| 摘要 |
PROBLEM TO BE SOLVED: To improve loss due to forward direction voltage drop of a diode. SOLUTION: An MOSFET 10 is connected with a part between a second terminal 5 and a fifth terminal 8. In the case of voltage step-up, the MOSFET 10 does not perform switching operation and is in the state of OFF. A step-up circuit is constituted of a choke coil 1, an MOSFET 11 and a Shottky diode 2. In the case of voltage step-down, the MOSFET 10 performs PWM control synchronously with an MOSFET 9. Thus a step-down circuit is constituted of the choke coil 1, the MOSFET's 9, 10 and the Shottky diode 2. Since when an inverse electromotive force generated in the choke coil is charged into a capacitor, in the case of operation of a step-down circuit, the MOSFET 10 turns to a conductive state by the on-control of the PWM control, and acts as an element for bypass which has an on-voltage smaller than the forward direction voltage drop of the Shottky diode.
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