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Registered Member #1533
Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46
Hi,
What's the highest frequency you've managed to push through IGBTs and what type were you using? Do you have any tips on how to get them to run at higher frequencies than intended?
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Usually, they have an "Switch-on" and "Switch-off" time, that cant be change (far as I know) by anything, so if the IGBT takes 100ns to turnon/turnoff, more than the frequency is near this rate more energy is wasted, until the IGBT doesnt switch anymore. That is the Fast, Very Fast, Ultra Fast, and Warp Speed ratings...
Other thing, is how much Gate Charge it has. The gate charge can be compared as basic a Capacitor that you need to charge with a "energy", so it means that some current needs to flow to charge it. As higher frequency are, more current will flow, and you can blow your drivers...
Someone correct me if I am wrong... I am't trully certain if this info is correct
Registered Member #1533
Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46
Mestre: Well, my gate driver is quite an overkill. I've been running IRFP460 HEXFETs with it at 250kHz. In fact it can supply an average current of 2A through a GDT to 4 transistors. Of course, it usually draws about 250mA average current in normal operation (with interrupter). I know for a fact that switch-off time of MOSFETs can be reduced by applying a reverse voltage on the gate to discharge the gate charge even sooner, thus extinguishing the conducting channel through the substrate. Alas, the switch-off time of BJTs cannot be improved by such measures since you cannot really speed up recombination of charge carriers by any external method that I know of. I assume the same applies to IGBTs but I'm an optimist so I thought I'd just drop the question anyway. ;)
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
For the igbts, the Discharge Negative voltage can be used too (and it does make a faster switch off), if you see the equivalent model of an IGBT is a mosfet on the BJT base, so Negative voltage will make the mosfet turns off quickly, and the bjt too. But I think the speed limit is that is described at datasheet ...
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High frequency IGBTs
