Re: BIG solid state devices...

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

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

Hi Jim,

At 07:20 PM 7/12/2002 -0700, you wrote:
>Of course, if the experiences my coworkers have had with 1000V FETs are any
>guide, you'd want to see some real live test data at the high voltages.

I have had a few hundred 1000V RF FETS blow up in my face to ;-))  During
R&D, we use big DC power supplies so there is no real current limiting.
The sound like a 30-6 round. =:O  The big problem with experimenting with
solid state gaps is that if anything goes wrong, you just throw it all away
and start over...  This type of R&D is more for a big company budget that
an amateur one for sure!  $1000 worth of silicon could be gone in a flash.

>
>For the IGBTs, switching time might also result in significant power loss..
>Rise and fall times at 500-1000 Amps look like a few microseconds.  The data
>sheet shows 1-2 Joule per pulse loss for 500-1000 Amps collector current.
>At 100 kHz switching rate, thats 100-200 kW in the switching losses...

They key is that we are NOT switching at 100kHz.  Were switching at 120
BPS.  A spark gap is just a switch we turn on every 8.333mS and back off
about 300uS later.  No fancy switching at all.  We just crank it "full on"
all through the firing cycle.  The tank circuit does all that RF stuff not
the gap.  My controllers would be all fancy in that they could control
quenching, sync, etc. but the on/off control pulses are just plain less
than 1000Hz square waves.  The initial turn one current is limited by the
LC of the tank but the IGBTs can outrun that easily.  At turn off, the
circuit could pretty much be run down so the loss is zero.  If you quench
in the current peak the losses are higher, but no reason to do that unless
you are playing :o)

you may want to see the scope pics at:

http://hot-streamer-dot-com/temp/2001-04/SScap1.jpg

This is just one little 1200V 150A IGBT I was running into a dead short.
Even though I was going through all fiber optic triggering and such, the
times are very fast and the voltages and currents are very high too.  They
really are wonderfully well behaved for this stuff.

Here was the setup:

http://hot-streamer-dot-com/temp/2001-04/TheFun.jpg

Here is the IGBT on a heat sink that allows it to run cool.  Trust me, the
power loss is very low ;-))

http://hot-streamer-dot-com/temp/2001-05/TheFun1.gif

Of course, you can switch at full Fo speeds as Ken's wonderful machine does:

http://hot-streamer-dot-com/temp/2001-05/KCH_tcg1.jpg

But I am hoping the solid stat gap only thing will be a bit simpler ;-)

http://hot-streamer-dot-com/temp/2001-06/KCH_tcg3.jpg

Cheers,

	Terry


>
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Friday, July 12, 2002 6:41 PM
>Subject: BIG solid state devices...
>
>
>> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>>
>> Hi,
>>
>> I note the Hitachi MBN1200D33C
>>
>> http://www.hitachi.co.jp/Div/ise/pdevice/igbt/index-e.htm
>>
>> http://www.hitachi.co.jp/Div/ise/pdevice/igbt/d-igbt/1200d33c.pdf
>>
>> switches 3300 volts at 1500 amps with 6 volts of CE drop...  If one were
>to
>> put 8 in series to run a 21kV firing voltage, you would get about 48 volts
>> drop or 48 x 21000 = 1008000 watts (i) of instantaneous power loss.  But
>> the system power is 1500 x 21000 = 31500000 watts (i)
>> >
>>
>