Re: Transformerless PSU using a zener/transil to drop voltage

[MooseFET <kensmith@xxxxxxxxx>]

On May 29, 9:01 am, and...@xxxxxxxxxxxxxxxx wrote:

> 2) if the above is not feasible, I was thinking about working on the low
> part of the AC waveform rather than on the peaks: maybe a high voltage
> MOSFET which conducts only when the serie voltage is under e.g. 20V? For
> the rest of the AC waveform the MOSFET would be turned off. I should use
> a 20V zener (in a high impedance way, something zeners really don't like)
> and a P-MOSFET, intuitively, or a depletion-mode N-MOSFET.
>
> Any suggestions/comments please?

Use a comparitor to switch the MOSFET off if the output voltage
exceeds 12V or the drop on the MOSFET exceeds, lets say, 6V.

The mains spends only a smallish time inthe 12V to 18V span so the
MOSFET needs to be able to conduct way more than 100mA when on.