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 headroom is all about. Once the miller capacitance is overcome the IGBT isconsidered 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 roomthat 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 parallelingWith 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 toaround 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 thatshould 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 avoltage doubler circuit common with CM600 IGBTs. D.C. CoxOn 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 DrakeOn 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 642VDCfor 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 ator near the 2,400 VDC rectified. This gives you better output because you go from642 VDC to 2400 VDC that is being switched into the primary inductor.Typically, with really large systems the only way to get from 220/440VAC 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 thespark 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. ResonanceOn 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 ofsolid state TC's was that you don't need a multi-kilovolt power supply.Arepole 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, isitpossible to parallel them? Lets say for kicks I'm building a dualpig powered 30kVa magnifier with a LTR cap (I'm clearly not, we aretalking theoretical here.) Clearly the peak currents will be beyond anyreasonablypriced IGBT, is it possible to parallel lesser current units to handletheload, 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 poorchoiceas far as thermal conductivity and the datasheet says it all 0.75C/W.Youwill not be able to remove enough heat from the surface of the IGBTdiequick enough between current pulses and the device will fail. They donothave a internal anti-parallel diode so adding that externally will addtothe final cost also. Not to mention doing that will add additionallooparea and stray inductance between units. One more thing is theswitchingtimes are surprisingly slow for that small of a unit. td(OFF) 96ns.It'snot that slow however it does seem slow for that small of a device.Ihave seen much better overall performance from larger IGBT's. My suggestionisto just spend more money and use IGBT's that have been used and proventowork in Tesla Coils time and time again. There must be some reasonthatwe 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, andashttp://www.newark.com/fairchild-semiconductor/hgtp12n60a4/single- igbsuch am in the market for IGBTs. I found these, which look veryinexpensive and have decent ratings.t-600v-54a/dp/90B5642My thinking is if heat is a problem or peak current, can I justparallelthem? at $1.50 a pop it seems infinitely better than 1 $18 IGBT ofnearly the same ratings... I didn't look at temperature or packageinformationyet, 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 alsohave to compare the mechanical ratings - in particular the thermalratings.This would be junction-to-case thermal impedances etc... The expensiveIGBTsthat are commonly used in DRSSTCs are usually ISOBLOC type packageswhichexcellent thermal impedances. Compare this vs. a TO-247 packageofthesamedie. And when comparing a TO-247 package to an ISOBLOC, keep in mind thatyouSTILL 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 approvedIGBTs,butat 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, sinceIGBTsaregate 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, thenagainI'veonly 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 listTesla@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
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