| 摘要 |
PROBLEM TO BE SOLVED: To properly perform the reduction of loss when a 100 VAC system is used, the arbitrary setting of output voltage when a 200 VAC system is used, and overcurrent protection when there is a short circuit current to a load or a power supply is started. SOLUTION: A first inverter 2 of step-down type and a second inverter 5 of step-up type are series-connected to the output of a full-wave rectifying circuit which is fed with alternating-current signals and outputs full-wave rectified signal. A control circuit 14 of power-factor improvement type controls a direct-current output voltage to a constant voltage and the switching of the first inverter 5, so that the waveform of alternating-current input current is made similar to the waveform of alternating-current input voltage, thereby improving the power factor. A switching control circuit 20 holds the switching element of the first inverter 2 in the on state when the 100 VAC system is used and the alternating-current input current is below a specified overcurrent protection value, and thus allow only the second inverter 5 to perform voltage increasing operation. If the 200 VAC system is used or the alternating-current input current is equal to or above the specified overcurrent protection value, the first inverter 2 is synchronized with the second inverter 5 to exercise switching control, thereby causing voltage increasing and decreasing operation. |
