[Amps] HV Diodes

[Manfred Mornhinweg]

Steve,

> The Alpha bridge modules discussed below are these:
> http://www.deantechnology.com/pdf/pdf24.pdf

Yes.

> It's P/N 2HVFWB5KB and uses glass passivated rectifier cells which are not
> 1N4007s, but ratings are similar.

Among the diodes I know, the 1N5622 fits the bill best. It is glass passivated, 
and has the same surge current and reverse current rating of that bridge. Just 
the forward drop doesn't agree, it's given as 1.2V, while the bridge's rating of 
4.8V for what must be 5 diodes would be 0.96V per diode. So, they must be using 
some different diodes. Maybe 4 diodes in each leg, rated at 1250V, but there are 
only a few types of this voltage, and they have higher forward drop. I don't 
know any that matches the other specs.

> Adding heat sinking and potting material around semiconductors doesn't change
> their surge rating in any way.  The surge rating is an instantaneous rating
> based on a 8.33 mS half sine wave and with or without any sort of heat
> sinking, this won't change.

Basically that's right. My only reason to think that the surge rating might 
change with potting, is due to a lower operating temperature. If a diode is 
potted in a resin that has decent thermal conductivity, and the package is put 
to a heatsink, the diode will work cooler then when operating in free air. In 
that case, there is a larger margin for surge currents _during operation_, 
because there is a larger thermal headroom through which the diode die can warm 
up from the surge. Of course the inrush surge rating when cold would not change, 
and thus the issue is really moot, and you are right! ;-)

Would be fun to discover what exact diode they used!

Manfred

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