Thank you for your help

[DRAINVILLE, Michel]

A couple of week ago I posted a message asking suggestions to make a 5v
power supply for the car (12-14volts input, 5 volts ouput) and not
having the problem of dissipating 7W.

I had very good feedback from the list and I will share with you the
result of my investigation.

One interrestiong suggestion was to use the stepdown power supply from
the power module in the car (about 7VDC) that feed the ECU. Then use a
7805 to regulate to 5vdc. It may not be available on some car.

I also had suggestions about using a 'simple switcher' from National.
The LM2825 and the LM2575. The 2825 seems to be more versatile but is
also more expensive. So I ordered a lm2575 and assembled it using the
basic configuration and to my surprise I was able to input a voltage
varying between 9 to 20 volts and the output was stable at 5Volts. I
used the TO220 case so it would be easier to mount a heat sink if needed
but I didn't need one. For my test I was draining 800mA. With a linear
regulator it would represent a dissipation of 12 watts!
All is needed is 2 caps, 1 diode and 1 coil.
Hope this can help someone else.

Thanks again digesters.
Michel Drainville
"on board dynamometer project, almost ready to install in the car!"