DIY voltage regulator: master class on how to make a simple voltage regulation device. Rectifiers with thyristor voltage regulator A simple do-it-yourself thyristor voltage regulator circuit

A semiconductor device that has 5 p-n junctions and is capable of passing current in the forward and reverse directions is called a triac. Due to the inability to operate at high frequencies of alternating current, high sensitivity to electromagnetic interference and significant heat generation when switching large loads, they are currently not widely used in high-power industrial installations.

There they are successfully replaced by circuits based on thyristors and IGBT transistors. But the compact dimensions of the device and its durability, combined with the low cost and simplicity of the control circuit, allowed them to be used in areas where the above disadvantages are not significant.

Today, triac circuits can be found in many household appliances from hair dryers to vacuum cleaners, hand-held power tools and electric heating devices - where smooth power adjustment is required.

Principle of operation

The power regulator on a triac works like an electronic key, periodically opening and closing at a frequency specified by the control circuit. When unlocked, the triac passes part of the half-wave of the mains voltage, which means the consumer receives only part of the rated power.

Do it yourself

Today, the range of triac regulators on sale is not very large. And, although the prices for such devices are low, they often do not meet consumer requirements. For this reason, we will consider several basic circuits of regulators, their purpose and the element base used.

Device diagram

The simplest version of the circuit, designed to work with any load. Traditional electronic components are used, the control principle is phase-pulse.

Main components:

• triac VD4, 10 A, 400 V;
• dinistor VD3, opening threshold 32 V;
• potentiometer R2.

The current flowing through potentiometer R2 and resistance R3 charges capacitor C1 with each half-wave. When the voltage on the capacitor plates reaches 32 V, the dinistor VD3 opens and C1 begins to discharge through R4 and VD3 to the control terminal of the triac VD4, which opens to allow current to flow to the load.

The opening duration is regulated by selecting the threshold voltage VD3 (constant value) and resistance R2. The power in the load is directly proportional to the resistance value of potentiometer R2.

An additional circuit of diodes VD1 and VD2 and resistance R1 is optional and serves to ensure smooth and accurate adjustment of the output power. The current flowing through VD3 is limited by resistor R4. This achieves the pulse duration required to open VD4. Fuse Pr.1 protects the circuit from short circuit currents.

A distinctive feature of the circuit is that the dinistor opens at the same angle in each half-wave of the mains voltage. As a result, the current does not rectify, and it becomes possible to connect an inductive load, for example a transformer.

Triacs should be selected according to the load size, based on the calculation of 1 A = 200 W.

Elements used:

• Dinistor DB3;
• Triac TS106-10-4, VT136-600 or others, the required current rating is 4-12A.
• Diodes VD1, VD2 type 1N4007;
• Resistances R1100 kOhm, R3 1 kOhm, R4 270 Ohm, R5 1.6 kOhm, potentiometer R2 100 kOhm;
• C1 0.47 µF (operating voltage from 250 V).

Note that the scheme is the most common, with minor variations. For example, a dinistor can be replaced with a diode bridge, or an interference-suppressing RC circuit can be installed in parallel with the triac.

A more modern circuit is one that controls the triac from a microcontroller - PIC, AVR or others. This circuit provides more accurate regulation of voltage and current in the load circuit, but is also more complex to implement.

Triac power regulator circuit

Assembly

The power regulator must be assembled in the following sequence:

1. Determine the parameters of the device on which the device being developed will work. Parameters include: number of phases (1 or 3), the need for precise adjustment of output power, input voltage in volts and rated current in amperes.
2. Select the type of device (analog or digital), select elements according to load power. You can check your solution in one of the programs for modeling electrical circuits - Electronics Workbench, CircuitMaker or their online analogues EasyEDA, CircuitSims or any other of your choice.
3. Calculate the heat dissipation using the following formula: voltage drop across the triac (about 2 V) multiplied by the rated current in amperes. The exact values ​​of the voltage drop in the open state and the rated current flow are indicated in the characteristics of the triac. We get the power dissipation in watts. Select a radiator according to the calculated power.
4. Purchase the necessary electronic components, radiator and printed circuit board.
5. Lay out contact tracks on the board and prepare sites for installing elements. Provide mounting on the board for a triac and radiator.
6. Install the elements on the board using soldering. If it is not possible to prepare a printed circuit board, then you can use surface mounting to connect the components using short wires. When assembling, pay special attention to the polarity of connecting the diodes and triac. If there are no pin markings on them, then there are “arcs”.
7. Check the assembled circuit with a multimeter in resistance mode. The resulting product must correspond to the original design.
8. Securely attach the triac to the radiator. Don’t forget to lay an insulating heat transfer gasket between the triac and the radiator. The fastening screw is securely insulated.
9. Place the assembled circuit in a plastic case.
10. Remember that at the terminals of the elements Dangerous voltage is present.
11. Turn the potentiometer to minimum and perform a test run. Measure the voltage at the regulator output with a multimeter. Smoothly turn the potentiometer knob to monitor the change in output voltage.
12. If the result is satisfactory, then you can connect the load to the output of the regulator. Otherwise, it is necessary to make power adjustments.

Triac power radiator

Power adjustment

The power control is controlled by a potentiometer, through which the capacitor and the capacitor discharge circuit are charged. If the output power parameters are unsatisfactory, you should select the resistance value in the discharge circuit and, if the power adjustment range is small, the potentiometer value.

