PWM controller. Pulse width modulation

On simple mechanisms it is convenient to install analog current regulators. For example, they can change the speed of rotation of the motor shaft. From the technical side, implementing such a regulator is simple (you will need to install one transistor). Suitable for adjusting independent speed of motors in robotics and power supplies. The most common two types of regulators are single-channel and two-channel.

Video No. 1. Single-channel regulator in operation. Changes the rotation speed of the motor shaft by rotating the variable resistor knob.

Video No. 2.

Increasing the rotation speed of the motor shaft when operating a single-channel regulator. An increase in the number of revolutions from the minimum to the maximum value when rotating the variable resistor knob. Video No. 3.

Two-channel regulator in operation. Independent setting of the torsion speed of motor shafts based on trimming resistors.

Functions and main characteristics

The load current of single-channel (photo 1) and two-channel (photo 2) regulators does not exceed 1.5 A. Therefore, to increase the load capacity, the KT815A transistor is replaced with KT972A. The numbering of the pins for these transistors is the same (e-k-b). But the KT972A model is operational with currents up to 4A.

Single channel motor controller

The device controls one motor, powered by voltage in the range from 2 to 12 volts.

1. Device design

The main design elements of the regulator are shown in the photo. 3. The device consists of five components: two variable resistance resistors with a resistance of 10 kOhm (No. 1) and 1 kOhm (No. 2), a transistor model KT815A (No. 3), a pair of two-section screw terminal blocks for the output for connecting a motor (No. 4) and input for connecting a battery (No. 5).

Note 1. Installation of screw terminal blocks is not necessary. Using a thin stranded mounting wire, you can connect the motor and power source directly.

1. Principle of operation

The operating procedure of the motor controller is described in the electrical diagram (Fig. 1). Taking into account the polarity, a constant voltage is supplied to the XT1 connector. The light bulb or motor is connected to the XT2 connector. A variable resistor R1 is turned on at the input; rotating its knob changes the potential at the middle output as opposed to the minus of the battery. Through current limiter R2, the middle output is connected to the base terminal of transistor VT1. In this case, the transistor is switched on according to a regular current circuit. The positive potential at the base output increases as the middle output moves upward from the smooth rotation of the variable resistor knob. There is an increase in current, which is due to a decrease in the resistance of the collector-emitter junction in transistor VT1. The potential will decrease if the situation is reversed.

1. Materials and details

A printed circuit board measuring 20x30 mm is required, made of a fiberglass sheet foiled on one side (permissible thickness 1-1.5 mm). Table 1 provides a list of radio components.

Note 2. The variable resistor required for the device can be of any manufacture; it is important to observe the current resistance values ​​​​for it indicated in Table 1.

Note 3. To regulate currents above 1.5A, the KT815G transistor is replaced with a more powerful KT972A (with a maximum current of 4A). In this case, the printed circuit board design does not need to be changed, since the distribution of pins for both transistors is identical.

1. Build process

For further work, you need to download the archive file located at the end of the article, unzip it and print it. The regulator drawing (file) is printed on glossy paper, and the installation drawing (file) is printed on a white office sheet (A4 format).

Next, the drawing of the circuit board (No. 1 in photo. 4) is glued to the current-carrying tracks on the opposite side of the printed circuit board (No. 2 in photo. 4). It is necessary to make holes (No. 3 in photo. 14) on the installation drawing in the mounting locations. The installation drawing is attached to the printed circuit board with dry glue, and the holes must match. Photo 5 shows the pinout of the KT815 transistor.

The input and output of terminal blocks-connectors are marked in white. A voltage source is connected to the terminal block via a clip. A fully assembled single-channel regulator is shown in the photo. The power source (9 volt battery) is connected at the final stage of assembly. Now you can adjust the shaft rotation speed using the motor; to do this, you need to smoothly rotate the variable resistor adjustment knob.

To test the device, you need to print a disk drawing from the archive. Next, you need to paste this drawing (No. 1) onto thick and thin cardboard paper (No. 2). Then, using scissors, a disc is cut out (No. 3).

The resulting workpiece is turned over (No. 1) and a square of black electrical tape (No. 2) is attached to the center for better adhesion of the surface of the motor shaft to the disk. You need to make a hole (No. 3) as shown in the image. Then the disk is installed on the motor shaft and testing can begin. The single-channel motor controller is ready!

