Mains voltage regulator 0-218 volts. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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Recently, in our everyday life, electronic devices are increasingly used to smoothly adjust the mains voltage. With the help of such devices, the brightness of the glow of the lamps, the temperature of the electric heaters, and the speed of the electric motors are controlled.

The vast majority of voltage regulators assembled on thyristors have significant drawbacks that limit their capabilities. Firstly, they introduce quite noticeable interference into the electrical network, which often adversely affects the operation of televisions, radios, and tape recorders. Secondly, they can only be used to control a load with active resistance - an electric lamp or a heating element, and cannot be used in conjunction with an inductive load - an electric motor, a transformer.

Meanwhile, all these problems can be easily solved by assembling an electronic device in which the role of a regulating element would be performed not by a thyristor, but by a powerful transistor.

The transistor voltage regulator contains a minimum of radio elements, does not interfere with the electrical network and works on a load with both active and inductive resistance. It can be used to adjust the brightness of a chandelier or table lamp, the heating temperature of a soldering iron or electric stove, the speed of rotation of a fan or drill motor, and the voltage on the transformer winding.

The device has the following parameters: voltage adjustment range - from 0 to 218 V; the maximum load power when using one transistor in the control circuit is no more than 100 watts. The regulating element of the device is the transistor VT1 (Fig. 1).

Fig. 1

The diode block VD1-VD4, depending on the phase of the mains current, directs it to the collector or emitter VT1. Transformer T1 lowers the voltage of 220 V to 5-8 V, which is rectified by the diode block VD6-VD9 and smoothed by capacitor C1. The variable resistor R1 serves to adjust the magnitude of the control voltage, and the resistor R2 limits the base current of the transistor. Diode VD5 protects VT1 from getting negative polarity voltage to its base. The device is connected to the mains with an XP1 plug. Socket XS1 is used to connect the load.

The regulator operates as follows. After turning on the power with the toggle switch Q1, the mains voltage is supplied simultaneously to the diodes VD1, VD2 and the primary winding of the transformer T1. In this case, the rectifier, consisting of a diode block VD6-VD9, a capacitor C1 and a variable resistor R1, generates a control voltage that is supplied to the base of the transistor and opens it. If at the moment the regulator is turned on, the network has a negative polarity voltage, the load current flows through the circuit VD2 - emitter-collector VT1-VD3. If the polarity of the mains voltage is positive, the current flows through the circuit VD1 - collector-emitter VT1-VD4. The value of the load current depends on the magnitude of the control voltage based on VT1. By rotating the engine R1 and changing the value of the control voltage, they control the collector current VT1. This current, and hence the current flowing in the load, will be the greater, the higher the level of the control voltage, and vice versa. With the extreme right position of the variable resistor engine according to the diagram, the transistor will be fully open and the "dose" of electricity consumed by the load will correspond to the nominal value. If the R1 slider is moved to the leftmost position, VT1 will be locked and no current will flow through the load.

By controlling the transistor, we actually regulate the amplitude of the alternating voltage and current acting in the load. At the same time, the transistor operates in a continuous mode, due to which such a regulator is free from the disadvantages inherent in thyristor devices.

Now let's move on to the design of the device. Diode blocks, a capacitor, a resistor R2 and a diode VD6 are mounted on a circuit board 55x35 mm in size, made of foil-coated getinax or textolite 1-2 mm thick (Fig. 2).

Fig. 2

The following parts can be used in the device. Transistor - KT812A(B), KT824A(B), KT828A(B), KT834A(B,V), KT840A(B), KT847A or KT856A. Diode blocks: VD1-VD4-KTs410B or KTs412V. VD6-VD9 - KTs405 or KTs407 with any letter index; diode VD5 - series D7, D226 or D237. Variable resistor - type SP, SPO, PPB with a power of at least 2 W, constant - VS, MLT, OMLT, S2-23. Oxide capacitor - K50-6, K50-16. Mains transformer - TV3-1-6 from tube radios and amplifiers, TS-25, TS-27 - from the Yunost TV or any other low-power one with a secondary winding voltage of 5-8 V. The fuse is designed for a maximum current of 1 A. Toggle switch - T3-C or any other network. XP1 - standard power plug, XS1 - socket.

All elements of the regulator are placed in a plastic case with dimensions of 150x100x80 mm. A toggle switch and a variable resistor equipped with a decorative handle are installed on the top panel of the case. The socket for connecting the load and the fuse socket are mounted on one of the side walls of the housing. On the same side there is a hole for the power cord. A transistor, a transformer and a circuit board are installed at the bottom of the case. The transistor must be equipped with a radiator with a dissipation area of ​​at least 200 cm² and 3-5 mm thick.

The regulator does not need adjustment. With proper installation and serviceable parts, it starts working immediately after being connected to the network.

Now a few recommendations for those who want to improve the device. The changes mainly concern the increase in the output power of the regulator. So, for example, when using the KT856 transistor, the power consumed by the load from the network can be 150 W, for KT834 - 200 W, and for KT847-250 W. If it is necessary to increase the output power of the device even more, several transistors connected in parallel can be used as a regulating element by connecting their respective terminals. Probably, in this case, the regulator will have to be equipped with a small fan for more intensive air cooling of semiconductor devices. In addition, the VD1-VD4 diode block will need to be replaced with four more powerful diodes, designed for an operating voltage of at least 250 V and a current value in accordance with the load consumed. For this purpose, devices of the D231-D234, D242, D243, D245-D248 series are suitable. It will also be necessary to replace VD5 with a more powerful diode, rated for current up to 1 A. Also, the fuse must withstand a larger current.

Author: V. Yantsev; Publication: cxem.net

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