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Old 08-04-2009, 11:58 AM   #2147 (permalink)
jyanof
Joe
 
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Quote:
Originally Posted by MPaulHolmes View Post
Hey Joe! Yes, the gate resistors were 30, but I changed them to 20 in the last 3 (yours, Bens, Adrians).
oh, that changes things slightly!

Heat generation at full frequency: 334W
Heat generation at half frequency: 217W
change: 35% reduction

Predicted temps should now be:
mosfet: 58
heatsink: 51

So, I guess the prediction is still too low, but it's a hair closer.

The numbers at the bottom of my post for reduction in heat generation were assuming 30 ohm gate resistors. They've dropped a little:

15 Ohm Rgate - 16% less heat generation
10 Ohm Rgate - 33% less heat generation
5 Ohm Rgate - 51% less heat generation

I'd like to put my scope on there and check out the voltage spikes...

Quote:
Originally Posted by MPaulHolmes View Post
I don't have any info on the number of hours for the mosfets/diodes at a given temp.
I asked about that - apparently, thermal cycles play a bigger role than actual temperature. I guess actual life is hard to estimate.
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