Two-channel motor controller

Used to independently control a pair of motors simultaneously. Power is supplied from a voltage ranging from 2 to 12 volts. The load current is rated up to 1.5A per channel.

1. Device design

The main components of the design are shown in photo.10 and include: two trimming resistors for adjusting the 2nd channel (No. 1) and the 1st channel (No. 2), three two-section screw terminal blocks for output to the 2nd motor (No. 3), for output to the 1st motor (No. 4) and for input (No. 5).

Note:1 Installation of screw terminal blocks is optional. Using a thin stranded mounting wire, you can connect the motor and power source directly.

1. Principle of operation

The circuit of a two-channel regulator is identical to the electrical circuit of a single-channel regulator. Consists of two parts (Fig. 2). The main difference: the variable resistance resistor is replaced with a trimming resistor. The rotation speed of the shafts is set in advance.

Note.2.

1. Materials and details

To quickly adjust the rotation speed of the motors, the trimming resistors are replaced using a mounting wire with variable resistance resistors with the resistance values ​​indicated in the diagram.

1. Build process

You will need a printed circuit board measuring 30x30 mm, made of a fiberglass sheet foiled on one side with a thickness of 1-1.5 mm. Table 2 provides a list of radio components.

After downloading the archive file located at the end of the article, you need to unzip it and print it. The regulator drawing for thermal transfer (termo2 file) is printed on glossy paper, and the installation drawing (montag2 file) is printed on a white office sheet (A4 format).

The circuit board drawing is glued to the current-carrying tracks on the opposite side of the printed circuit board. Form holes on the installation drawing in the mounting locations. The installation drawing is attached to the printed circuit board with dry glue, and the holes must match. The KT815 transistor is being pinned. To check, you need to temporarily connect inputs 1 and 2 with a mounting wire.

Any of the inputs is connected to the pole of the power source (a 9-volt battery is shown in the example). The negative of the power supply is attached to the center of the terminal block. It is important to remember: the black wire is “-” and the red wire is “+”.

The motors must be connected to two terminal blocks, and the desired speed must also be set. After successful testing, you need to remove the temporary connection of the inputs and install the device on the robot model. The two-channel motor controller is ready!

The necessary diagrams and drawings for the work are presented. The emitters of the transistors are marked with red arrows.

To regulate the rotation speed of low-power brush-type electric motors, a resistor is usually used, which is connected in series with the motor. But this method of switching provides very low efficiency, and most importantly, does not allow for smooth adjustment of speed (finding a variable resistor of sufficient power for several tens of ohms is not at all easy). And the main disadvantage of this method is that sometimes the rotor stops when the supply voltage decreases. PWM controllers

, which will be discussed in this article, allow for smooth adjustment of speed without the disadvantages listed above. In addition, PWM controllers can also be used to adjust the brightness of incandescent lamps. Figure 1 shows a diagram of one of these. Field-effect transistor VT1 is a sawtooth voltage generator (with a repetition frequency of 150 Hz), and the operational amplifier on the DA1 chip works as a comparator that generates a PWM signal based on transistor VT2. The rotation speed is controlled by a variable resistor R5, which changes the width of the pulses. Due to the fact that their amplitude is equal to the supply voltage, the electric motor will not “slow down”, and in addition, it is possible to achieve a slower rotation than in normal mode.

The circuit of PWM regulators in Fig. 2 is similar to the previous one, but the master oscillator here is made using an operational amplifier (op-amp) DA1. This op-amp functions as a triangular voltage pulse generator with a repetition rate of 500 Hz. Variable resistor R7 allows for smooth adjustment of rotation.

In Fig.3. A very interesting regulator circuit is presented. This PWM regulator made on integral timer NE555. The master oscillator has a repetition frequency of 500 Hz. The duration of the pulses, and therefore the rotor speed of the electric motor, can be adjusted in the range from 2 to 98% of the repetition period. Generator output PWM regulator on NE555 timer connected to a current amplifier made on transistor VT1 and actually controls the electric motor M1.

The main disadvantage of the schemes discussed above is the absence of elements for stabilizing the shaft speed when the load changes. But the following diagram, shown in Fig. 4, will help solve this problem.

