Drive circuit for a permanent magnet motor

A drive circuit for an electric motor comprising a stator and a permanent magnet rotor rotatable with respect to the stator, the stator comprising a stator core and a stator coil wound on the stator core, the drive circuit comprising:

• a controllable bidirectional AC switch connected in series with the stator coil between two terminals for connecting to an AC power supply;
• a first position sensor and a second position sensor for detecting positions of the magnetic poles of the permanent magnet rotor, the first position sensor directly coupled to a control electrode of the controllable bidirectional AC switch via a first unidirectional conductive switch and the second position sensor directly coupled to the control electrode of the controllable bidirectional AC switch via a resistor;
• and
• a voltage regulating circuit connected between the two terminals and the controllable bidirectional AC switch and configured to supply power to the first sensor during a positive cycle of the AC power supply and to the second position sensor during a negative cycle of the AC power supply such that the first and second position sensors alternatively output a signal to the controllable bidirectional AC switch to directly switch the controllable bidirectional AC switch between a conductive state and a non-conductive state in a predetermined manner, thus enabling the stator coil to urge the rotor only in a fixed direction during start-up of the motor, and
• wherein the voltage regulating circuit comprises a first zener diode and a second zener diode reversely connected in parallel between two terminals of the AC power supply at least via a first resistor and a second resistor respectively, a positive power supply terminal of the first position sensor is connected to a cathode of the first zener diode, a negative power supply terminal of the second position sensor is connected to an anode of the second zener diode, and a negative power supply terminal of the first position sensor and a positive power supply terminal of the second position sensor are connected to a reference voltage.