Regulator heat sink question

[jdub]

Just wanted a second opinion: If I'm using the GGG bipolar power supply being fed by an 18vac wall wart and regulating down to +/-15v (using 7815 and 1915 regulators in TO-220 package), and powering an effect that draws 50ma, do I need a heat sink on the regs?  Calculating for power dissipation, (Vin - Vout)*current draw (in amperes), I get (18v-15v)*.05= 3*.05 = .15 W.  Does this sound correct? At far less than 1W dissipation, are heat sinks necessary or should the tabs on the regs be sufficient?  Thanks 

[R.G.]

If you look at the datasheet for the regulator, it will list the thermal resistance from junction (that is, the insides of the silicon chip) to ambient (the air around it), which is what you get when there is no heat sink. This will be about 65 degrees C per watt. The datasheet will also list the maximum junction temperature, which is usually 150C for silicon. With a dissipation of 0.15W and no heat sink, the junction gets 65*0.15 = 9.75C hotter than the surrounding air. The surrounding air is probably no hotter than about 43C (that's 110F) so the internals will only get to 52.75C, so you're safe by over 90C.

Yes, you can ignore additional heat sinking.

The TO-220 package as most manufacturers make it can just live with about 2W dissipation with no heat sink in free air.

[jdub]

Thanks, R.G.