Button delay lighting switch

VDl~VD5, LED, Rl and C2 form a simple bridge rectifier, voltage step-down and voltage stabilizing circuit. Normally, the capacitors Cl and
C2 are full of charges, the transistor VT is cut off, and the thyristor VS is off because it cannot get the trigger current. In the off state, at this time,
the light-emitting diode LED indicates the position of the switch on the controller, making it easy to find the switch at night, and the bulb H does not light up. When turning on
the light, just press the switch SB, the charge stored in C2 is injected into the base of the transistor VT through SB, VT is turned on,
the thyristor VS is turned on because the gate obtains the trigger current through the "e pole" of VT, and the bulb H lights up Emit light. At the same time,
the charge stored in cl is quickly discharged through SB. After releasing the key switch SB, since the 9V voltage at both ends of C2 charges Cl, the
charging maintains the continued conduction of VT, so vs can still maintain In the on state, the bulb H still emits light. When the capacitor C1
is fully charged, VT changes from the on-state to the off-state, vs loses the trigger voltage. When the alternating current crosses zero, it turns off and
the bulb H goes out. The delay time of the circuit is mainly It is determined by the charging time constant of R2 and Cl. In addition, the voltage regulation value of VD5, the trigger sensitivity
of vs and the electric power of the bulb H also have an impact on the delay time.