Patent ID: 6963183

Claim:
A control circuit for a d.c. motor, comprising: a freewheeling diode circuit; an electrolytic capacitor circuit coupled in parallel with the d.c. motor; and a polarity reversal protection device situated outside a power supply circuit of the d.c. motor, the protection device including a transistor switch and a diode coupled in parallel with the transistor switch, the protection device being coupled into the freewheeling diode circuit and being coupled into the electrolytic capacitor circuit; wherein the transistor switch includes an n-channel power MOSFET, the transistor switch having a drain terminal coupled to a negative terminal of an electrolytic capacitor of the electrolytic capacitor circuit and to an anode of a freewheeling diode of the freewheeling diode circuit, a cathode of the freewheeling diode being coupled to a positive side of the d.c. motor, a source terminal of the transistor switch being coupled to a negative side of the d.c. motor, a gate terminal of the transistor switch being coupled across a resistor to a positive voltage.