說到開關電源的難題， PCB cloth plate problems is not very difficult, but if want to cloth up a refined PCB must be one of the difficulties in switching power supply (PCB design is not good, may cause no matter how to debug parameter debugging cloth out of the situation, so not scaremongering) when reason was the PCB board consideration or a lot of, such as: 電氣性能、工藝路線、安全要求、EMC影響等； 在要考慮的因素中，電氣是最基本的，但EMC是最難理解的，很多項目的瓶頸都在於EMC。 下面從22個方向分享PCB板和EMC。

1、成熟的電路可以從容的PCB設計EMI電路

以上電路對EMC的影響可想而知，輸入濾波器在這裡； Lightning-proof pressure sensitivity; 電阻R102防止衝擊電流（帶繼電器減少損耗）； Key error mode X capacitance and Y capacitance with inductor filtering; 有保險絲影響安全板； 這些設備中的每一個都至關重要，應仔細了解每個設備的功能和作用。 The EMC severity level should be considered when designing the circuit, such as the number of filters to be set, the number and location of the y-capacitor quantity. The choice of pressure-sensitive size and quantity is closely related to our requirements for EMC. Welcome to discuss the seemingly simple EMI circuit that actually contains profound truths for each component.

2.電路和EMC：（最熟悉的反激式主拓撲，看電路的哪些關鍵部分包含EMC機制）

The circled parts in the circuit in the figure above are very important for EMC (note that the green part is not), such as radiation. It is known that electromagnetic field radiation is spatial, but the basic principle is the change of magnetic flux, which involves the effective cross-sectional area of magnetic field, namely the corresponding loop in the circuit. The electric current can produce a magnetic field, which is stable and cannot be converted into an electric field. 但是變化的電流會產生變化的磁場，變化的磁場也會產生電場（其實這是著名的麥克斯韋方程，我用的是通俗易懂的語言），變化的電場也會產生磁場場地。 所以一定要注意有開/關狀態的地方，這是EMC的來源之一，這是EMC的來源之一。 For example, the dotted line loop in the circuit is the opening and closing loop of the switch tube. Not only the switching speed can be adjusted during the design of the circuit, but also the area of the wiring loop of the layout board has an important influence on EMC! 另外兩個迴路是吸收迴路和整流迴路，先提前了解，再講！

3、PCB設計與EMC的關聯

1.PCB loop has a very important influence on EMC, such as flyback main power loop. If it is too large, the radiation will be poor.

2. Filter wiring effect, filter is used to filter out interference, but if PCB wiring is not good, filter may lose the effect it should have.

3、結構部分，散熱器設計接地不好會影響屏蔽版的接地；

4、敏感部分如果離干擾源太近，如EMI電路、開關管等，必然會導致EMC不良，需要有清晰的隔離區。

5、RC吸收迴路接線。

6.Y capacitor grounding and wiring, and the position of Y capacitor is also critical!

我將談論這個，我將更多地談論它，但我要給你一個線索。

這是一個簡單的示例：

如上圖中虛線框所示，X電容引腳接線已經縮進。 您可以學習如何在外部進行電容器引腳接線（使用擠壓電流接線）。 這樣，X電容的濾波效果才能達到最佳狀態。

4、PCB設計的準備：（如果你準備充分，設計可以一步步穩健，避免設計翻車重新開始）

There are roughly the following aspects, are their own design process to consider, all the content has nothing to do with other tutorials, are just their own experience summary.

1. Appearance structure size, including positioning hole, air channel flow direction, input and output socket, need to match with the customer system, also need to communicate with the customer assembly problems, height limit and so on.

2. Safety certification, products do what kind of certification, where do the basic insulation creepage distance to leave enough, where do strengthen the insulation to leave enough distance or slot.

3. Packaging design: there is no special period, such as preparation for customized packaging.

4、工藝路線選擇：單面板雙面板選擇，或多層板，根據原理圖和板子尺寸、成本等綜合評估。

5. Other special requirements of customers.

The structure and process will be relatively more flexible, safety regulations or relatively fixed part, what certification to do, what safety standards, of course, there are some safety regulations are common in many standards, but there are also some special products such as medical treatment will be more stringent.

