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contemplating induction heating with Fairchild FGH80N60FD/2

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Tiberius

Tue Jul 29 2008, 11:24PM

Registered Member #1484 Joined: Wed May 14 2008, 03:24PM
Location: Cary, NC, USA
Posts: 27

I've been collecting data regarding building a larger induction heater for a few weeks now and I've been looking at these apparently fairly new IGBTs Fairchild is offering:

http://www.fairchildsemi.com/pf/FG/FGH80N60FD2.html (datasheet)

http://www.fairchildsemi.com/pf/FG/FGH80N60FD.html (datasheet)

For the life of me I can't figure out what the difference between these two models is aside from the "2" at the end and about 1$ per unit, so that would certainly be my first question.

They appear to be rated 40A @ 100C and 80A @ 25C. I would like to push a microcontroller-driven full bridge of these to around 15kVA input (60A 240Vac input), but I have noticed that in similar applications I've found here (e.g. Steve's DRSSTC-2 and DRSSTC-3) the manufacturer's specified current for the IGBTs is heavily derated in actual use. I'm wondering if my planned power level would be unrealistic for these transistors, particularly considering my intent to water cool the transistors as in my last heater?

GeordieBoy

Wed Jul 30 2008, 10:19AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

What are your predicted conduction losses and switching losses? 15kW is a lot of power, and you said nothing about the switching frequency in your post. 80W dissipation in each device might be reasonable.

Provided you can get the heat out of the devices fast enough they should be okay. If the calculations don't look good, there's always ISOTOP packages which have better thermal characteristics.

Remember that the device can only carry 80A if you can maintain the internal die temperature at 25'C. Something that is quite hard to do when the device is carrying 80A.

-Richie,

Steve Ward

Wed Jul 30 2008, 04:24PM

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

Remember that the device can only carry 80A if you can maintain the internal die temperature at 25'C.

Do you mean the *case* temp at 25 C? If the die is at 25C, then you could really push it infinitely hard, since its not melting, right? We aren't concerned with secondary effects like latch up, so really die temp is the only limit.

I do agree though, that 15kW with those 247 devices seems like a stretch. The numbers that are going to be increasingly critical for you are the thermal impedance, usually stated as something like Rth(j-c). Big monster IGBT bricks have like 0.05 to 0.1 *C/W ratings, while little 247 sized IGBTs are at like 0.5 *C/W. This, and the Vce sat being lower at higher currents are really the only things that set big IGBTs apart from little ones.

Dr. Dark Current

Wed Jul 30 2008, 05:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Steve Ward wrote ...

Do you mean the *case* temp at 25 C? If the die is at 25C, then you could really push it infinitely hard, since its not melting, right? We aren't concerned with secondary effects like latch up, so really die temp is the only limit.

This is getting really OT but what limits pulse current are the die bonding wires, so even if you kept the die at 25Â°C the bonding wires might fuse.

Anyway I never ever run devices near their maximum ratings if I want them to last, I wouldn't really go over 30-40A for a 80A rated device.

Hernan

Thu Jul 31 2008, 05:56PM

Registered Member #1614 Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52

Hi Guys,I'm HernÃ¡n from Argentina . I decided to join the forum because I'm building a 5KW induction coreless furnace at 30KHz .I'm using a half bridge voltage source inverter with mosfets to drive an 1:1 ferrite transformer with LCLR on secondary side.But now I thinking to use a full bridge with IGBT modules.These IGBT would be a good choice for me. I hope I could get some of them here.

I found The dual IGBT module IRGTI140U06 is rated at 140A 600Vces 10-30KHz

regards!

EEYORE

Thu Jul 31 2008, 06:08PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

How about the famous (infamous?) 40N60'?
They have been great in DRSSTC's...Should fare better at these much lower frequencies too, right? I once screwed around with my halfbridge made from them for my old drsstc awhile back and got decent results. (For induction heating that is) They heated up a bit, but I really wasnt doing any active cooling aside from blowing on them with my mouth

.
I dont know how much you want to spend though, as they can be pricey.
Matt

Dr. Dark Current

Thu Jul 31 2008, 06:29PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hernan wrote ...

I'm using a half bridge voltage source inverter with mosfets to drive an 1:1 ferrite transformer with LCLR on secondary side.

What is the purpose of a 1:1 ferrite transformer?

Dago

Thu Jul 31 2008, 07:36PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

Dr. Kilovolt wrote ...

Hernan wrote ...

I'm using a half bridge voltage source inverter with mosfets to drive an 1:1 ferrite transformer with LCLR on secondary side.

What is the purpose of a 1:1 ferrite transformer?

Offer galvanic isolation I'd assume.

Marko

Thu Jul 31 2008, 09:10PM

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

How about the famous (infamous?) 40N60'?

Those were great IGBT's, but obsolete now (not sure why did they have such apparently ''short life''.

30N60's in SOT227 package are minimum 60 pieces in digikey.

Exploring digikey I found something interesting though:

If you guys can arrange a group buy maybe these would be great replacement for 40N60's.

Still, for 15kW I think it would be very preferable to use three phase supply (50V), and 1200V IGBT's... some of those bricks appearing on ebay would probably be just OK.

I don't think either TO247 package would be good for that much power..

GeordieBoy

Thu Jul 31 2008, 09:12PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> Do you mean the *case* temp at 25 C? If the die is at 25C, then you could really push it infinitely hard, since its not melting, right?

Yes, that's how it's usually spec'd although it is die temperature that really matters, but that is harder to measure during operation. Continuous rated current is usually spec'd at two case temperatures. Either way the 25'C figure is largely "fictional" and somewhat optimistic as it requires perfect thermal conductivity to the theoretical infinite heatsink to hold the case at 25'C whilst the device is producing a hundred watts or more of heat.

This page gives a reasonable explanation:

Allowable Id derates with increasing case temperature Tc because there is less temperature headroom left for the thermal drop of the die-to-case thermal-resistance. Obviously continuous Id doesn't allow for switching losses, diode recovery losses, or heatsink thermal resistances.

-Richie,

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