Re: [TCML] IGBT paralleling

[Steve Ward <steve.ward@xxxxxxxxx>]

The DC current rating for an IGBT is basically just the power dissipated
(Vce sat @ Ic) times the thermal resistance from die to case, keeping the
peak temperature < ~150C.  At least several of the IGBTs i looked at
appeared to arrive at the current spec in this way.

I typically ignore the current rating and instead look at conduction losses,
switching losses and thermal impedance, because honestly thats the bottom
line.  The amp rating is just some number that is almost never applicable to
the application.

As far as voltage headroom goes, operating at 50% of the part rating is
quite good for most cases.  Ive pushed some of my bridges all the way up to
their voltage rating (zero headroom), and that might work under controlled
conditions.  Ive also tested some older IGBTs for their ruggedness to
transients caused by hard switching of the IGBT or diode.  It seemed like it
took very big and high energy transients before my CM300DY failed, and that
normal "switching noise" kind of stuff would not really bother it much.
This suggests that running a higher bus voltage may be worth it.
Reliability data to settle disputes like this seems scarce.

I think a lot of coilers tend to neglect the thermal aspects of whats going
on in the IGBT (among other things).  Admittedly, its not a simple task, it
requires knowledge of some sort of SPICE program, and to extract the thermal
time constants from the data-sheets plots of Zth vs time.  Ive done it
before to check the temperature peaks that i expect my IGBTs to see, and
also to figure out the average die temperature after a minute or so of
operation.  I suspect thermal stress is a leading factor in the failure of
most DRSSTCs, particularly when someone tries to push 500A through a TO-247
device... the thermal mass is much smaller than a brick, and you dont see
people pushing bricks proportionally as hard.

To give the real numbers on the coil DC is talking about, it was CM300s
operating at ~1800Apk playing 4-note polyphony.  With no power factor
correction on the AC line, we were maxing the 100A meter installed on the
variac.  The RMS primary current is estimated to be (via pspice simulation)
in the 200A range.

Steve

On Wed, Jul 14, 2010 at 9:10 AM, Michael Twieg <mdt24@xxxxxxxx> wrote:

