Light controlled switch circuit diagram of bidirectional thyristor

This circuit can control the on and off of 200W power load on the 220V AC power grid. If the power is only 50W, the triac does not need to be connected to the radiator. The action point with a certain hysteresis loop is approximately 100lx sunlight. When the light is weak, the light-sensitive resistor has a high resistance value, so the input voltage of the threshold switch TCA345 is higher than 0.7 times the voltage of pin 2. The output terminal of the threshold switch has a high resistance value, and the bidirectional thyristor is triggered to turn on through the transistor cycle. On the contrary, if the ambient illumination exceeds 100lx, the threshold switch output terminal becomes negative. At this time, the subsequent transistor and bidirectional thyristor are turned off, and the light goes out.

Diodes D1 and D2 in the circuit are used for rectification and output a control current of about 15mA. The entire circuit consumes an effective AC current of approximately 40mA (at 220V), which contains a high reactive power component.
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