• extend lamp life, adjust lighting or soldering iron temperature A simple and inexpensive regulator using triacs will help.
• select the circuit type and component parameters according to the planned load.
• work it out carefully circuit solutions.
• be careful when assembling the circuit, observe the polarity of semiconductor components.
• do not forget that electric current exists in all elements of the circuit and it is deadly to humans.

Thyristor voltage regulators are devices designed to regulate the speed and torque of electric motors. Regulation of rotation speed and torque is carried out by changing the voltage supplied to the motor stator, and is carried out by changing the opening angle of the thyristors. This method of controlling an electric motor is called phase control. This method is a type of parametric (amplitude) control.

They can be performed with both closed and open control systems. Open-loop regulators do not provide satisfactory speed control. Their main purpose is to regulate torque to obtain the desired operating mode of the drive in dynamic processes.

The power part of a single-phase thyristor voltage regulator includes two controlled thyristors, which ensure the flow of electric current at the load in two directions with a sinusoidal voltage at the input.

Thyristor regulators with closed control system are used, as a rule, with negative speed feedback, which makes it possible to have fairly rigid mechanical characteristics of the drive in the low-speed zone.

Most effective use thyristor regulators for speed and torque control.

Power circuits of thyristor regulators

In Fig. 1, a-d shows possible circuits for connecting the rectifier elements of the regulator in one phase. The most common of them is the diagram in Fig. 1, a. It can be used with any stator winding connection scheme. The permissible current through the load (rms value) in this circuit in continuous current mode is equal to:

Where I t - permissible average value of current through the thyristor.

Maximum forward and reverse voltage of the thyristor

Where k zap - safety factor selected taking into account possible switching overvoltages in the circuit; - effective value of the line voltage of the network.

Rice. 1. Diagrams of power circuits of thyristor voltage regulators.

In the diagram in Fig. 1b there is only one thyristor connected to the diagonal of the bridge of uncontrolled diodes. The relationship between the load and thyristor currents for this circuit is:

Uncontrolled diodes are selected for a current half as much as for a thyristor. Maximum forward voltage on the thyristor

The reverse voltage across the thyristor is close to zero.

Scheme in Fig. 1, b has some differences from the diagram in Fig. 1, and on the construction of a control system. In the diagram in Fig. 1, and control pulses to each of the thyristors must follow the frequency of the supply network. In the diagram in Fig. 1b, the frequency of control pulses is twice as high.

Scheme in Fig. 1, c, consisting of two thyristors and two diodes, in terms of control capability, loading, current and maximum forward voltage of the thyristors is similar to the circuit in Fig. 1, a.

The reverse voltage in this circuit is close to zero due to the shunting effect of the diode.

Scheme in Fig. 1, g in terms of current and maximum forward and reverse voltage of the thyristors is similar to the circuit in Fig. 1, a. Scheme in Fig. 1, d differs from those considered in the requirements for the control system to ensure the required range of change in the control angle of the thyristors. If the angle is measured from zero phase voltage, then for the circuits in Fig. 1, a-c the relationship is correct

Where φ - load phase angle.

For the diagram in Fig. 1, d a similar relationship takes the form:

The need to increase the range of angle changes complicates things. Scheme in Fig. 1, d can be used when the stator windings are connected in a star without a neutral wire and in a triangle with the inclusion of rectifier elements in the linear wires. The scope of application of the specified scheme is limited to non-reversible, as well as reversible electric drives with contact reverse.

Scheme in Fig. 4-1, d is similar in its properties to the diagram in Fig. 1, a. The triac current here is equal to the load current, and the frequency of the control pulses is equal to double the frequency of the supply voltage. The disadvantage of a circuit based on triacs is that the permissible values ​​of du/dt and di/dt are significantly lower than those of conventional thyristors.

For thyristor regulators, the most rational diagram is in Fig. 1, but with two back-to-back thyristors.

The power circuits of the regulators are made with back-to-back thyristors connected in all three phases (symmetrical three-phase circuit), in two and one phase of the motor, as shown in Fig. 1, f, g and h, respectively.

In regulators used in crane electric drives, the most widespread is the symmetrical connection circuit shown in Fig. 1, e, which is characterized by the least losses from higher harmonic currents. Higher loss values ​​in circuits with four and two thyristors are determined by voltage asymmetry in the motor phases.

Basic technical data of thyristor regulators of the PCT series

Thyristor regulators of the PCT series are devices for changing (according to a given law) the voltage supplied to the stator of an asynchronous motor with a wound rotor. Thyristor regulators of the PCT series are made according to a symmetrical three-phase switching circuit (Fig. 1, e). The use of regulators of this series in crane electric drives allows for regulation of rotation speed in the range of 10:1 and regulation of engine torque in dynamic modes during start-up and braking.

Thyristor regulators of the PCT series are designed for continuous currents of 100, 160 and 320 A (maximum currents, respectively, 200, 320 and 640 A) and voltages of 220 and 380 V AC. The regulator consists of three power blocks assembled on a common frame (according to the number of phases of back-to-back thyristors), a block of current sensors and an automation block. The power blocks use tablet thyristors with coolers made of drawn aluminum profiles. Air cooling is natural. The automation unit is the same for all versions of regulators.

Thyristor regulators are made with a degree of protection IP00 and are intended for installation on standard frames of magnetic controllers of the TTZ type, which are similar in design to controllers of the TA and TCA series. Overall dimensions and weight of PCT series regulators are indicated in table. 1.

