Incandescent lamp life extension electronic controller (3)

Close the power switch S. During the positive half cycle of the power supply, the power supply charges the capacitor C through VD1, Rl, and VD2.
The voltage gradually increases, but is far lower than the threshold voltage of the zener diode VD5. VD5 is in the cut-off state and can The silicon controlled vs. non-touch
friendly current is in the off state, and no current flows through the bulb H at this time. During the negative half cycle of the alternating current, the current
provides a negative polarity trigger current to the thyristor vs through VD3 and R2, causing vs to turn on, and half-wave alternating current passes through the bulb H for preheating. As long as
the voltage across the capacitor C is less than the regulated value of VD5, in one cycle of AC power, the current flowing through the bulb H is only half a cycle
, which is the soft start process of the bulb. As time goes by, the voltage at both ends of C continues to rise. When it rises to exceed
the stable voltage value of VD5, VD5 turns on and provides a pull-up current to the thyristor vs. Therefore, in the positive half cycle of the alternating current, vs also turns on.
At this time, the bulb soft start process ends, and the bulb H enters the full voltage power supply state. The soft start time is mainly
determined by the capacitance value of capacitor C.