Most applications of the equipment meet the requirements of standard EMC, with only one exception for non-standard EMC. Therefore, it is non-standard. EMC can be regarded as a part of the standard EMC filling and optimization and cannot be used as a separate way and method to get rid of the standard EMC structure EMC standard design and rectification measures EMC design rectification measures before implementation and improvement. Therefore, the non-standard EMC design and rectification measures are also based on the conclusion that the non-standard EMC is considered together.
Normative non-standard EMC design and rectification measures are equivalent to normative or non-standard treatment equipment. The operational failure of EMC affecting the environment is equal to flood. In the early stage of planning, namely schematic diagram and schematic diagram. PCB perfect design specification non-standard EMC design can prevent and deal with the vast majority of electromagnetic compatibility, which is a problem between the lowest cost governance. The rectification in the EMC test is only the repair and improvement after the flood. Fluctuation is the root cause of errors, and reducing or eliminating fluctuations is the governance principle. EMC design and countermeasures have three methods: dredging, blocking and treatment.
1. One of EMC's countermeasures: sparse
Dredging is to reduce the influence current entering the sensitive circuit by reducing the impedance of other ways. It can also be divided into two types: dirty land protection and weak housing
1.1 Dirty ground maintenance
Dirty ground maintenance should take the ground plane as the basic approach, and bypass the influence current, so it is also called dirty ground. This method should develop a corresponding plan before planning, and evaluate all possible impacts of all systems under the limited cost PCB specification, but for non-standard systems, EMC, the least physical channel in the middle of all cable sockets includes all affected components.
The first step is to clarify the way of dirty ground, that is, the path from the impact channel to the internal reference ground and PE protection area of the middle PCB at the exit, so as to avoid the sensitive area. The following countermeasures can be taken:
1) There should be capacitance from the cable socket to the reference ground or E plane to determine this capacitance. The Y capacitor and the jumper capacitor between different areas should keep the dirty ground as short as possible to avoid the signal wiring and chips in sensitive areas such as protection, control and communication.
2) If the PCB is divided into multiple protection areas, a certain bridging capacitance or Y capacitance is required to avoid affecting the probability of current flowing to the power line as much as possible.
3) The embedded cable has multiple socket capacitors. Y decouples or spreads capacitive coupling according to the chip, protection device, power line, etc. to improve the candidate's dirty ground mode and prevent impact. EMC design needs to understand this more.
4) The non-standard EMC dirty ground also includes the signal and power plane near the power cable socket.
5) Sensitive signal wiring and countercurrent should be far away from all predictable impact paths, and the smaller the part parallel or overlapping with the impact path, the better.
6) Adding capacitor to the empty pin of non-standard EMC cable interface can increase the additional impact on the drainage channel.
7) Non-standard EMC can avoid the total number and length of signal cables as much as possible, which can effectively reduce the impact of current flowing through PCB.
The second step is to reduce the impedance of dirty ground as much as possible, so that it can drain most of the affected current (. The following countermeasures can be taken:
1) The reference ground plane and PE plane of each area of PCB should be large enough to prevent termination or slotting, and the number of layers should be sufficient. The position of solid through-holes, especially near cable sockets (that is, affecting current exit), should be sufficient and comprehensive to ensure low impedance.
2) Note that the surface PE has high current, plane and continuity due to the skin effect.
3) Non-standard EMC dirty ground also includes power supply plane, so it is necessary to understand the integrity of Shenyuan plane, especially near the cable plug, to ensure low impedance.
4) The impedance of Y capacitance, cable interface capacitance and jumper capacitance from both sides to the ground power supply, PE plane or power line should be as small as possible.
5) Non-standard EMC raising or expanding Y capacitance may have a negative effect because it will expand the influence current of Y capacitance. Therefore, do not blindly place or increase Ya capacitance, and try to remove unnecessary Y capacitance. The Y capacitance value near the power cord socket should be as small as possible during the standardized EMC test.
