The device has a diode (14) connected in parallel with a winding (12) which is connected in series with a battery (2). A MOS transistor (15) is connected between the winding and the battery. A drive circuit (17,18,19) generates signals for switching the MOS transistor on and off to drive the gate of the MOS transistor. A delay circuit (16) is arranged between the drive circuit and the MOS transistor and delays the signal generated from the drive circuit to switch the MOS transistor from the off state to the on state. The signal is delayed such that the MOS transistor is switched from a fully switched off state to a fully switched on state over a predetermined period of time which is longer than the block delay time of the diode (14).