> Literally no amount of circuitry can eliminate ringing and spikes due to a
> device's internal inductance.  The actual collector of the device is not
> accessible to protection circuitry (unless you plan on tearing off the case
> and soldering directly to the die).
>
> And "pushing" current is very different from pushing voltage.  The current
> ratings for IGBTs are given under the assumption that they are being hard
> switched, which causes far more power dissipation than if they were soft
> switched.  That's why the current ratings can be pushed so far for tesla
> coil bridges.  It's not that the manufacturers are being conservative with
> their ratings (they have no incentive to do so), it's that we're not
> operating them in a typical fashion.
>
> Unlike the current ratings, the voltage ratings can't be pushed.  It's a
> pretty hard limit which is independant of what load you're driving.  If you
> try to operate your bus voltage above those ratings, they will fail very
> quickly.  And any sane engineer will give at least 25% headroom on the bus
> voltage (much more if they don't have very good snubbers).
>
> -Mike
>
> On Tue, Jul 13, 2010 at 10:23 PM, DC Cox <resonance@xxxxxxxxxxxx> wrote:
>
> > Proper circuit design eliminates the spikes and ringing problems.
> >
> > Most IGBT circuits are "pushed" a bit.  Steve Ward, at my open house, was
> > pushing his CM600s with up to 80 Amps RMS at 220 V input.
> >
> > Dr. Resonance
> >
> >
> >
> >
> >
> > On Mon, Jul 12, 2010 at 4:48 PM, John Forcina <forcijo10@xxxxxxxxx>
> wrote:
> >
> > > Apparently so.  I would like to see how DC will be able to get away
> with
> > > this with these mysterious IGBT's because if he claims they are rated
> at
> > > 2400V and 1650*1.414=2333.1v that gives almost zero headroom for
> voltage
> > > spikes ringing etc...
> > >
> > > It is pretty much impossible to make a bus layout that can accommodate
> > > these
> > > igbt's.  Even with a very low inductance laminated layout the sheer
> slow
> > > switching speed will create large switching spikes and will lead to a
> > > certain death to the igbt's.  Not to mention, any decent power engineer
> > > will
> > > know to de-rate the igbt's by several hundred volts to accommodate for
> > this
> > > and also because it's just good practice.
> > >
> > > On Mon, Jul 12, 2010 at 1:12 PM, Drake Schutt <drake89@xxxxxxxxx>
> wrote:
> > >
> > > > So DC you're saying that you raise AC voltage to 1.7kV before
> > > > rectification?
> > > >
> > > > Sent from my iPhone
> > > >
> > > >
> > > > On Jul 12, 2010, at 9:08 AM, "Brian" <brianv@xxxxxxxx> wrote:
> > > >
> > > >  Hmmm Im a little confused, 2400 vdc IGBT is the handling voltage of
> > the
> > > >> device , once an IGBT is on...it is on, I am not sure what this
> wasted
> > > >> head
> > > >> room is all about. Once the miller capacitance is overcome the IGBT
> is
> > > >> considered on and now connects the rail voltages. Whether it is big
> > > >> voltage
> > > >> or little voltage it don't matter. If you wish to drive them hard at
> > > full
> > > >> rated with 2400Vdc then drive them hard if you wish not too then
> > don't.
> > > I
> > > >> am
> > > >> not sure where the idea came in that there is a bunch of wasted head
> > > room
> > > >> that has to be filled...maybe I am missing something in this
> dialogue
> > > >> somewhere...
> > > >>
> > > >> -----Original Message-----
> > > >> From: DC Cox [mailto:resonance@xxxxxxxxxxxx]
> > > >> Sent: Sunday, July 11, 2010 6:27 PM
> > > >> To: Tesla Coil Mailing List
> > > >> Subject: Re: [TCML] IGBT paralleling
> > > >>
> > > >> With a 2,400 VDC IGBT, running it at a line doubled 220 VAC gives
> 2400
> > > VDC
> > > >> -
> > > >> 616 VDC --- over 1,784 Volts of wasted headroom that needs to be
> > filled,
> > > >> hence the use of a power transformer to boost the AC input from 220
> to
> > > >> around 1700 VAC.  The headroom I'm referring to is similar to your
> > audio
> > > >> reference only in this case wasting AC power headroom on a large
> IGBT
> > > that
> > > >> should be driven at higher potential to maximize coil output.
> > > >>
> > > >> This is, of course, all not relevant with standard medium size coils
> > > using
> > > >> rectified line drive (such as CM300 circuits) or line rectified
> drive
> > > with
> > > >> a
> > > >> voltage doubler circuit common with CM600 IGBTs.
> > > >>
> > > >> D.C. Cox
> > > >>
> > > >>
> > > >>
> > > >>
> > > >> On Sun, Jul 11, 2010 at 4:13 PM, Drake Schutt <drake89@xxxxxxxxx>
> > > wrote:
> > > >>
> > > >>  Dc- what do you mean when you refer to headroom in this post?  I'm
