Circuit design of thyristor AC voltage regulator module

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SCR is a new type of semiconductor device, which has the advantages of small size, light weight, high efficiency, long life, fast action and convenient use. At present, AC voltage regulators mostly use thyristor voltage regulators. Here, a thyristor AC voltage regulator with simple circuit, easy installation and convenient control is introduced, which can be used as a voltage regulating device for household appliances to control. In the figure, RL is the load (lighting lamp, electric fan, electric iron, etc.). This regulator has an output power of 100W, which can be used by ordinary household appliances.

Circuit principle: The thyristor AC voltage regulator consists of two parts : a controllable rectifier circuit and a trigger circuit. The circuit schematic is shown in the figure below. As can be seen from the figure, the diodes D1 - D4 form a bridge rectifier circuit, and the double base diode T1 constitutes a relaxation oscillator as a synchronous trigger circuit of the thyristor. When the voltage regulator is connected to the market, 220V AC is rectified by the diode D1—D4 through the load resistor RL, and a pulsating DC voltage is formed across the A and K sides of the thyristor SCR. The voltage is stepped down by the resistor R1 as a trigger circuit. DC power supply. At the positive half cycle of the alternating current, the rectified voltage charges the capacitor C through R4 and W1. When the charging voltage Uc reaches the peak voltage Up of the single junction transistor T1, the single junction transistor T1 becomes conductive by the turn-off, so that the capacitor C is rapidly discharged through the e, b1 junction and R2 of the T1 tube, resulting in a sharp point on R2. pulse. This pulse is sent as a control signal to the gate of the thyristor SCR, turning the thyristor on. The tube voltage drop after the thyristor is turned on is very low, generally less than 1V, so the relaxation oscillator stops working. When the AC power passes through the zero point, the thyristor is turned off. When the alternating current is in the negative half cycle, the capacitor C is recharged again, so that the power on the load RL can be adjusted.

Component selection: The regulator potentiometer of the regulator is a WH114-1 type synthetic carbon film potentiometer with a resistance of 470KΩ. This potentiometer can be directly soldered on the circuit board. The resistor should be used for the metal film with a power of 1W except for R1. Outside the resistor, the rest uses a carbon film resistor with a power of 1/8W. D1—D4 select silicon rectifier diodes with reverse breakdown voltage greater than 300V and maximum rectification current greater than 0.3A, such as 2CZ21B, 2CZ83E, 2DP3B, etc. SCR selects thyristor rectifier devices with forward and reverse voltages greater than 300V and rated average current greater than 1A, such as the domestic 3CT series.