At 04:00 PM 3/7/97 GMT, you wrote:
>The 38 Special manual tells us to use heatsinking compound on the
>back of the IRF510 (5 watt mod), and nylon screws/nuts for mounting
>to the case of the rig -- but do not ground the case
>The heatsink compound at RS says that it is highly conductive -- not
>sure if they are speaking of electrical or heat only. It is a
>silicon based product. Is this stuff ok?
Many of the MOSFet's (and transistors) have their drain (or collector)
electrically connected to the metal tab. When fastening the tab to the heat
sink, the tab must be electrically insulated from the heat sink. This is
typically done using a thin mica insulating washer. In addition metal
hardware is typically used to fasten the device and a through the hole
washer (teflon) must also be used.
The heat sink compound has good termo conductivity. However, only apply a
very thin coating. Its purpose is to fill the small imperfections in the
surfaces and thus provide better heat transfer. Using to much is wasteful,
messy and will actually provide less heat transfer.
Note: Some semiconductors have their emitters connected to the metal body.
Examples are MRF479, MRF477 (TO 220 type cases) and most flange mount devices.
Check you data book. If the emitter is at ground potential in your circuit,
use only a thin application of heat sink compound (do not use insulating
washers).
Ed
W1AAZ
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]