APPLICATION NOTE
1
Purpose
This application note discusses the Importance of Ferrite Beads for in Electromagnetic Interference (EMI) and
using these Models in High Speed designs. This document also gives guidelines on the selection of a Bead
model.
Ferrite Beads
Ferrite Beads are passive electric components that suppresses high frequency noise in electronic circuits.
Figure 1. Images of EMI Filters
Ferrite Beads were traditionally used to make high frequency low pass filters and to keep transistors from
oscillating. With today's high performance systems, it is important to consider the bead's real properties and to
analyze the resulting bead circuit.
Popular Ferrite Bead Models of Fair-Rite #43 and #73 are discussed in this document.
#43 is a Nickel-Zinc Ferrite Bead used for suppression of conducted EMI from 20 MHz to 250 MHz and #73 is a
Manganese-Zinc Ferrite Bead to suppress conducted EMI frequencies below 50 MHz.
The most important factors in ferrite bead-based design are:
• Impedance vs. bead size
• Impedance vs. frequency
• Impedance vs. DC current bias
• Impedance vs. number of turns on the bead
Significance of Ferrite Beads
Ferrite Beads have the following advantages:
1. EMI Suppression
2. Improving Supply decoupling
3. Controlling parasitic Oscillations
4. Reducing RF Coupling
