Requirements for Power PCB circuit board design 2021-11-09

In the making of circuit board ,PCB Design occupies a very important position , It can be said that a good printed circuit board is made from PCB The design started . Take the power supply for example ,PCB Design for power supply EMC performance 、 Output noise 、 Anti interference capability has a direct impact on . that , Power Supply pcb Do you know the requirements for board design ？ The following jetobang PCB Xiaobian will explain it to you .

spacing
Power Supply PCB It belongs to high voltage products , Line spacing must be considered , It is best if the spacing required by the corresponding safety regulations can be met , But those products that do not need certification and cannot meet certification , It depends on a wealth of experience to determine the spacing . How wide is the spacing ？ This needs to consider whether the production can ensure the cleanness of the board surface 、 ambient humidity 、 Other pollution, etc .
If it is mains power input , Even if the board surface can be kept clean 、 seal up ,MOS The source of the tube drain is close to 600V, Less than 1mm In fact, it is more dangerous .

Components at the edge of the board
In place PCB Edge of the chip capacitor or other easily damaged devices , Must consider PCB Plate splitting direction , As shown in the figure below, the stress magnitude of the device under different placement is compared .

From this we can see that , The device shall be far away from and parallel to the edge of the partition , Otherwise, it may be because PCB Component damage caused by plate splitting .

Loop area
Whether it's input 、 Output or power loop 、 Signal loop , The loop area should be as small as possible . The power loop emits electromagnetic fields , Will result in poor EMI Characteristic or large output noise , At the same time, if it is received by the control ring , It is likely to cause exceptions . On the other hand , If the power loop area is large , The equivalent parasitic inductance will also increase , May increase drain noise spikes .

Key routing
because di/dt effect , The inductance at the dynamic node must be reduced , Otherwise, strong electromagnetic fields will be generated .

The inductance can be reduced by reducing the wiring length , Increasing the width can also reduce , But the effect is small .

The signal line
When wiring the whole control part, it should be considered to be far away from the power part , If the two are close because of other restrictions , The control line should not be paralleled with the power line , Otherwise, the power supply may work abnormally 、 The phenomenon of oscillation .

In addition, if the control line is very long , A pair of lines that should be returned in the future , Or put both in PCB On both sides of the , Thus, the loop area is reduced , Avoid being disturbed by the electromagnetic field of the power part . As shown in the figure A、B Between two , Correct and wrong signal wiring methods .

reminder ： The signal line shall minimize the number of vias for connection .

Copper laying
Sometimes it is completely unnecessary to lay copper , You should even avoid . If the copper area is large enough and its voltage changes constantly , On the one hand, it may serve as an antenna , Radiate electromagnetic waves around ; On the other hand, it is easy to pick up the noise . It is usually only allowed to lay copper at static nodes , For example, for the output end “ The earth ” Node copper laying , The output capacitance can be increased equivalently , Filter out some noise signals .

mapping
For a loop , Can be in PCB One side of the is paved with copper , It will be based on PCB The wiring on the other side is automatically mapped , Minimize the impedance of this loop . It is like a group of impedance with different impedance values in parallel , The current will automatically select the path with the lowest impedance to flow through . It can be connected on one side of the control circuit , On the other hand “ The earth ” Node copper laying , The two surfaces are connected through a through hole .

Output rectifier diode
If the output rectifier diode is close to the output end , It should not be placed parallel to the output . Otherwise, the electromagnetic field generated at the diode will penetrate into the loop formed by the power output and the external load , Increase the measured output noise .

Ground wire
It has to be 100% Be careful with the wiring of the ground wire , A slight error may cause EMS、EMI Poor performance and other performance . About switching power supply PCB Of “ The earth ”, Here are two points to note ：
1. Power ground and signal ground , Single point connection shall be used ;
2. There should be no earth loop .

Y capacitance
Input and output are often connected to Y capacitance , Sometimes for some reason , It may not be possible to hang it on the input capacitor ground , At this time, remember , Be sure to connect to the static node , Such as high voltage end .

For power supply PCB Design in addition to the above requirements , There are other issues to consider , Include ：“ The varistor shall be close to the protected circuit ”、“ Common mode electrical induction increases discharge teeth ”、“ chip VCC Ceramic chip capacitance shall be added at the power supply ” wait . There is also copper foil 、 Whether special treatment is required for shielding, etc , These are all in PCB Problems to be considered during design .

The above is what Xiao Bian shared today “ Power Supply pcb What are the requirements for board design ”, Of course, what Xiaobian shares today is only the most common power supply PCB Design , Most engineers will choose the power module as the basis of system power supply , It can make the whole product or system stable 、 Reliable power supply .

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