I have many mosfet and diode in an high power h-bridge circuit. I guess I need heat sink to cool them.
Because of the TO220 casing of those component, the back metal part is connected to the drain of mosfet and output of diode, I guess I cannot put all the mosfet/diode on the same heatsink.
What are the common setup to for this kind of job? Does every component has its own little heat sink? Is there some isolating paint or padding that still conduct heat for this kind of job?
Yes, don't use mica, its old tech and not very good, you need something soft that
conforms to the device and heatsink to eliminate any air-gap. For low voltage a thinner
heat patch is good, better heat conductivity.
Yes, any piece of metal can be a heatsink. I've used a 50-cent (Australian) coin in the past, when the cheapest heatsink I could get quickly cost 85 cents.
Aluminum is the best. Buy a small piece at the hardware store and cut it to whatever shape you like.
Thermal paste/pads works much better under pressure.
Thermal paste works better than pads (messier to use)
Thermal epoxy exists as well, it isn't as good of a thermal conductor as comparable pastes, but you can glue your parts to the heatsink with it (be sure to clamp it, so the layer of epoxy between the part and sink is nice and thin)
Copper is a better heatsink than aluminum. They make all sorts of little heatsinks for TO-220 packages - and if you're a good scrounger, you can get em free - obsolete TVs and home stereo crap gets thrown out all the time, and they've all got heatsinks in them for the audio.
DrAzzy:
Thermal paste/pads works much better under pressure.
Thermal paste works better than pads (messier to use)
Thermal epoxy exists as well, it isn't as good of a thermal conductor as comparable pastes, but you can glue your parts to the heatsink with it (be sure to clamp it, so the layer of epoxy between the part and sink is nice and thin)
Copper is a better heatsink than aluminum. They make all sorts of little heatsinks for TO-220 packages - and if you're a good scrounger, you can get em free - obsolete TVs and home stereo crap gets thrown out all the time, and they've all got heatsinks in them for the audio.
But I guess that the thermal past isn't non cnductive, which is bad for many mosfet on the same heatsink
Paste by itself doesn't prevent metal-to-metal contact, whether its conductive or not,
the patches/pads prevent metal to metal contact and have a voltage breakdown rating
depending on thickness.
Heatsinks are usually limited by the air around them, aluminium is plenty good enough
in practice because its lighter and cheaper, therefore can be bigger and push heat out to
the air better for the same weight (or money)
MarkT:
Heatsinks are usually limited by the air around them, aluminium is plenty good enough
in practice because its lighter and cheaper, therefore can be bigger and push heat out to
the air better for the same weight (or money)
Indeed. From a practical standpoint there aren't many advantages to copper at all. Aluminium is cheaper, lighter, easier to machine, easier to protect against corrosion. When given the choice between expensive thermal conductivity and cheap surface area... surface area usually wins.
