| 摘要 |
PROBLEM TO BE SOLVED: To prevent the appearance of surge current and absorb surge voltage by clamping operation by discharging parasitic capacitors which are equivalently parallelly connected to first to fourth switching means respectively just before turning those switching means ON. SOLUTION: In order to make an adjustment to the output voltage by controlling the ratio of an ON duration to an OFF duration of a first or a third switching element 3 or 9 or the ratios of both of the switching elements, first to fourth parasitic capacitors 5, 8, 11, 14 are charged and discharged just before turning ON first to fourth switching elements 3, 6, 9, 12. Therefore, the appearance of surge-like short-circuit current is reduced and the efficiency can be increased and the generation of noise can also be suppressed. When the first and the second switching element 3, 6 and the third and the fourth switching element 9, 12 turn off, a first and a second diode 7, 4 and a third and a fourth diode 11, 13 turn on and therefore surge voltages in a turn off state of the first and the second switching element 3, 6 and of the third and the fourth switching elements 9, 12 caused by leakage inductance of a transformer are voltage-clamped. |
