Abstract: A motor protection circuit which generates a signal having a value proportional to the magnitude of the input current of the motor and a motor speed signal having a value proportional to the difference between the rated motor speed and the actual motor speed. The motor speed signal is multiplied by the input motor current proportional signal to derive a product signal. The product signal is summed with the input motor current proportional signal to derive a sum signal. The sum signal is compared with respect to a preset level to determine if it is greater than a preset level. If it is greater than a preset level, the sum signal is coupled to the input of a voltage controlled oscillator which generates an output signal having a value proportional to the magnitude of the sum signal. The output of the voltage controlled oscillator is counted in an up/down counter and an output is gated when the total count reaches a predetermined level.

Abstract: A voltage snubber connected to the output terminals of a transistorized, push-pull inverter for supplying bidirectional current to an inductive load comprises a snubber capacitor and relatively large valued resistor connected in series with each other across the output terminals of the inverter and a switching circuit for bypassing the resistor during turn-off periods of the inverter transistors. The value of the snubber resistor is high enough to provide slow recharging of the snubber capacitor during turn-on periods of the inverter transistors to reduce transistor power dissipation. When the resistor is bypassed by the switching circuit during the inverter transistor turn-off periods, the snubber is gated on to suppress high voltage surges generated by the inductive load. The snubber switching circuit is responsive to current sensors or logic commands connected in circuit with the inverter to detect turn-off transistors of the inverter transistors.