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what do you think of these bricks?

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LAN_403

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Sat Aug 05 2006, 09:38PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Well considering that Reaching has about 10in^2 he shouldn't have any worries

Steve Ward

Sat Aug 05 2006, 10:01PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

My CM300 bridge gets pretty stinking hot without forced air cooling. The dissipation is in the 300W range. I try to apply the thermal grease as evenly as possible, with the recomended thickness of 8 mils. The cooler you keep the IGBTs, the harder you can push them

Reaching

Sun Aug 06 2006, 12:05AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah steve is right, the brick sized igbts get very hot, i remember from my old brick sstc that a temparature of the big heatsink of 100 degrees celsius was normal for longer periods of time, okay without a fan.

lets take a look at my bridge or the pieces i already have. today i cutted the heatsink in 3 pieces, with a normal handsaw!!nobody wanted to cut it for me for a few bucks so i made it.

when my fans arrive every heatsink gets 2x 120mm fans with an air flow of 92mÂ³ per hour, should be enough for extended runtimes

Steve Ward

Sun Aug 06 2006, 02:08AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Those are some excellent heatsinks! You might want to check out my CM600 bridge for ideas on a low inductance layout:

You can ignore the first half of those pics, just waveforms of the gate rise and fall time (25nS measured at the terminals). This was of course slowed down to something more realistic (about 500nS rise time and 200nS fall time)

Reaching

Sun Aug 06 2006, 12:39PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

thanks steve, good idea, need some copper sheets

.i want to use similar capacitors 12000yf 350volt, 2 in series 2 paralelled for a total of 12000yf 700volt dc
so, now the igbts are screwed on the heatsinks, and now i have to build a good power driver to drive these bricks, i thought of 2 fullbridges with 30v + and -15v input, each fullbridge driving 2 bricks, every brick has its own 1:1gdt, okay never needed such a high power to drive a brick but i think it should work, or will the waveform look like crap cause of the many gdts?

Steve Ward

Sun Aug 06 2006, 07:55PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The GDTs will not transfer the -15V +30V driver properly. It will come out as +/- 22.5V on the gates. You could try the "standard" gate drive scheme with just +/- 30V from a GDT, but the GDT will limit the peak current due to its stray inductance. For really big bricks, you simply must use high side drivers that connect straight to the IGBT. It might seem like a lot of extra work, but its really the best way. Those 1200V 210A IGBTs you have might work OK from GDT drive, with a healthy gate driver behind it (maybe 4 parallel UCC 9A drivers for a 36A gate driver). Try to minimize the GDT inductance. It might be worth going "coaxial" where your primary is simply a foil shield around the several secondary windings inside (imagine coax, but with 4 conductors inside instead of 1).

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Sun Aug 06 2006, 11:10PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Might I suggest Blackplasma's uberdrivers? Seem like an easy solution to a complex problem

Marko

Sun Aug 06 2006, 11:59PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

UberdriversÂ® are unable to charge above 15 volts so IGBT's would die when overstressed.

I think Ward's solution is simplest and best at time.

Another way for making UberGDTÂ® could be using a bunch of thin wires (0,1..0,2mm) wound multifilary, and braided together tightly. It is a bit pain to find your leads after but coupling is reallly high and leakage inductance low. Altough I'm not sure if it is really better than shielded networking cable GDT. (maybe you can get little less ohmic resistance?).

Steve Conner

Mon Aug 07 2006, 09:40AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Meh. I looked at all these schemes for driving IGBT bricks and in the end I decided to make a driver similar to Ward's (there's also a similar design by Dan Strother)

However, I seem to remember Jimmy Hynes was successful driving bricks off a GDT with a 1:2 stepup ratio to give +/-30V drive. But I think he did have a lot of trouble getting good looking waveforms.

Reaching your heatsink is "Supergeil"

Reaching

Mon Aug 07 2006, 10:30AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

hehe, yeah , supergeil is the right word for these uberbig heatsinks

i started to build the low inductance wiring and it looks nice. i left enough space to change the driving pcbs on each brick so i can experiment with some different driving shemes,. the problem is i dont understand exactly how wards brick driver works, first it looks like some sort of halfbridge driven by a ucc driver ic, but from expierience the ucc driver ic is very sensible for high side driving igbts or mosfets, but i wonder about the smps is it really needed, or can i simply build a transformer based powersupply for the drivers?. firstly i want to try the normal gdt sheme, the igbts only have a gate capacitance of 38nF , i already wired a 50nF brick with gdts and a resonant frequency of around 100khz and it worked well for me, .

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