POWER SUPPLY DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a power supply device which can avoid the malfunctioning of a lighting circuit which is caused by noise inputted from the output terminal of a step-up circuit without adding a filter circuit. SOLUTION: A DC voltage from a DC power supply 1 is converted and supplied to a discharge lamp La by a lighting circuit 2. A detection unit 3 for detection of a load state and a filter circuit 4 for high frequency choking are inserted between the lighting circuit 2 and the discharge lamp La. The lighting circuit 2 is controlled by a control circuit 5 in accordance with the load state obtained by the detection unit 3. A step-up circuit 6 is connected to the. lighting circuit 2 and the output voltage of the step-up circuit is applied to the discharge lamp La via a pulse generating circuit 7. One end of a capacitor C1 connected between the output terminals of the step-up circuit 6 is connected in common to the detection unit 3 and one of the output terminals of the lighting circuit 2 and grounded. Therefore, even if noise is mingled between the step-up circuit 6 and the pulse generating circuit 7, the noise does not pass through the detection unit 3 and hence the load state can be detected accurately.