Abstract: The rotor of a generator is provided with permanent magnets to ensure start-up of electricity generation without externally supplied field current after a vehicle engine starts. When the generation is detected, the external field current is supplied from a battery so that the battery is charged by the generator, thereby to prevent battery discharge in a low speed range.

Abstract: Duty ratio of a power switching transistor connected to the field coil is controlled according to whether or not a high-power load is connected. When the high power load is not connected, the duty ratio is made 60%, for example, so that excessive power not generated. On the other hand, when the high power load is connected, the duty ratio is increased to 100% so that full power is generated by the generator. The power switching transistor is also controlled according to the battery voltage in a well known manner.

Abstract: A sector pulse generating apparatus for multiple zone recording includes only first and second counters. The first counter counts reference clock pulses and outputs a present position signal. The second counter is incremented in response to a increment signal and outputs a next sector number signal. A first register stores the sector length of a zone in which a head is located. A multiplier outputs a next sector position signal representative of a multiplication of the next sector number and the sector length. A first comparator compares the magnitude of the present position and the next sector position. When the present position and the next sector position match, a sector pulse generating device generates a sector pulse and a first increment device outputs the increment signal.