Patent ID: 7203042

Claim:
A protective circuit for a motor, comprising: a motor with a rotor, providing a first coil set and a second coil set; a drive unit, further comprising a drive IC, which has an out 1 pin, out 2 pin, a VTH pin, a CT pin, an IN+ pin and an IN− pin, and a Hall element, which has a positive voltage output end and a negative voltage end, wherein the positive voltage output end is connected to the IN+ pin and the negative output end is connected to the IN− pin, and the out 1 pin is connected to the first coil set and the out 2 pin is connected to the second coil set; a control unit, further comprising a comparator, which has a positive phase input end, a negative phase input end and an output end, wherein the positive phase input end connects with the CT pin, the negative phase input end connects with an end of a first resistor and an end of a second resistor, the output end connects with an end of a third resistor, the positive phase input end further connects with a capacitor in parallel, another end of the first resistor connects with a direct current power source, another end of the second resistor is grounded, another end of the third resistor connects with an end of a fourth resistor in series, another end of the fourth resistor is grounded, and a joint between the third resistor and the fourth resistor is connected to the VTH pin; characterized in that when the motor stops running, the Hall element is incapable of sensing the magnetic pole change of the rotor such that no positive voltage and negative voltage outputting to IN+ and IN− pins and then the CT pin sends a signal to the capacitor to perform charge and discharge; and once the capacitor is charged, voltage at the positive phase input end is greater than a first branch voltage signal of the negative phase input received from the first and the second resistors such that the output end produces a high reference voltage signal and the high reference voltage signal is treated by the third and the fourth resistors as a second branch signal received by the VTH pin to limit currents sent to the first and second coil sets for avoiding to produce high instantaneous pulse current and voltage.