This PWM regulator, like most similar devices, has a master voltage pulse generator of a triangular shape (repetition frequency 2 kHz), made on DA1.1.DA1.2, a comparator on DA1.3, an electronic switch on transistor VT1, as well as a pulse duty cycle regulator , and essentially the rotational speed of the electric motor is R6. A feature of the circuit is the presence of positive feedback through resistors R12, R11, diode VD1, capacitor C2, and DA1.4, which ensures a constant rotational speed of the electric motor shaft when the load changes. When connected PWM regulator to a specific electric motor, using resistor R12, the POS depth is adjusted, at which self-oscillations of the rotation speed do not occur when the load on the motor shaft increases or decreases.

Element base. In the circuits presented in the article, the following analogues of parts can be used: the KT117A transistor can be replaced with a KT117B-G or, as an option, with a 2N2646; KT817B - KT815, KT805; microcircuit K140UD7 to K140UD6, or KR544UD1, TL071, TL081; timer NE555 on S555, or KR1006VI1; chip TL074 to TL064, or TL084, LM324. If you need to connect a more powerful load to the PWM controller, the KT817 key transistor must be replaced with a more powerful field-effect transistor, alternatively, IRF3905 or similar. The specified transistor is capable of passing currents up to 50A.

The 555 timer is widely used in control devices, for example, in PWM - speed controllers for DC motors.

Anyone who has ever used a cordless screwdriver has probably heard a squeaking sound coming from inside. This is the whistling of the motor windings under the influence of the pulse voltage generated by the PWM system.

It is simply indecent to regulate the speed of an engine connected to a battery in another way, although it is quite possible. For example, simply connect a powerful rheostat in series with the motor, or use an adjustable linear voltage regulator with a large radiator.

A variant of a PWM regulator based on a 555 timer is shown in Figure 1.

The circuit is quite simple and is based on a multivibrator, albeit converted into a pulse generator with an adjustable duty cycle, which depends on the ratio of the charge and discharge rates of capacitor C1.

The capacitor is charged through the circuit: +12V, R1, D1, the left side of the resistor P1, C1, GND. And the capacitor is discharged along the circuit: upper plate C1, right side of resistor P1, diode D2, pin 7 of the timer, bottom plate C1. By rotating the slider of resistor P1, you can change the ratio of the resistances of its left and right parts, and therefore the charging and discharging time of capacitor C1, and, as a consequence, the duty cycle of the pulses.

Figure 1. PWM regulator circuit on a 555 timer

This scheme is so popular that it is already available in the form of a set, as shown in the following figures.

Figure 2. Schematic diagram of a set of PWM regulators.

Timing diagrams are also shown here, but, unfortunately, the part values ​​are not shown. They can be seen in Figure 1, which is why it is shown here. Instead of bipolar transistor TR1, without altering the circuit, you can use a powerful field effect one, which will increase the load power.

By the way, another element has appeared in this diagram - diode D4. Its purpose is to prevent the timing capacitor C1 from discharging through the power source and the load - the motor. This ensures stabilization of the PWM frequency.

By the way, with the help of such circuits you can control not only the speed of a DC motor, but also simply an active load - an incandescent lamp or some kind of heating element.

Figure 3. Printed circuit board of a PWM regulator kit.

If you put in a little work, it is quite possible to recreate this using one of the programs for drawing printed circuit boards. Although, given the small number of parts, it will be easier to assemble one copy using a hinged installation.

Figure 4. Appearance of a set of PWM regulators.

True, the already assembled branded set looks quite nice.

Here, perhaps, someone will ask a question: “The load in these regulators is connected between +12V and the collector of the output transistor. But what about, for example, in a car, because everything there is already connected to the ground, the body, of the car?”

Yes, you can’t argue against the mass; here we can only recommend moving the transistor switch to the gap in the “positive” wire. A possible version of such a scheme is shown in Figure 5.

Figure 5.

Figure 6 shows the MOSFET output stage separately. The drain of the transistor is connected to +12V of the battery, the gate simply “hangs” in the air (which is not recommended), a load is connected to the source circuit, in our case a light bulb. This figure is shown simply to explain how a MOSFET transistor works.

Figure 6.

In order to open a MOSFET transistor, it is enough to apply a positive voltage to the gate relative to the source. In this case, the light bulb will light up at full intensity and will shine until the transistor is closed.

