The power-supply unit of on vehicle light tool which has the DCDC converter and this DCDC converter

摘要

P To vary on-duty for regulating the operation of a switch in response to a switching frequency. PSOLUTION: A DC-DC converter includes a control unit 16 which controls a voltage step-down switch 18 and a voltage step-up switch 28. The control unit 16 turns ON and OFF the voltage step-down switch 18 and turns OFF the voltage step-up switch 28 in a voltage step-down mode satisfying Ve1 Vo, turns ON the voltage step-down switch 18 and turns ON and OFF the voltage step-up switch 28 in a voltage step-up mode satisfying Ve1 Vo, and turns ON the voltage step-down switch 18 and turns OFF the voltage step-up switch 28 in a conductive mode satisfying Ve1≈ Vo. The control unit 16 also changes a switching frequency in a range of 2 to 250 kHz through comparison between comparison waves A to E periodically changing upper limit values A1 to E1 and an error voltage Ve2 and turns ON and OFF the voltage step-down switch 18 in response to an on/off signal with approximately 100% on-duty or turns ON and OFF the voltage step-up switch 28 in response to an on/off signal with approximately 0% on-duty at the time of switching between the voltage step-down mode and the conductive mode or between the conductive mode and the voltage step-up mode. PCOPYRIGHT: (C)2010 and JPO& INPIT