What heat sink to use with LM317?

[shimster]

Hi guys,
  In 2 of my previous pedals I used the 7812 voltage regulator bolted to the chassis to keep them cool.  In my current build I'm trying to do the same with an LM317 except this time the tab is Vout so I can't use the chassis.  Can someone suggest a heat sink, and/or a way to conduct the heat to the chassis without shorting out the circuit?
-Dan

[frequencycentral]

I think the heat dissipated is dependent upon the current drawn. So, the size of the heatsink would depend on the current you're drawing. Am I right?

I used a LM317 in this build. It's providing 1.25 volts and the current draw is 100ma. The heatsink I used appears to be up to the job. I sourced it from Maplin in the UK - I doubt they have a branch near you though!

[theehman]

You can install a thermal pad between the chassis and regulator w/ some thermal compound.

[Mick Bailey]

You need to use a TO220 insulation kit for the heatsink. It consists of a thermally conductive rectangular washer and an insulated washer.

http://media.digikey.com/photos/Keystone%20Elect%20Photos/4724.jpg

[maarten]

Depends on both the voltage dropped over the regulator and the current drawn. In pedals both usually are not very high, that's why we usually don't bother with this problem. You might check after some minutes whether it is getting too hot (if you can't touch it: use a heatsink); repeat this maybe 30 minutes, 60 minutes later. More scientific approach: calculate the dissipation (in watts) and look for a guideline in the LM317 specs.

You can use just some piece of aluminium or iron for cooling the regulator, that's what I sometimes do. Also, there are isolation sets to secure your IC, transistor or whatever, to the chassis. The conductance of the heat to the chassis in this case can be further improved by using some heatconducting gel. All of these materials can be bought in an electronic components store.
Maarten

[shimster]

I've ordered the TO-220 insulation kit. Thanks Mick Bailey!  I think that'll do the trick.  I'm using the lm317 to drop 18V down to 12.6V with a current of about 350mA.  This produces enough heat to cause the lm317 to shut down without a heatsink in less than a minute, but I've been able to run it using a small binder-clip in the place of a proper heat sink.  I believe I'll be done with the rest of the build by the time the insulation kit arrives.  I'll post my progress.
Thanks!
-Dan

[Ripthorn]

That is almost 2W, what I am doing in a similar situation is using thermal adhesive (nonconductive) to attach the chips to the chassis.  I also do that with zener diodes to drop the voltage a little bit to lessen the load on the regulator.  Works quite well.  The heatsinks were getting blazing hot, but the chassis only gets mildly warm and only in the vicinity of the chips.

[shimster]

I finally installed the insulation kit into my pedal and it works great! I think the lm317 generates less heat than I had thought.  I think I was getting more heat because it was shorting out.  But using the insulation kit prevents the regulator from shutting down on hot summer days.  Now, if only my pedal didn't sound so wrong! Aargh! Hehe. Back to the breadboard...