Jinx wrote:

>>I'm assuming I need a heat sink
>>    
>>
>
>Not necessarily. Use a series resistor between wallwart +ve and
>7805 i/p. This will take the brunt of the voltage drop and heat up
>instead of the regulator. Something around 15-22 ohms should do,
>preferably not a carbon for longer life. Choose so that voltage at
>7805 is still up around 8-ish volts. Probably need a 2W, you'll have
>work that out from actual current passed.
>
HUH?  You calculated the ENTIRE dissipation is "about 0.5W".

> With the figures you gave
>it looks like the 7805 is generating about 0.5W heat (assuming,
>optimistically, actual 12V), with the added bonus that it's already at
>120F. With a dropping resistor you should be able to keep the
>7805 in that region
>
>  
>

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  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.net
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