TO-220 thermal pad choice - Page 1
Forum section: electronics / beginners

author: blah2222
author_rank: Newbie
timestamp: August 27, 2014, 03:44:00 am
content: Hello,I'm setting up a classic LM317 adjustable supply and am curious what product and brand of thermal pads/sheets that people go for and where they buy them from. The stores don't seem to have them here.I have found the following kits (with all the parts) on Digikey/Mouser which is appealing as I don't have the bolts/shoulder washer/nuts on me yet, but wondering if there are other better options that others have used.Aavid Thermalloy - 4880G - $2.89 CADhttp://www.digikey.ca/product-detail/en/4880G/HS417-ND/1625654Keystone Electronics - 4724 - $2.55 CADhttp://www.digikey.ca/product-detail/en/4724/4724K-ND/109792Thank you,Jason

author: Pedram
author_rank: Regular Contributor
timestamp: August 27, 2014, 10:14:44 am
content: it's just LM317. use anything you want.BTW. digikey price is tooooo high. $2.5 for a thermal pad and some other stuff?i can buy them here for $0.1 MAX.

author: wraper
author_rank: Unknown
timestamp: August 27, 2014, 10:23:24 am
content: Yeah those are very expensive. Generally you can use any silicone one. If pushing IC to the limits on a larger heatsink, better use mica + thermal paste.

author: mariush
author_rank: Super Contributor
timestamp: August 27, 2014, 12:49:57 pm
content: You probably don't need thermal pad for a simple lm317 power supply. Just get a heatsink and put a drop of thermal paste you normally use with computers between the heatsink and the regulator. It will do just fine.

author: mariush
author_rank: Super Contributor
timestamp: August 27, 2014, 02:55:27 pm
content: Yes, but a thermal pad alone is not a solution to insulate the to-220 package from the heatsink. You would also need a plastic/nylon spacer to keep the screw from touching the metal of the to-220 package.Here's how those look, just one of the first results in google :http://www.toppier.co.uk/shop/en/insulator-shoulder-bushing/1117-toppier-to-220b-50pcs-nylon-plastic-insulator-shoulder-bushing-washers-grain-hole-size-3mm-1-8.htmlSome termal pads also aren't insulating... have to be careful about that.

author: David Hess
author_rank: Super Contributor
timestamp: August 27, 2014, 03:33:46 pm
content: Another option is to find an LM317 or other regulator which is in a TO-220 overmold package like the TO-220F.http://www.mouser.com/ProductDetail/NJR/NJM317F/?qs=Nqu9TKSR3gnT5wjzeWrytg%3d%3dI usually use a shoulder washer, mica insulator, and thermal grease with a normal TO-220 package. There are some inexpensive elastomer insulators available as well though if you want to avoid the thermal grease.

author: mrkev
author_rank: Regular Contributor
timestamp: August 27, 2014, 04:50:06 pm
content: IMHO the best way to do it is to count the worst case. Take minimum output voltage, maximum input voltage, subtract those two (you'll get maximum voltage on LM317), multiply that by maximum output current and you will get the power that you need to dissipate.For few Watts, it's usualy better to use small heatsink without thermal pad (mind that it's gonna be connected to output pin as mentioned before). You can even screw that heat sink to the board in the place where the output route is.I would personally use thermal pad and spacer only if it's necessary (f.e. for more than one device on the same heatsink, when you use the back of the case as heatsink or if the output voltage gets too high), as it always adds some thermal resistance.

author: blah2222
author_rank: Newbie
timestamp: August 29, 2014, 03:17:53 am
content: Thank you for the replies and advice!