Choosing the Right EMC Ferrite
This article from Würth outlines six types of ferrites and helps you select the best ferrite for your design. There are a wide variety of EMC ferrites to choose from.
Types of EMC Ferrites
Snap ferrites from Würth Elektronik
The snap ferrites of Würth Elektronik are suited for retrospective fitting on existing cable lines. The special lock, the so-called key technology, on the Würth Elektronik snap ferrites offers assurance against unauthorised opening – cue CE mark. At the same time, the plastic case protects against mechanical damage and its construction offers increased contact pressure on the ferrite halves.
The result is very high impedance, or in other words interference suppression. Typical applications are signal lines, monitor leads, printer cables, mouse cables, data transmission lines etc.
Ferrite sleeves and ferrite rings
Unlike snap ferrites or ferrites with nylon clamps, the ferrite sleeves or rings can be slid onto the cable prior to final assembly and fixed by using a heat shrinking tube or potting process. This solution is found on every computer monitor today. The closer the inner diameter is adapted to the cable diameter, the greater the suppression effect. Also with multiple winding turns, as with snap ferrites, the inductive part can be emphasised while achieving greater impedance.
6-hole ferrite beads
The 6-hole beads – commonly known as VHF chokes – or our SMD type WE-SUKW (5-hole ferrite bead) usually come with 2.5 windings and withstand high levels of current over long periods without going into saturation. They achieve effective RF interference suppression directly on the board. Typical applications are ground decoupling, supply voltage decoupling in association with blocking capacitors and data line filters.
Multiline ferrites
The multiline ferrite is a universally applicable suppression component: Firstly as a 4-turn current- compensated choke with a high current rating of typically 4 A. The impedance or the current can be increased with the appropriate circuit. Furthermore, a dual current-compensated wideband choke can also be achieved with the right connection (cf. Fig. 1).
SMD Ferrites of Würth Elektronik
Current is also passed through the ferrite in the SMD ferrites; for the signal, it acts as a low impedance connection (RDC → 0 Ω); however for the interference spectrum as a high loss resistance (impedances up to 5 kΩ).
With a multilayer construction current loads up to 6 A are achievable depending on the ferrite design. The following sizes are available 0402, 0603, 0805, 1206, 1210, 1806 and 1812 as standard.
In the pre-design stage, the engineer can design short-circuited solder pads at critical points, which can be separated and the appropriate SMD ferrites mounted after EMC measurement.
Choosing the right ferrite
The correct choice of ferrite can only be confirmed by measurements in the EMC lab. The calculation of the dynamic impedance (system impedance) of a high frequency electronic circuit is generally not possible. This is dependent on many factors, which are hard to describe mathematically, especially in the RF range.
Nevertheless, initial selection can be made with comparative measurements and experience:
Supply voltage lines and ground lines have a circuit impedance in the range 1–10 Ω, useful signal lines again have a circuit impedance between 50–100 Ω and video, clock and data lines have higher circuit impedance depending on the application (e.g. bus systems such as CAN, SCSI etc.)
Starting from this system impedance (ZA and ZB) and the required interference suppression, the ferrite impedance (ZF) can be calculated by using the equation above. According to the impedance of the ferrite and the application the correct part can be chosen now, e.g. a ferrite sleeve or an SMD ferrite.
Ferrite Design Kits
Want to learn more about Ferrites? Visit the Würth catalog where you can purchase one of their ferrite design kits and ask questions from the ferrite experts.
Information and media in this post was provided by Würth Elektronik.
