The United States of America As Represented by the Secretary of

Thomas J Fisher

Roger L King

James C Cawley

Marcus H Uhler

Michael D DiMartino

An intrinsically safe power supply employing a binary current interrupter connected between the power source and the electrical load. Normally the load is situated in a potentially dangerous environment, like a coal mine, and the intrinsically safe power supply at a safe remote location, e.g., on the earth's surface. The interrupter has a pass and switching transistor, current sensor, gating circuitry, a flip-flop switch, and means to delay the turning on of the transistor--but not its turning off. If an overcurrent or overvoltage condition is sensed between the input and output of the intrinsically safe power supply, load current will cease to flow. In normal operation, only the current interrupter pass transistor will open. A reset signal from an oscillator internal of the interrupter may be used to reset the flip-flop after actuation or upon its initial setting, thereby causing the flow of power into the load.

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Munhall, PA, United States of America

Thomas J Fisher