Table 1 Dimensions and weight of voltage regulators of the PCT series

The TTZ magnetic controllers are equipped with direction contactors for reversing the motor, rotor circuit contactors and other relay contact elements of the electric drive that communicate between the command controller and the thyristor regulator. The structure of the regulator control system can be seen from the functional diagram of the electric drive shown in Fig. 2.

The three-phase symmetrical thyristor block T is controlled by the SFU phase control system. With the help of the command controller KK in the regulator, the speed setting of the BZS is changed. Through the BZS block, as a function of time, the acceleration contactor KU2 in the rotor circuit is controlled. The difference between the task signals and the TG tachogenerator is amplified by amplifiers U1 and US. A logical relay device is connected to the output of the ultrasonic amplifier, which has two stable states: one corresponds to turning on the forward direction contactor KB, the second corresponds to turning on the reverse direction contactor KN.

Simultaneously with the change in the state of the logical device, the signal in the control circuit control circuit is reversed. The signal from the matching amplifier U2 is summed with the delayed feedback signal for the motor stator current, which comes from the TO current limiting unit and is fed to the input of the SFU.

The BL logic block is also influenced by a signal from the current sensor block DT and the current presence block NT, which prohibits switching of contactors in the direction under current. The BL block also carries out nonlinear correction of the rotation speed stabilization system to ensure the stability of the drive. Regulators can be used in electric drives of lifting and moving mechanisms.

Regulators of the PCT series are made with a current limiting system. The current limiting level for protecting thyristors from overloads and for limiting motor torque in dynamic modes varies smoothly from 0.65 to 1.5 of the rated current of the regulator, the current limiting level for overcurrent protection is from 0.9 to. 2.0 rated current of the regulator. A wide range of changes in protection settings ensures operation of a regulator of the same standard size with motors differing in power by approximately 2 times.

Rice. 2. Functional diagram of an electric drive with a thyristor regulator of the PCT type: KK - command controller; TG - tachogenerator; KN, KB - directional contactors; BZS - speed setting unit; BL - logic block; U1, U2. Ultrasound - amplifiers; SFU - phase control system; DT - current sensor; IT - current availability block; TO - current limiting unit; MT - protection unit; KU1, KU2 - acceleration contactors; CL - linear contactor: R - switch.

Rice. 3. Thyristor voltage regulator PCT

The sensitivity of the current presence system is 5-10 A of the effective value of the current in the phase. The regulator also provides protection: zero, against switching overvoltages, against loss of current in at least one of the phases (IT and MT units), against interference with radio reception. Fast-acting fuses of the PNB 5M type provide protection against short-circuit currents.

Content:

In modern amateur radio circuits, various types of parts are widespread, including a thyristor power regulator. Most often, this part is used in 25-40 watt soldering irons, which under normal conditions easily overheat and become unusable. This problem is easily solved with the help of a power regulator, which allows you to set the exact temperature.

Application of thyristor regulators

As a rule, thyristor power regulators are used to improve the performance properties of conventional soldering irons. Modern designs, equipped with many functions, are expensive, and their use will be ineffective for small volumes. Therefore, it would be more appropriate to equip a conventional soldering iron with a thyristor regulator.

Thyristor power regulator is widely used in lighting systems. In practice, they are ordinary wall switches with a rotating control knob. However, such devices can only work normally with ordinary incandescent lamps. They are not at all perceived by modern compact fluorescent lamps, due to the rectifier bridge with an electrolytic capacitor located inside them. The thyristor simply will not work in conjunction with this circuit.

The same unpredictable results are obtained when trying to adjust the brightness of LED lamps. Therefore, for an adjustable lighting source, the best option would be to use conventional incandescent lamps.

There are other areas of application of thyristor power regulators. Among them, it is worth noting the ability to adjust hand-held power tools. Regulating devices are installed inside the housings and allow you to change the number of revolutions of a drill, screwdriver, hammer drill and other tools.

The principle of operation of a thyristor

The operation of power regulators is closely related to the operating principle of the thyristor. On radio circuits it is indicated by an icon resembling a regular diode. Each thyristor is characterized by one-way conductivity and, accordingly, the ability to rectify alternating current. Participation in this process becomes possible provided that a positive voltage is applied to the control electrode. The control electrode itself is located on the cathode side. In this regard, the thyristor was previously called a controlled diode. Before the control pulse is applied, the thyristor will be closed in any direction.

In order to visually determine the serviceability of the thyristor, it is connected to a common circuit with the LED through a constant voltage source of 9 volts. Additionally, a limiting resistor is connected together with the LED. A special button closes the circuit and the voltage from the divider is supplied to the control electrode of the thyristor. As a result, the thyristor opens and the LED begins to emit light.

When the button is released, when it is no longer held down, the glow should continue. If you press the button again or repeatedly, nothing will change - the LED will still shine with the same brightness. This indicates the open state of the thyristor and its technical serviceability. It will remain in the open position until such a state is interrupted under the influence of external influences.

In some cases there may be exceptions. That is, when you press the button, the LED lights up, and when you release the button, it goes out. This situation becomes possible due to the current passing through the LED, the value of which is less compared to the holding current of the thyristor. For the circuit to work properly, it is recommended to replace the LED with an incandescent lamp, which will increase the current. Another option would be to select a thyristor with a lower holding current. The holding current parameter for different thyristors may vary widely; in such cases, it is necessary to select an element for each specific circuit.

