source:Industry News Popular:adapter release time:2022-04-22 09:53:29 Article author:yu
After designing the circuit structure and device location, the EMI control of the PCB becomes extremely important for the overall design. How to avoid PCB electromagnetic interference in switching power supplies has become a topic of great concern to developers. In this article, Senshuqiang Electronics will introduce how to control EMI through the control of component layout.
Component layout practice has proved that even if the circuit schematic design is correct, the printed circuit board is not properly designed, which will adversely affect the reliability of electronic equipment. For example, if the two thin parallel lines of the printed board are very close, the delay of the signal waveform will be formed, and the reflection noise will be formed at the end of the transmission line; The performance is degraded, so care should be taken to use the correct method when designing the printed circuit board.
Each switching power supply has four current loops:
1. Power switch AC circuit;
2,
3. Output rectifier AC circuit;
4.
3. Input signal source current loop;
4. Output load current loop The input loop charges the input capacitor through an approximate DC current, and the filter capacitor mainly plays the role of a broadband energy storage; similarly, the output filter capacitor is also used to store the high-frequency energy from the output rectifier, while eliminating the Output the DC energy of the load circuit. Therefore, the terminals of the input and output filter capacitors are very important, and the input and output current loops should be connected to the power supply only from the terminals of the filter capacitors; if the connection between the input/output loop and the power switch/rectifier loop cannot be The terminals are directly connected, and the AC energy will be radiated into the environment by the input or output filter capacitors.
The AC loop of the power switch and the AC loop of the rectifier contain high-amplitude trapezoidal currents with high harmonic content, the frequency of which is much higher than the switching fundamental frequency, the peak amplitude can be up to 5 times the amplitude of the continuous input/output DC current, and the transition time is usually about 50ns. These two loops are most likely to generate electromagnetic interference, so these AC loops must be laid out before other traces in the power supply are routed. The three main components of each loop, filter capacitors, power switches or rectifiers, inductors or transformers, should be connected to each other. Place them next to each other, adjusting the position of the components so that the current paths between them are as short as possible. The best way to establish a switching power supply layout is similar to its electrical design, and the best design flow is as follows:
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