Power supply apparatus for light source

摘要

A power supply apparatus for a light source includes an input-side rectifier (32) which converts an input AC signal to a DC signal, and a high-frequency inverter (36) which converts the DC signal to a high-frequency signal. An output-side rectifier (42) converts the high-frequency signal to a DC output signal for application to the light source. Power detecting means (52) detects the power supplied to the light source through the application of the DC output signal thereto, and develops a power representative signal. A control circuit (38), a summer (54) and an error amplifier (58) cooperate to control the high-frequency inverter (36) in accordance with the power representative signal in such a manner that power of a predetermined value can be supplied to the light source. An input current detector (60) detects the input AC signal current value and develops an input current representative signal. When the input current representative signal is smaller than a predetermined input current reference value, a summer (62) and an error amplifier (66) cooperate to provide the summer (54) with such a control signal as to maintain the input AC signal current value at a predetermined value.