DC/DC CONVERTER

PURPOSE:To always operate the switching mode of a switch in a similar mode, and to simplify a switching control by so constructing to turn on all the switches if an input voltage is of a predetermined value or less. CONSTITUTION:In a switched capacitor type DC/DC converter, capacitors C1, C2, and a plurality of switches 1, 2, 3, 5, 6, 7 are associated, and the duty ratio of the switching operations of the switches 1, 2, 3, 5, 6, 7 is altered to control the charging voltage of a smoothing capacitor C3. The series connection state of the capacitors C1, C2 is switched by the switching operations of the plurality of switches 1, 2, 3, 5, 6, 7, the discharged capacitors C1, C2 are charged by a DC power source 10, the charged capacitors C1, C2 are discharged, and the capacitor C3 is charged. If the voltage of the power source 10 is high, the duty ratio of the switching operations is controlled in a range in which all the switches are not simultaneously turned ON, while if the voltage of the power source 10 is of a predetermined value or less, all the switches are simultaneously turned ON. Thus, if the voltage of the power source 10 is reduced, the voltage of the power source 10 can be applied directly to a load.