Capacitive soft start circuit diagram

The picture below is a soft-start circuit composed of LM317 . At the moment of power-on, the voltage on C2 cannot change suddenly. VT is biased by R2 and R3 and conducts in saturation. This makes R1 short-circuited, which is equivalent to the adjustment terminal of LM317 being grounded. The power output is 1.25V. As the charging time of C2 increases, the output voltage gradually rises. According to the component parameters in the figure, the time to reach the rated output voltage is 3s. The function of VD is to quickly release the charge on C2 after turning off the power supply to ensure that Normal soft start at first boot.
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