How about putting a diode (or more) reversed bias parallel to the power source. If the polarity IS reversed, you will only get a negative voltage equal to the forward voltage drop of the diode. This will work as long at the current doesn't kill the diode, so don't try using with a lead-acid battery application! If you know your supply current , you can use a current limit resistor. Use R=(Vsource-Vdiode)/Imax diode. You can then double check to ensure the supply voltage will not drop too much. Good luck Current Limiting (Vs)---------/\/\/\/---------------------> To device | _ Diode ^ 1N4005 | ----------------------------------> Gnd TAS ----------------------------------------------------------------- Sent from the desk of: Terry Allen Steen, EE engineering@marinapower.com 332 McLaws Circle, Ste 111 757-258-8800 (Voice) Williamsburg, Va 23185 757-258-8805 (FAX) ----------------------------------------------------------------- !I AM A WHALE MAIL USER! If you have a large file to send, goto http://www.whalemail.com send them to: mplengineer Give me your account and I will use it also ----------------------------------------------------------------- Visit our web-site: www.marinapower.com -----------------------------------------------------------------