| 摘要 |
A pulse width modulator generates a PWM signal whose duty ratio is feedback-controlled so that a detection voltage according to a current across a secondary coil of a transformer is brought close to a reference voltage. A logic control unit performs a switching control of the current across the primary coil of the transformer, based on the PWM signal outputted from the pulse width modulator. A first protection circuit detects a circuit failure of an inverter and stops the switching control of the inverter when the circuit failure continues for a predetermined duration of error detection time. A second protection circuit monitors a feedback voltage corresponding to an output voltage of the inverter, and lowers the reference voltage sets the duration of error detection time short when the feedback voltage is lower than a predetermined threshold voltage.
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