An easy way to unoad the regulator is to put a series resistor in the
input.  Let it dissipate as much of the heat as possible.  Size it such
that you always maintain the minimum input voltage required by the
regulator.  If, for example, the 7805 needs a minimum of 7 volts at its
input and you have a 24 volt source, use a resistor that will drop 17 volts
at your load's maximum current draw.

Mark Peterson

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