Heatsink calculation question.

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AudioGeek

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Joined 2004
#1
I need to dissipate 50W in a to247 MOSFET. Also some 85W in a 10 ohm resistor.

What heatsink size do i need for the MOSFET and resistor? Or can i mount the resistor open air if i pick the correct size of resistor?

Oh and where is best place to pick up some nice heatsinks?

Thanks!
 
#4
Also you need to look at the power rating of the TO247 , the insulator used and the heatsink. Like the IRF240 a 150W device buy the time you use an insulator is going to need a large heatsink. And if you are using one of those metal case resistors there power rating is based on them being on a heatsink. Now if you are building a small class A amp you might look at using a light bulb as the power resistor as has been done in 2 of the Pass amps.
 
#5
Yeah i know its a lot of power. i can get 2x 20ohm 50W Mills power resistors... still need a small heatsink for them.

The issue is really the mosfet and whether i can dissipate that much heat.

Its basically the SEWA amp with a 45v supply... yeah i know its a lot of power wasted but thats the fun of diy.
 
#9
It might work for a while if you had a huge heatsink. I am all for
simplicity but I would look at reducing the voltage just a little bit
or going to a 15 ohm load resistor to drop the current a little. Of
cource you know that the efficiency would be a whole lot higher
if you used a current source as the load.
 
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