Electrical control circuit, especially for a fuel supply device of an internal combustion engine

A fuel supply system for an internal combustion engine comprising, in combination, a normally closed electromagnetic valve for metering a supplementary quantity of fuel to said engine, a first control circuit comprising the series connection of a battery, an engine starting switch, a relay having a normally open switch and a PTC resistor, a second control circuit comprising the series connection of said electromagnetic valve, said normally open switch, said starting switch and said battery, said PTC resistor having a low resistance below a predetermined minimum temperature to permit the flow of current in said first control circuit when said starting switch is closed for energizing said relay and closing said relay switch to permit the flow of current in said second control circuit for opening said electromagnetic valve to meter said supplementary fuel quantity, said current flow in said first control circuit producing a heating-up of said PTC resistor to said predetermined temperature within a period of time determined by the characteristics of said PTC resistor whereby the resistance of said PTC resistor rises substantially at said predetermined temperature to interrupt the flow of current in said first control circuit for deenergizing said relay and interrupting said second control circuit terminating the metering of said supplementary fuel quantity.