Heatsink, with MICA or NO ???

[aldovan]

Dear friends

I am making a amplifier and I have a doubt.
Is best use a Mica between the power transistor and the heatsink, or is best the direct contact between the transistor and heatsink ? I am speak in hot dissipation .
My transistor do not need colector isolation.

Thanks,

Aldovan

[Nico Ras]

If you do not need isolation then do not use mica washers.

[gni]

The heatsink will be at the potential of the collector of the transistor
if the collector is the back of the transistor (which is most power
transistors).

That could be a bunch of -Ve or +Ve. But the possibility of better
heat transfer and no concern of breaking mica insulator.

NPNs and PNP cannot share the same heatsink; if bias transistor
and drivers are mounted on heatsink. . .they need to be
isolated with an insulator unless they have the same collector voltage.
The bias transistor will only respond to the NPN or PNP, but not both.

The heatsinks will need to be isolated from the enclosure.

That's all I know. . . there are some other good people here that could
straighten this out better. . . AndrewT and anatech come to mind. . .
they have saved my life several times.

Both my Yamaha M-45s and Rotel RB850 use silicon rubber. Pluses
and minuses to mica vs silicon rubber. . . can't hardly crack a silicon
rubber washer; mica washers are delicate but transfer heat better
I think.

[MaxS]

Hi,

Search for " Mica and goop " thread in Pass Labs directory.

[gni]

Perfect discussion there. Covers all the topics. . . and ongoing.

[aldovan]

Friends

In my case, I am building a class A hybrid anplifier.
I have one type of transistor( only NPN) in the heatsink.
I have a isolation between the heatsink and the chassis ground.
For me, the direct contact in the heatsink is best for transfer the hot. A termic paste is good for best results, too.

Thanks for the replays.

Aldovan

[gni]

Very good. . . .

[AndrewT]

Originally posted by aldovan
In my case, I am building a class A hybrid anplifier.
I have one type of transistor( only NPN) in the heatsink.
I have a isolation between the heatsink and the chassis ground.
For me, the direct contact in the heatsink is best for transfer the hot. A termic paste is good for best results, too.

This must be a single ended. Are all the collectors fed from the same voltage potential? The sink could be the power supply rail.
The current sink cannot be more active devices on this same heatsink. Is the current sink a resistor?

Don't drop a metallic tool in there with a live sink.

[pooge]

You don't say whether or not the heatsink is isolated from body contact, or whether you are using a fan. If you are electrically isolating it from the chassis, not necessarily a good thing, it should be inside of the enclosure so it can't be touched. In that case, the air circulation around the heat sink may be more detrimental than an external heat sink with mica insulators.