In car power supply

[Dave J. Andruczyk]

> Hi everyone. This is my first post to this list. I'm building a
> dynamometer and performance analyser for my car, using a Atmel 8952.
> I'm now in the power supply section and faced to the heat dissipation
> problem. I'm not using a DC-DC converter because of the price.
> I tried to use a 7809 and 7805 together and also a 7805 with a bypass
> transistor but both setups generate a lot of heat. (7 to 8 watts).
> My circuit draws about 800ma including LCD and backlight.

Try this:
take about 7 7805's and parallel them.  IT would seem at first that they
would tend to fight over each other having their outputs tied together,
but they don't and tend to stay very well behaved.  IF your worried
problems use a .1 ohm resistor from the output to the "tie point", to keep
them all balanced.  The load will be split among all the 7805's, and the
heat should be a bit easier to handle. (heat sink them if necessary)

This is documented in Popular Electronics and I have tried it myself and
it DOES work, even though one might think that the outputs would try to
feed into each other.

Dave