is wound with a thicker wire, therefore, its active resistance is less, and the quality factor is higher. This allows you to get a voltage of approximately 24 ... 25 V at the output of the rectifier with doubling VD3VD4.
It should also be noted that the switching power supply circuit in Fig. 3 can operate from a unipolar supply voltage of 3.3 V.
Input and output voltages, current consumption and pulse repetition rates for the circuit in Fig. 3 are given in Table 3.
