Patent ID: 6252752
Filing Date: 2001-06-26
Classification: H02H

Abstract:
An overload protection apparatus comprising:a semiconductor switch installed in a power supply line for a motor;an overload detection circuit including a current detector, installed in the power supply line, for detecting a motor driving current, an overload detection reference value setting circuit for setting an overload detection reference value and a first operational amplifier for comparing a voltage that is proportional to the motor driving current detected by the current detector with the overload detection reference value set by the overload detection reference value setting circuit, and for outputting a signal corresponding to the result of the comparison;a starting circuit including a first comparator for comparing a voltage corresponding to the motor driving current upon starting the motor with a first reference value that is a reference voltage at the time of starting the motor, and for outputting a signal corresponding to the result of the comparison;a trip circuit including a second operational amplifier for comparing a value of integration obtained by integrating an output of the first operational amplifier with a second reference value, and for outputting a signal corresponding to the result of the comparison, and a second comparator for comparing an output of the second operational amplifier with the first reference value, and for outputting a signal corresponding to the result of the comparison; anda switch operation circuit, installed between a constant-voltage source and an output end of the second comparator and/or an output end of the first comparator, for outputting a signal in response to the outputs of the first and second comparators so as to open and close the semiconductor switch.