Electric power regulator. Scheme, description

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

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Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power

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Suppose you have an electric stove, and its power is not regulated. So the spiral burns to full heat when a quarter of the rated power is enough, pointlessly wasting precious kilowatt-hours. There is a way out - to make a power regulator to the electric stove. The scheme of the first version of the regulator is shown in fig. 1. It allows you to adjust the power in the load, designed to be connected to a 220 V network, from 5 ... 10 to 97 ... 99% of the rated power. The efficiency of the regulator is not less than 98%.

Electric stove power regulator

The control elements of the device - trinistors VS1 and VS2 - are connected in series with the load. The change in the power consumed by the load is achieved by changing the opening angle of the trinistors.

The node that provides a change in the opening angle of the trinistors is made on a unijunction transistor VT1. Capacitor C1, connected to the emitter of the transistor, is charged through resistors R2 and R3. As soon as the voltage on the capacitor plates reaches a certain value, the unijunction transistor opens, a short current pulse passes through the I winding of the transformer T1. Pulses from the winding II or III of the transformer will open the trinistor VS1 or VS2 - depending on the phase of the mains voltage, and from that moment until the end of the half-cycle, current will flow through the load. By changing the resistance of the resistor R3, it is possible to control the charging rate of the capacitor C1 and, consequently, the opening angle of the trinistors and the average power in the load.

The node for adjusting the opening angle of the trinistors is powered by a full-wave rectifier made according to the bridge circuit (VD1). The voltage across the unijunction transistor is limited by the zener diodes VD2, VD3. The filter capacitor is missing here - it's not needed.

The unijunction transistor KT117 can be used with the letters A and B. You can also use an analogue of a unijunction transistor, made on two bipolar transistors of different structures (see Fig. 50). Bridge rectifier VD1 can be types KTS402, KTS405 with any letters. You can also use four diodes of types D226, D310, D311, D7 with any letters, including them according to the rectifier bridge circuit. When replacing trinistors VS1, VS2 with other types, it should be remembered that they must be designed to supply both direct and reverse voltages of at least 400 V. Transformer T1 is of the MIT-4 or MIT-10 type. A self-made transformer can be made on a ferrite ring magnetic circuit M2000NM, size K20x10xb. All windings are made with PEV-1 0,31 wire and contain 40 turns each. Winding is carried out simultaneously in three wires, and the turns are evenly distributed over the body of the magnetic circuit ring. The winding terminals of the same name are indicated by dots in the diagram.

SCRs VS1 and VS2 are installed on radiators with a cooling surface of at least 200 cm ^ 2 each. In this case, the maximum load power can be 2 kW.

The setting of the power regulator is to select the resistance of the resistor R2 according to the maximum power in the load. Resistor R3 is temporarily closed with a jumper wire. The moment of return to the load of maximum power is best controlled by an oscilloscope. In the case of using a self-made transformer T1, you should select the desired polarity for connecting the winding leads, which must correspond to that indicated in the diagram.

The power regulator can also be used in conjunction with low-power electric furnaces, incandescent lamps and other active loads. The described trinistor power controller has disadvantages. Firstly, with a change in temperature in the regulator housing (and it will increase during operation due to heating of the thyristors), the capacitance of capacitor C1 will change. This will lead to a change in the opening angle of the trinistors, as well as to a change in the power in the load. In order to eliminate this drawback to some extent, it is necessary to use capacitor C1 with small values of TKE (temperature coefficient of capacitance), for example, K73-17, K73-24.

Secondly, the trinistor stabilizer induces a high level of interference in the mains. These interferences occur at the moments of abrupt switching on of the trinistor. Switching noise not only propagates through the network, causing unstable operation of various devices (electronic clocks, computers, etc.), but also interferes with the normal operation of some devices that are not galvanically connected to the network (for example, in a radio receiver located not far from the trinistor regulators, one hears noise crackling). Therefore, reducing switching interference in trinistor power controllers is an important task.

The most accessible way to reduce interference is such a control method, in which the switching of the trinistor occurs at the moments when the mains voltage passes through zero. In this case, the power in the load can be controlled by the number of full half-cycles during which current flows through the load. The disadvantage of this method of regulation in comparison with the traditional ones is the large fluctuations in the instantaneous power values in the load during the regulation period, which is much longer than the period of the sinusoidal voltage and can reach several seconds. However, for such inertial energy consumers as an electric oven, iron, electric stove, powerful electric motor, this disadvantage is not decisive.

Publication: cxem.net

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