SOLID-STATE LOAD PROTECTION SYSTEM HAVING ELECTRONIC SIMULATION OF MOTOR HEATING

摘要

A solid-state load protection system having electronic simulation of motor heating characteristics. A current sensing function is utilizes so as to produce an output signal which is related to the current in an electrical circuit. Attached to the current sensing function is an inverse time delay circuit and has a signal path for charging and discharging a capacitor. The voltage across the capacitor is related to the thermal state of the load. Depending upon the voltage across the capacitor, the inverse time delay circuit which is essentially an overcurrent and timing function which is monitoring the voltage will initiate either a time-out or trip sequence or a reset sequence. The time before time-out or reset is proportional to the voltage across the capacitor. An output function which is connected to the overcurrent and timing 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 the load. Upon receiving a reset signal the output function prohibits the light-emitting diode from conducting and energizes a contactor thereby connecting the current source with the load.