# IGBT module vs chip



## Nate (Jul 10, 2008)

*IGBT chips have to be matched. Unlike MOSFETs an IGBT will lower its internal resistance when it gets hotter. This means the hot IGBT chip will keep taking on more of the load and getting hotter until it fails. A module has individual units inside it but they are all matched with one another.*


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## manic_monkey (Jun 24, 2008)

Nate said:


> *IGBT chips have to be matched. Unlike MOSFETs an IGBT will lower its internal resistance when it gets hotter. This means the hot IGBT chip will keep taking on more of the load and getting hotter until it fails. A module has individual units inside it but they are all matched with one another.*


thank you, i knew i had to be missing something! I take it MOSFETS wouldnt have the same problem when parralleled?


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## ga2500ev (Apr 20, 2008)

manic_monkey said:


> thank you, i knew i had to be missing something! I take it MOSFETS wouldnt have the same problem when parralleled?


Not exactly. With MOSFETs the current carrying capacity goes down with temp. That means that when paralleled they tend to evenly share the load.

The problem is that occurs when fully on. During a switch a faster part can get a significant amount of load while the others are catching up. Could be a problem.

Generally derating the AMP rating solves the problem. So if you need to carry 400 AMPs instead of using 4x100 AMP MOSFETS you may use 4X200 AMP parts to derate by 50% for example.

ga2500ev


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## Nate (Jul 10, 2008)

*If you have two MOSFETs in parallel and one starts to get warmer than the other its internal resistance goes up which throws more load to the cooler one. They balance out this way. *

*If you have two IGBTs in parallel and one starts to get warmer than the other its internal resistance goes down which throws more load to the hot one making it hotter.*

*Some tricks are using the same heat sinks, then heat from the hotter IGBT warms the cooler one and throws more load to the cooler one. The problem with this is if they are to close their heat outputs can add in a localized area.*

*Matching is not difficult if you have some simple tools and know how to use them. It will take some time though. *


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## Nate (Jul 10, 2008)

*I see ga2500ev posted while I was writing,  switching is a whole other beast. If your switching is not correct you will have more issues than just uneven amperages.*


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## manic_monkey (Jun 24, 2008)

If one were to take the route of matching transistors, would it be better than to use mosfet or igbt? do you have any links to how matching is done, etc.

the reason im asking all of this is the price of large igbt's in england are around £150 each, where as the same power could be reached using parallel singles for £10. even if you factor in the price of a shared heat sink, thermal bonding compound and fan, the price would still be many times cheaper


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## ga2500ev (Apr 20, 2008)

manic_monkey said:


> If one were to take the route of matching transistors, would it be better than to use mosfet or igbt? do you have any links to how matching is done, etc.
> 
> the reason im asking all of this is the price of large igbt's in england are around £150 each, where as the same power could be reached using parallel singles for £10. even if you factor in the price of a shared heat sink, thermal bonding compound and fan, the price would still be many times cheaper


There's a simpler solution then. Ebay has surplus IGBT modules for $50 USD which should be about £25.

I'm planning on working my homebrew controller starting with IGBT modules. You can believe they are going to come cheap.

ga2500ev


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## tblount70 (Jun 4, 2008)

I'm thinking of the same approach. Seems like a single 1200V 600A IGBT ought to get me freeway capable, you agree? It seems like the tricky part is the gate driver, but Powerex has "seems" to have an off-the-shelf circuit to handle that. The digital part of the design doesn't bother me - I've done hobby-level PIC programming before including the PWM part. But I'd really rather copy someone else's proven power section.

With all the talk about this, has anyone done one (the power section)? Wanna share that circuit?


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## ga2500ev (Apr 20, 2008)

tblount70 said:


> I'm thinking of the same approach. Seems like a single 1200V 600A IGBT ought to get me freeway capable, you agree?


Yup. There will be some heatsink and range loss issues, because IGBTs will drop about 3V which is 300W @ 100A for example.



> It seems like the tricky part is the gate driver, but Powerex has "seems" to have an off-the-shelf circuit to handle that. The digital part of the design doesn't bother me - I've done hobby-level PIC programming before including the PWM part. But I'd really rather copy someone else's proven power section.
> 
> With all the talk about this, has anyone done one (the power section)? Wanna share that circuit?


There's a homebrew controller thread here in Tech that has some circuits. I'm still looking for someone to describe how testing has gone.

ga2500ev


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## etischer (Jun 16, 2008)

Im using 1200v 600a igbts for my project. Im only at the stage of turning on a light bulb but I just bought my car and got started a month ago. I need a scope before I can go any further. Im doing a 3 phase system. For a DC system I've got something that would work, just need a 10 volt pwm signal and you'd be good to go. 


Im planning on using a smaller hp vfd to fire my igbt pack. Anyone out there have experience doing this? I noticed I can give the IGBT a 10v pulse, and it will stay on unitl I give it a 0v pulse. 



Heres a pic of my IGBT 








and a pic of my setup.


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## gerd1022 (Jun 9, 2008)

Yeah i am using the same module, and am noticing the same thing. This could be a very bad thing, because it gives more possibility to fail on... 

not really sure why it works that way... anyone have any advice?


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## Madmac (Mar 14, 2008)

The gate of an IGBT is high capacitance and also high impedance. If you charge the gate up it will stay on until the voltage leaks away. This is why gate drivers are needed, to push high current to charge the capacitance fast and turn on, then pull current out to turn off quickly. Put a 2k2 resistor from gate to emitter and it will turn off.

The gate is also voltage sensitive if you exceed the max rating you will pop the device. It is a good idea to clamp the gate with a zener diode while you experiment.

Madmac


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## tblount70 (Jun 4, 2008)

Madmac,

For the technically-challenged among us (me), please elaborate on "clamp the gate with a zener diode". I assume this means a diode connected opposite the trigger signal across the gate? Also, what voltage/wattage does the diode need to be?

Learning...


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