Incandescent lamp life extension switch circuit (4)

It is an incandescent lamp life extension switching circuit composed of high-power field effect transistors and other components . Its soft-start
performance is quite good. When the switch S is closed, the voltage across the capacitor C is zero and cannot mutate, so the field
effect transistor VF is in a cut-off state and the lamp E cannot light up immediately. As time goes by, C passes through R. Being
gradually charged, VF also gradually turns from the cut-off state to
the saturated state through the amplification area, and the current of its drain D
gradually increases from zero to the rated current of the bulb . This avoids the impact of strong current on the filament
due to the small cold resistance of the filament at the moment the light is turned on , causing the power supply voltage to slowly increase to both ends of the bulb as the filament temperature gradually increases . In the circuit, the time for VF to change from cut-off to saturated conduction is the soft boating time of the light bulb . According to the parameters of the central component, the measured time is about 15s. After the lamp stops shining normally, since VF is in a deeply saturated state, its tube voltage drop is less than 15V, and the tube voltage drop generated by VD1-VD4 is less than 14V, so the power consumption of the open circuit itself is very small, and the brightness of E is less than 1.5V. The same as when directly connected to both ends of 220V AC power,     the VF should use an IRF821 high-efficiency field effect transistor with The tube is packaged in T0-220 plastic and requires additional installation area when operating. Sufficient heat dissipation plate. When welding field effect tubes, the soldering iron shell must be well grounded to prevent AC induced voltage from breakdown and damage to the tube.