Production of Silicon Controlled AC Voltage Regulator

Thyristor is a new type of semiconductor device, which has the advantages of small size, light weight, high efficiency, long life, fast action and easy use. At present, most AC voltage regulators use thyristor voltage regulators. Here we introduce a thyristor AC voltage regulator with simple circuit, easy installation and convenient control. It can be used as a voltage regulator for household appliances for control. In the figure, RL is the load (lighting, electric fan, electric iron, etc.). The output power of this voltage regulator is 100W, which can be used for general household appliances.

1. Circuit principle:

The circuit diagram is as follows

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The thyristor AC voltage regulator consists of two parts: a controlled rectifier circuit and a trigger circuit. The circuit diagram is shown in the figure below. As can be seen from the figure, diodes D1-D4 form a bridge rectifier circuit, and the double base diode T1 forms a relaxation oscillator as the synchronous trigger circuit of the thyristor. When the voltage regulator is connected to the mains, the 220V AC is rectified by the load resistor RL through the diodes D1-D4, forming a pulsating DC voltage at both ends of A and K of the thyristor SCR. This voltage is stepped down by the resistor R1 and used as the DC power supply of the trigger circuit. In the positive half cycle of the AC, 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 changes from cut-off to on, so the capacitor C is quickly discharged through the e and b1 junctions of the T1 tube and R2, resulting in a sharp pulse on R2. This pulse is sent to the control electrode of the thyristor SCR as a control signal, turning on the thyristor. The tube voltage drop of the thyristor after turning on is very low, generally less than 1V, so the relaxation oscillator stops working. When the AC passes through the zero point, the thyristor turns off automatically. When the AC is in the negative half cycle, the capacitor C is recharged... This cycle repeats itself, and the power on the load RL can be adjusted.

2. Component selection

The voltage regulator uses a WH114-1 synthetic carbon film potentiometer with a resistance of 470KΩ. This potentiometer can be directly soldered on the circuit board. Except for R1, which uses a 1W metal film resistor, the rest use 1/8W carbon film resistors. D1-D4 use silicon rectifier diodes with a reverse breakdown voltage greater than 300V and a maximum rectifier current greater than 0.3A, such as 2CZ21B, 2CZ83E, 2DP3B, etc. SCR uses a thyristor rectifier device with a forward and reverse voltage greater than 300V and a rated average current greater than 1A, such as the domestic 3CT series.