Circuit of the simplest power regulator

The thyristor participates in rectifying alternating voltage in the same way as an ordinary diode. This leads to half-wave rectification within negligible limits with the participation of one thyristor. To achieve the desired result, two half-cycles of the network voltage are controlled using power regulators. This becomes possible thanks to the back-to-back connection of thyristors. In addition, thyristors can be connected to the diagonal circuit of the rectifier bridge.

The simplest circuit of a thyristor power regulator is best considered using the example of adjusting the power of a soldering iron. There is no point in starting the adjustment directly from the zero mark. In this regard, only one half-cycle of the positive mains voltage can be regulated. The negative half-cycle passes through the diode, without any changes, directly to the soldering iron, providing it with half the power.

The passage of a positive half-cycle occurs through the thyristor, due to which the adjustment is performed. The thyristor control circuit contains simple elements in the form of resistors and a capacitor. The capacitor is charged from the top wire of the circuit, through resistors and the capacitor, the load and the bottom wire of the circuit.

The control electrode of the thyristor is connected to the positive terminal of the capacitor. When the voltage across the capacitor increases to a value that allows the thyristor to turn on, it opens. As a result, some part of the positive half-cycle of the voltage is passed into the load. At the same time, the capacitor is discharged and prepared for the next cycle.

A variable resistor is used to regulate the charging rate of the capacitor. The faster the capacitor is charged to the voltage value at which the thyristor opens, the sooner the thyristor opens. Consequently, more positive half-cycle voltage will be supplied to the load. This circuit, which uses a thyristor power regulator, serves as the basis for other circuits used in various fields.

DIY thyristor power regulator

Voltage regulators are widely used in everyday life and industry. Many people know such a device as a dimmer, which allows you to continuously adjust the brightness of lamps. This is an excellent example of a 220V voltage regulator. It is quite easy to assemble such a device with your own hands. Of course, it can be purchased in a store, but the cost of a homemade product will be much lower.

Purpose and principle of operation

Using voltage regulators, you can change not only the brightness of incandescent lamps, but also the rotation speed of electric motors, the temperature of the soldering iron tip and so on. These devices are often called power regulators, which is not entirely correct. Devices designed to regulate power are based on PWM (pulse width modulation) circuits.

This allows you to obtain different pulse repetition rates at the output, the amplitude of which remains unchanged. However, if a voltmeter is connected in parallel to the load in such a circuit, the voltage will also change. The fact is that the device simply does not have time to accurately measure the amplitude of the pulses.

Voltage regulators are most often made on the basis of semiconductor parts - thyristors and triacs. With their help, the duration of passage of a voltage wave from the network to the load is changed.

It should be noted that voltage regulators will be most effective when working with resistive loads, such as incandescent lamps. But using them to connect to an inductive load is impractical. The fact is that the inductive current is much lower compared to resistive current.

Assembling a homemade dimmer is quite simple. This will require some basic knowledge of electronics and a few parts.

Based on triac

Such a device operates on the principle of phase shift of key opening. Below is The simplest dimmer circuit based on a triac:

Structurally, the device can be divided into two blocks:

• A power switch, in the role of which a triac is used.
• Unit for creating control pulses based on a symmetrical dinistor.

A voltage divider is created using resistors R1-R2. It should be noted that resistance R1 is variable. This allows you to change the voltage in line R2-C1. A DB3 dinistor is connected between these elements. As soon as the voltage indicator on capacitor C1 reaches the opening threshold of the dinistor, a control pulse is applied to the switch (triac VS1).

As a result, the power switch turns on, and electric current begins to flow through it to the load. The position of the regulator determines in which part of the wave phase the power switch should operate.

Thyristor based

These partings are also quite effective, and their patterns are not very complicated. The role of the key in such a device is performed by a thyristor. If you carefully study the circuit diagram of the device, you will immediately notice the main difference between this circuit and the previous one - for each half-wave, its own switch with a control dinistor is used.

The operating principle of the thyristor device is as follows:

• When a positive half-wave passes through line R5-R4-R3, capacitor C1 is charged.
• After reaching the switching threshold of dinistor V3, it is triggered, and electric current flows to switch V1.
• When a negative half-wave passes, a similar situation is observed for the line R1-R2-R5, the control dinistor V4 and the key V2.

Using phase regulators, you can control not only the brightness of incandescent lamps, but also other types of loads, for example, the number of revolutions of a drill. However, it should be remembered that a thyristor-based device cannot be used to work with LED and fluorescent light bulbs.

Capacitor regulators are also used in everyday life. However, unlike semiconductor devices, they do not allow smooth voltage changes. Thus, for self-production it is best Thyristor and triac circuits are suitable.

Finding all the parts needed to make the regulator is not difficult. However, you don’t have to buy them, but can be removed from an old TV or other radio equipment. If desired, you can make a printed circuit board based on the selected circuit, and then solder all the elements into it. The parts can also be connected using regular wires. The home master can choose the method that seems most attractive to him.

Both devices discussed are quite easy to assemble, and you don’t need to have serious knowledge in the field of electronics to complete all the work. Even a novice radio amateur can make a 220V voltage regulator circuit with his own hands. At a low cost, they are practically in no way inferior to their factory counterparts.

