| 摘要 |
PROBLEM TO BE SOLVED: To make the detection point of the overcurent of a main output constant irrespective of the load state of an auxiliary output in a switching power supply which comprises a plurality of output circuits. SOLUTION: Main outputs from a plurality of secondary windings at an identical transformer and a plurality of auxiliary outputs are taken out. A voltage control signal based on a main output voltage is fed back to a control circuit 4. The pulse width of a primary-winding current is modulated. The main output voltage is stabilized. The pulse width is controlled by an overcurrent signal based on the overcurrent state of a primary winding. The main output voltage is droped. Current detection parts 12 to 1n are installed respectively at respective auxiliary output circuits. An adder 2 is installed. Outputs of the respective current detection parts are added. A subtractor 3 is installed. The output of the adder 2 is subtracted from the output of a current detection part 11 at the primary winding. An overcurrent detection signal is generated when the output of the subtractor 3 exceeds a prescribed threshold value in an amplifier 6 which is installed at the control circuit 4. Thereby, the overcurrent detection signal is generated on the basis of only the overcurrent state of a main output circuit. |
