Mithun_K_Das
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If you review similar circuits published at Edaboard, you'll notice that most have a current limiting resistor, e.g. 100 ohm/1W in series with the capacitor. It's absolutely required to limit inrush current and transients.
I don't think that NTC solves the problem. For 50 mA output, you need 100 mA AC input current in half-wave rectifier circuit. With 2.2 µF capacitor (about 1.5 µF is the minimal value) and modified square wave, you get about 20W losses in series resistor. Without series resistor, peak current would rise to > 10A.
just curious....
What makes you think a triac helps in that circuit?
Brian.
Yes, usually for unexpected high voltage spikesTRIAC concept comes to protect the circuit from spikes.
The current passing through C3 has to be reasonably symetrical so moving the Zener to the right side of the rectifier will simply result in C3 charging to DC. It would work if a bridge rectifier was used so the polarity across C3 alternates.
I fear there is no simple and safe (assuming an isolated load) solution to the problem except adding the series resistor as already recommended.
Brian.
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