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Old 05-01-2013, 12:33 PM   #1 (permalink)
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Should I short the outputs of the fet drivers together

Hi Guy's
I am rebuilding my controller after all the fets blew up.

My controller has 10 MOSFET's of the type used in the cougar 144v dc controller but I am using 10 mosfet drivers connected to the fets via 2R2 ohm resistors, instead of one. So all the fets have their own driver.

What I was wondering is, would there be any advantage to commoning all the driver outputs together.
This would ensure all the fets switch together (the driver inputs are all shorted together) but would there be any drawbacks?
I can see if I get a gate short then all drivers will be dead but if one driver goes dead the others will continue to drive, unless of course the output goes short.

Or maybe with a switching speed of 15Khz slight differences in response times wont be important and the extra connections wont be worth the risk.

Any one got any idea's on the subject???


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Old 05-28-2013, 08:47 AM   #2 (permalink)
PaulH
 
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I don't think you should connect the outputs together. If one output is held low while another turns on (due to time delays in the turn-ons) it will be a huge current through very puny mosfets inside the driver, and those mosfets have terrible thermal properties due to the packaging (dip 8).
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Old 05-28-2013, 11:25 AM   #3 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
I don't think you should connect the outputs together. If one output is held low while another turns on (due to time delays in the turn-ons) it will be a huge current through very puny mosfets inside the driver, and those mosfets have terrible thermal properties due to the packaging (dip 8).
Hi Paul.
Thanks for the feedback.
I have already had a re-think and have gone with one 4451 as in the cougar but in a to220 package. I was worrid about outputs failing. But initially I had ten drivers wired separately and it still blew up so I was thinking of other ways. My ten drivers were tc429 which had a 6amp output.

I am now driving the 160a/80a IGBT's that have finally been shipped, thro 10ohm resistors, it works out at exactly 12amp pulsed and the extra bit of heat sink will keep it happy. (I hope).

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