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Re: [TCML] IGBT paralleling

Hi John,
By chance is there a compiled list somewhere of "good IGBTs" that are used and those that aren't. Anyway back to the original question, is it possible to parallel them? Lets say for kicks I'm building a dual pig powered 30kVa magnifier with a LTR cap (I'm clearly not, we are talking theoretical here.) Clearly the peak currents will be beyond any reasonably priced IGBT, is it possible to parallel lesser current units to handle the load, and what would that entail? Thanks. 

Scott Bogard.

On 7/10/2010 5:09 PM, John Forcina wrote:

Those IGBT's seem far from ideal.  The TO220 package is a very poor choice
as far as thermal conductivity and the datasheet says it all 0.75C/W.  You
will not be able to remove enough heat from the surface of the IGBT die
quick enough between current pulses and the device will fail.  They do not
have a internal anti-parallel diode so adding that externally will add to
the final cost also.  Not to mention doing that will add additional loop
area and stray inductance between units.  One more thing is the switching
times are surprisingly slow for that small of a unit.  td(OFF) 96ns.  It's
not that slow however it does seem slow for that small of a device.  I have
seen much better overall performance from larger IGBT's.  My suggestion is
to just spend more money and use IGBT's that have been used and proven to
work in Tesla Coils time and time again.  There must be some reason that we
all use them ;)

On Sat, Jul 10, 2010 at 4:38 PM, Scott Bogard<sdbogard@xxxxxxxxx>  wrote:


Interesting,
        I am in the wee beginning stages of building my first SISG, and as
such am in the market for IGBTs.  I found these, which look very inexpensive
and have decent ratings.

http://www.newark.com/fairchild-semiconductor/hgtp12n60a4/single-igbt-600v-54a/dp/90B5642
My thinking is if heat is a problem or peak current, can I just parallel
them?  at $1.50 a pop it seems infinitely better than 1 $18 IGBT of nearly
the same ratings...  I didn't look at temperature or package information
yet, so maybe there is a problem there.

Scott Bogard.


On 7/10/2010 8:26 AM, McCauley, Daniel H wrote:


Scott,

The electric ratings may be the same or similar, but you also have to
compare the mechanical ratings -  in particular the thermal ratings.  This
would be junction-to-case thermal impedances etc...  The expensive IGBTs
that are commonly used in DRSSTCs are usually ISOBLOC type packages which
excellent thermal impedances.  Compare this vs. a TO-247 package of the same
die.

And when comparing a TO-247 package to an ISOBLOC, keep in mind that you
STILL NEED to add a thermal insulator between the TO-247 and heatsink, which
just makes the thermal impedance even worse.  The ISOBLOC (or SOT-227)
doesn't require a thermal interface other a small smidgeon of thermal grease
or a graphite pad.

Dan
http://www.easternvoltageresearch.com
DRSSTC, SSTC, Flyback, Plasma Speaker Kits




-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Scott Bogard
Sent: Friday, July 09, 2010 9:52 PM
To: Tesla Coil Mailing List
Subject: EXTERNAL: [TCML] IGBT paralleling

Greetings all,
        So, after a bit of researching I've noticed there are IGBTs on
Newark with exactly the same ratings as some of the SSTC approved IGBTs, but
at 1/10th the price.  What makes these others so special that they are
better, and if it is just a matter of peak current ratings, since IGBTs are
gate driven, can we just parallel a few to get the required pulse current
rating?  I ask because I've not heard of anybody doing this, then again I've
only begun to research SSTC a little bit ago.  Just musing.

Scott Bogard.
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