Electronics > Projects, Designs, and Technical Stuff
DC load using a CPU cooler
Christopher:
Why not attach the fet to the heatsink, bend the pins up thru the board?
Some tall-ish spacers on the heatsink for some thermal insulation?
microbug:
OK, I've found my MOSFETs: IXTH40N50L2. They're designed for linear operation so they're ideal for this. Two of them will be fine for 300W operation, I think I'll have a max voltage limit of 100V. They're TO-247, so they'll fit nicely under the cooler as previously discussed. There were a couple of alternatives from the same company, but that's the cheapest one I can get from Farnell UK which has a minimum order cost of £20 rather than £50 like everyone else.
On the subject of cooling, as SeanB said, the copper heat pipes won't make great contact without a copper plate underneath them (thermal epoxy again). What about the back side of the MOSFETs (between them and the board)? Options as I see them:
- Cutout on the board, glue the MOSFETs to the copper plate;
- No cutout on the board, glue upside-down MOSFETs to the copper plate;
- No cutout on the board, MOSFETs sandwiched between back brace made from insulating material (e.g., FR4) and copper plate.
I'm currently investigating hardware over-voltage / over-current protection (watching Dave's video on multimeter input protection seems like a start).
Spikee:
--- Quote from: microbug on September 21, 2014, 08:35:41 am ---OK, I've found my MOSFETs: IXTH40N50L2. They're designed for linear operation so they're ideal for this. Two of them will be fine for 300W operation, I think I'll have a max voltage limit of 100V. They're TO-247, so they'll fit nicely under the cooler as previously discussed. There were a couple of alternatives from the same company, but that's the cheapest one I can get from Farnell UK which has a minimum order cost of £20 rather than £50 like everyone else.
On the subject of cooling, as SeanB said, the copper heat pipes won't make great contact without a copper plate underneath them (thermal epoxy again). What about the back side of the MOSFETs (between them and the board)? Options as I see them:
- Cutout on the board, glue the MOSFETs to the copper plate;
- No cutout on the board, glue upside-down MOSFETs to the copper plate;
- No cutout on the board, MOSFETs sandwiched between back brace made from insulating material (e.g., FR4) and copper plate.
I'm currently investigating hardware over-voltage / over-current protection (watching Dave's video on multimeter input protection seems like a start).
--- End quote ---
get the 75v version and contact IXYS. They like these kind of projects and should have no problem sampling 2-4 mosfets for free.
I have used the arctic silver adhesive before and it works reasonably. To get it off again just soak it in ipa and you can twist the mosfets off the heatsink.
microbug:
I assume you mean IXTP80N075L2 (TO220)?
EDIT: Yes, they look suitable. They have a significantly lower Rds(on). Given the extended SOA, two would be fine for 300W. Should I get two in the TO247 package or 3/4 in TO220?
EDIT 2: So far for input protection, I'm thinking of a fuse for each MOSFET, reverse protection diode, MOV(s) and a thermal cutoff on the heatsink. There will be some protection in software too (shut off output relay in overload condition).
timb:
I ordered some 5mm copper today. You're using the A30, right microbug? I'll grab one off Amazon and make something very slick for mounting. I've got a really good idea. (I'll draw it up tonight and post it here.)
Sent from my Smartphone
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