| 摘要 |
PROBLEM TO BE SOLVED: To protect a power supply against breakdown even when an external sync signal is stopped and switched to an internal sync signal by preventing the occurrence of interference noise in the output from the power supply. SOLUTION: The power supply comprises a DC-DC converter having a switching element operating under PWM control synchronized with any one of an external sync signal or an internal sync signal being switched wherein a monitor circuit 17 detects the interruption of input of the external sync signal and delivers an alarm signal to a PWM control section 12. Since the monitor circuit 17 delivers an alarm signal, the operation of the switching element provided in the DC-DC converter 11 can be stopped while protecting the switching element against breakdown. Consequently, the occurrence of interference noise in the output from the power supply is prevented and the power supply is protected against breakdown. COPYRIGHT: (C)2005,JPO&NCIPI
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