| 摘要 |
PROBLEM TO BE SOLVED: To provide an AC-DC converter used for charging a lithium ion battery, etc., which has a small number of constituent parts but has a desired performance and which has a high efficiency with small heat generation. SOLUTION: The output voltage converted into DC by an output rectifying circuit 7 is controlled by an LED 8 and a shunt regulator 9. Then, a control signal is transmitted to a photo transistor 5 to control the switching voltage at the primary side of a transformer 2 and obtain stabilized DC voltage, which is a characteristic near the full-charging voltage of a battery. Depending on the output voltage, three types of modes are generated by three transistors Q11, Q12, Q13. The three modes are an initial charging mode of a small constant current, a rapid charging mode of a large constant current, and a constant voltage region mode. Because of this structure, a circuit suitable for charging can be obtained with a small number of components. By installing a means for differentiating part of the flyback voltage generated in the collector of a switching transistor 3 and adding part of the output of the means to a positive feedback loop, a switching speed is increased. By keeping the saturated voltage of the collector of the transistor 3 low, generation of heat can be suppressed.
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