SWITCHING POWER SUPPLY UNIT

摘要

PROBLEM TO BE SOLVED: To provide a switch overcurrent protecting circuit to the instance of an electric-discharge lamp start without causing loss or component increase, in a switch power supply for an electric-discharge lamp. SOLUTION: In a DC-DC converter 1, the output voltage is detected by an output voltage detecting circuit 2, and the output current or a current in the converter 1 which is nearly equivalent to the output current is detected by an output current or equivalent current detecting circuit 3. The output is controlled by a control circuit 4. The output of the detector circuit 3 increases according to the output load. When an output peak reaches a specified value of a switch current peak limiting circuit 5, it operates in such a manner that the switch current peak in the converter 1 is not instantaneously increased further.