Do you know how to use component layout to improve circuit board EMI?

How to improve the EMI of the circuit board? What method do you know? In the design of switching power supply PCB, electromagnetic interference is a headache for engineers! After designing the circuit structure and device location, controlling the EMI of the PCB is crucial to the overall design. Very important. So how to avoid PCB electromagnetic interference in switching power supplies? Today I will introduce to you how to control EMI through component layout control. Friends who want to know more should not miss it~

Component layout practice has proven that even if the circuit schematic is designed correctly and the printed circuit board is improperly designed, it will have an adverse impact on the reliability of electronic equipment. For example, if two thin parallel lines on a printed circuit board are very close to each other, a delay in the signal waveform will be formed, and reflected noise will be formed at the terminal of the transmission line; interference caused by insufficient consideration of the power supply and ground wires will cause the product to malfunction. Performance degrades, so care should be taken to adopt the correct approach when designing printed circuit boards.

Every switching power supply has four current loops:

(1), power switch AC circuit;

(2) Output rectifier AC circuit;

(3) Input signal source current loop;

(4) The output load current loop input loop charges the input capacitor through an approximately DC current. The filter capacitor mainly plays a broadband energy storage role; similarly, the output filter capacitor is also used to store high-frequency energy from the output rectifier. At the same time, the DC energy of the output load loop is eliminated. Therefore, the terminals of the input and output filter capacitors are very important. The input and output current loops should be connected to the power supply only from the terminals of the filter capacitor respectively; if the connection between the input/output loop and the power switch/rectifier loop cannot be connected to the capacitor terminals are directly connected, the AC energy will be radiated to the environment by the input or output filter capacitor.

The AC loop of the power switch and the AC loop of the rectifier contain high-amplitude trapezoidal currents. The harmonic components of these currents are very high. Their frequencies are much greater than the fundamental frequency of the switch. The peak amplitude can be up to 5 times the continuous input/output DC current amplitude. The transition time is usually About 50ns. These two loops are most likely to produce electromagnetic interference, so these AC loops must be laid out before other printed circuits in the power supply. The three main components of each loop, filter capacitors, power switches or rectifiers, and inductors or transformers, should be connected to each other. Place components adjacent to each other, positioning the components so that the current path between them is as short as possible. The best way to establish the layout of a switching power supply is similar to its electrical design. The best design process is as follows:

Place the transformer

Design power switch current loop

Design output rectifier current loop

Control circuit connected to AC power circuit

Design the input current source loop and input filter. Design the output load loop and output filter. When laying out all components of the circuit according to the functional units of the circuit, the following principles must be followed:

(1) First consider the PCB size. When the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase; if it is too small, the heat dissipation will be poor, and adjacent lines will be susceptible to interference. The best shape of the circuit board is rectangular, with an aspect ratio of 3:2 or 4:3. The components located on the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board.

(2) When placing devices, consider future welding and do not place them too densely.

(3) Take the core component of each functional circuit as the center and lay out around it. Components should be arranged evenly, neatly and compactly on the PCB, minimize and shorten the leads and connections between components, and decoupling capacitors should be as close as possible to the VCC of the device.

(4) For circuits operating at high frequencies, the distribution parameters between components must be considered. In general circuits, components should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to assemble and weld, and easy to mass produce.

(5) Arrange the position of each functional circuit unit according to the flow of the circuit, so that the layout facilitates signal circulation and keeps the signal in the same direction as possible.

(6) The first principle of layout is to ensure the routing rate of wiring. When moving devices, pay attention to the connection of flying wires and put connected devices together.

(7) Reduce the loop area as much as possible to suppress the radiated interference of the switching power supply. The above are some methods on how to control and suppress the electromagnetic interference in the PCB circuit board through the placement and layout of components. A slight mistake in these steps may cause the EMI of the product to fail, so it is very necessary to fully understand it. The above are some methods to improve the EMI of the circuit board. I hope it can help you.