Applicable Part Numbers
DK Part # | Mfr Part # | Description | Series |
---|---|---|---|
732-10084-ND | 742700 | EMI SUPPRESSION AXIAL FERRITE BE | WE-AFB |
732-10085-ND | 742711 | SNAP FERRITES | - |
732-10086-ND | 742841 | SMD FERRITES WE-CBF HF | WE-CBF |
732-10146-ND | 744230 | SMD COMMON MODE LINE FILTERS WE- | WE-CNSW |
732-10147-ND | 744630 | COMMON MODE POWER LINE CHOKES WE | WE-LF |
732-10148-ND | 744725 | SMD COMMON MODE LINE FILTERS | - |
732-10150-ND | 744800 | COMMON MODE POWER LINE CHOKES WE | WE-CMBNC |
732-10151-ND | 744821 | COMMON MODE POWER LINE CHOKES WE | WE-CMB |
732-10152-ND | 744825 | COMMON MODE POWER LINE CHOKES WE | WE-CMB, WE-CMBH |
732-10153-ND | 782013 | AXIAL EMI SUPPRESSION FERRITES W | Automotive, AEC-Q200, WE-AEFA |
732-10154-ND | 782792 | SMD EMI SUPPRESSION FERRITE BEAD | WE-CBA |
732-10180-ND | 760801 | POWER FACTOR CORRECTION CHOKES W | WE-PFC |
732-11546-ND | 74271151 | FERRITE 417OHM HINGED 15.01MM | Star-Tec |
732-11547-ND | 74271151S | FERRITE 417OHM HINGED 15.01MM | Star-Tec |
732-11548-ND | 74271251 | FERRITE 525OHM HINGED 24.99MM | Star-Tec |
732-11549-ND | 74271251S | FERRITE 525OHM HINGED 24.99MM | Star-Tec |
732-13172-ND | 74271733S | SNAP FERRITE W/FLEXIBLE CABLE FI | Star-Fix |
732-13448-ND | 74272142 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13457-ND | 74272131 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13458-ND | 74272132 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13459-ND | 74272151 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13460-ND | 74272211 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13461-ND | 74272221 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13462-ND | 74272222 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13463-ND | 74272251 | STAR-TEC LFS SNAP FERRITE WITH S | Star-Tec LFS |
732-13464-ND | 7427014 | WE-TOF EMI SUPPRESSION TOROIDAL | WE-TOF |
732-13466-ND | 74270051 | WE-AFB EMI SUPPRESSION AXIAL FER | WE-AFB |
732-13468-ND | 74271633 | STAR-GAP SNAP FERRITE FOR RF APP | WE-STAR-GAP |
732-13478-ND | 7427141 | SNAP-RING SNAP FERRITE WITH PLAS | Snap-Ring |
732-13480-ND | 742701716 | WE-TOF EMI SUPPRESSION TOROIDAL | WE-TOF |
732-13483-ND | 74271622 | STAR-GAP SNAP FERRITE FOR RF APP | WE-STAR-GAP |
732-13485-ND | 742724759 | STAR-FLAT SNAP FERRITE WITH SAFE | WE-FLAT |
732-13783-ND | 7427502 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13784-ND | 74275043 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13785-ND | 7427504 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13786-ND | 7427501 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13787-ND | 74275013 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13788-ND | 7427503 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13789-ND | 74275022 | WE-UKW EMI SUPPRESSION 6-HOLE FE | WE-UKW |
