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Old 09-06-2009, 02:55 AM
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Quote:
Originally Posted by Harvey View Post

EDIT: Regarding the heat sink. You have 3 choices here - bond it electrically to the drain, isolate it and tie it to a potential like ground, isolate it and let if float. In the first case you risk the heat sink acting as an antenna and dumping stuff onto the drain. In the latter two, you have to deal with the capacitance formed between the drain tab and the heat sink and how that may interact in the circuit. I think if you ask TK you will find that insulating them was not his goal, but rather it had more to do with the ease of using a sil-pad for heat transfer.
Hi Harvey,

I think your right about the antenna, if you check between the Mosfet Drain and the Mosfet back plane that the heat sink attaches to they are connected internally I also found some information on insulators for heat sinks ...

Heat Sinks

And then the Wiki ...

Mica insulator - Wikipedia, the free encyclopedia
Quote:
Heat sink insulation can also be necessary to prevent the heat sink from acting like an antenna if the component is connected to a rapidly varying signal.

The Question is the aluminum bar stock Aaron used for the last circuit addition "Ainslie-Murakami Negative Dominant Waveform Generator" I'm working on how was that Mosfet Connected to the Heat Sink bar ??

I couldn't find just the Mosfet insulators at the electronics store but found several packaged with some semi conductors ( high speed switching ) .... I got one of each because the insulators are the same for a TO-220 or TO-247

http://www.nteinc.com/specs/500to599/pdf/nte597.pdf
http://www.nteinc.com/specs/200to299/pdf/nte241.pdf

Glen
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