Best type of insulator pad for a to-220 LM317 power supply?

[george graves]

I'm thinking of building a power supply using a lm-317.  The tab is connected to the output pin.  So I'm assuming it would be a good idea to insulate that from the heat sink that will be sticking out of the case?

I see there are silicon( or "silica") pads, and "Mica" pads.  What performs better?  What should I use?

[Rerouter]

Mica is generally better under significant heat,

[ejeffrey]

Silpads are the easiest to use and the most repeatable.  Mica is good but suffers from poor thickness and flatness control, and its performance depends on how well you apply the thermal grease.  I would generally use a sil-pad unless I was really pushing the edge.  In that case I would probably go straight to an aluminum heat spreader insulated from the main heat sink by kapton film.

[LukeW]

Silicone is easier, it doesn't require separate thermal interface grease, whilst mica does.

[Zero999]

When I built an LM317 PSU, I soldered the heat sink directly to a piece of copper bar which was fixed to the metal case, for insulation I used plain old Sellotape which worked perfectly.

[Mechatrommer]

plain old Sellotape

if you talking about that transparent plastic shiny sellotape, extreme heat will screw it up, electrical tape is better heat resistant. if the op dont have a screw and nut to stick to the heatsink, my way is silicone that people used to seal aquarium (in tube) in between any insulation used. or the "elephant" glue, not sure what its called, but usually it has elephant picture on the bottle and if you put one drop between your fingers and put together, the fingers will stick each other within seconds.

[Rerouter]

elephant glue sounds like superglue, and really, you never want to heat superglue over 75 degrees, parts of it vapourises, and it burns your eyes and nose even hours later :/

[Zero999]

plain old Sellotape

if you talking about that transparent plastic shiny sellotape, extreme heat will screw it up, electrical tape is better heat resistant.

I never had a problem, partly because the LM317 was already soldered to a piece of copper bar which spread the heat more evenly. Oh and electrical tape will be worse because it's normally made of PVC which has a lower melting point than cellophane or polypropylene which is what Sellotape is made from.