| 摘要 |
PROBLEM TO BE SOLVED: To stop a voltage output while there is almost no effect of a residual ripple when an input voltage is dropped during an AC input in a power supply device for both of AC/DC inputs. SOLUTION: An AC voltage from each terminal 1a, 1b is rectified by a bridge rectifier 2. A DC voltage is passed through as it is. It is impressed to the primary winding of a switching transformer 3. The voltage induced to a secondary winding by on/off-operations of a switching element 4 is rectified by a rectification part 5. It is outputted from a terminal 6. The output voltage is returned to a control 9. The switching element is controlled by a control unit corresponding to the fluctuation of the output voltage. Thus, the output voltage is made constant. The operation of the switching element is stopped by a lower limit voltage discrimination part 8 by the control unit when a power supply voltage is below an operation lower limit voltage. Accordingly, the output is blocked. However, when an input power supply is an alternate current, the operation lower limit voltage of a switching circuit is increased compared with that during DC input. When the input voltage is dropped, the voltage output is stopped while the residual ripple is small resulting in blocking bad effects to a load circuit. COPYRIGHT: (C)2005,JPO&NCIPI
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