SOLID STATE PROTECTION CIRCUIT FOR ELECTRICAL APPARATUS

摘要

Electrical equipment (14) is safeguarded from damage due to faults by a circuit that provides several levels of protection. A semiconductor switch (18) and a current sensor (24) are placed in series with the electrical equipment (14). When the current to the equipment exceeds a first threshold for a predefined period of time, the semiconductor switch (18) is rendered non-conductive until the circuit is specifically reset. When the current to the equipment exceeds a greater second threshold, a pulsed signal alternately places the semiconductor switch (18) in conductive and non-conductive states so that the average current applied to the equipment (14) is within an acceptable level. Should the current exceed an even greater third threshold, the semiconductor switch (18) is immediately rendered non-conductive until the circuit is manually reset.