732-13997-ND | 742722 | FLAT FERRITE CORES WE-FLAT | WE-FLAT |
732-14008-ND | 74271722S | STAR-FIX SNAP FERRITE WITH FLEXI | Star-Fix |
732-1499-ND | 7427246 | FERRITE CORE 194 OHM HINGED | Star-Flat |
732-1500-ND | 7427247 | FERRITE CORE 192 OHM HINGED | Star-Flat |
732-1501-ND | 7427248 | FERRITE CORE 180 OHM HINGED | Star-Flat |
732-1502-ND | 74272475 | FERRITE CORE 114 OHM HINGED | Star-Flat |
732-1503-ND | 74271112 | FERRITE CORE 321 OHM HINGED 6MM | Star-Tec |
732-1504-ND | 74271131 | FERRITE CORE 246 OHM HINGED | Star-Tec |
732-1505-ND | 74271132 | FERRITE CORE 241 OHM HINGED | Star-Tec |
732-1506-ND | 74271221 | FERRITE CORE 270 OHM HINGED | Star-Tec |
732-1507-ND | 74271222 | FERRITE CORE 265 OHM HINGED | Star-Tec |
732-1508-ND | 7427153 | FERRITE CORE 165 OHM HINGED 8MM | Star-Ring |
732-1509-ND | 7427151 | FERRITE CORE 119 OHM HINGED | Star-Ring |
732-1510-ND | 7427154 | FERRITE CORE 130 OHM HINGED 16MM | Star-Ring |
732-1511-ND | 7427155 | FERRITE CORE 110 OHM HINGED 27MM | Star-Ring |
732-1513-ND | 74271622S | FERRITE CORE 140 OHM HINGED | Star-Gap |
732-1514-ND | 74271633S | FERRITE CORE 100 OHM HINGED 8MM | Star-Gap |
732-1515-ND | 74270111 | FERRITE CORE 50 OHM SOLID 3.3MM | WE-TOF |
732-1517-ND | 742701121 | FERRITE CORE 123 OHM SOLID 5MM | WE-TOF |
732-1520-ND | 74270162 | FERRITE CORE 94 OHM SOLID 6.76MM | WE-TOF |
732-1522-ND | 74270117 | FERRITE CORE 161 OHM SOLID 10MM | WE-TOF |
732-1540-ND | 74270033 | FERRITE CORE 162 OHM SOLID | WE-AFB |
732-1541-ND | 74270030 | FERRITE CORE 158 OHM SOLID 5MM | WE-AFB |
732-1545-ND | 74270037 | FERRITE CORE 199 OHM SOLID 5.6MM | WE-AFB |
732-1551-ND | 74270034 | FERRITE CORE 160 OHM SOLID 7.3MM | WE-AFB |
732-1553-ND | 74270052 | FERRITE CORE 170 OHM SOLID 8MM | WE-AFB |
732-1558-ND | 74270091 | FERRITE CORE 170 OHM SOLID 9.5MM | WE-AFB |
732-1644-ND | 742792 | KIT DESIGN FERRITE CHIP BEAD | WE-CBF |
732-1913-ND | 74271722 | FERRITE CORE 270 OHM HINGED | Star-Fix |
732-1914-ND | 74271733 | FERRITE CORE 246 OHM HINGED 8MM | Star-Fix |
732-1915-ND | 742791 | KIT FERRITE SMD 1206-1812 SIZES | WE-CBF |
732-1916-ND | 742790 | KIT FERRITE SMD 0402-0805 SIZES | WE-CBF |
732-1920-ND | 744864 | KIT CHOKE FC SERIES | WE-FC |
732-2395-ND | 7427221 | FERRITE CORE 166 OHM SOLID | WE-FLAT |
732-2404-ND | 74272733 | FERRITE CORE 62 OHM HINGED 8MM | STAR-FIX LFS |
732-2405-ND | 742730021 | FERRITE BEAD 170 OHM RADIAL 4LN | WE-MLS |
732-2406-ND | 742730022 | FERRITE BEAD 248 OHM RADIAL 4LN | WE-MLS |
732-2407-ND | 74273002 | FERRITE BEAD 249 OHM RADIAL 4LN | WE-MLS |
732-2408-5-ND | 74273001 | FERRITE BEAD 264 OHM RADIAL 3LN | WE-MLS |
732-2409-5-ND | 742730023 | FERRITE BEAD 334 OHM RADIAL 4LN | WE-MLS |
732-3086-ND | 74272722 | FERRITE CORE 40 OHM HINGED | STAR-FIX LFS |
732-3090-ND | 7427727 | FERRITE CORE 100 OHM SOLID | WE-AFB LFS |
