| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to achieve high efficiency over the wide load range with the small configuration, by providing the first selecting means which selects any of the input terminals of the primary winding, and the second selecting means which selects the output terminal wherein the transformation ratio corresponds to the input terminal of the primary winding selected by the first selecting means. SOLUTION: A transformer 1 is constituted of the primary winding 1Na1 wherein the wire diameter for a light load is thin and the winding number is Na1, the second wiring 1Nb1 of the winding number Nb1, the primary winding 1Na2 of the winding number Na2 wherein the resistivity is low because the wire diameter is thick for both light load/heavy loads, and the secondary winding 1Nb2 of the winding number Nb2. The terminal 2a of a switch 2 is connected to a terminal 1a-1 on the primary side of the transformer 1, and a terminal 2b is connected to a center tap 1a-2. Then, the terminal 1a-3 of the transformer 1 is connected to the source electrode of a transistor 3. The terminal 1b-1 on the secondary side of the transistor 1 is connected to a junction point 4a of a switch 4, and a center tap 1b-2 is connected to a junction point 4b.
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