Re: Simple power supply overheating components, shorting zener


"Ban" <bansuri@xxxxxxxxxxxx> wrote in message
news:XSrQg.5342$K8.5137@xxxxxxxxxxxxxxxxxxxxx
cbarn24050@xxxxxxx wrote:
Eeyore wrote:
He has got 2 in series ! An X-type might be better though.

Graham

I know, thats only 500v, not enough! and he has no charge balancing
resistors nor any transient suppressors. A supply destined to fail
time and time again.

Right, it is bound to fail, because of 2 violated max. ratings. He didn't
consider the inrush current. When you switch on in the wrong moment there
is over 20A running through the zener and 100u in parallel. The zener is
probably rated for 3 or 4A non repetitive surge. Also this violated the
dI/dt of the caps and it has already shorted one cap, because even with a
dead short acroo the O/P the current can not be higher than 70mA, but the
OP measured 100mA.
It is also a safty hazard to leave a 1u/400V charged capacitor open
circuit waiting to zap the technician even after days.
--
ciao Ban
Apricale, Italy

Ban,
For some reason they are not buying changing the 1/2 wave to a full wave
rectifier. Just takes two more diodes and drops the coupling cap's value in
half. This drops the surge currents in half and allows one cap of 0.47uF.
The zener should be a transzorb.
cheers,
Harry


.

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