Many power supplies will make noise when they work. Next, let's analyze:
The first method that can effectively improve the output voltage noise of the switching power adapter is that engineers can use a chip three terminal capacitor and a common electrolytic capacitor at the output end of the adapter to improve the high-frequency characteristics of the filter. Before introducing the specific operation mode of this method, we need to first understand why the adapter has noise voltage peaks. Without any additional measures, the output end of the adapter usually contains a large noise voltage peak, which is caused by the imperfect characteristics of the electrolytic capacitor at high frequency. Because electrolytic capacitors can be equivalent to capacitors, resistors and inductors in series at high frequency, the bypass effect of capacitors on noise is not obvious at high frequency. Due to the existence of resistance and inductance, the noise voltage is reflected at the output of the switching power supply adapter.
After understanding the cause of the 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. The first method is to split the electrolytic capacitor at the output into several, that is, a large capacity electrolytic capacitor is replaced by several small capacity electrolytic capacitors in parallel. Although this proposal can not suppress the generation of noise voltage at all, the peak to peak value of signal noise voltage generated by the new method is smaller than the original one. The second method is to connect a small capacity high-frequency ceramic capacitor in parallel next to the electrolytic capacitor, and use the low capacitive reactance of the high-frequency capacitor at high frequency to greatly attenuate the output noise voltage. Of course, the ceramic capacitor on the printed circuit board should also maintain a relatively short wiring length and keep the line impedance as small as possible.
The second method that can effectively improve the output voltage noise of switching power adapter is that engineers can use high-performance surface mount filter to improve the noise peak. The internal circuit of the mount filter can be equivalent to a π type filter circuit. A mount high-performance filter is connected to the output end of the switching power adapter. Compared with the original output noise voltage peak, it will be greatly reduced. In the test, the noise voltage peak is almost displayed as a straight line on the oscilloscope, indicating that the noise of the output voltage has been significantly suppressed, Thus, the function of surface mount high performance filter in this circuit is well explained.
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