Transistor voltage regulator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Transistor voltage regulator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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In several issues of the journal "Radioamator" circuits of thyristor-based mains voltage regulators were printed, but such devices have a number of 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 (electric lamp, heating element) and cannot be used simultaneously with an inductive load (electric motor, 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. I propose such a design, and any, even an inexperienced radio amateur, can repeat it, while spending a minimum of time and money. The transistor voltage regulator contains few radio elements, does not interfere with the electrical network and works on the 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, electric fireplace, the speed of rotation of an electric motor, fan, electric drill, or the voltage on the transformer winding.

The device has the following parameters: voltage adjustment range from 0 to 218 V; the maximum load power depends on the transistor used and can be 500 W or more. The regulating element of the device is the transistor VT1 (see figure).

Transistor voltage regulator

The diode block VD1-VD4, depending on the phase of the mains voltage, directs this voltage 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 out 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 S1, 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 VD1-collector-emitter VT1-VD4 circuit. By rotating the R1 slider and changing the control voltage, you can control the collector current VT1. This current, and hence the current flowing in the load, will be the greater, the higher the control level and vice versa. With the extreme right position of the R1 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 one. 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.

Design. The diode block, diodes, capacitor and resistor R2 are installed on a circuit board 55x35 mm in size, made of foil textolite 1-2 mm thick.

The following parts can be used in the device: transistors KT840A, B (P=100 W), KT856A (P=150 W), KT834A, B, V (P=200 W), KT847A (P=250 W).

If the power of the regulator needs to be increased even more, then several transistors must be used 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.

Diodes VD1-VD4 type KD202R, KD206B or any other small-sized diodes for voltage over 250 V and current in accordance with the current consumed by the load.

Diode block VD6-VD9 type KTs405, KTs407 with any letter index. Diode VD5 - D229B, K, L or any other for a current up to 1 A. Variable resistor R1 type SP, SPO, PPB with a power of at least 2 watts. Fixed resistor R2 type BC, MLT, OMPT, S2-23 with a power of at least 2 watts. Oxide capacitor type K50-6, K50-16. Network transformer type TVZ-1-6 - from tube radios and amplifiers, TS-25, TS-27 - from the Yunost TV, but any other low-power one with a secondary winding voltage of 5-8 V can be successfully used. Fuse FU1 on voltage 250 V and current according to the maximum power rating of the transistor. The transistor must be equipped with a radiator with a dissipation area of at least 200 cm2 and a thickness of 3-5 mm.

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

Author: D.A. Shandrenko, Kyiv

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