Shim at 555 with feedback. Powerful PWM regulator

Another electronic device with wide application.
It is a powerful PWM (PWM) controller with smooth manual control. It operates at a constant voltage of 10-50V (it is better not to go beyond the range of 12-40V) and is suitable for regulating the power of various consumers (lamps, LEDs, motors, heaters) with a maximum current consumption of 40A.

Sent in a standard padded envelope




The case is held together with latches that break easily, so open it carefully.


Inside the circuit board and the removed regulator knob


The printed circuit board is double-sided fiberglass, soldering and installation are neat. Connection via a powerful terminal block.




Ventilation slots in the case are ineffective, because... almost completely covered by the printed circuit board.


When assembled it looks something like this


The actual dimensions are slightly larger than stated: 123x55x40mm

Schematic diagram of the device


The declared PWM frequency is 12kHz. The actual frequency varies in the range of 12-13kHz when adjusting the output power.
If necessary, the PWM operating frequency can be reduced by soldering the desired capacitor in parallel with C5 (initial capacitance 1nF). It is not advisable to increase the frequency, because switching losses will increase.
The variable resistor has a built-in switch in the leftmost position that allows you to turn off the device. There is also a red LED on the board that lights up when the regulator is operating.
For some reason, the markings on the PWM controller chip have been carefully erased, although it’s easy to guess that it’s an analogue of NE555 :)
The regulation range is close to the stated 5-100%
Element CW1 looks like a current stabilizer in the diode body, but I’m not sure exactly...
As with most power regulators, regulation is carried out via the negative conductor. There is no short circuit protection.
There are initially no markings on the mosfets and diode assembly; they are located on individual radiators with thermal paste.
The regulator can operate on an inductive load, because At the output there is an assembly of protective Schottky diodes, which suppresses the self-induction EMF.
A test with a current of 20A showed that the radiators heat up slightly and can draw more, presumably up to 30A. The measured total resistance of the open channels of field workers is only 0.002 Ohm (drops 0.04V at a current of 20A).
If you reduce the PWM frequency, you will pull out all the declared 40A. Sorry I can't check...

The NE555 integrated timer circuit (domestic analogue of KR1006VI1) has found wide application in control devices and in particular in PWM speed controllers for DC motors.

There are several ways to regulate the speed of direct current motors (DCM):
1. Rheostatic regulation.
2. Pulse regulation.
The use of rheostatic control of the speed of the DPT leads to the need to install powerful rheostats that generate a large amount of heat. The most economical way can be considered PWM speed control of the DFC (Figure 1).

Picture 1.

The basis of the pulse motor speed control circuit is a multivibrator based on the NE555 timer. The above circuit allows you to adjust the duty cycle of the pulses, determined by the ratio of the charging and discharging time of capacitor C1.

Capacitor C1 is charged via the following circuit: +12V - R1 - D1 - left side of resistor P1 - C1 – GND. Capacitor discharge circuit:: upper plate C1 - right side of resistor P1 - D2 - pin 7 of the timer - bottom plate C1. The charging and discharging time is determined by the value of the active resistance P1 in the circuit (the position of the variable resistor motor).

Another option for implementing a DC motor speed control circuit is shown in Figure 2. A distinctive feature of this circuit is the presence of diode D4, which prevents the discharge of the timing capacitor through the load (motor).

Figure 2.

A change in the duty cycle of the control pulse leads to a change in the voltage at the armature of the DC motor (Figure 3).

Figure 3.

The appearance of the PWM speed controller for a DC motor based on the NE555 integrated timer chip is shown in Figure 4.

Figure 4.

Another option for implementing the previously discussed DPT control principle can be the following scheme:

Figure 5.

In the above diagram, the transistor switch is connected to the “positive wire” of the power source. Opening the transistor in the output stage of the circuit will require an additional power source. In the above circuit, its function is performed by capacitor C1. The opening of transistor VT1 is carried out only when transistor VT2 is open through the circuit of capacitor C2. The output transistor is turned off when its gate is connected to the source (transistor VT3 is open). Turning the output transistor on and off leads to bypassing the optocoupler OP1 and turning off/on the load.

Recently there was a need to adjust the charging current in the charger, and as it should be in such cases, I did a little searching on the Internet and found a simple diagramPWM regulator on timer 555.

This PWM regulator is well suited for adjusting:

Engine speed

LED brightness

Adjusting the current in the charger

The circuit works perfectly in the range up to 16V without modification. The field-effect transistor practically does not heat up in loads up to 7A, so it does not need a radiator.

