Hi list,

I'm working on a home project (a drum machine based around a PIC!) that uses
a couple of 15V regulators in TO220 packages - a 7815 and 7915. They're both
providing about 200mA, and I'm expecting the total voltage drop across them
to be about 5V (15-0-15vrms transformer...), hence they'll both be
dissipating roughly 1W. According to the National Semi. datasheet and having
done some rough calculations myself I know that the device temperature will
be well within spec even if the device is used in free-air, i.e. without a
heatsink. However, I'm wondering if I should go back and redesign my (rather
dense) PCB before getting it printed, to allow space for a heatsink anyway.

My question is, can anyone suggest a reason why I *should* consider a
heatsink, especially if the device is switched on for very long periods of
time, i.e. days? Should I consider a much higher Ta in my calculations as
the air inside the enclosure warms up? There will be lots of space above the
regulator (within a 2u 19" rack).

Thanks in advance for any advice offered.

Regards,

Trev


Trevor Page
Pace Micro Technology PLC
01274 538379

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