Transformerless power supply

197

03:26:52

Danger: output is not isolated from mains. Capacitor next to AC mains source limits current from AC mains and its reactivity determines the amount of current output. Zener diode limits voltage. Resistor at diode bridge to ground limits current during startup. Capacitor closest to output filters ripple.

published 1 year ago

592azy2circuitdude

1 year ago

Hi. Neat circuit. I don't know too much about these kinds of power supplies, so I have a question. Why do you use a 100nF capacitor at the beginning to limit current when you could use a resistor?

johntron

1 year ago

Ah, that's the most important thing about this circuit: a resistor would not I'm fact limit current. With mains, you can have all kinds of unexpected transients - like an HVAC fan starting up and drawing many amps from anywhere it can, including through an almost-certainly-underrated resistor. Since capacitors don't allow current to flow *through* them, this isn't a problem - only the *voltage* caused by transients is a concern.

592azy2circuitdude

1 year ago

OK, that does help me. Thank you.

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