| 摘要 |
PURPOSE:To prevent malfunction originating from a dropout compensating circuit, and to perform normal servo locking, by decreasing the detection sensitivity of a dropout detection part during unlocking operation. CONSTITUTION:An unlocked state of a speed servo system 9 is detected by a lock detector 10 to turn on a switching element Q1, and a capacitor C2 is connected in parallel to the capacitor C1 of the time constant circuit 71 of a retriggerable MMV7. Therefore, the time constant of the MMV7 is greater during unlocking operation than in locking operation, so the pulse width of the MMV7 increases to decrease dropout detection sensitivity. Consequently, a sink chip level is never regarded as a dropout during the low-speed rotation of a spindle motor 11 while a spindle servo loop is turned off, thus preventing the generation of a dropout detecting signal. |
