On 28/09/2020 11:04, Roger Hayter wrote:
I think the secret is low current consumption. To drop (most of) 240V at,
say, 5mA needs only to dissipate 240 x 5 x 10^-3, that is about 1.2W and the
large resistor can probably do that even air cooled.

don't even need that. A capacitor of as it happens about 0.63µF will
deliver 5mA into a small circuit and be more reliable cooler and cheaper.
Feed that into a diode bridge and, if my back of envelope is right, 50µF
and you will have less than 1V of ripple at 5mA.



Only few low power
components are needed to voltage limit, smooth and regulate the low voltage
supply. There should be an electrolytic capacitor though, unless anyone can
give a clue how to avoid it.

well yes, and that's by going v high frequency, but then you need a
choke or transformer instead...


--
Climate Change: Socialism wearing a lab coat.