When developing an adjustable power supply without a high-frequency converter, the developer is faced with the problem that with a minimum output voltage and a large load current, the stabilizer dissipates a lot of power on the regulating element. Until now, in most cases, this problem was solved this way: they made several taps at the secondary winding of the power transformer and divided the entire output voltage adjustment range into several subranges. This principle is used in many serial power supplies, for example, UIP-2 and more modern ones. It is clear that the use of a power source with several subranges becomes more complicated, and remote control of such a power source, for example, from a computer, also becomes more complicated.

It seemed to me that the solution was to use a controlled rectifier on a thyristor, since it becomes possible to create a power source controlled by one knob for setting the output voltage or by one control signal with an output voltage adjustment range from zero (or almost from zero) to the maximum value. Such a power source could be made from commercially available parts.

To date, controlled rectifiers with thyristors have been described in great detail in books on power supplies, but in practice they are rarely used in laboratory power supplies. They are also rarely found in amateur designs (except, of course, for chargers for car batteries). I hope that this work will help change this state of affairs.

In principle, the circuits described here can be used to stabilize the input voltage of a high-frequency converter, for example, as is done in the “Electronics Ts432” TVs. The circuits shown here can also be used to make laboratory power supplies or chargers.

I give a description of my work not in the order in which I carried it out, but in a more or less orderly manner. Let's look at general issues first, then “low-voltage” designs such as power supplies for transistor circuits or charging batteries, and then “high-voltage” rectifiers for powering vacuum tube circuits.

Operation of a thyristor rectifier with a capacitive load

The literature describes a large number of thyristor power regulators operating on alternating or pulsating current with a resistive (for example, incandescent lamps) or inductive (for example, an electric motor) load. The rectifier load is usually a filter in which capacitors are used to smooth out ripples, so the rectifier load can be capacitive in nature.

Let's consider the operation of a rectifier with a thyristor regulator for a resistive-capacitive load. A diagram of such a regulator is shown in Fig. 1.

Rice. 1.

Here, as an example, a full-wave rectifier with a midpoint is shown, but it can also be made using another circuit, for example, a bridge. Sometimes thyristors, in addition to regulating the voltage at the load U n They also perform the function of rectifier elements (valves), however, this mode is not allowed for all thyristors (KU202 thyristors with some letters allow operation as valves). For clarity of presentation, we assume that thyristors are used only to regulate the voltage across the load U n , and straightening is performed by other devices.

The operating principle of a thyristor voltage regulator is illustrated in Fig. 2. At the output of the rectifier (the connection point of the cathodes of the diodes in Fig. 1), voltage pulses are obtained (the lower half-wave of the sine wave is “turned” up), indicated U rect . Ripple frequency f p at the output of the full-wave rectifier is equal to twice the network frequency, i.e. 100 Hz when powered from mains 50 Hz . The control circuit supplies current pulses (or light if an optothyristor is used) with a certain delay to the thyristor control electrode t z relative to the beginning of the pulsation period, i.e. the moment when the rectifier voltage U rect becomes equal to zero.

Rice. 2.

Figure 2 is for the case where the delay t z exceeds half the pulsation period. In this case, the circuit operates on the incident section of a sine wave. The longer the delay when the thyristor is turned on, the lower the rectified voltage will be. U n on load. Load voltage ripple U n smoothed by filter capacitor C f . Here and below, some simplifications are made when considering the operation of the circuits: the output resistance of the power transformer is considered equal to zero, the voltage drop across the rectifier diodes is not taken into account, and the thyristor turn-on time is not taken into account. It turns out that recharging the filter capacity C f happens as if instantly. In reality, after applying a trigger pulse to the control electrode of the thyristor, charging the filter capacitor takes some time, which, however, is usually much less than the pulsation period T p.

Now imagine that the delay in turning on the thyristor t z equal to half the pulsation period (see Fig. 3). Then the thyristor will turn on when the voltage at the rectifier output passes through the maximum.

Rice. 3.

In this case, the load voltage U n will also be the largest, approximately the same as if there were no thyristor regulator in the circuit (we neglect the voltage drop across the open thyristor).

This is where we run into a problem. Let's assume that we want to regulate the load voltage from almost zero to the highest value that can be obtained from the existing power transformer. To do this, taking into account the assumptions made earlier, it will be necessary to apply trigger pulses to the thyristor EXACTLY at the moment when U rect passes through a maximum, i.e. t z = T p /2. Taking into account the fact that the thyristor does not open instantly, but recharging the filter capacitor C f also requires some time, the triggering pulse must be submitted somewhat EARLIER than half the pulsation period, i.e. t z< T п /2. The problem is that, firstly, it is difficult to say how much earlier, since it depends on factors that are difficult to accurately take into account when calculating, for example, the turn-on time of a given thyristor instance or the total (taking into account inductances) output resistance of the power transformer. Secondly, even if the circuit is calculated and adjusted absolutely accurately, the turn-on delay time t z , network frequency, and therefore frequency and period T p ripples, thyristor turn-on time and other parameters may change over time. Therefore, in order to obtain the highest voltage at the load U n there is a desire to turn on the thyristor much earlier than half the pulsation period.

Let's assume that we did just that, i.e. we set the delay time t z much less T p /2. Graphs characterizing the operation of the circuit in this case are shown in Fig. 4. Note that if the thyristor opens before half the half cycle, it will remain in the open state until the process of charging the filter capacitor is completed C f (see the first pulse in Fig. 4).

Rice. 4.

