Delay lamp circuit using bidirectional thyristor (3)

It is a delay lamp circuit used with single-junction transistors. Normally, the thyristors VI and H are turned off, and
the light does not light up. When turning on the light, just press SB, and the light F will light up. When the light is off, the 220V AC power is stepped down by T, rectified by VD1 and VD2, and then provides the door panel triggering current
to VTH through the resistor R. When VTH is turned on, the button SB will be self-locked. , the lamp can continue to shine. Then, the full-wave DC power is filtered by VD3 and capacitor c^, and passes through RP to C. Charge. When the voltage across G rises to the conduction peak voltage of single-junction transistor vu, vU is turned on, and VTH is trapped and loses the trigger current. When the alternating current crosses zero, it is turned off and the lamp E goes out. Adjusting RP can change the delay time of the circuit . VD3 plays an isolation role. If VD3 is cancelled, when VTH is turned off, the trigger current can be fed to VTH through R due to C, so that the gate tube cannot be turned off. T-cho uses a 220V/9V×2, 3VA small power transformer, and there are no special requirements for other components .