>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).

I would recommend a heatsink anyway, even just a flat sheet of plain
aluminium. It does not take much to halve the temperature rise, but it may
well save you chasing your tail trying to find out why your circuit goes
crazy after a coupe of hours under spot lights, as the internal temperature
cutout of the regulator takes effect.

Also remember that the tab of 7900 series regulators is NOT at earth
potential, so if they are on the same piece of metal this one needs
insulating.

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