For the new entry engineer friends are not dazzled;

Next list some general products general, the following is summarized for IEC60065 specific cloth requirements, for safety needs to keep in mind, encounter specific products will be targeted processing:

1、輸入保險絲焊盤距離安規要求大於3.0mm，實際板為3.5mm（簡單來說保險絲的爬電距離為前3.5mm，後3.0mm）。

2. Before and after the rectifier bridge, the safety requirements are 2.0MM, and the plate layout is 2.5MM.

3. After rectification, safety regulations generally do not require, but the distance between high and low voltage is left according to the actual voltage, and 400V high voltage is left above 2.0mm.

4、第一級安規要求6.4mm（電氣間隙），爬電距離7.6mm。 （注意這與實際輸入電壓有關，具體計算需參考表格，提供的數據僅供參考，以實際情況為準）

5. Cold ground and hot ground are clearly marked for the first stage; L、N標誌、INPUT AC INPUT標誌、熔斷器警告標誌等應清晰標明；

It is reiterated that the actual safety distance is related to the actual input voltage and the working environment, so it is necessary to refer to the table for specific calculation. The data provided is for reference only and shall prevail in the actual situation.

5. Consider other factors for PCB design safety

1. 了解他們的產品做了哪些認證，屬於哪些產品類別。 比如醫療、通訊、電力、電視等不同，但也有很多相似之處。

2、在安規中，了解與PCB板靠近的地方的絕緣特性，哪個地方是基本絕緣，哪個地方是加強絕緣，不同的標準絕緣距離是不一樣的。 最好檢查標準，可以計算電氣距離、爬電距離。

3. Focus on the safety devices of the product, such as the relationship between the magnetism of the transformer and the original side;

4. Radiator and surrounding distance problem, radiator insulation is not the same as the ground is not the same, the ground is cold, hot insulation is the same cloth.

5. Special attention should be paid to the distance of insurance, requiring the strictest place. The distance between front and rear of the fuse is consistent.

6. Y電容與漏電流和接觸電流的關係。

等等，它會詳細解釋如何保持距離，如何做安全要求。

6、電源佈局PCB設計

1.先測量PCB的尺寸和元器件的數量，這樣才能達到好的密度，不然密了，疏了就難看了。

2、電路模塊化，以核心器件為中心，先放關鍵器件。

3、裝置立式或臥式反定位，一是美觀，二是插拔操作方便，特殊情況可考慮傾斜。

4. Take cabling into consideration and arrange the layout in the most reasonable position for subsequent cabling.

5. 佈局時盡量減少環路面積。 這四個循環將在後面詳細解釋。

Do the above points, of course, flexible use, more reasonable layout will be born soon.

以下是我畫的第一張處女PCB，很多年前，很難完成，中間可能有一個小問題，但總體佈局值得學習：

In this figure, the power density is still relatively high. The control part of LLC, the auxiliary source part and the BUCK circuit driver (high-power multi-channel output) part are on the small board, which is not taken out. Let’s take a look at the layout characteristics of the main power:

1、輸入輸出端子固定，不可移動。 板子是長方形的。

這裡的佈局是從下到上，從左到右，散熱依賴於外殼。

2.EMI電路還是要明確流向，這一點很重要，否則不美觀，對EMC不利。

3. The position of large capacitor should consider PFC loop and LLC main power loop as far as possible;

4. The current of the side side is relatively large. In order to run the current and dissipate the heat of the rectifier tube, this layout is adopted. 高功率的頂層通常為負，底層為正。

Each board has its own characteristics, of course, also has its own difficulties, how to reasonably solve the key, we can understand the layout of reasonable selection of meaning?

7、PCB實例鑑賞

I think it is a good place to do it. Of course, there will always be defects, which can also be pointed out. It is not easy for a single panel to be so compact, so you can use this board to learn and discuss! 後面也會為這個板子講解學習，大家先欣賞一下。

8. Understanding of the four loops of PCB design :(the basic requirement of PCB layout is the small area of the four loops)

另外，吸收迴路（RCD吸收、MOS管的RC吸收和整流管的RC吸收）也很重要，也是產生高頻輻射的迴路。 如果您對上圖有任何疑問，歡迎討論。 我們不怕任何問題。

9、PCB設計熱點（浮電位點）和地線：

注意事項：

1. Pay special attention to hot spots (high-frequency switching points), which are high-frequency radiation points. Cable layout has a great impact on EMC.

2、熱點形成的迴路小，走線短，走線不要越粗越好，但只要電流足夠。

3. 地線必須單點接地。 主電源地和信號地分開，採樣地分開。

4、散熱器的地線需要連接到主電源地。