In this figure, the easiest way to turn off the transistor is to short-circuit the gate to the source. And such a manual closure is quite suitable for checking the transistor, but in a real circuit, especially a pulse circuit, you will have to add a few more details, as shown in Figure 5.

As mentioned above, an additional voltage source is required to turn on the MOSFET transistor. In our circuit, its role is played by capacitor C1, which is charged via the +12V circuit, R2, VD1, C1, LA1, GND.

To open transistor VT1, a positive voltage from a charged capacitor C2 must be applied to its gate. It is quite obvious that this will only happen when transistor VT2 is open. And this is only possible if the optocoupler transistor OP1 is closed. Then the positive voltage from the positive plate of capacitor C2 through resistors R4 and R1 will open transistor VT2.

At this moment, the input PWM signal must be at a low level and bypass the optocoupler LED (this LED switching is often called inverse), therefore, the optocoupler LED is off and the transistor is closed.

To turn off the output transistor, you need to connect its gate to the source. In our circuit, this will happen when transistor VT3 opens, and this requires that the output transistor of the optocoupler OP1 be open.

The PWM signal at this time is at a high level, so the LED is not shunted and emits the infrared rays assigned to it, the optocoupler transistor OP1 is open, which as a result turns off the load - the light bulb.

One of the options for using such a scheme in a car is daytime running lights. In this case, motorists claim to use high beam lamps turned on at full intensity. Most often, these designs are on a microcontroller; there are plenty of them on the Internet, but it’s easier to do it on a 555 timer.

Drivers for MOSFET transistors on 555 timer

The 555 integrated timer found another application in three-phase inverters, or as they are more often called variable frequency drives. The main purpose of “frequency drivers” is to regulate the rotation speed of three-phase asynchronous motors. In the literature and on the Internet you can find many schemes of homemade frequency drives, interest in which has not disappeared to this day.

In general the idea is this. The rectified mains voltage is converted into three-phase using the controller, as in an industrial network. But the frequency of this voltage can change under the influence of the controller. The methods of change are different, from simply manual control to regulation by an automatic system.

The block diagram of a three-phase inverter is shown in Figure 1. Points A, B, C show the three phases to which the asynchronous motor is connected. These phases are obtained by switching transistor switches, which are shown in this figure as special IGBT transistors.

Figure 1. Block diagram of a three-phase inverter

The inverter power switch drivers are installed between the control device (controller) and the power switches. Specialized microcircuits such as IR2130 are used as drivers, allowing you to connect all six keys to the controller at once - three upper and three lower, and in addition, it also provides a whole range of protections. All details about this chip can be found in the Data Sheet.

And everything would be fine, but such a microcircuit is too expensive for home experiments. And here our old friend integrated timer 555, also known as KR1006VI1, comes to the rescue again. The diagram of one arm of a three-phase bridge is shown in Figure 2.

Figure 2. Drivers for MOSFET transistors on a 555 timer

KR1006VI1 operating in Schmitt trigger mode are used as drivers for the upper and lower switches of power transistors. When using a timer in this mode, it is enough to simply obtain a gate opening pulse current of at least 200 mA, which ensures fast switching of the output transistors.

The transistors of the lower keys are connected directly to the common wire of the controller, so there are no difficulties in controlling the drivers - the lower drivers are controlled directly from the controller by logical signals.

The situation with the upper keys is somewhat more complicated. First of all, you should pay attention to how the upper key drivers are powered. This method of eating is called “booster”. Its meaning is as follows. The DA1 microcircuit is powered by capacitor C1. But how can it be charged?

When transistor VT2 opens, the negative plate of capacitor C1 is practically connected to the common wire. At this time, capacitor C1 is charged from the power source through diode VD1 to a voltage of +12V. When the transistor VT2 closes, the diode VD1 will also close, but the energy reserve in the capacitor C1 is enough to trigger the DA1 chip in the next cycle. To achieve galvanic isolation from the controller and among themselves, the upper keys must be controlled through optocoupler U1.

This power supply method allows you to get rid of the complexity of the power supply and get by with just one voltage. Otherwise, three isolated windings on the transformer, three rectifiers and three stabilizers would be required. More details about this method of power supply can be found in the descriptions of specialized microcircuits.

Boris Aladyshkin, http://electrik.info