| US 7,564,196 B2 | ||
| Power supply device, and LED device and electronic device using same | ||
| Yohichi Shiwaya, Toyonaka (Japan); Toshiki Kishioka, Toyonaka (Japan); and Koichi Hagino, Kawanishi (Japan) | ||
| Assigned to Ricoh Company, Ltd., Tokyo (Japan) | ||
| Filed on Mar. 14, 2008, as Appl. No. 12/48,968. | ||
| Claims priority of application No. 2007-070932 (JP), filed on Mar. 19, 2007. | ||
| Prior Publication US 2008/0231209 A1, Sep. 25, 2008 | ||
| Int. Cl. H05B 37/02 (2006.01) | ||
| U.S. Cl. 315—291 [315/209 R; 315/307; 323/234; 323/282] | 10 Claims |
| 1. A power supply device, comprising:
a step-up circuit configured to supply a driving voltage to a load and include multiple operation modes each outputting a
given voltage not lower than a power source voltage;
a comparison circuit configured to compare an output voltage from the load with a reference voltage; and
a control circuit configured to control the step-up circuit to operate in one of the multiple operation modes based on a comparison
result generated by the comparison circuit;
wherein the control circuit maintains a current operation mode of the step-up circuit until the output voltage from the load
decreases to below the reference voltage and, when the output voltage from the load is less than the reference voltage, switches
the operation mode to another operation mode to output a voltage higher than a voltage output in the current operation mode.
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