Each power diode in an ORed direct-current power distribution system has connected thereacross, between the respective load and source terminals of the power diode, a series connection of respective first and second light-emitting diodes (LEDs) with the LEDs being similarly poled with respect to their...http://www.google.co.uk/patents/US4394647?utm_source=gb-gplus-sharePatent US4394647 - Voltage monitoring arrangement for ORed power diodes
