[Amps] HV Diodes

[Steven Katz]

It may well be a non-standard diode (no "1N" JEDEC number -- there are billions of such items manufactured).

The 1N5622 1.2V Vf spec was actually based on the Semtech design, when it was registered as a JAN/JANTX/JTXV1N5622 under MIL-S-19500/427.  That's a "max" rating at 25C.  At higher temps, the Vf is lower.  The reason it seems "so high" is at the time, the triple-layer suprataxial junction Semtech was using had higher Vf than double diffused or common epitaxial designs, but it was used because it's very rugged and very low leakage, irrespective of the actual specification.   Due to the cost of the materials and construction used, this was never really intended to be a commercial device.

-WB2WIK

-----Original Message-----
From: Manfred Mornhinweg [mailto:manfred at ludens.cl] 
Sent: Thursday, October 16, 2014 1:55 PM
To: Steven Katz
Cc: Amplifier Mailing List
Subject: Re: [Amps] HV Diodes

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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