LINE IMPEDANCE STABILIZATION NETWORKS (LISNS)

Line Impedance Stabilization Networks (LISNs)

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1. Overview

A line impedance stabilization network (LISN) is a tool used when performing EMC/EMI tests. A LISN is essentially a low-pass filter placed between a power source and the DUT (device under test).

A LISN performs the following functions:

  • Provides a well-known impedance to the power input of the DUT.

  • Prevents high-frequency noise from the power supply entering into the DUT, making the measurements of the DUT seem worse than they actually are (isolation of the power supply).

A "50uH" LISN is a common choice, which provides impedance control down to 10kHz. Below 10kHz, impedance control is difficult[mil-std-461e].

MIL-STD-461E mandates the use of LISNs to control the impedance of power sources for many of it’s measurement procedures:

The impedance of power sources providing input power to the EUT shall be controlled by Line Impedance Stabilization Networks (LISNs) for all measurement procedures of this document unless otherwise stated in a particular test procedure.

— MIL-STD-461E
Section 40.3.6 (4.3.6): Power source impedance

2. CISPR 25

CISPR 25 sets limits and procedures for the measurement for EMI in the frequency range of 150kHz to 2.5GHz[cispr-25]. Among other utilities, the standard is applicable to vehicles, and it is a popularly referenced standard among automobile electronic design. It specifies the uses of a \(5uH\) LISN when performing EMI measurements, is one of the main reasons you will see \(5uH\) LISN devices available for purchase.

The TexBox TBOH01 (5uH LISN) is a LISN designed to be compliant with CISPR 25, and retails for around US$250.

References

  • [mil-std-461e] Department of Defense (1999, August 20). MIL-STD-461E: Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment. Quick Search. Retrieved 2021-06-30, from https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=35789

  • [cispr-25] IEC (2016). Vehicles, boats and internal combustion engines - Radio disturbance characteristics - Limits and methods of measurement for the protection of on-board receivers. Retrieved 2021-07-02, from https://webstore.iec.ch/publication/26122


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