General circuit of photo-controlled thyristor photosensitive normally closed AC contactor

Photocoupler

As shown in the figure, the working principle of the circuit is: when there is no light, the AC power is rectified through the AC contactor KM, the resistor R1 and the Bridge Rectifier VD1~VD4, and more than ten volts DC voltage is obtained at both ends of A and B. Sex is positive at the A end and negative at the B end. When there is no light, the light-controlled thyristor is in the off state. At this time, the VT is biased and turned on by R2, and the voltage across the capacitor C is clamped within the corner voltage range of the hell bidirectional trigger diode VTD2, so the VTD2 is cut off, VTD1 Shutdown, KM is in the off state, which is why the AC contactor is normally open.
When light is irradiated onto the photosensitive surface of the photo-controlled thyristor, the VTL is turned on, and VT is turned off, and the capacitor C quickly establishes a potential higher than the turning voltage of the bidirectional trigger diode VTD2, so that VTD1 is turned on and KM is pulled.