732-3302-ND | 74275812 | FERRITE CORE 200 OHM HINGED 5MM | STAR-BUENO |
732-3303-ND | 74275813 | FERRITE CORE 200 OHM HINGED | STAR-BUENO |
732-3304-ND | 74275815 | FERRITE CORE 350 OHM HINGED | STAR-BUENO |
732-3419-ND | 74271142 | FERRITE CORE 182 OHM HINGED 5MM | Star-Tec |
732-3420-ND | 74271142S | FERRITE CORE 182 OHM HINGED 5MM | Star-Tec |
732-3617-ND | 7427153S | FERRITE CORE 165 OHM HINGED 8MM | Star-Ring |
732-3619-ND | 74271222S | FERRITE CORE 265 OHM HINGED | Star-Tec |
732-3621-ND | 74271221S | FERRITE CORE 270 OHM HINGED | Star-Tec |
732-3623-ND | 74271132S | FERRITE CORE 241 OHM HINGED | Star-Tec |
732-3625-ND | 74271131S | FERRITE CORE 246 OHM HINGED | Star-Tec |
732-3627-ND | 74271112S | FERRITE CORE 321 OHM HINGED 6MM | Star-Tec |
732-3629-ND | 74271111S | FERRITE CORE 320 OHM HINGED 5MM | Star-Tec |
732-3635-ND | 7427151S | FERRITE CORE 119 OHM HINGED | Star-Ring |
732-3636-ND | 7427155S | FERRITE CORE 110 OHM HINGED 27MM | Star-Ring |
732-3637-ND | 7427154S | FERRITE CORE 130 OHM HINGED 16MM | Star-Ring |
732-3977-ND | 74270024 | FERRITE CORE 119 OHM SOLID | WE-SAFB |
732-3978-ND | 74270023 | FERRITE CORE 160 OHM SOLID 4MM | WE-SAFB |
732-3979-ND | 742700221 | FERRITE CORE 45 OHM SOLID 4MM | WE-SAFB |
732-3980-ND | 74270022 | FERRITE CORE 59 OHM SOLID 4MM | WE-SAFB |
732-3981-ND | 74270021 | FERRITE CORE 88 OHM SOLID 3MM | WE-SAFB |
732-3982-ND | 74270020 | FERRITE CORE 108 OHM SOLID 2.4MM | WE-SAFB |
732-3983-ND | 7427002 | FERRITE CORE 125 OHM SOLID 1.2MM | WE-SAFB |
732-3985-ND | 74270015 | FERRITE CORE 95 OHM SOLID 2MM | WE-SAFB |
732-3992-ND | 742700726 | FERRITE CORE 278 OHM SOLID 4MM | WE-SAFB |
732-3993-ND | 7427007141 | FERRITE CORE 45 OHM SOLID 2MM | WE-SAFB |
732-3996-ND | 74271111 | FERRITE CORE 320 OHM HINGED 5MM | Star-Tec |
732-7427143-ND | 7427143 | SNAP-RING SNAP FERRITE | - |
732-7427144-ND | 7427144 | SNAP-RING SNAP FERRITE | - |
732-78271111-ND | 78271111 | CAR-TEC SNAP FERRITE ; 316 ; 3.5 | WE-CAR-TEC |
732-78271111S-ND | 78271111S | CAR-TEC SNAP FERRITE ; 316 ; 3.5 | WE-CAR-TEC |
732-78271112-ND | 78271112 | CAR-TEC SNAP FERRITE ; 316 ; 4.5 | WE-CAR-TEC |
732-78271112S-ND | 78271112S | CAR-TEC SNAP FERRITE ; 316 ; 4.5 | WE-CAR-TEC |
732-78271131-ND | 78271131 | CAR-TEC SNAP FERRITE ; 235 ; 6.0 | WE-CAR-TEC |
732-78271131S-ND | 78271131S | CAR-TEC SNAP FERRITE ; 235 ; 6.0 | WE-CAR-TEC |
732-78271132-ND | 78271132 | CAR-TEC SNAP FERRITE ; 235 ; 7.0 | WE-CAR-TEC |
732-78271132S-ND | 78271132S | CAR-TEC SNAP FERRITE ; 235 ; 7.0 | WE-CAR-TEC |
732-9640-ND | 74271211 | FERRITE CORE 425 OHM HINGED 21MM | Star-Tec |
732-9641-ND | 74271211S | FERRITE CORE 425 OHM HINGED 21MM | Star-Tec |
7427114-ND | 7427114 | FERR SLV SNAP W/CASE 5.0MM GRY | SNAP-SLEEVE |
7427122-ND | 7427122 | FERRITE CORE 273 OHM HINGED | - |
74271833-ND | 74271833 | FERRITE CORE 113 OHM HINGED 8MM | Star-Gap |