Patent ID: 7948299

Claim:
A power supply apparatus for performing constant current driving of a load circuit, comprising: a constant current circuit which is disposed on a path for driving the load circuit; a voltage generating circuit structured to output a driving voltage to the load circuit; and a monitoring circuit structured to monitor a voltage across the two ends of the constant current circuit; wherein the monitoring circuit includes a threshold voltage source structured to generate a threshold voltage that follows the fluctuation of the voltage at which the constant current circuit can operate stably, and wherein the monitoring circuit structured to control the voltage generating circuit on the basis of a result obtained by comparing the voltage across the two ends of the constant current circuit and the threshold voltage generated by the threshold voltage source, wherein the voltage generating circuit is a charge pump circuit which switch among a plurality of boosting ratios, and a boosting ratio of the charge pump circuit is switched on the basis of a result of voltage comparison of the monitoring circuit.