Lets Cool some FETs!

Heya guys,

I have little space to work with, so what I need is a little help on a cooling solution.

My FETs are crowded, so I'm looking for either some kind of TEC which moves heat perpendicular to the cold side, or some other kind of cooling method.

I'm trying to think of a heatsink shape that would fit around them, but my mind is running blank.

I was told that I would have about 30 sec before the FETs over-heat, so wouldn't I be able to keep my little heatsinks and just place a nice fan next to the circuit?

Thoughts, opinions, and suggestions are all welcome.

Erm, you may as well take those heatsinks off for all the good thier doing!

The only solution i could see for you if thats the maximum size you can have it to do what they do in laptop psu's, have a "wall" of aliminuim encasing the circuit all the way round, though you'd have to move your FET's to the edge and screw them to the aluminium. Using TEC's wont get you anywhere as the FETS will generate a lot more heat than the TEC's can dissipate, without forced air cooling (fans).

Or mount the circuit in a metal case and screw the FET's to the case, either way its gonna get pretty warm with those power FET's, also make sure your caps are rated 105oC (if you decide to use any electrolytics that is) .

As ped has said, those heatsinks are doing next to nothing.

At this point in time, you have two options.

1. Install a heatsink with a larger head that can still fit between the gap.

2 (more feasible one) Run wires from the PCB to the FETs, and mount the FETs on a proper heatsink, not mounted on the PCB.

You're going to need hefty heatsinks, unless you use active air cooling, where you will be able to get away with using smaller heatsinks.

If you're going with the second option, old CPU heatsinks from the 486 days work well. They're more or less the right size, and can be easily mounted to a chassis.



They'll be easy to find under eBay, look for "Socket 7 cooler" or "486 cooler".

If the circuit is a switching, wiring the FETs far from the PCB can cause problems .....

Anyway, you have a lot of extra space, having the PCB so far from the case plate ..... just using shorter spacers, you can gain a lot in height space ..... and this may end in a custom heatsink, maybe including a small fan, too, placed over the board ..... this may permit you to left the FETs in the same place, if the circuit can't work with them wired far from it .....

Seeing as it is a single layer PCB, one can always mount the FETs on the other side of the PCB, and attach a fan cooled heatsink to them.

At the very least, flip that FET on the right side so that its mounting base is facing outwards (first pic).

Then I would buy some better heatsinks like these. They're 1" (2.5cm) tall, so I don't know if that'll fit into your space budget.

If that won't work, you can wrap metal plates around in a rectangular shape (not touching if your circuit doesn't allow that.

Hmm... many good sounding ideas so far.

According to Xplorer887, and many other ZVS users, the FETs aren't supposed to be getting very warm.

http://laserpointerforums.com/f54/video-my-high-voltage-zvs-flyback-driver-55459.html

"-If you're running it at less than 20v you probably wont even need heatsinks. Mine barely even get warm even when the circuit draws over 500W"

The FETs are switching, and shouldn't be connected far from the PCB. However, the FETs supposedly switch when there is 0V across them- hence ZVS. Zero Voltage Switching.

I am inclined to think that a nice blower mounted next to the board should help somewhat.

Does anyone have any laserbee style heatsinks laying around? Perhaps something like that might fit...
BBs link to Mouser is out of stock.

I'll be running mine at 25V.

The circuit is very symmetrical, so that why I have the FETs facing the same way...

BUT I do like the idea of mounting them under the board. That wouldn't be very hard, plus it would let me throw a nice blower under there.. Hmm...

thinking... thoughts...

I didnt realise thats what your using it for, want to see a pic of my HV tesla driver?

Meatball said:

Does anyone have any laserbee style heatsinks laying around? Perhaps something like that might fit...

Click to expand...

I do, and a lot more, small to large.

If you can assemble that ZVS driver for me, I'll let you have what you need. I have nearly all the parts for the ZVS, and some extra components you can have that you may have some use for.

Here are the small to mid size sinks.

Oops, I didn't realize that one in particular is out of stock. They have some 38mm tall ones compared to those 25mm ones. It's bigger though, so I don't know if it'll work for your setup. Here's the whole list.

Hey BB, I flipped the FETs!

Here's a 12V run I did!

YouTube - ZVS Flyback Driver Test - Low Power