Solid-state load protection system having an improved inverse time delay

Abstract

A solid state load protection system having an inverse time delay circuit. A current sensing function is utilized so as to produce an output current which is proportional to the current in an electrical circuit. Attached to the current sensing function is a load resistor which converts the current produced by the current sensing function to a voltage which is proportional to the current utilized by the load. Attached to the load resistor is an inverse time delay circuit which serves as an overcurrent and timing function. The overcurrent and timing function monitors the level of voltage from the load resistor initiating a time-out sequence when the voltage across the load resistor, which is proportional to the current utilized by the load, exceeds a predetermined level for a predetermined period of time. The overcurrent and timing function utilizes two diode paths for prohibiting the charging or discharging of a capacitor during a normal or overcurrent condition, respectively. Encircling the connections to the capacitor is a guardband for minimizing impedances from associated circuitry which affect the timing of the inverse timing circuit. During an overcurrent condition, the capacitor charges up to a specific value initiating a trip signal which is sent to an output function. The output function upon receiving a trip signal causes a light-emitting diode to conduct and also deenergizes a contactor through which a current source is connected to a load.