It turns out that for a short delay time t z fluctuations in the output voltage of the regulator may occur. They occur if, at the moment the trigger pulse is applied to the thyristor, the voltage on the load U n there is more voltage at the output of the rectifier U rect . In this case, the thyristor is under reverse voltage and cannot open under the influence of a trigger pulse. One or more trigger pulses may be missed (see second pulse in Figure 4). The next turn on of the thyristor will occur when the filter capacitor is discharged and at the moment the control pulse is applied, the thyristor will be under direct voltage.

Probably the most dangerous case is when every second pulse is missed. In this case, a direct current will pass through the winding of the power transformer, under the influence of which the transformer may fail.

In order to avoid the appearance of an oscillatory process in the thyristor regulator circuit, it is probably possible to abandon pulse control of the thyristor, but in this case the control circuit becomes more complicated or becomes uneconomical. Therefore, the author developed a thyristor regulator circuit in which the thyristor is normally triggered by control pulses and no oscillatory process occurs. Such a diagram is shown in Fig. 5.

Rice. 5.

Here the thyristor is loaded onto the starting resistance R p , and the filter capacitor C R n connected via starting diode VD p . In such a circuit, the thyristor starts up regardless of the voltage on the filter capacitor C f .After applying a trigger pulse to the thyristor, its anode current first begins to pass through the trigger resistance R p and then when the voltage is on R p will exceed the load voltage U n , the starting diode opens VD p and the anode current of the thyristor recharges the filter capacitor C f . Resistance R p such a value is selected to ensure stable startup of the thyristor with a minimum delay time of the trigger pulse t z . It is clear that some power is uselessly lost at the starting resistance. Therefore, in the above circuit, it is preferable to use thyristors with a low holding current, then it will be possible to use a large starting resistance and reduce power losses.

Scheme in Fig. 5 has the disadvantage that the load current passes through an additional diode VD p , at which part of the rectified voltage is uselessly lost. This drawback can be eliminated by connecting a starting resistor R p to a separate rectifier. Circuit with a separate control rectifier, from which the starting circuit and starting resistance are powered R p shown in Fig. 6. In this circuit, the control rectifier diodes can be low-power since the load current flows only through the power rectifier.

Rice. 6.

Low voltage power supplies with thyristor regulator

Below is a description of several designs of low-voltage rectifiers with a thyristor regulator. When making them, I took as a basis the circuit of a thyristor regulator used in devices for charging car batteries (see Fig. 7). This scheme was successfully used by my late comrade A.G. Spiridonov.

Rice. 7.

The elements circled in the diagram (Fig. 7) were installed on a small printed circuit board. Several similar schemes are described in the literature; the differences between them are minimal, mainly in the types and ratings of parts. The main differences are:

1. Timing capacitors of different capacities are used, i.e. instead of 0.5m F put 1 m F , and, accordingly, a variable resistance of a different value. To reliably start the thyristor in my circuits, I used a 1 capacitorm F.

2. In parallel with the timing capacitor, you do not need to install a resistance (3 k Win Fig. 7). It is clear that in this case a variable resistance may not be required by 15 k W, and of a different magnitude. I have not yet found out the influence of the resistance parallel to the timing capacitor on the stability of the circuit.

3. Most of the circuits described in the literature use transistors of the KT315 and KT361 types. Sometimes they fail, so in my circuits I used more powerful transistors of the KT816 and KT817 types.

4. To base connection point pnp and npn collector transistors, a divider of resistances of a different value can be connected (10 k W and 12 k W in Fig. 7).

5. A diode can be installed in the thyristor control electrode circuit (see the diagrams below). This diode eliminates the influence of the thyristor on the control circuit.

The diagram (Fig. 7) is given as an example; several similar diagrams with descriptions can be found in the book “Chargers and Start-Chargers: Information Review for Car Enthusiasts / Comp. A. G. Khodasevich, T. I. Khodasevich -M.:NT Press, 2005.” The book consists of three parts, it contains almost all chargers in the history of mankind.

The simplest circuit of a rectifier with a thyristor voltage regulator is shown in Fig. 8.

Rice. 8.

This circuit uses a full-wave midpoint rectifier because it contains fewer diodes, so fewer heatsinks are needed and higher efficiency. The power transformer has two secondary windings for alternating voltage 15 V . The thyristor control circuit here consists of capacitor C1, resistances R 1- R 6, transistors VT 1 and VT 2, diode VD 3.

Let's consider the operation of the circuit. Capacitor C1 is charged through a variable resistance R 2 and constant R 1. When the voltage on the capacitor C 1 will exceed the voltage at the point of resistance connection R 4 and R 5, transistor opens VT 1. Transistor collector current VT 1 opens VT 2. In turn, the collector current VT 2 opens VT 1. Thus, the transistors open like an avalanche and the capacitor discharges C 1 V thyristor control electrode VS 1. This creates a triggering impulse. Changing by variable resistance R 2 trigger pulse delay time, the output voltage of the circuit can be adjusted. The greater this resistance, the slower the capacitor charges. C 1, the trigger pulse delay time is longer and the output voltage at the load is lower.

Constant resistance R 1, connected in series with variable R 2 limits the minimum pulse delay time. If it is greatly reduced, then at the minimum position of the variable resistance R 2, the output voltage will disappear abruptly. That's why R 1 is selected in such a way that the circuit operates stably at R 2 in the minimum resistance position (corresponds to the highest output voltage).

The circuit uses resistance R 5 power 1 W just because it came to hand. It will probably be enough to install R 5 power 0.5 W.

Resistance R 3 is installed to eliminate the influence of interference on the operation of the control circuit. Without it, the circuit works, but is sensitive, for example, to touching the terminals of the transistors.

