| 摘要 |
A switching type power supply unit adapted to generate a positive output voltages though conversion of a power supply voltage has an negative output voltage generation circuit switchably connected, via a changeover switch, between the first node of a coil and a switch and the second node receiving the power supply voltage or between the first node and the ground. The negative output voltage generation circuit is connected to the second node when the voltage difference between the positive output voltage (Vp) and the power supply voltage (Vbat) is sufficiently large, while the circuit is connected to the ground when the difference voltage is small. Thus, the power supply unit efficiently provides a negative output voltage having a predetermined level along with a positive output voltage (Vn) generated from the power supply voltage through conversion thereof.
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