mounting TO-220 devices

[CarlyBoy]

How is anyone isolating (non-PCB mounted) TO-220 devices in which the tab is also one of the pins? I guess I could just solder to the pins and let the device and attached heat sink float in free air but it just seems there's got to be a better way.

[astouffer]

I screwed a small piece of delrin plastic to the case and then screwed the transistor and heatsink onto that. You could also use a plastic standoff to isolate the tab from the chassis and then use a nylon screw to hold it all down. I don't trust those thermal pads and small shoulder washers when the voltage is in the hundreds.

[Geek]

Shoulder washers and mica pads for HOT dissipation, silicone for lower dissipation.

Use a fibre or ceramic shoulder washer, the plastic ones just don't cut it unless their teflon (and unless it's for RF, you're just wasting your money on those).

Used them up to 1200V (ceramic, 600V fibre), never had a breakdown.

For ease of use for the experimentor, I have used #4 metal screws and tied the device straight to the case (with a shoulder washer and pad of course).

Silicone or Kapton - regardless what the salseman or datasheet says, silicone sucks for heat transfer. Buy the thinnest one possible. Kapton, always use a little compound with them, as they don't "fill the gaps" like silicone. Kapton is more expensive, but worth it.

Cheers!

[andyjevans]

I mount devices on heatsinks and then use nylon threaded standoffs to bolt the whole thing to the chassis.

One thing that annoys me is that those black washers that go through the hole of the device are longer than they need to be so if for example you are mounting two devices back to back with the same hole on the same heatsink you have to cut the ends off them.

andy

[Geek]

Originally Posted by andyjevans

I mount devices on heatsinks and then use nylon threaded standoffs to bolt the whole thing to the chassis.

That's my trick for LV supplies... works great

One thing that annoys me is that those black washers that go through the hole of the device are longer than they need to be so if for example you are mounting two devices back to back with the same hole on the same heatsink you have to cut the ends off them.

Yeah!

The long ones I save for thick pieces of metal (I make my own sinks where I can), otherwise these are superb
Digi-Key - HS418-ND (Manufacturer - 7721-7PPSG)


Scavenger's tip: dead computer PSU's are great places to find about 1/2 dozen pads, ceramic shoulder washers and associated hardware


Cheers!