Jai Dhar wrote:
> -24 is nearing the -25 limit, which is probably why it's getting hot
> - but -12 is still probably a bit more than it needs. Can you drop it
> down to 7 for testing purposes? As long as the rest of your circuit
> is right, and your sure it's drawing 280mA... there doesn't seem to
> be an obvious reason why it would heat up.

If you think that 280mA x 19V (more than 5W) is not hot enough to burn your
finger, than I wonder your finger is dead already... :)

I would suggest you to use some voltage drop device to reduce this 24V to
something around 9 to 12V, so the 7905 heat dissipation would be less than
1 Watt, what would be nice, isn't it?

Suggestions would go from power resistors to lamps in series with the input
of the 7905. Lets see, a regular 50 ohms 5 Watts resistor would drop the
input voltage to the 7905 to around 10V.  A truck (24V x 10W) would reduce
the voltage to around 9V.  All of this if your circuit continuous to drain
around 290mA.

Of course, there are nice dc-dc conversions that will produce 5V with much
less power dissipation loss.

Wagner.

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