A switching circuit includes a first switch and a second switch respectively connecting a first terminal and a second terminal of an electrical coil to a positive terminal of a voltage source, a third switch and a fourth switch respectively connecting the first terminal and the second terminal of the electrical coil to a negative terminal of the voltage source, and a controller to control the switching circuit in a current control mode to alternate a voltage polarity of the voltage source to thereby control a magnitude and direction of the electrical current of the electrical coil, and to control the switching circuit in a current hold mode to disconnect the electrical coil from the voltage source and to short-circuit the electrical coil to maintain the magnitude and direction of the electrical current at the transition time when the switching circuit switched to the current hold mode.
