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Registered Member #3670
Joined: Mon Feb 07 2011, 04:09PM
Location:
Posts: 2
Hi all, i've bought some big mosfets (ste40nk90zd) and set them up as a half bridge. in the past my coil ran perfectly with low power irf840's that only have about 1nF of input capacitance, using ucc37322 etc gdt drivers. these new fets have about 40nf (measured) with result, im pushing about 5 amps into my gdt(full bridge discrete driver), but the fets still cant switch fast enough(500khz). if anyone knows a way to drive these large die mosfets, any help would be appreciated. also, are these power levels normal?! 5 amps just to drive a mosfet! thanks.
Registered Member #2922
Joined: Sun Jun 13 2010, 12:08AM
Location:
Posts: 226
You can use a power MOSFETs like IRF540/9540 to drive the GDT, this method is used to drive high power IGBTs with GDT. And drive a high power IGBT in highs frequencys is really dificult..
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
reaperarch wrote ...
yip, im using a full bridge of 530/9530s for gdt. i think i've learned my lesson. never buy mosfets from st again.
What's the problem with ST mosfets?? You are trying to run a huge mosfet (600nC gate charge) at 500kHz... That is really pretentious and of course you need a powerful gate driver...
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
What sort of gate drive circuit are you using? A common trick to reduce the gate drive power requirement is to place a PNP transistor at the gate to handle the turnoff and then the drive transformer only has to supply the charge to turn the mosfet on.
Also as others have mentioned, 500 kHz is extremely high for such large mosfets. Parts like that are typically run at 15-50 kHz, occasionally up to 100 kHz or so in more extreme cases. To go beyond that you're gonna need a really beefy driver, no way around that.
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help with big mosfets for sstc!
