At 09:46 AM 10/13/2009, Wouter van Ooijen wrote:

>The current is only 30 mA anyway, so at 24V some 0.6W is dissipated.

Do you need the accuracy of a regulator?  If not, why not consider a 
zener diode and suitable resistor instead?  You could use a 1W or 2W 
metal-oxide resistor and a 1W zener for about the same cost as a 7805.

You could also use a resistor and zener in front of your regulator as 
a pre-regulator.  Choose the zener voltage to be above the above the 
normal input voltage so that the zener is not conducting all the time 
(if possible).

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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