How to adjust switching power adapter voltage noise?

Switching Power Adapter in the process of working, is easy to be affected by the surrounding electromagnetic environment, resulting in unstable performance and other problems, so how to adjust the switching power adapter voltage noise? The following power adapter manufacturer YHY for you to explain in detail.

The first method that can effectively improve the output voltage noise of the switching Power Supply Adapter is that engineers can use a chip three-terminal capacitor combined with an ordinary electrolytic capacitor at the output end of the adapter to improve the high-frequency characteristics of the filter. Before we look at the specific mode of operation of this method, we need to first understand why the adapter has noise voltage spikes. Without any additional measures, the output end of the adapter usually contains a large peak noise voltage, which is caused by the imperfect characteristics of electrolytic capacitors at high frequencies. Because the electrolytic capacitor can be equivalent by series of capacitor, resistor and inductor at high frequency, the capacitor's bypass effect on noise is not obvious at high frequency. Due to the presence of resistance and inductance, the noise voltage is reflected in the output of the switching power adapter instead.

After understanding the cause of output noise peak, in order to better suppress the output noise of switching power adapter, there are usually two methods that can be adopted by product developers. Method one is to split the output electrolytic capacitor into several, that is, a large-capacity electrolytic capacitor is replaced by several small-capacity electrolytic capacitors in parallel. Although this suggestion can not inhibit the generation of noise voltage fundamentally, the peak-peak value of noise voltage produced by the new method is smaller than the original one. Method two is to parallel a small capacity of high frequency ceramic capacitor next to the electrolytic capacitor, the use of high frequency capacitor at high frequency reflected in the low reactance, so that the output noise voltage is greatly attenuated, of course, the ceramic capacitor on the printed circuit board should also maintain a relatively short wiring length, to maintain as small as possible line impedance.

A second way to improve the output voltage noise of Switching Power Adapters is to use high-performance surface-mount filters to improve the noise peaks. The internal circuit of the mount filter can be equivalent to a π type filter line, and a high performance filter is mounted on the output string of the switching power adapter. Compared with the original output noise voltage peak value, the peak noise voltage is almost displayed as a straight line on the oscilloscope in the test, which indicates that the noise of the output voltage has been significantly suppressed. The function of surface-mounted high performance filter in this circuit is explained.