| 摘要 |
PROBLEM TO BE SOLVED: To switch an on/off state of a switching element even when no PWM signal is outputted because of an occurrence of defects in a control circuit outputting a PWM signal.SOLUTION: Although an FET 2 is turned off and a gate of an FET 1 of a drive circuit part 7 is biased and turned on when an external switch 11 is turned off, power of a power supply B is not supplied to a load 3 because the external switch 11 is turned off. When the external switch 11 is turned on, a controller 9a of a control circuit part 9 outputs a PMW signal to a gate of the FET 2, and the FET 2 is turned on during an off period of the PMW signal. Thereby, the FET 1 performs an on/off operation (is turned off during an on period of the PMW signal, and turned on during the off period) in synchronization with change in a signal level of the PMW signal. In addition, when the FET 2 of the control circuit part 9 becomes in a state that it cannot be turned on during the on state of the external switch 11, the gate of the FET 1 of the drive circuit part 7 is maintained to be at a bias potential, and thus, the FET 1 is maintained to be in an on state. |
