Simple delay light circuit (1)

Figure 5-7 is a simple delay light circuit. It is connected to the electric lamp E using a two-wire connection. Therefore,
when the bar is installed, it can directly replace the ordinary wall switch without changing the original indoor wiring. When the key switch
SB is pressed, the 220V alternating current is rectified by the VD half-transition, and then directly added to the gate of the thyristor VT through R, Z, Z,
so that the VT is triggered and turned on, and the lamp E lights up. At the same time, the charge stored in capacitor C is discharged to the pin through SB.
After releasing SB, the power supply passes through VD and R. When C is charged, its charging current can keep VT open, so the light
E will not go out. When C is fully charged, VT is turned off and lamp E goes out on its own.
    C should use a high-voltage electrolytic
capacitor with a withstand voltage of 300V, and the leakage current should be small. If the leakage current is
large, the VT may not turn off. At this time, a ikfl resistor
can be connected in parallel between the gate and cathode of the VT , or a thyristor with a slightly larger trigger current can be used, but the delay time will be shortened. When the light bulb E in the circuit is lit, the current flowing through the bulb is Bi-wave alternating current, so the light is darker, but the service life of the bulb is longer.