> > > >>> used to the term only in music production referring to dB.
> > > >>>
> > > >>> Regards
> > > >>> Drake
> > > >>>
> > > >>>
> > > >>> On Jul 11, 2010, at 3:22 PM, DC Cox <resonance@xxxxxxxxxxxx>
> > > wrote:With
> > > >>> CM300s or CM600s you can just double the 220 VAC line to get 642
> > > >>>
> > > >>> VDC
> > > >>>
> > > >>>> for a good match.
> > > >>>>
> > > >>>> If running, perhaps, a CM2400, you want to go up to near 2,400 VDC
> > on
> > > >>>> the drive, so you end up using a 220/480 Volt 3 phase to get up to
> > at
> > > >>>> or near the 2,400 VDC rectified.  This gives you better output
> > > >>>> because you go from
> > > >>>> 642 VDC to 2400 VDC that is being switched into the primary
> > inductor.
> > > >>>>
> > > >>>> Typically, with really large systems the only way to get from
> > 220/440
> > > >>>> VAC to produce the 2400 VDC drive max is to use a small 25 to 50
> kVA
> > > >>>> xmfr (surplus pole units).
> > > >>>>
> > > >>>> Not a dual pole pig unit, just a 220/440 VAC 3 phase xmfr
> delivering
> > > >>>> around 1650 VAC before rectification.
> > > >>>>
> > > >>>> The main point with large DRSSTC type coils is efficiency ---
> > > >>>> eliminating all those losses in the heat & UV light production in
> > the
> > > >>>> spark gap, and obtaining quicker dI/dt rates.
> > > >>>>
> > > >>>> As you pointed out small and medium size coils run just fine
> without
> > > >>>> using any pole xmfrs.  Usually above 15-18 ft long sparks the pole
> > > >>>> xmfr boost helps out get to the higher potential of the larger
> IGBTs
> > > >>>> without wasting a lot of headroom.
> > > >>>>
> > > >>>> Dr. Resonance
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>> On Sun, Jul 11, 2010 at 2:14 PM, Gary Lau <glau1024@xxxxxxxxx>
> > wrote:
> > > >>>>
> > > >>>> I'm going to bare my ignorance here.  I thought that the whole
> point
> > > >>>> of
> > > >>>>
> > > >>>>> solid state TC's was that you don't need a multi-kilovolt power
> > > supply.
> > > >>>>> Are
> > > >>>>> pole pigs really used to power these?  A _dual_ pig powered
> > > >>>>> magnifier???
> > > >>>>>
> > > >>>>> Regards, Gary Lau
> > > >>>>> MA, USA
> > > >>>>>
> > > >>>>> On Sun, Jul 11, 2010 at 12:16 PM, Scott Bogard <
> sdbogard@xxxxxxxxx
> > >
> > > >>>>> wrote:
> > > >>>>>
> > > >>>>> 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-igb
> > > >>>>> t-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.
> > >  >>>>>>>>>
> > > >>>>>>>>> _______________________________________________
> > > >>>>>>>>> Tesla mailing list
> > > >>>>>>>>> Tesla@xxxxxxxxxx
> > > >>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>>>>> _______________________________________________
> > > >>>>>>>>> Tesla mailing list
> > > >>>>>>>>> Tesla@xxxxxxxxxx
> > > >>>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>>>>>
> > > >>>>>>>>> _______________________________________________
> > > >>>>>>>>>
> > > >>>>>>>>> Tesla mailing list
> > > >>>>>>>>>
> > > >>>>>>>> Tesla@xxxxxxxxxx
> > > >>>>>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>>>>
> > > >>>>>>>> _______________________________________________
> > > >>>>>>>>
> > > >>>>>>>>  Tesla mailing list
> > > >>>>>>> Tesla@xxxxxxxxxx
> > > >>>>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>>>
> > > >>>>>>> _______________________________________________
> > > >>>>>>>
> > > >>>>>>>  Tesla mailing list
> > > >>>>>> Tesla@xxxxxxxxxx
> > > >>>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>>
> > > >>>>>> _______________________________________________
> > > >>>>>>
> > > >>>>> Tesla mailing list
> > > >>>>> Tesla@xxxxxxxxxx
> > > >>>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>>
> > > >>>>> _______________________________________________
> > > >>>>>
> > > >>>> Tesla mailing list
> > > >>>> Tesla@xxxxxxxxxx
> > > >>>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>>
> > > >>>>  _______________________________________________
> > > >>> Tesla mailing list
> > > >>> Tesla@xxxxxxxxxx
> > > >>> http://www.pupman.com/mailman/listinfo/tesla
> > > >>>
> > > >>>
> > > >>
> > > >> _______________________________________________
> > > >> Tesla mailing list
> > > >> Tesla@xxxxxxxxxx
> > > >> http://www.pupman.com/mailman/listinfo/tesla
> > > >>
> > > > _______________________________________________
> > > > Tesla mailing list
> > > > Tesla@xxxxxxxxxx
> > > > http://www.pupman.com/mailman/listinfo/tesla
> > > >
> > > _______________________________________________
> > > Tesla mailing list
> > > Tesla@xxxxxxxxxx
> > > http://www.pupman.com/mailman/listinfo/tesla
> > >
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla