Electronics > Power & Renewable Energy

Very simple, possibly transformer-less AC to 5v dc power supply

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--- Quote from: xtv on July 13, 2021, 06:31:16 pm ---Would it be possible (or smart) a design that would allow current to flow and charge an output capacitor only when AC input is close to 5v?
--- End quote ---
This is possible of course but I have never seen such design in practice.
It seems your design has to use some kind of active switch that clamps to 5V capacitor just when mains is passing +5V (which lasts for super short time on 230V mains). And this switch has to be capable to withstand full mains voltage + transients, but it is idling most of the time. So instead of charging 5V cap with huge currents for super short time (1mA continuous out means you need ~1A if charge lasts 1/1000th of the time) when crossing 5V, why not charge and discharge some inductor during all the cycle? You already have the active switch for the rated voltage, also evenly loaded switch is much smaller then.

And that is how we got to an offline buck converter.

These mains buck converters are super simple and cheap but not suitable for such low powers, I think there is no market for 5mW mains switchers. For 1mA just use capacitive dropper which has higher efficiency than any mains buck switcher, and is also super cheap.

inrush resistor
cap rated for transients
bridge rectifier
output capacitor


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