Diode VD 3 eliminates the influence of the thyristor on the control circuit. I tested it through experience and was convinced that with a diode the circuit works more stable. In short, there is no need to skimp, it’s easier to install D226, of which there are inexhaustible reserves, and make a reliably working device.

Resistance R 6 in the thyristor control electrode circuit VS 1 increases the reliability of its operation. Sometimes this resistance is set to a larger value or not at all. The circuit usually works without it, but the thyristor can spontaneously open due to interference and leaks in the control electrode circuit. I have installed R 6 size 51 Was recommended in the reference data for thyristors KU202.

Resistance R 7 and diode VD 4 provide reliable starting of the thyristor with a short delay time of the trigger pulse (see Fig. 5 and explanations thereto).

Capacitor C 2 smoothes out voltage ripples at the output of the circuit.

A lamp from a car headlight was used as a load during the experiments with the regulator.

A circuit with a separate rectifier for powering the control circuits and starting the thyristor is shown in Fig. 9.

Rice. 9.

The advantage of this scheme is the smaller number of power diodes that require installation on radiators. Note that the diodes D242 of the power rectifier are connected by cathodes and can be installed on a common radiator. The anode of the thyristor connected to its body is connected to the “minus” of the load.

The wiring diagram of this version of the controlled rectifier is shown in Fig. 10.

Rice. 10.

To smooth out output voltage ripples, it can be used L.C. -filter. The diagram of a controlled rectifier with such a filter is shown in Fig. eleven.

Rice. eleven.

I applied exactly L.C. -filter for the following reasons:

1. It is more resistant to overloads. I was developing a circuit for a laboratory power supply, so overloading it is quite possible. I note that even if you make some kind of protection circuit, it will have some response time. During this time, the power source should not fail.

2. If you make a transistor filter, then some voltage will definitely drop across the transistor, so the efficiency will be low, and the transistor may require a heatsink.

The filter uses a serial choke D255V.

Let's consider possible modifications of the thyristor control circuit. The first of them is shown in Fig. 12.

Rice. 12.

Typically, the timing circuit of a thyristor regulator is made of a timing capacitor and a variable resistance connected in series. Sometimes it is convenient to construct a circuit so that one of the terminals of the variable resistance is connected to the “minus” of the rectifier. Then you can turn on a variable resistance in parallel with the capacitor, as done in Figure 12. When the engine is in the lower position according to the circuit, the main part of the current passing through the resistance 1.1 k Wenters timing capacitor 1mF and charges it quickly. In this case, the thyristor starts at the “tops” of the rectified voltage pulsations or a little earlier and the output voltage of the regulator is the highest. If the engine is in the upper position according to the circuit, then the timing capacitor is short-circuited and the voltage on it will never open the transistors. In this case, the output voltage will be zero. By changing the position of the variable resistance motor, you can change the strength of the current charging the timing capacitor and, thus, the delay time of the trigger pulses.

Sometimes it is necessary to control a thyristor regulator not using a variable resistance, but from some other circuit (remote control, control from a computer). It happens that the parts of the thyristor regulator are under high voltage and direct connection to them is dangerous. In these cases, an optocoupler can be used instead of a variable resistance.

Rice. 13.

An example of connecting an optocoupler to a thyristor regulator circuit is shown in Fig. 13. Type 4 transistor optocoupler is used here N 35. The base of its phototransistor (pin 6) is connected through a resistance to the emitter (pin 4). This resistance determines the transmission coefficient of the optocoupler, its speed and resistance to temperature changes. The author tested the regulator with a resistance of 100 indicated in the diagram k W, while the dependence of the output voltage on temperature turned out to be NEGATIVE, i.e., when the optocoupler was very heated (the polyvinyl chloride insulation of the wires melted), the output voltage decreased. This is probably due to a decrease in LED output when heated. The author thanks S. Balashov for advice on the use of transistor optocouplers.

Rice. 14.

When adjusting the thyristor control circuit, it is sometimes useful to adjust the operating threshold of the transistors. An example of such adjustment is shown in Fig. 14.

Let's also consider an example of a circuit with a thyristor regulator for a higher voltage (see Fig. 15). The circuit is powered from the secondary winding of the TSA-270-1 power transformer, providing an alternating voltage of 32 V . The part ratings indicated in the diagram are selected for this voltage.

Rice. 15.

Scheme in Fig. 15 allows you to smoothly adjust the output voltage from 5 V to 40 V , which is sufficient for most semiconductor devices, so this circuit can be used as a basis for the manufacture of a laboratory power supply.

The disadvantage of this circuit is the need to dissipate quite a lot of power at the starting resistance R 7. It is clear that the lower the thyristor holding current, the greater the value and the lower the power of the starting resistance R 7. Therefore, it is preferable to use thyristors with low holding current here.

In addition to conventional thyristors, an optothyristor can be used in the thyristor regulator circuit. In Fig. 16. shows a diagram with an optothyristor TO125-10.

Rice. 16.

Here the optothyristor is simply turned on instead of the usual one, but since its photothyristor and LED are isolated from each other; the circuits for its use in thyristor regulators may be different. Note that due to the low holding current of the TO125 thyristors, the starting resistance R 7 requires less power than in the circuit in Fig. 15. Since the author was afraid of damaging the optothyristor LED with large pulse currents, resistance R6 was included in the circuit. As it turned out, the circuit works without this resistance, and without it the circuit works better at low output voltages.

