Power for automotive circuits

Having finished a project to applied in a car you are sometimes faced with the fact, that you don't have a suitable power supply.

Connecting e.g. CMOS-circuits to the car electric system unprotected will cause their sudden (not unexpected) death as soon as the alternator is working.

Here is a small circuit taking care of proper supply for MCU based circuits.

This circuit has proved to protect an ATmega8 for more than two years. I supplies unregulated board power for connected loads (up to 3A) and regulated 5V for MCUs with an extra output for AVCC, which should have an extra supression coil for best performance of the MCU.

The secret of proper spike suppression is a transil-diode (NXP) which is available as unipolar and bipolar device. It takes high current for needle pulses and won't let them pass to the connected circuit.

The PCB design is purely single sided. Using high current on the regulator output I suggest to make it double sided and use the copper area as heat sink.

As always, there is certainly room for improvement - so suggestions are welcome.

For those interested in the Eagle files please PM me leaving your email address.

Regards to all

Boncuk

P.S. Board size is 1.9X1.9inches

I'm doing an ATMega328 in an auto and going to do a pc board so an Eagle file and components list would help (sewalt77@gmail.com). Thanks.