| 摘要 |
A protective circuit for use with a single power supply (11) for supplying a voltage to a control unit (12) and to an external device (13) separated from the control unit through a pair of power supply lines (PSL1 min , PSL2 min ), comprises a fault contact detector (141) and a short-circuit detector (142) connected between the power supply (11) and the external device (13). The fault contact detector (141) includes an overvoltage detector circuit (141a) for detecting an overvoltage imposed between the power supply lines (PSL1 min , PSL2 min ) due to fault contact with another power supply line of a different voltage, switching means (141b) energizable in response to detection of the overvoltage for short circuiting the power supply lines (PSL1 min and PSL2 min ) and circuit breaker (141c) for being connected between the external device (13) and the switching means (141b), the circuit breaker (141c) being openable in response to energization of the switching means (141b), when the overvoltage detector circuit (141a) detects the overvoltage for severing the power supply (11) from the external device (13) to thereby protect the control unit (12) against malfunctioning or destruction which would otherwise be caused by the overvoltage. The short-circuit detector (142) includes a current detector circuit (142a) for detecting a current flowing through one of the power supply lines (PSL1 min ), a comparator (142b) for comparing the current (Ia) as detected with a reference current (Ir) and for producing a signal indicative of detection of an overcurrent when the current (Ia) is larger than the reference current (Ir), and switching means (142c) for severing the power supply (11) from the external device (13) when the overcurrent flows due to short-circuiting between the power supply lines (PSL1 min , PSL2 min ) to thereby protect the control unit (12) against malfunctions or destruction due to the overcurrent. |
