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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
I may be wrong, but typical mosfet body diodes have Trr around 500ns like this one
For this reason, we place faster diodes between the source and drain to handle the reverse current to protect the mosfet. My question, since I have not done the testing myself, is how fast is fast enough? Are switching losses minimized up to the point of using a schottky with Trr = 0, or is a diode with a Trr of around 60ns sufficient?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
I'm not using any mosfets. I simply picked that one at random to make the point about the recovery time of some of these chips. I am not looking for fast mosfets, but I am asking a question about how fast does the body diode has to be in order to minimize reverse currents that could destroy the chip in a power switching application.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
the internal body diodes have gotten better, but theyre generally not relied on. They are a unwanted but unavoidable artifact of lithography, implantation and what not of production.
Generally i and i think others keep the heat of the bad diode out of the case by using a better external diode ultra-close to the mosfet pins. this way the internal diode never gets a chance to take part in switching or recovery.
i think others will agree if i understood the question.
On a side note we all know the extra parts needed to support gate drive to push high rate of rise voltage by pushing huge charge into the gate. Infinion is taking the traditional TO-247 case with 3 pins and adding a 4th pin, from what i understand it make the gate easier to drive.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615
IamSmooth wrote ...
, but I am asking a question about how fast does the body diode has to be in order to minimize reverse currents that could destroy the chip in a power switching application.
Thats a bit like asking "how long is a piece of string?" The answer is going to vary for every circuit. And its not just about recovery time, its also about recovery charge.
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mosfets and body diode
