English
简体中文
EnglishDuring the normal operation of the switching smart adapter, once the output voltage noise occurs, it will not only interfere with the work of the system, but also bury hidden dangers for safe operation, requiring engineers to take timely countermeasures. This article will introduce two solutions that can effectively improve the output voltage noise of switching power adapters. Let's take a look.
The first method that can effectively improve the output voltage noise of switching power adapters is that engineers can use a combination of chip three-terminal capacitors and ordinary electrolytic capacitors at the output of the 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 peaks in noise voltage 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 switching power adapter, there are usually two methods that can be used by product developers. The first method is to disassemble the electrolytic capacitors at the output end into several parts, that is, a large-capacity electrolytic capacitor is replaced by several small-capacity electrolytic capacitors in parallel.
Although this proposal cannot fundamentally suppress the generation of noise voltage, the peak-to-peak value of the signal noise voltage produced 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 frequencies to greatly attenuate the output noise voltage. 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 switching power adapters is that engineers can use high-performance surface-mount filters to improve the noise peaking 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, indicating 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.
