Electric lamp delay switch circuit analysis

Press the button to activate the time delay circuit and turn on the light at the same time. After the preset delay time, it automatically extinguishes the lamp. The potentiometer is used to preset the delay time, which can range from a few seconds to 3 seconds. When the SW2 button is pressed, capacitor C1 is filled with DC voltage through D3, which depends on the diode bridge. When the switch is reset, the fully charged capacitor is connected across the R12, R3 and potentiometer R4 series circuits. The capacitors discharge through the equivalent voltage determined by these resistors, so they determine the delay time. Diode D0 (connected to the junction of resistors R2 and R3) applies a portion of the attenuated DC voltage (Vc1) to the control gate of the thyristor (Q1), which triggers Q1 into conduction, as long as it is controllable There is enough voltage on the silicon gate to keep it on. Once this voltage decays to the minimum sustain voltage of the thyristor (Q1), it will break at the alternating point of the next cycle.