Heatsinks

Kurt_ · Post by **Kurt_** » Sun Apr 02, 2006 12:50 pm

I'm wondering...what's the use of heatsinks on 7805 regulators and such?

I can understand the bit about computers and electronics running better cold, but with a 7805 all that gets hot is the regulator. And it's not like it gets hot enough to melt the regulator or anything.

What would happen if you left the regulator unheatsinked for a week or so?

timmeh87 · Post by **timmeh87** » Sun Apr 02, 2006 1:04 pm

it would probably get so hot that it would break.

you also gotta worry about diffusion. a linear reg usually has either a transistor or a diode in it, both which have n-p silicon junctions. the dopant will diffuse across the junction, decreasing its effectiveness over time. it happens much faster at higher temperatures.

Dr.Weasel · Post by **Dr.Weasel** » Sun Apr 02, 2006 4:16 pm

Tim? couldnt you have just walked upstairs of something to tell him? You two being brothers and all. lol

-Hayden

timmeh87 · Post by **timmeh87** » Sun Apr 02, 2006 10:44 pm

well... didnt you want to know the answer too? *shrug*

its the other way around... i was upstaris.

A.J. Franzman · Post by **A.J. Franzman** » Mon Apr 03, 2006 12:41 am

7xxx series regulators also have built-in thermal limiting circuitry. Without a heat sink, you would be lucky to get 500 mA out of it (depending on the input voltage) before it goes into shutdown. If you put a big enough heat sink on it, you can put 30 volts in and get 5 volts out at up to 1 amp (there is also current-limiting circuitry in it, so 1 amp is usually the maximum, but there are some versions with higher limits).

Post by **marshallh** » Mon Apr 03, 2006 7:21 am

If you're looking for 7805 heatsinks, search for a TO-220 package heatsink. Most linear regulators come in that package (except for the really low amperage ones.)