Re: Cross for Keltron diodes?

On Thu, 26 Aug 1999, Rodger Boots wrote:

> First rule of flyback supplies is that you use FAST
> diodes. 1N4000 series, for example, will die a quick
> death and possibly take other parts with them. WHY?
> If the part can't turn on and off quickly they will try to
> conduct briefly in the reverse direction. That causes
> heating.
>
> An NTE552 would be a good replacement for either
> number.

        Thanks for the help, Rodger. I just wanted to follow-up on your
message. Another diode that crosses to an NTE 552 is a 1N4937, which is
pretty much commonly available (it was available at all 3 of my local
electronics stores, so that makes it commonly available in my book) and
is, of course, cheaper than the equivalant NTE part. The 1N4937 is a
600V, 1A fast recovery part.

        In any case, I fixed my Keltron supply, and it turned out NOT to
be the diode. Although I was getting a short in both directions across
the diode (in circuit) the real culprit was the .036 uF capacitor (It
might be C41, but I don't remember for sure) which looks like it AC
couples the output of the voltage quadrupler into the +90V rectifier
circuit. That aforementioned cap was shorted. What's wierd is that that
cap isn't strictly in parallel with the diode, so it's wierd that I read a
short across the diode. There's probably a good explanation for it, I'm
sure, but it was late, and I didn't think about it too much.

        I had to scavenge a replacement for that cap from a spare Keltron
supply, so I need to get one of those caps. I'm not sure what type it is
(it looks like an epoxy cylinder wrapped in yellow tape.) I suppose any
.036, 100V, 5% capacitor will do, but I'm kinda curious as to what that
type of capacitor is called. Anyone know what I'm talking about?

Joe
Received on Fri Aug 27 10:55:46 1999