[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Sold state IGBT disruptive coil spark gap idea (SISG)

Original poster: Sparktron01@xxxxxxxxxxx
Hi Terry,

A few comments to your post...

> I have been studying if SCRs could be used instead of IGBTs, a much
> cheaper option, but the high dI/dt punch through problem seems
> devastating....  I ordered the "magic" SCR though just to
> "try"...  They are, again, only available in the "SUPER 247" box...
SCR's have a definite dI/dT limit about as "hard" as IGBT Vceo limits.
Good news is you are switching a RF sine wave (i.e. you are starting
from effectively a current zero).  Try it and let us know if we can see
the "blue glow over the horizon..."   ;^)

> 2 - The "SUPER 247" package from IR is "unique"...  A great idea
> since eliminating the hole allows room for a lot more die and the
> massive copper slab give great thermal transfer!!!  I used to write
> company internal papers 15 years ago about such things ;-)))  They
> did everything I told "other" people to do :o)))  The super 247 is
> also significantly cheaper for the power and this project needs all
> the "cheaper" it can get ;-))
> However....  There is not a darn "real available commercial heatsink"
> out there form them.  Nobody mounts a 600W device with a
> "clip"...  All the TO-220 clip heat sinks are not wide enough for the 247...
So make a "stradle clamp assembly" using two flat surface Al heatsinks
and make a minature "hockey puck" style mount.  Use commercial heatsinks
and 8 or 10-32 mounting screws on either side of full pack TO247 and
silicon grease BOTH sides of the device.  Now you are conducting heat
bidirectionally away from die in a similar fashion to IR's DirectFET (R)
devices.  I can be a "Tim Allen" of Power Electronics too...           :^D

BTW, I used this method on a 80V, 1.2kA darlington transistor in
a linear power supply at work (water cooled).  Worked like a champ
at up to 1.2kW disappation (device rated 2.1kW...    ;^D   )

> So I am thinking of thermal glue like this:
> http://www.arcticsilver.com/arctic_silver_thermal_adhesive.htm
> http://www.siliconacoustics.com/arsiltherad.html
> But our case is only like 10W, so maybe just JBweld  or "common"
> epoxy would work just fine....  I worry about air bubbles in the
> layer but with the copper slab that is not a big deal...  I used to
> work with the latest and greatest things there, but that was stuff I
> was glad "I did not have to pay for" (the above silver epoxy is two
> orders of magnitude cheaper though...)  Non-conductive is real cool
> since it can easily shoot arcs over the surface of silver filled
> non-conductive epoxies...  But I would not trust that property over
> time.  Best not to be messy with the epoxy ;-))  Isopropyl alcohol
> wipes it up real good before it cures...  Good Ol' JBweld is very
> good at thermal shock and all kinds of real world "not failing"
> issues...  Probably the best...
I don't recommend a non-removeable epoxy.  If you ever have to
disassemble / repair system, you're in deep (you know what...  :^C  )

> Cheers,
> 	Terry
Best Regards

Dave Sharpe, TCBOR/HEAS
Chesterfield, VA, USA