| 摘要 |
A switching power supply in which high efficiency is obtained by further reducing a loss occurring in a PNP type transistor as a rectifying element, particularly in case of making a switching frequency higher. Further, the switching power supply is a boost/buck converter in which an application range of an input voltage is broadened by causing a circuit not to perform intermittent operation when the voltage VIN is higher than an output voltage Vo. One end of a choke coil L1 is connected to an input terminal 1 and another end thereof is connected to an emitter of a PNP type transistor Q2 as a rectifying element. A base of transistor Q2 is connected to a collector of a driving transistor Q3 via a resistor R4. The base of the driving transistor Q3 is connected to another end of the choke coil L1 via a series circuit of a capacitor C3 and a resistor R3. Further, the base of the transistor Q2 is connected to one end of the input terminal side of the choke coil via an auxiliary bias circuit 4 or an impedance circuit 5.
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