| 摘要 |
PURPOSE:To prevent a disk motor from being over-drive toward an abnormal high speed without any special sensor by inserting a limiter means selectively turned on/off in response to a signal detection state from a disk to an output path of an accelerating direction control pulse for a disk servo. CONSTITUTION:A DM+ supply line 24 outputted from a servo control circuit 18 is connected to ground via a Zener diode ZD and a transistor (TR) operated as a limiter. The TR is turned on/off by a limiter on/off signal outputted in response to a signal detection state from a disk. When the TR is turned off, the Zener diode ZD is turned off and the level DM+ is led as it is to an operational amplifier 20. When the TR is turned on, the Zener diode ZD is turned on, the level DM+ is attenuated and led to the operational amplifier 20 and a torque of the disk motor 10 is weakened.
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