Thyristor power regulation circuit

Working Principle of the Circuit
The schematic diagram of the circuit is shown in Figure 1. The charging and discharging rate of capacitor C1 can be changed by adjusting the gear position of the band switch SA. The AC voltage across C1 is used to trigger the bidirectional thyristor VS to conduct through the bidirectional trigger diode VD3, and the conduction angle of VS is changed, so that the AC voltage across the load RL changes accordingly.
The light-emitting diodes VD2 and VD5 are used as signal indicators. Due to the different conduction angles, the brightness of the light is different. When SA is set to "1", VD5 is displayed; when SA is set to "4", VD2 is displayed; R5 is a current limiting resistor used to protect VS. Resistor R7 and capacitor C2 are an absorption circuit used to absorb the interference pulses generated by SA when selecting gears. Otherwise, it will cause certain interference to televisions, stereos and other electroacoustic devices during the SA gear selection process;

Component Selection

Capacitor C1 is 0.1uF/160V, C2 is 0.022uF/400V (polyester capacitor). Resistor R1 is 56kΩ, 1/2W, R2 is 39kΩ, 1/4W, R3 is 27kΩ, 1/4W, R4 is 2kΩ, 1/4W, R5 is 47Ω, 1/2W, R6 is 100kΩ, 1/2W (variable), R7 is 300Ω, 1/4W, R8 is 43kΩ, 1/2W. Diodes VD1 and VD4 use 1N4004. Light-emitting diode VD2 uses BT104 (yellow), and VD5 uses BT103 (green). Trigger diode VD3 is DB3 or VR60. Bidirectional thyristor V5 uses TLC226B (3A/400V) or TLC336A (3A/600V). The band switch SA uses KZX-1-2D-11W. The load RL is AC 220V/300W (electric furnace wire).

Preparation method and instructions for use

The core device of this circuit is the bidirectional thyristor, so its quality must be tested. Since the circuit is simple, you can design the printed circuit board yourself. As long as the connection is correct according to the diagram, it can work without debugging.