You can use any diodes, capacitors of approximately the same value as in the diagram. Deviations within one order of magnitude do not significantly affect the operation of the device. At 4.7 nanofarads set in C1, for example, the frequency drops to 18 kHz, but it is almost inaudible.

If after assembling the circuit the key control transistor gets hot, then most likely it does not open completely. That is, there is a large voltage drop across the transistor (it is partially open) and current flows through it. As a result, a lot of power is dissipated for heating. It is advisable to parallel the circuit at the output with large capacitors, otherwise it will sing and be poorly regulated. To avoid whistling, select C1, the whistling often comes from it.

If you need to smoothly adjust the speed of an electric motor or the brightness of a lamp, you should look towards PWM control. PWM is short for the long and scary name “pulse width modulation”. What this terrible name is, you will easily understand later from photographs of the oscilloscope screen, but for now let’s look at the diagram of the future device (regulator).

The scheme is classic; it is probably impossible to find the author. In any case, thanks to him for this reliable, time-tested circuitry! The heart of the regulator is a generator assembled on a device known under a dozen names. To begin with, you should take a chip in a DIP package; it is easier to solder it on a breadboard (for example, we use a solderless breadboard).

We collect the elements according to the diagram. It turned out something like this:

Now in more detail about the elements of the circuit:

Capacitor C1 is the main element that sets the operating frequency of our PWM regulator. In this case, we installed a capacitor with a capacity of 10nF or 0.001 μF (indicated on the case by the number 102). In this case, the generator frequency will be about 35 kHz. You may have to reduce the operating frequency of the circuit; to do this, you need to INCREASE the capacitance of capacitor C1.

Diode D3 is needed to “reset” reverse inductive voltage surges, where they come from - don’t think about it for now, we’ll remember the school physics course later... The main thing, pay attention - the diode must be Schottky!!! A simple rectifier diode (not fast) is not capable of high-quality operation at such frequencies and will quickly go to another world, to silicon valley.

Regarding the mosfet transistor... Any transistor that suits your current value will do. There is no need to try to install a transistor with a five-fold current reserve; keep in mind that the more powerful the mosfet, the greater the capacitance of its gate and, accordingly, the longer it takes to charge the gate. When the gate is charged for a long time, the transistor operates in a heavy transient mode and begins to cause global warming on earth, however, this quickly ends in the death of the transistor. In this case, it is necessary to reduce the frequency of the generator by increasing the capacitance C1.

The circuit is operational with a power supply from 5 to 18 Volts; for higher voltages, it is necessary to reduce the supply voltage to the timer chip, for example, through an integrated circuit.

In this tutorial I will show you how to create a simple PWM (Pulse Width Modulation) controller from a 555 chip, a timer and some other components. It's very simple and the NE555's circuitry works well for controlling LEDs, light bulbs, servo motors or DC motors.

My 555 PWM controller can only change the duty cycle from 10% to 90%.

Step 1: What is PWM

Pulse width modulation (PWM) of a signal or power supply involves modulating its duty cycle to either convey information over a communication channel or control the power being sent. The simplest method of generating a PWM signal requires only a sawtooth or triangle waveform (easily generated using a simple oscillator) and a comparator.

When the value of the reference signal (green sine wave in Figure 2) is greater than the modulation signal (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state. But in my PWM I will not use a comparator.

Step 2: PWM Types

There are three types of PWM:

1. The center of the ripple can be fixed in the middle of the time window, and both edges of the pulse are moved to compress or expand the width.
2. The leading edge of the ripple can be kept at the leading edge of the time window, and the trailing edge will be modulated.
3. The tail edge of the pulsation can be fixed, while the leading edge will be modulated.

Three types of PWM signals (blue): leading edge modulation (top row), trailing edge modulation (middle row), and middle ripple (both edges modulated, bottom row). The green lines are the sawtooth signals used to generate PWM signals using the intersection method.

Step 3: How can PWM help us?

Nutrition:
The PWM can be used to reduce the total amount of power supplied to the LOAD without the losses typically incurred when limiting the power supply by resistive means. This is because the average power supplied is proportional to the modulation cycle.

At a high enough modulation rate, passive electronic filters can be used to smooth the pulse train and restore the average analog signal.