High voltage power supplies with thyristor regulator

When developing high-voltage power supplies with a thyristor regulator, the optothyristor control circuit developed by V.P. Burenkov (PRZ) for welding machines was taken as a basis. Printed circuit boards were developed and produced for this circuit. The author expresses gratitude to V.P. Burenkov for a sample of such a board. The diagram of one of the prototypes of an adjustable rectifier using a board designed by Burenkov is shown in Fig. 17.

Rice. 17.

The parts installed on the printed circuit board are circled in the diagram with a dotted line. As can be seen from Fig. 16, damping resistors are installed on the board R 1 and R 2, rectifier bridge VD 1 and zener diodes VD 2 and VD 3. These parts are designed for 220V power supply V . To test the thyristor regulator circuit without alterations in the printed circuit board, a TBS3-0.25U3 power transformer was used, the secondary winding of which is connected in such a way that the alternating voltage 200 is removed from it V , i.e. close to the normal supply voltage of the board. The control circuit works similarly to those described above, i.e. capacitor C1 is charged through a trimmer resistance R 5 and a variable resistance (installed outside the board) until the voltage across it exceeds the voltage at the base of the transistor VT 2, after which the transistors VT 1 and VT2 open and capacitor C1 is discharged through the opened transistors and the LED of the optocoupler thyristor.

The advantage of this circuit is the ability to adjust the voltage at which the transistors open (using R 4), as well as the minimum resistance in the timing circuit (using R 5). As practice shows, having the ability to make such adjustments is very useful, especially if the circuit is assembled amateurishly from random parts. Using trimmers R4 and R5, you can achieve voltage regulation within a wide range and stable operation of the regulator.

I started my R&D work on developing a thyristor regulator with this circuit. In it, the missing trigger pulses were discovered when the thyristor was operating with a capacitive load (see Fig. 4). The desire to increase the stability of the regulator led to the appearance of the circuit in Fig. 18. In it, the author tested the operation of a thyristor with a starting resistance (see Fig. 5.

Rice. 18.

In the diagram of Fig. 18. The same board is used as in the circuit in Fig. 17, only the diode bridge has been removed from it, because Here, one rectifier common to the load and control circuit is used. Note that in the diagram in Fig. 17 starting resistance was selected from several connected in parallel to determine the maximum possible value of this resistance at which the circuit begins to operate stably. A wire resistance 10 is connected between the optothyristor cathode and the filter capacitorW. It is needed to limit current surges through the optoristor. Until this resistance was established, after turning the variable resistance knob, the optothyristor passed one or more whole half-waves of rectified voltage into the load.

Based on the experiments carried out, a rectifier circuit with a thyristor regulator was developed, suitable for practical use. It is shown in Fig. 19.

Rice. 19.

Rice. 20.

PCB SCR 1 M 0 (Fig. 20) is designed for installation of modern small-sized electrolytic capacitors and wire resistors in ceramic housings of the type S.Q.P. . The author expresses gratitude to R. Peplov for his help with the manufacture and testing of this printed circuit board.

Since the author developed a rectifier with the highest output voltage of 500 V , it was necessary to have some reserve in the output voltage in case of a decrease in the network voltage. It turned out to be possible to increase the output voltage by reconnecting the windings of the power transformer, as shown in Fig. 21.

Rice. 21.

I also note that the diagram in Fig. 19 and board fig. 20 are designed taking into account the possibility of their further development. To do this on the board SCR 1 M 0 there are additional leads from the common wire GND 1 and GND 2, from the rectifier DC 1

Development and installation of a rectifier with a thyristor regulator SCR 1 M 0 were conducted jointly with student R. Pelov at PSU. C with his help photographs of the module were taken SCR 1 M 0 and oscillograms.

Rice. 22. View of the SCR 1 M module 0 from the parts side

Rice. 23. Module view SCR 1 M 0 solder side

Rice. 24. Module view SCR 1 M 0 side

Table 1. Oscillograms at low voltage

No.	Minimum voltage regulator position	According to the scheme	Notes
		At the VD5 cathode	5 V/div 2 ms/div
		On capacitor C1	2 V/div 2 ms/div
		i.e. connections R2 and R3	2 V/div 2 ms/div
		At the anode of the thyristor	100 V/div 2 ms/div
		At the thyristor cathode	50 V/div 2 ms/de

Table 2. Oscillograms at average voltage

No.	Middle position of voltage regulator	According to the scheme	Notes
		At the VD5 cathode	5 V/div 2 ms/div
		On capacitor C1	2 V/div 2 ms/div
		i.e. connections R2 and R3	2 V/div 2 ms/div
		At the anode of the thyristor	100 V/div 2 ms/div
		At the thyristor cathode	100 V/div 2 ms/div

Table 3. Oscillograms at maximum voltage

No.	Maximum voltage regulator position	According to the scheme	Notes
		At the VD5 cathode	5 V/div 2 ms/div
		On capacitor C1	1 V/div 2 ms/div
		i.e. connections R2 and R3	2 V/div 2 ms/div
		At the anode of the thyristor	100 V/div 2 ms/div
		At the thyristor cathode	100 V/div 2 ms/div

To get rid of this drawback, the regulator circuit was changed. Two thyristors were installed - each for its own half-cycle. With these changes, the circuit was tested for several hours and no “emissions” were noticed.

Rice. 25. SCR 1 M 0 circuit with modifications