Voltage noise improvement method of power adapter,adapter manufacture

　　  During the normal operation of the power adapter, once the output voltage noise occurs, it will not only interfere with the system operation, but also lay a hidden danger for safe operation. So what are the ways to improve the voltage noise? Let's follow the manufacturer to find out!

　　   The first method that can effectively improve the output voltage noise of the desktop power adapter is that engineers can use a combination of chip three-terminal capacitors and ordinary electrolytic capacitors at the output of the high-power power adapter to improve the high-frequency characteristics of the filter. Before introducing 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 of the adapter will often contain large noise voltage peaks due to the imperfect characteristics of electrolytic capacitors at high frequencies. Because electrolytic capacitors can be equivalent to the series connection of capacitors, resistors and inductors at high frequencies, the bypass effect of capacitors on noise is not obvious at high frequencies. Due to the existence of resistance and inductance, the noise voltage is reflected in the output end of the switching power adapter.

　　  After understanding the cause of the output noise peak, in order to better suppress the output noise of the power adapter, there are usually two methods that can be used by product developers.

　　  Method 1: Disassemble the electrolytic capacitors at the output end into several pieces, that is, replace a large-capacity electrolytic capacitor with several small-capacity electrolytic capacitors in parallel. Although this proposal cannot suppress the generation of noise voltage fundamentally, the peak-to-peak value of the signal noise voltage produced by the new method is smaller than the original one.

　　Method 2: A small-capacity high-frequency ceramic capacitor is connected in parallel next to the electrolytic capacitor, and the output noise voltage is greatly attenuated by using the low capacitive reactance of the high-frequency capacitor at high frequencies. Ceramic capacitors should also keep trace lengths relatively short, keeping the trace impedance as low as possible.

　　   The second method that can effectively improve the output voltage noise of the power adapter is that engineers can use high-performance surface mount filters to improve the noise peak situation. The internal circuit of the mounted filter can be equivalent to a π-type filter circuit. A mounted high-performance filter is connected in series at the output end of the switching power adapter. Compared with the original output noise, the voltage peak value will be greatly reduced. In the test, the noise The voltage peak appears almost as a straight line on the oscilloscope, which shows that the noise of the output voltage has been significantly suppressed, which is a good illustration of the role of the surface mount high performance filter in this line.

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