Re: Heatsink cooling


"Ignoramus18299" <ignoramus18299@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:BiXuf.30818$Aa7.15597@xxxxxxxxxxxxxxxxxxxxxxxx
> Would you say
> that this amount of cooling should be enough?

Measure It - you should have an idea what the losses are; since you have a
prototype that actually runs you can even measure the difference between the
input power and output power. Assuming 80% goes in the heat-sink is a good
first guess IMO.

The hard part of cooling is determining the heat-sink to air thermal
resistance - often it is easier to use high-wattage resistors to dump power
in the heat sink and *measure* how hot it gets in the real situation rather
than trying to calculate it. Especially with natural convection.


If you want to be really clever, you can mount your devices then run them as
constant-current sinks and apply the appropriate voltage for the desired
dissipation. Then measure the temparture close to the device and work back
to chip temparature. *really clever* is using part of the internal structure
to measure the chip temparature - some MOSFETS (IRF, I think) come with an
extra pin for this purpose. If you cannot use the real device - some large
IGBT's have electronics in them so they can only be used for switching -
then you have to use the thermal resistance of the target device to
calculate what it's temparature will be.


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