| 摘要 |
PURPOSE:To prevent breakdown of a MOS semiconductor and improve reliability of an apparatus as a whole by detecting an over-voltage before it is applied to a load to set a switching means to the cut-off condition. CONSTITUTION:An abnormal input voltage protective circuit comprises a switching means 24 inserted between a rectifier circuit 15 and a load 14, an input voltage detecting circuit 25, a delay circuit 26 having the predetermined delay time and a drive circuit 27 to be controlled by an output of the delay circuit 26. When the voltage detecting circuit 25 is in the off-state because an input voltage is within the specified voltage range, the irregular input voltage protection circuit charges the delay circuit 26 and then turns on the switching means 24 via the drive circuit 27 when the charging voltage exceeds a constant value after the preset time to supply the voltage in the specified range to a load 14. When the input voltage exceeds the specified range, while the voltage is delayed by the charging time constant t of the delay circuit 26, the voltage detecting circuit 25 turns on, terminating the delay circuit 25, turning off the driver circuit 27, also turning off the switching means 24. Thereby an over- voltage is not supplied to the load 14 for protection from breakdown. |
