Some switching power supplies produce audio noise during the whole load test. Such as communication industry in the test standard of switching power supply, the dynamic load is defined as the period 1 ms, slope 0.1 A/s, according to 25% - 50% - _25%75% and 75% - _50% A two step load change rule, is the excitation converter, for example, the output inductor current the output current ripple and step current of two parts, the current ripple frequency and the heaven same frequency of the power supply, general won't produce audio noise, and step current cycle and A given step load cycle is consistent, when the relatively small output capacitance, step current di/dt rate is too high, At this time, the solution to audio noise is to increase the output capacitance. Due to the limitation of the internal volume of the power supply, the output capacitance can't be very large in general. At this time, we can also try to delay the reaction time of the loop, and correspondingly reduce the rate of current change, so as to play a certain inhibitory role. However, it should be noted that the reaction time of the delayed loop will make the overshot or drop of the output voltage much larger, which is also a compromise issue.