开关电源的EMI整改经验处理对策

开关电源的EMI处理经验对策小结

王旭飞 2013/6/28

开关电源EMI整改中，关于不同频段干扰原因及抑制办法：

1MHZ以内----以差模干扰为主

1.增大X电容量；

2.添加差模电感；

3.小功率电源可采用PI型滤波器处理(建议靠近变压器的电解电容可选用较大些)。

1MHZ---5MHZ---差模共模混合，

采用输入端并联一系列X电容来滤除差摸干扰并分析出是哪种干扰超标并以解决，

1.对于差模干扰超标可调整X电容量,添加差模电感器，调差模电感量;

2.对于共模干扰超标可添加共模电感,选用合理的电感量来抑制；

3.也可改变整流二极管特性来处理一对快速二极管如FR107一对普通整流二极管1N4007。

5M---以上以共摸干扰为主，采用抑制共摸的方法。

对于外壳接地的，在地线上用一个磁环串绕2-3圈会对10MHZ以上干扰有较大的衰减作用;

可选择紧贴变压器的铁芯粘铜箔, 铜箔闭环.

处理后端输出整流管的吸收电路和初级大电路并联电容的大小。

对于20--30MHZ，

1.对于一类产品可以采用调整对地Y2电容量或改变Y2电容位置；

2.调整一二次侧间的Y1电容位置及参数值；

3.在变压器外面包铜箔；变压器最里层加屏蔽层；调整变压器的各绕组的排布。

4.改变PCB LAYOUT；

5.输出线前面接一个双线并绕的小共模电感；

6.在输出整流管两端并联RC滤波器且调整合理的参数；

7.在变压器与MOSFET之间加BEAD CORE；

8.在变压器的输入电压脚加一个小电容。

9. 可以用增大MOS驱动电阻.

30---50MHZ 普遍是MOS管高速开通关断引起，

1.可以用增大MOS驱动电阻；

2.RCD缓冲电路采用1N4007慢管；

3.VCC供电电压用1N4007慢管来解决；

4.或者输出线前端串接一个双线并绕的小共模电感；

5.在MOSFET的D-S脚并联一个小吸收电路；

6.在变压器与MOSFET之间加BEAD CORE；

7.在变压器的输入电压脚加一个小电容；

8.PCB心LAYOUT时大电解电容，变压器，MOS构成的电路环尽可能的小；

9.变压器，输出二极管，输出平波电解电容构成的电路环尽可能的小。

50---100MHZ 普遍是输出整流管反向恢复电流引起，

1.可以在整流管上串磁珠；

2.调整输出整流管的吸收电路参数；

3.可改变一二次侧跨接Y电容支路的阻抗,如PIN脚处加BEAD CORE或串接适当的电阻；

4.也可改变MOSFET，输出整流二极管的本体向空间的辐射（如铁夹卡MOSFET; 铁夹卡DIODE，改变散热器的接地点）。

5.增加屏蔽铜箔抑制向空间辐射.

200MHZ以上开关电源已基本辐射量很小，一般可过EMI标准。

补充说明:

开关电源高频变压器初次间一般是屏蔽层的,以上未加缀述.

开关电源是高频产品,PCB的元器件布局对EMI.,请密切注意此点.

开关电源若有机械外壳,外壳的结构对辐射有很大的影响.请密切注意此点.

主开关管,主二极管不同的生产厂家参数有一定的差异,对EMC有一定的影响.请密切注意此点.

Switching Power Supply EMI's experience in dealing with countermeasures Summary

EMI switching power supply reform, on a different frequency interference and suppression of the reasons:

1MHZ within ---- mainly to differential mode interference

1. X increased capacity;

2. Add differential mode inductors;

3. Low-power power supply PI-filter can be dealt with (the proposed transformer near the electrolytic capacitor can use some more).

1MHZ --- 5MHZ --- differential-mode-mode hybrid,

To adopt a series of parallel input X capacitor to filter out bad touch and analysis of the interference is a kind of excessive interference and to resolve,

1. Differential mode interference over the X adjustable capacitance, add differential mode inductors, poor transfer mode inductance;

2. For the common mode interference can add standard-mode inductors,

a reasonable choice to cur

b inductance;

3. Rectifier diodes can also be changed to deal with the characteristics of a pair of fast diode FR107 such as a pair of ordinary rectifier diode 1N4007.

5M --- to a total of more than touch the main interference, suppression of touch.

The shell of the earth, and in line with a magnetic ring around the string 2-3 circles will be more than 10MHZ interference attenuation greater role;

May choose to stick close to transformer core of the copper foil, copper foil closed.

For 20 - 30MHZ,

1. For a class of products that can be used to adjust for Y2 capacitance capacitors or change the location of Y2;

2. Adjustment of a secondary side of the inter-Y1 capacitance of the location and value;

3. Transformer outside the copper foil packets; transformer in the Canadian shield layer; adjustment of the transformer windings of the arrangement.

4. Changes in PCB LAYOUT;

5. Output line after another in front of around two-and small-mode inductors;

6. Rectifier output in parallel both ends of the RC filter and a reasonable adjustment parameters;

7. MOSFET in the transformer and between BEAD CORE;

8. Transformer at the foot of the input voltage capacitor, a small increase.

9. MOS driver can increase resistance.

30 --- 50MHZ is a universal high-speed control MOS arising from the opening turn-off,

1. MOS driver can increase resistance;

2.RCD buffer circuit 1N4007 slow pipe;

3.VCC supply voltage with 1N4007 slow to solve the tube;

4. Outputs, or two-line front-end and around a series of small-mode inductors;

5. MOSFET in the DS feet parallel to absorb a small circuit;

6. MOSFET in the transformer and between BEAD CORE;

7. Transformer in the input voltage capacitor, a small increase in foot;

8.PCB heart when LAYOUT large electrolytic capacitors, transformers, MOS circuit consisting of a small ring as much as possible;

9. Transformer, output diodes and output wave-electrolytic capacitor circuits consisting of a small ring as much as possible.

50 --- 100MHZ universal rectifier output is caused by reverse recovery current,

1. Rectifier in the string of beads;

2. Adjustment to absorb the output rectifier circuit parameters;

3. Can change a jumper secondary side of the Y capacitor slip resistance, such as PIN Department feet plus or BEAD CORE series of appropriate resistance;

4. Can also change the MOSFET, output rectifier diodes space radiation to the body (such as card Tiega MOSFET; Tiega card DIODE, then change the location of the radiator).

5. Inhibition to the increase in copper foil shield in space radiation. 200MHZ more than switching power supply has been basically a very small amount of radiation, generally over EMI standards.

Added:

High-frequency switching power transformer is usually the first

inter-shielding layer, reference is made up of more than not.

Is a high-frequency switching power supply products, PCB layout of the components of the EMI., Please pay close attention to this point.

If so, switching power supply machinery shell, the shell structure on a lot of radiation. Please pay close attention to this point.

The main control switch, the main manufacturer of diodes in different parameters have some differences, some of EMC. Please pay close attention to this point.