【Networking Power Supply】ISN testing on Switching Power Supply

All the electronic devices need to pass EMI Conduction Tests before they can be sold on the markets. During the process of the Conduction Test, the noise output from the telecommunications port may affect the communication quality of mobile phones and the network transmission speed. As a result, most the telecommunication devices must undergo ISN tests regarding the interference caused by telecommunications ports, in addition to the tests on the conduction of power supply. During the tests, both LISN and ISN will be applied. Usually, the test on power supply ports is also called the LISN testing, while the test on the output port is called the ISN testing. The reference standard is EN55032/FCC Part 15.

ISN: The Impedance Stabilization Network (ISN) is usually used in computers or electronic devices with telecommunications capabilities. Generally, ISN testing is performed on telecommunications devices, mainly for testing the common mode disturbances on the DSL port (RJ45).

LISN: In the EMI Conduction Test, the Line Impedance Stabilization Network (LISN) is applied to isolate the grids from the device under testing and then couple the interference signals of the tested device onto the EMC analyzer.

The main difference between LISN testing and ISN testing is that LISN is to test the interference on the power supply port, while ISN is to test the interference output from the telecommunication port. Below figures respectively indicate the schematic diagrams of LISN and ISN.

The tests are usually carried out according to the standards of EN55032, and it is easier to pass the ISN testing. However, ISN testing regulations are different in some countries and regions. For example, the Deutsche Telekom (DT) In German has more stringent ISN testing. Thus, the magnitude of common mode disturbances at the output port of the switching power supply becomes very critical.

DT regulations are much more different in terms of the limits of frequency and common mode voltage, if compared with those required by the EN55032. The test waveforms can be referred to as follows:


For many years, the Asian Power Devices (APD) Group has dedicated itself to the development of power supply products for peripheral electronic devices. We have accumulated many years of experience in helping foreign customers, able to quickly provide solutions for ISN testing on power supply ports.