| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply of a primary side control system which improves a load response in the case of a sudden change from a light load to a heavy load.SOLUTION: At a primary side of a transformer T, an output voltage detection part 16 detects a change of a DC output voltage Vout, a control circuit 13 outputs a gate signal Vg in a frequency corresponding to the change of the DC output voltage Vout, and the DC output voltage Vout is stabilized. A sudden load change detection part 17 including capacitors C4 and C6, a capacitor C5 and/or a resistor R5 is provided and the sudden load change detection part 17 detects reduction of the DC output voltage Vout caused by the sudden load change. Thus, while the control circuit 13 performs switching control in a long cycle under the light load, the sudden load change detection part 17 detects the sudden load change without awaiting the timing for the detection until the switching of the next cycle and the frequency corresponding to the heavy load is made variable, thereby suppressing the reduction of the DC output voltage Vout in the sudden change to the heavy load.SELECTED DRAWING: Figure 1 |
