DC-DC converter with reduced energy loss under lowered load impedance

摘要

The DC-DC converter is provided which comprises a switching element 3 connected in series to a DC power source 1 and a primary winding 2a of a transformer 2; a control circuit 10 for turning the switching element 3 alternately ON and OFF; a second output smoothing circuit 7 connected to a drive winding 2c of the transformer 2 for supplying electric power to the control circuit 10; and a voltage control circuit 26 for detecting output voltage of the drive winding 2c under a trigger level V_ON for driving the control circuit 10. The control circuit 10 is operable and inoperable when voltages of a trigger level V_ON and an inoperative level V_OFF respectively are applied on the control circuit 10. When the load impedance is remarkably lowered, the voltage control circuit 26 can be operated to decrease the output voltage of the second output smoothing circuit 7 to the inoperative level V_OFF for ceasing operation of the control circuit 10 when the second output smoothing circuit 7 is electrically charged to the trigger level V_ON through the trigger circuit 11.