Re: OLTC Thoughts

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Richard,

At 04:14 PM 8/11/2002 -0400, you wrote:
>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.

The data sheet is at:

http://hot-streamer-dot-com/temp/irg4pf50wd.pdf

>
>> 
>> >Have you calculated the resonate oscillatory frequency of the primary
>tank
>> >without the switches?  Also consider moving the switch(s) outside the LC
>> >tank altogether to allow the tank to oscillate freely and transfer even
>> >more energy before you electronically quench it.  I'll leave these design
>> >thoughts up to your fertile electronics imagination.
>> 
>> They are fairly well outside it now.  
>
>Your schematic places the IGBTs right in the LC tank circuit.  See
>http://hot-streamer-dot-com/temp/OLTC8-10-01.gif et subsequent.

Yes, the IGBTs act just like a normal spark gap.  The coils basic function
is just like that of any disruptive coil.

>
>Another consideration is that with ten IGBTs and ten 4.7 mF caps, not only
>does turn on have to be right on the money, BUT turn off has to also be
>exactly the same for all IGBTs.  

It can really be very sloppy.  If one turns on 1.3uS early, no problem.
The key is that the current in the tank is pretty slow to come up due to
the tank inductor.  The IGBT's will easily outrun it.

>Post firing, as the tank oscillates and it
>is also charged by the PS, differences in IGBT turn off timing will affect
>residual charge imparted on each 4.7 mF cap.

I can actually leave them charged negative for even higher power.

http://www.pupman-dot-com/listarchives/2002/August/msg00424.html

>
>What is your proposed IGBT firing rate and dwell time?

120BPS and around 130uS.  The firing rate is automatically controlled and
the dwell is from a 555 timer.

http://www.pupman-dot-com/listarchives/2002/August/msg00391.html
http://www.pupman-dot-com/listarchives/2002/August/msg00414.html

>
>RWW
> 
>--- Richard Wayne Wall
>--- rwall-at-ix-dot-netcom-dot-com
>
>
>