Operational amplifier having an improved feedback system including an integrator having a hurry-up circuit, and an electric motor control using the same for inverse trip selection

A motor controller is adaptable to a wide range of motor currents by using an integrator circuit having an additional feedback arrangement for affecting the effective time constant of the integrator under specified conditions. The operational amplifier has an amplifier having a first input, a second input, and an output, an input resistor connected between an input of the operational amplifier and the first input of the amplifier, and a feedback impedance connected between the output of the amplifier and the first input of the amplifier. A voltage at the input of the operational amplifier is compared with a voltage at the first input of the amplifier. An auxiliary current path for the feedback impedance is provided when the voltage at the input of the operational amplifier has a predetermined relationship to the voltage at the input of the amplifier. When used as an integrator hurry-up circuit, the feedback impedance has an integrating capacitor, and the auxiliary current path for the integrating capacitor changes the time required for the capacitor to either charge or discharge, thereby effectively changing the integration time constant. An electric motor controller overload circuit using the improved operational amplifier permits switchably selecting a starting class for a selected electric motor.