Improvement of the power regulator. Encyclopedia of radio electronics and electrical engineering

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

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For over 15 years I have been using the device described in the article by S. Lukashenko "A power regulator that does not create interference" ("Radio", 1987, No. 12, pp. 22, 23) to control the power of the smokehouse electric heater. In general, a good design, but, unfortunately, not without flaws.

Firstly, a pulsating current flows through the load, which means that only an active load can be powered from the regulator. Secondly, in some positions of the switch SA1, an odd number of half-cycles of the mains current flows through the load, which negatively affects the load of an inductive nature included in the network. Thirdly, the insufficient reliability of the device was revealed: the K176J1E5 chip failed several times.

There are two reasons: the voltage exceeding the clock frequency at the inputs of the DD1.1 element of the supply voltage (by the voltage drop across the VD4 diode), which is not recommended, and an "open" in the input circuit of the DD1.4 element (pin 8) when switching power - for a while span of the movable contact of the switch SA1, this conclusion "hangs" in the air, which is unacceptable. The disadvantages also include the lack of indication that the regulator is connected to the network (it got into trouble several times due to a malfunction of the network extension cable) and a rather large own current consumption: significant power is dissipated on the VD5-VD8 diode bridge and resistor R1. Finally, the limitation of the load power to 2 kW does not allow the use of the regulator in many cases that occur in practice.

Rice. 1 (click to enlarge)

To eliminate these shortcomings, the scheme was redesigned (Fig. 1). The power supply of the improved device is made transformerless with a ballast capacitor C1, the resistor R3 limits the current pulses that occur when the device is connected to the network to a safe level for the diode bridge VD2-VD5. The rectified voltage is stabilized by a parametric stabilizer on a VD6 zener diode. Turning on the HL1 LED in series with it made it possible to introduce an on indication, while "saving" the current-limiting resistor and a few milliamps of the output current of a low-power power supply. Capacitors C2 and C3 - filtering (C2 eliminates the low-frequency component of the rectified voltage, C3 - high-frequency, as well as switching noise in the power circuits that occur during the operation of digital microcircuits). Reducing the current consumption (compared to the prototype) has reduced the capacitance of the oxide capacitor C2.

On the resistors R1, R2 and the zener diode VD1, a clock pulse generator with a frequency of 50 Hz is made (unlike the prototype, in which their frequency is 100 Hz). Through this circuit, the capacitor C1 is also discharged when the device is disconnected from the network, which increases the electrical safety of the device. The amplitude of the clock pulses is almost 2 V (voltage drop across the HL1 LED) less than the supply voltage. The Schmitt trigger on the elements DD.1 and DD1.2 improves the shape of the clock pulses (Fig. 2, diagram 1).

Fig. 2

A binary decimal counter with a decoder DD2 is triggered by the edge of the clock pulses, generating positive pulses at the outputs with a duration equal to the period of the mains voltage, shifted one relative to the other by the duration of the period. RS-trigger on the elements DD1.3 and DD1.4 is triggered by the front of the input pulses. When a high level counter DD0 appears at output 2 (Fig. 2, diagram 2), the RS flip-flop switches, and the same level appears at its output (diagram 4). In this case, the transistor VT1 opens, the emitting diode of the optosimistor U1 turns on, and it goes into a conducting state. As a result, the thyristors VS1 and VS2 connected in anti-parallel are opened in turn: the first of them passes positive half-waves of the mains current into the load, the second - negative ones (diagram 5). The thyristors are open until a high level appears at the output of the counter DD2, to which the movable contact of the SA1 switch is connected (for example, at output 3 - diagram 3). On the edge of this pulse, the RS flip-flop turns off, and the current through the load stops. The introduction of the resistor R6 made it possible to avoid the operation of the DD1.4 element with a "hanging" input.

The switching of thyristors occurs at moments when the amplitude of the mains voltage does not exceed 10 V, while the interference is minimal. When the SA1 switch is set to the "100%" position, the RS-trigger does not switch, the thyristors are open all the time and full power is released on the load.

At any position of the switch SA1, an even number of half-cycles of the mains current passes through the load, which excludes the appearance of its constant component. This, as well as the use of two back-to-back thyristors, made it possible to increase the load power to 4 kW, which is sufficient for domestic purposes. The flow of alternating current through the load made it possible to include not only active, but also inductive loads into the XS1 socket. For example, using a step-down transformer, regulate the power of a low-voltage load - an electric winder, a bee knife for opening honeycombs, etc. (previously, a bulky and heavy LATR had to be used for this purpose), and by connecting a fan to the device, regulate the speed of its electric motor (when feeding voltage, it accelerates, during pauses it slows down, as a result, the rotational speed decreases).

In the manufacture of the device, a printed circuit board was used (Fig. 3 in the mentioned article), from which the parts R1, VD1-VD4, C1 were dismantled.

The newly introduced parts are placed on a fragment of a universal breadboard with dimensions of 20x55 mm, which is installed vertically in place of the dismantled parts. Thyristors VS1, VS2 are mounted on heat sinks with a cooling surface area of ​​150 cm2. Diodes VD7 and VD8 are soldered directly to their terminals.

Capacitor C1 is a film noise suppressor, it can be replaced by two K73-17 capacitors connected in series with a capacity of 0,47 microns and a rated voltage of 630 V, resistors R1 and R3 are MLT-0,5, the rest are of any type.

Optosimistor operation current must not exceed 10 mA, and the permissible switching voltage must not be less than 500 V (MOC3052, MOC3053, MOC3062, MOC3063, MOC3082, MOC3083 meet these requirements).

The device does not require adjustment.

The improved power regulator has been in operation for more than five years, while he is satisfied with his work.

Author: K. Moroz

See other articles Section Power regulators, thermometers, heat stabilizers.

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