Cooling Scythe 3.5" Fan Controller Mosfets

[Vario]

I'd like some advice on proper heatsink for these mosfets. Should I mount, with screw and nut, the heatsink to the metal tab on the backside? Or should the heatsink be on the black plastic side? Do I need insulating mica if I mount to the metal tab side? Is the metal tab a drain? I was going to put thermal paste on the surfaces regardless.

A second set of questions:
I have some old thermaltake copper mini heatsinks that mount with adhesive. If I was to use these with arctic alumina, do I need mica? What side is best to mount it on, the plastic side or the metal side?

Thanks, I am an electronics noob.

edit: this is the p/n: NEC D882P

edit2: I guess these are BJT Transistors not mosfets. What would be a good substitute that can handle more wattage? My highest wattage fans are around 12 watts.

 

[NviGate Systems]

Looking at the spec sheet for those NEC chips, I found this:

Total dissipation at Tc = 25°C 12.5 W
Storage temperature -65 to 150 °C
Max. operating junction temperature 150 °C

I'm a bit of a newbie when it comes to this stuff but am slowly teaching myself and watching videos etc. Here's what I was able to figure out:

These things could definitely use cooling if you are running many fans, especially at higher values. Now, the output will drop as temperature goes up, partly through throttling and loss of efficiency. The max values in the datasheet are not what you are aiming for, those are pretty much worst case scenarios (or peak, ie; for short periods).

Now, i'm having a hard time deciphering the datasheet, but it looks as though these will support roughly 1-2 Amps (remember 2 is peak) per NPN. As it's designed to work at 12V, your 12W fan has a good chance of working but will produce heat. And the ambient temperature has to be taken into account.

Those heatsinks should work well. I would probably use thermal epxoy. You always put the heatsink on the metal side with thermal material. The NPN's have holes in them which is actually used to screw heatsinks on. If you check local electronics shops or eBay, you probably will find people selling those heatsinks. http://www.ebay.ca/itm/Original-Pul...773254?hash=item3609ed3006:g:-JEAAOSwPCVX6E5q is an example of a NPN with attached heatsink.

Looking at the photo, it almost looks like they have 2 NPN's sandwiched together. Can you confirm this? In that case you would need heatsink on each side which would be easier with epoxy (thermal) rather than bolting them on, which requires more space.

In case you want datasheets, http://pdf1.alldatasheet.com/datasheet-pdf/view/170798/STMICROELECTRONICS/D882.html

 

[Vario]

@NviGate Systems thanks for the helpful reply!

I replaced the NPN BJT with new ones, used epoxy and put 1/2 cut of a thermaltake ram heatsink (model A1978) on each side, then soldered them in. There were only one BJT, not two stuck together.

The finger tip temperature readings are much better.

Still have problems with this controller, #3 channel is slow and #4 channel is fast. Not sure what component is the problem, I tested a few with the DMM and they all looked okay. I had these problems before I replaced the BJT. My solder joints look good.

 

[NviGate Systems]

There are some Diodes and Resistors, perhaps check and see if they are within spec.

 

[Vario]

There are some Diodes and Resistors, perhaps check and see if they are within spec.

Channels 3 and 4 seem to have the same readouts as channels 1 and 2, I'll have to do more research, I am decent at soldering but as far as components, an electronics noob.