Heat sink for regulators

[Diynot]

Merry Christmas and Happy Holidays folks! Quick question, Would either a 7815 or 7915 +/- 15v regulator need a heat sink? Supply voltage is 18v AC

 

[Chuck D. Bones]

Depends on the power dissipation. My conservative rule of thumb is anything under 200mW does not need a heatsink.

Pd = (Vin - Vout) * Iload

We know Vout = 15VDC

18VAC (rms) = 25V peak Take off 1V for losses in the rectifier & filter, Vin = 24VDC

Vin - Vout = 9V

Therefore, if Iload is under 22mA, no heatsink req'd. That's a conservative rule, so there is some wiggle room. If you do install a heatsink, keep in mind that the regulator's tab or metal case is electrically hot.

 

[Diynot]

Thanks Chuck for the little Christmas edumecation. Knowledge really is the best gift. I see that @Betty Wont checked my thread so probably knows why I am asking. That said, did you use heat sinks on your haplochlaena build?

 

[Betty Wont]

Thanks Chuck for the little Christmas edumecation. Knowledge really is the best gift. I see that @Betty Wont checked my thread so probably knows why I am asking. That said, did you use heat sinks on your haplochlaena build?

I didn't use heat sinks on mine. They don't get very hot on this one. On builds where the regulator does get hot I make a heat sink by sticking a chunky bolt and nut through the mounting hole.

 

[Diynot]

Awesome! Thanks erybody

 

[Stickman393]

If you do install a heatsink, keep in mind that the regulator's tab or metal case is electrically hot.

Also, if you run into a situation where clearance becomes an issue, there are lots of rubberized or ceramic heatsink mounting kits available that electrically insulate the body of your regulator from the heatsink.

If that isn't an issue, a little dab of thermal conductive paste never hurt no one.

 

[danfrank]

Ta-Da!!
I do use a plastic isolation washer and mica. For a heatsink, use whatever fits.