Undervoltage protection device

Claim 1

A protection device for a voltage source and a load, comprising means for establishing a current path between said voltage source and said load, first and second switching means connected in said current path, each adapted to move to an open position to provide an open circuit in said current path, first circuit means responsive to said first switching means being closed for closing said second switching means, said first circuit means being operable, unless disabled, to open said second switching means a predetermined time interval after said first switching means closes, and second circuit means responsive to a predetermined voltage output from said voltage source to disable said first circuit means from opening said second switching means, wherein said second switching means is in the form of a relay switch, wherein said first circuit means comprises a coil adapted to energize said relay switch to close same and a switching transistor responsive to said first switching means being moved to a closed position for connecting said coil in said current path, wherein said switching transistor is connected in said current path by means of a capacitor in a manner so that said transistor is turned on only during the charging of said capacitor in response to said first switching means being closed, wherein said second circuit means comprises a zener diode connected in said current path between said second switching means and the base of said switching transistor, and wherein said second circuit means further comprises a diode connected in series with said zener diode, said diode connected so as to prevent said capacitor from charging through said load.