On Sun, 11 Jan 2004 19:44:19 +0800, Richard Hosking
wrote:

Dear all
I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Richard

Rick,
one way for reverse protection is to include a bridge recifier in the
rigs power line ( internally fitted ), but this causes a drop in
available volts.

I prefer a diode into a relay coil, with the relay contacts enabling
the power when the relay coil is correctly polarised and powered (
also internally fitted ).

This enables full volts to the rig and also gives reverse protection,
however this is at the cost of further ( and some may say excessive )
drain of the power source.
Over voltage should be by fuse and a crowbar circuit. Do a search on
crowbar for details.

The diode + relay circuit should be obvious to you, I use a 9v relay
coil with a 1N4001 in the activation side and a DPDT contact,in
parallel, to switch the power. For the power you are talking about a
14pin DIL relay should be adequate.

HTH, Mike W, G8NXD qthr