Dephir Electronics & Technical Kunshan Co., LTD
Technical Support

Technical Suports


Dephir Electronics & Technical (Kunshan) Co.,LTD 

Tel: +86-512-57821163 ext:601

Mobile:+86-15850300213 (Jacky)


Post code:215300 

Position: Home > Technical Suports > Basic Knowledge
Basic Knowledge

Basic knowledge of EMI filter

Ⅰ. Our power filters are designed in compliance with IEC60939-2《passive filter units for which safety tests are appropriate-tests methods and general requirements 》and UL1283《Electromagnetic interference filters》.

Ⅱ. Our filters are passive low-pass filters composed of passive components(L, C, R) , and based on the theory of impedence mismatch between the filter and the filter input. With a filtering range between 10KHz and 30MHz, filters supplied by our company can efficiently suppress the electromagnetic interference along power lines.

Ⅲ. Electromagnetic interference(EMI)
Electromagnetic interference is such electromagnetic signal which can degrade the performance of equipments, devices or systems。
With the rapid development of electronic technology, electronic equipments, electromagnetic equipments and industrial control devices are widely used, as a result electromagnetic interference (EMI) which causes serious problems to surrounding equipments, such as malfunction, crash , performance degradation and greatly life shorten becomes more and more serious.
Electromagnetic interference (EMI) on the whole could be divided into conducted interference, radiated interference, etc. Power filters are the key components to solve the conducted interference which includes common mode interference and differential mode interference, shown as below:


Dephir Elctronics


Connection between the load which creates noise and power supply network are shown as the diagram above. Both the load and power supply network have line (L), neutral line (N) and earth line (E), therefore the EMI noise along power line includes two parts: L and N for differential mode interference(DM), L(or N) and E for common mode interference (CM).

IV.Basic technical data of EMI filters
1. Rated voltage
Rated voltage means the voltage when EMI filter is working under the appointed frequency.
2. Rated current
Rated current means the maximal allowable continuous current when EMI filter is working under the appointed frequency, rated voltage and appointed ambient temperature (It is 40℃ if not specially indicated). The calculation formula of allowable current of EMI filter is as the following:



Dephir Elctronics

IN- - - - - - -Nominal Rated current
Θ- - - - - - -Ambient temperature

3. Leakage current
Leakage current is the current passing through phase line or neutral line to ground when rated voltage is applied to the filter. The testing principle is as the following:


Dephir Elctronics


Note: Considering safety factors as well as different standard requirements of different industries in different countries, we can design EMI filters which meet your special leakage current requirement.
4. Test voltage
Test voltage means the test voltage of line to line and line to ground

Notes :
(1) Test method: The voltage should start from zero, then rise to test voltage slowly with a speed lower than 150V/S and last for 1 minute, the following phenomena shouldn’t occur such as filter sparking, breakthrough, damage, etc.
(2) We implement voltage test for all the filters sent out. Customers should not repeat to apply test voltage to filters for many times.
(3) Once the test is done, please make sure to drop the voltage to zero and discharge the voltage of the internal components of filter through a suitable resistor.

5. Insertion Loss
Insertion loss measures the performance of a filter, reflecting filters’ ability to attenuate interference signal. It is the ratio of terminal voltage before filter is inserted to that when filter is inserted (measured in dB). It is tested on empty load and 50Ω- 50Ωaccording to the international standard UL1283,the formula is as the following:

IL=20lgV1/V2 (dB)
V1 -------------- Terminal voltage before the insertion of EMI filter
V2--------------- Terminal voltage after the insertion of EMI filter

Insertion loss is composed of common mode and differential mode, and the test schematic shows as below:

Dephir Elctronics Dephir Elctronics

         Common mode                   Differential mode

Notes: The insertion loss of filters provided by our company is measured according to the UL1283 Standard, using Spectrum Network Analyzer under the ideal condition of empty load, 50Ω-50Ω. The actual effect please follow the field data of real application.

6. Note for EMI filter selection
Choice of appropriate filter for your equipment should be based on the actual interference along with the working principle of filter. As aforementioned the work principle of power filter is impedence mismatch between the filter and access port, you can refer to the following table when choose filter to achieve the maximum filtering effect and to meet your requirement.


Dephir Elctronics


7. Climatic Category
Climatic Category means the working environmental category of EMI filter. According to IEC, it is composed of three codes, eg. 25/085/21
25 represents the lowest working environment -25℃,
085 represents the highest working environment +85℃
21 is the testing days of filter quality test under stable hot and humid conditions


Hits:  UpdateTime:2012/04  【Printing】  【Close