As all electronic engineers must know, PCB design plays an important role in design. Taking power supply as an example, PCB design will directly affect the EMC performance of power supply, output noise, anti-interference ability, and even basic functions. The PCB wiring in the power supply is slightly different from other hardware. How to design it?
For high voltage products, line spacing must be taken into account. The spacing to meet the safety requirements is of course the best, but in many cases the spacing is determined by experience for products that do not require or are not able to meet the certification requirements.
How wide is the spacing suitable? Must consider whether the production can ensure that the panel cleaning, environmental humidity, other pollution and so on.
For power input, even if the plate can be guaranteed clean, sealed, MOS pipe drain between nearly 600V, less than 1mm in fact is more dangerous!
Board edge component
At the edge of the PCB patch capacitor or other easily damaged devices, the direction of the PCB splitter must be taken into account when placing, such as the figure is a variety of placement methods, the device is subjected to a comparison of the size of the stress.
It can be seen that the device should be far away from and parallel to the edge of the splitter, otherwise it may be damaged because of the PCB splitter.
whether input or output, power loop or signal loop, should be as small as possible. The power loop emits electromagnetic field, which will result in poor EMI characteristics or large output noise, and may cause anomalies if received by the control loop. On the other hand, if the power loop area is large, the equivalent parasitic inductance will increase, which may increase the peak of leakage noise.
For the whole control part, we should consider keeping it away from the power part. If the two are close due to other restrictions, the control line should not be parallel with the power line, otherwise it may lead to abnormal operation of the power supply and oscillation.
In addition, if the control line is very long, the back and forth pair of lines should be approached, or the two lines should be placed on the two sides of the PCB and are facing each other, so as to reduce the loop area and avoid interference by the electromagnetic field of the power part. Figure 2 illustrates the correct and wrong signal wiring method between two points of AHB.
Sometimes copper is completely unnecessary and should even be avoided. If the area of copper is large enough and its voltage is constantly changing, on the one hand it may be used as an antenna to radiate electromagnetic waves around it.
on the other hand, it can easily pick up noise. Copper is usually only allowed at static nodes, such as "floor" nodes at the output end, which can be equivalent to increasing the output capacitance and filtering out some noise signals.