On Wed, Feb 15, 2006 at 02:51:59PM -0500, David VanHorn wrote:
> You have a couple of problems here.
> 
> First there is the turn-on surge, which is going to be limited only by the
> transformer's ability to deliver current.

Substantial for sure... 

> Second, you're going to have a relatively low conduction angle because of
> the large filter caps, which means that at N amps of output current, your
> diode current will the several times N.

So will that repetively stress the diodes at each 60hz cycle? So at each
"charge" they get a fast burst of current through them?

> Third, diodes don't share current well. Putting them in parallel without a
> ballasting resistor ends up with one diode having slightly lower Vf than the
> other, and taking more current. The positive temp coefficient will tend to
> help you here, otherwise it would go into runaway, with the hot diode taking
> more current till it pops.

I don't think that's the problem. The diodes are rated, individually,
for 2x more current than is the steady state. They are in parallel not
because I need extra current capacity, but simply because it was
cheapest to buy them packaged like that.

-- 
pete@petertodd.ca http://www.petertodd.ca
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