Cooling and dimming light switch

The circuit of the gradually brightening and gradually dimming lighting switch is shown in Figure 1-12. In the figure, S is the light switch and H is the controlled lighting lamp. Transistors
VT1, VT2 and resistor-capacitor components form a fade-in and fade-out control circuit. Since the transistors VTl and V12 must work in the DC state
, the circuit uses four diodes VDl~VD4 to form a bridge rectifier circuit to convert the 220V AC power into a full-wave DC
pulsating voltage for circuit operation.