1.2 Protect the weak and give up the strong
Weak protection and strong rejection: in other error-free or strong anti-interference circuits (such as filtering effect, high voltage), additional influence drainage methods are added according to the coupling mode of Y capacitance or jumper capacitance to reduce the influence separation of the affected area. It should be noted that it is not necessary to affect the normal operation of the introduced part. Or add ground capacitance on other non-influenced hazard signals in the same area. The capacitance part should be close to the cable socket. non-standard EMC design needs to know this more.
2. EMC countermeasure 2: blocking
This is only an alternative. Whether to adopt the EMC evaluation test conclusion should be based on the actual situation. Remember not to turn strength into weakness. On the contrary, blocking and correction are reduced by enlarging the influence path impedance of the sensitive area. According to the influence current of path 5, it can be divided into population jam and outlet jam.
2.1 Channel blocking
If the channel is blocked, the impedance will be expanded on the only way to affect the source of current introduction. This scheme requires impedance in schematic diagram and schematic diagram. PCB design considerations include: 1) isolation measures for sensitive signal enhancement, improving the path impedance through optical, capacitive or magnetic coupling isolation;
2) Reduce or delete the physical capacitance across the received sensitive area:
3) Add common-mode inductance, magnetic beads, etc. at the power supply and its signal connection
4) Non-standard EMC inevitably affects the discharge of current from the signal cable, so the power line needs to have sufficient filtering measures, such as RC, LC, common-mode inductance, etc. The capacitor in the power line should be close to the cable socket as far as possible to prevent the overlapping of the affected current and sensitive signal wiring.
2.2 Outlet plug
When the outlet is blocked, the impedance will increase to the area where the current flows from the sensitive circuit. This scheme is usually used for equipment. EMC has made the following rectification for the impact problems in the test:
1) Add common-mode inductance and small resistance of magnetic beads at the entrance and exit of the affected hazard signal;
2) For non-standard EMC equipment above, power line decoupling capacitor or protective device shall be added between cable socket.
3. EMC countermeasure 3: treatment
According to the overlap between the wiring and the dirty ground path, and the phenomenon that the wiring itself affects the path, the capacitance should be increased or reduced, and the resistance should be added in the middle of the inductance or magnetic beads that affect the high resistance of the frequency band. The signal wiring around the EMC signal socket must increase enough capacitance, reduce the current of PCB signal wiring and signal cable affecting the high frequency band, or connect the resistance, inductance or magnetic beads in series after the capacitance. For the treatment of headache, foot pain, and where there is a problem, add capacitance or series resistance. This scheme is applicable to the rectification. Generally, when there is an impact problem in the test, EMC will carry out the rectification S:
1) For the increased capacitor, the resistance part should overlap with the influence current;
2) The larger the capacitance is, the better. The equivalent series inductance plus the equivalent inductance of the signal wiring should be selected. The resonant frequency of the capacitance value is within the range of the working frequency;
3) The root cause of the error is the noise of the ground plane, and adding capacitors can not solve the problem with certainty:
4) Non-standard EMC, expanding the capacitance around the signal socket may be counterproductive, because it will expand the impact of current in the signal. Therefore, appropriate capacitance value should be selected, or resistance and magnetic beads should be connected after the capacitance.
4. Summary of EMC countermeasures
See Table 1 for various EMC design and rectification measures, steps taken and priorities.
Table 1. Phases of EMC countermeasures and suggestions
It is recommended to use equipment R&D to design EMC evaluation and design process, as shown in Figure 1.
Figure 1. Standard&non-standard EMC evaluation design process
EMC recommends using the test rectification link. The steps of EMC rectification measures are shown in Figure 2
Figure 2. Standard&non-standard EMC test rectification process
From the analysis of non-standard EMC, we can see that most common EMC design and rectification measures can also be applied to non-standard EMC, but some standard EMC measures will also increase the risk of non-standard EMC, and non-standard EMC also has special points to pay attention to in electronic design. When evaluating the performance of EMC in product design, we should not only consider its performance on standard EMC, but also evaluate its ability on non-standard EMC. Some equipment with a wide range of applications and complex use environment and operation mode need to add non-standard EMC related design and test. Non-standard EMC is the supplement and improvement of standard EMC. The application of non-standard EMC enables the equipment to show strong EMC capability and applicability in more complex and harsh electromagnetic environment, thus effectively improving the technical advantages and product competitiveness of the equipment.