Ordinary transistor triggered unidirectional thyristor dimming light circuit

It is a unidirectional thyristor dimming light circuit triggered by an ordinary triode . VT2 and V are composed of a complementary amplifier to form the trigger circuit
of the thyristor VT1 . The 220V alternating current passes through the bulb E and is bridge -rectified by VD1~VD4 to output a full-wave pulsating voltage. This voltage is measured through the ruler, R. , RP sends electricity to the capacitor (1 gram, causing the IH position of the VT3 emitter to continue to rise. When it is 0.65V higher than its base, VT3 and VT2 are turned on, and the gate of the thyristor VT1 gets a trigger pulse. VT1 is turned on. At this time, C is discharged through VT:3, VT2 and R, and the positive power supply charges it again through R, R, and RI'... Therefore, adjusting the resistance of the potentiometer Rl will change the VT2 emitter output The advance or lag of the pulse time changes the conduction angle of the thyristor VT1, that is, the brightness of the lamp E can be adjusted.