High frequency PWM power control systems are easily implemented using solid state switches. Discrete modulation on/off states are used to control the state of the switch(es), which control the voltage accordingly. The main advantage of this system is that the switches are either off and have no current flow, or on and (ideally) have no voltage loss around them. The product of current and voltage at any given time determines the power dissipated by the switch, so (ideally) no power is dissipated at all.

In reality, solid state switches are not ideal, but it is still possible to build high performance controllers with them.

PWM is also often used to control the flow of electrical power to another device, such as in controlling the speed of electric motors, adjusting the volume of Class D audio amplifiers, or adjusting the brightness of light sources, and many other power electronics applications. For example, light dimmers for home use use some type of PWM control.

Home light dimmers typically include electronic circuits that suppress current at specific portions of each AC mains voltage cycle. Adjusting the brightness of the light emitted by a light source is simply a matter of adjusting the voltage (or phase) in the AC cycle in which the dimmer begins to apply electrical current to the light source (for example, using an electronic switch such as a triac). In this case, the PWM duty cycle is determined by the frequency of the mains voltage (50 Hz or 60 Hz depending on the country). These fairly simple types of dimmers can be used effectively with inert (or relatively slow-responding) light sources, such as incandescent lamps for example, for which the additional modulation in the supplied electrical energy caused by the dimmer causes only minor additional variations in the emitted light.

However, some other light sources, such as LEDs, turn on and off very quickly and appear to flicker if they come with low voltage. The reproducible flicker effects from such fast response sources can be reduced by increasing the switching frequency. If the light fluctuations are fast enough, the human visual system can no longer register them, and the eye perceives the average intensity of the time without flicker (see flicker fusion threshold).

Voltage regulation:
PWM is also used in efficient voltage regulators. By switching the voltage to the load with the appropriate duty cycle, the output will approximate the voltage at the desired level. Switching noise is usually filtered by an inductor and a capacitor.

One method measures the output voltage. When it is below the desired voltage, it turns on the switch. When the output voltage is higher than the desired voltage, it turns off the switch.

Computer fan speed controllers typically use PWM because it is much more efficient than a potentiometer.

PWM is sometimes used in audio synthesis, particularly subtractive synthesis, because it produces a sound effect similar to a choir or slightly detuned oscillators playing together. (PWM is actually equivalent to the difference of two sawtooth waves.) The relationship between high and low levels is usually modulated by a low-frequency oscillator or LFO.

A new class of audio amplifiers based on the PWM principle has become popular. Called "Class D amplifiers", these amplifiers produce the PWM equivalent of an analog input signal, which is fed to the loudspeaker through a suitable filter network to block the carrier and restore the original audio signal. These amplifiers are characterized by very good efficiency figures (around 90%) and compact size/light weight for high output powers.

Historically, a crude form of PWM has been used to reproduce PCM digital audio on a PC speaker, which is only capable of producing two levels of audio. By carefully determining the duration of the pulses and relying on the physical filtering properties of the speaker (limited frequency response, self-inductance, etc.), it is possible to obtain approximate reproductions of mono PCM samples, albeit at very low quality, and with very different results between implementations.

In more recent times, the Digital Stream digital encoding technique was introduced, which uses a generalized form of pulse width modulation called pulse density modulation at a sampling rate high enough (typically on the order of MHz) to cover all acoustic frequencies with sufficient accuracy. This method is used in the SACD format, and the reproduction of the encoded audio signal is essentially the same as the method used in Class D amplifiers.

Speaker: Using PWM, the arc (plasma) can be modulated and if it is within hearing range, it can be used as a speaker. This type of speaker is used in a Hi-Fi sound system as a tweeter.

Cool, isn't it?

Step 4: Required Components

It's a simple one chip circuit so you don't need many components

• NE555, LM555 or 7555 (cmos)
• I recommend using two 1n4148 diodes, but 1n40xx series diodes will also work
• Potentiometer 100K
• Green capacitor 100nf
• Ceramic capacitor 220pf
• Printed circuit board
• Semiconductor transistor

Step 5: Building the Device

Just follow the diagram and place all the parts on the layout. Double check the location of each component before turning on the device. If you want to effectively control and control the brightness of a light source or motor, you can put only a power transistor at its output, but if you only want to control the light source or motor, then it is recommended to put a capacitor capacitor, for example, 2200uf. If you install this capacitor and turn on the motor at a load of 40%, the motor will be 60% more efficient at the same speed and torque.

There are two videos here that show how my PWM works. In the first one you can see that the fan starts spinning at 90% duty cycle. On the second one you can see the LEDs are blinking and the fan is running at 80%.