Patent ID: 7888993

Claim:
An apparatus that is coupled to a plurality of power sources and that provides a bias current, the apparatus comprising: a crude bias generator that generates a startup current and that is coupled to at least one of the power sources; a current selector that receives the startup current and a reference current, wherein the current selector outputs the larger of the startup current and the reference current as the bias current; and a fault mode supply that is coupled to each power source and that generates a supply voltage for the current selector, wherein the fault mode supply includes: a diode that is coupled to the largest of the power sources; a first resistor that is coupled to the largest of the power sources; an FET that is coupled to the diode at its drain and that is coupled to the resistor at its gate; a zener diode coupled between the gate of the FET and ground; and a second resistor that is coupled to the source of the FET and that is coupled to the current selector.