| 摘要 |
<p>A power supply device is provided with a charge pump circuit (54), which generates a desired output voltage (Vo) from an input voltage (Vi) and supplies a load (LED) with the output voltage, by periodically turning on/off a plurality of charge transfer switches (Q1-Q4) corresponding to clock signals (c1, c2) and by charging/discharging a charge accumulating capacitor (C1); an output current detecting circuit (57) for detecting an output current (Io) (reference current (Im) in Fig. 1) to the load; and a clock signal control means (frequency converting circuit (52) in Fig. 1) for variably controlling the frequency of the clock signals (c1, c2) based on the detection results of the output current (Io). Thus, the power efficiency is improved corresponding to the level of the load.</p> |
