| 摘要 |
A minimum pulse signal generating circuit generates a minimum pulse signal having a predetermined minimum duty ratio, synchronously with a PWM signal. When the duty ratio of the PWM signal is smaller than the minimum duty ratio, a corrected pulse signal generating circuit fixes the logical level of the PWM signal to the level that turns off a switching transistor. A driver circuit drives the switching transistor according to a corrected PWM signal output from the corrected pulse signal generating circuit. In a case in which the level of the PWM signal is fixed by means of the corrected pulse signal generating circuit, a stop signal generating circuit generates a stop signal at a predetermined first level. When the stop signal is at the predetermined first level, at least an oscillator used for pulse modulation is stopped.
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