Like usual you have again right, but as I said already ( and test on about
100 hours with my measuring tools and more than 2 years just with my
eyes...) it's no need any zenner on load or resistor across the capacitor
if:

- never plug on the supply without computed load connected ( and no other
load ! )
- use a best quality polyester or PMP capacitor with nominal voltage 2 or
3 times greater than maximum voltage you may have (have big size ! )

I other condition I use a 5W 12V zenner as you've mentioned, but I don't
like this sort of supplies (I've repaired many supplies like this,
produced at Ganz-Hungary in some energetic equipment, here the capacitor
was protected with a varistor who crashed frequently, also the
protective zenner diode crashed ...), it's easy to develop a
comutation supply up to
100W with only one power transistor, an a cheap UC344 or TL494, a little
transformer, some fast diodes and some capacitors.
You don't need to know only Faraday's low and some tricks about projecting
a good pcb. Maybe in my next web page...

Cheers, Vasile



On Thu, 26 Jul 2001, Roman Black wrote:

> Vasile Surducan wrote:
> >
> > I've done one, some time ago, see
> > http://www.geocities.com/vsurducan/c520.htm
> > at the bottom of the page, up to 150mA, but I don't recommend such power
> > supplies for production devices ( maybe on 120V mains, only )
> > Note that in my design, the supply don't like to remain without load...
> > Vasile
>
>
> Hi Vasile! Great web page! But that picture power.gif
> scares me a bit! The only thing limiting the voltage
> across C5 is the current drawn by the load!!
> Maybe you could put a 8v 1w or larger zener diode
> across it. Would improve safety a lot!
> :o)
> -Roman
>
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