Re: OLTC Thoughts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Eddie Burwell by way of Terry Fritz <twftesla-at-qwest-dot-net>" <eburwell-at-columbus.rr-dot-com>

At 02:36 PM 8/11/02 -0600, you wrote:
>Original poster: "Wall Richard Wayne by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
>
>Terry,
> 
>> The IGBTs have big powerful anti-parallel diodes in them already ;-))
>
>Excellent, do you know the speed (Reverse Recovery time) of these diodes? 
>If they're too slow you may need to add supplemental fast diodes.  Your
>fast CE MOVs or snubbers are also good ideas.
>
<snip>
>--- Richard Wayne Wall
>--- rwall-at-ix-dot-netcom-dot-com
>

Reverse recovery shouldn't be a problem. The IGBT will be forward conducting
as soon as the current reverses except for the last cycle where the IGBT is
turned off to "quench the gap". So the diode might have a true reverse
recovery 120 times per second. I say might because that will depend if you
quench at a notch or not.

The bad thing about the reverse diode is that if you quench at the first
notch the diode will tend to rectify the voltage coupled back to the primary
and recharge the caps with the energy leached from the secondary. Of course
if the streamer has already eaten most of the energy it's no big deal.

Eddie Burwell