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IGBT peak currents

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Steve Conner
Fri Oct 04 2013, 01:12PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I'm not too sure, that's why I stick near to the 1x Icm end of the spectrum where the manufacturer already worried about it for me.

But given the device has a MTBF of 100us at 6x Icm, and 10 years at 1x Icm, some sort of power law would seem like a good bet. "The MTBF halves for every N percent increase in current above Icm": find N.
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Dr. Dark Current
Sat Oct 05 2013, 08:52AM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
In the datasheet they usually state, that the pulse width of the maximum peak current is "limited by maximum junction temperature". The peak current rating is repetitive. Doesn't this imply, that the junction temperature rise during the pulse can be as high as 125 °C (25 to 150 °C) without a limit on the number of pulses?
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Steve Conner
Sat Oct 05 2013, 01:00PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It certainly does imply it but Steve Ward and I think the implication is incorrect, at least for particularly short and intense pulses.
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Steve Ward
Thu Oct 17 2013, 11:34PM
Steve Ward Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Doesn't this imply, that the junction temperature rise during the pulse can be as high as 125 °C (25 to 150 °C) without a limit on the number of pulses?

Hah! *I* dont think so! Thats where engineering experience comes into play: interpreting the data sheets. Sure you can probably pulse it to 150C die temp for awhile, but who really knows when its gonna pop. All that statement means to me is that crossing 150C means it could go pop *immediately* instead of just wearing out due to fatigue. I think that statement is also a reminder to the designer to check your peak die temp calculations.

Powerex has application notes on using IGBT modules that talk a little bit about thermal fatigue with respect to the die solder connection to the base plate. "All available information has indicated that thermal fatigue is not an issue when [delta] Tj is kept below 30°C."

Link2

see also

Link2
Link2

I havent found anyone really referencing thermal fatigue on small IGBTs that lack the aluminum nitride insulator (maybe thermal fatigue is less of a problem?). Their application is for traction drives, where the temp goes up and down over seconds/minutes, and they still have a rather finite cycle life. Spiking the temp at 100s of hz seems like it would wear them out real fast... It would be an interesting test to see how many shots you could get with fast temp spikes.

If you are blowing up IGBTs and want to figure out why, do all the thermal calculations outlined in those ap notes, if you exceed delta Tj of 30C, or Tj max of say 120C, then it probably means your IGBTs are failing *by design* and that you need to increase your safety margins. I can say for a fact that lots of my old semiconductor failures were simply due to thermal stress, mainly because i had no real design method and just threw stuff together with the TLAR method (Coined by Finn Hammer, "That Looks About Right"). Now every power device i build (hobby or professionally) gets a rather thorough thermal analysis considering worst case operation.
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Uspring
Fri Oct 18 2013, 10:19AM
Uspring Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711
@Steve W. Thank you for the interesting links.

Steve C. wrote:
But given the device has a MTBF of 100us at 6x Icm, and 10 years at 1x Icm, some sort of power law would seem like a good bet. "The MTBF halves for every N percent increase in current above Icm": find N.
Figure 3.16 in Link2 seems to imply just such a power law. Your bet looks good, if you replace pulsed I by deltaT.

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Kizmo
Sat Oct 19 2013, 02:30PM
Kizmo Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Speaking of thermal stress, I found this from fuji U4B (5th gen.) igbt datasheet:


1382193006 599 FT157660 Endurance Tests
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