Application Note The use of soft ferrites for interference suppression The Use of Soft Ferrites for Interference Suppression

Contents

Introduction 3

General principles of EMC 4

EMC regulations 4

Material specifi cations 9

EMI-suppression product lines 12

Applications 14

Design considerations 18

Impedance concept 18

Literature, software and sample boxes 19

1 Ferroxcube Assortment of EMI-suppression ferrite products

2 Ferroxcube 1. Introduction The most important regulations than in the fi nal design phase. In such are the European Norms (EN) cases extra suppression components In the fi eld of electromagnetic which are applicable in all European are necessary, like ferrites, capacitors compatibility several trends attribute Union (EU) and European Free or shielding elements. to a growing necessity of EMC Trade Associated (EFTA) countries, Ferrites provide a solution to engineering. FCC in United States and VCCI in many problems of conducted and Japan. The uniform legislation in the (indirectly) radiated interference. In signal processing : European Union is along the lines of They can be applied almost • Change from analog to digital the EMC directive 89/336/EEC. For anywhere : (steep pulse edges, overshoot, every product to which no specifi c • Shifted on wire or cable as beads, ringing). European norm applies, a general tubes or cable shields. • Increase of clock frequencies. regulation is mandatory. These are • Mounted on PCB as beads-on-wire, the so called Generic Requirements wideband chokes, SMD inductors, In power conversion : (residential, commercial and light multilayer suppressors or • Change from linear to switched- industry: EN 61000-6-3 for emissions integrated inductive components. mode supplies (high switching and EN 61000-6-1 for immunity). • Ring cores or U cores in mains frequency, harmonics). This includes all electric and fi lters, in the circuit, in a separate • Increase of switching frequencies. electronic products, no matter how box or moulded in a connector. trivial they seem to be ! • Wideband chokes or coiled rod These trends, directed to functional inductors in electrical appliances or Of course the fi rst step to avoid upgrading or reducing cost, inevitably motors. interference problems is a good also contribute to an increasing level design practice, to tackle the of electromagnetic interference No ground connections are problem right from the start. This (EMI) emissions. Together with the necessary as ferrites are connected can be insuffi cient if the interference increasing use of electronics this in series with the interfering circuit is directly related to the inherent leads to a general EMC degradation. and not in parallel as in the case operating principle and too late if the As a consequence, EMC legislation is of a capacitor. The wideband, lossy interference is detected not earlier getting world-wide more strict. impedance makes ferrites well-suited as RF suppressor component.

3 Ferroxcube 2. General principles they are very fast, harmonic Common-mode : disturbances if the basic frequency is Phase and null interference voltages of EMC high or if the deviation from a sine are equal. This is likely to occur if wave is considerable. phase and null are close together 2.a. Regulations and interference is coupling in from Historically, all EMI regulations stated Interferences can propagate as an an external fi eld (radiation or cross- emission limits only. These defi ne electromagnetic wave in free space. talk). the maximum level of interference Suppression then requires shielding Differential-mode : allowed as a function of frequency. with conductive materials. Also Phase and null interference voltages In case of conducted interference it propagation occurs via conductive have opposite phase angle but equal applies to the voltage on all inputs paths such as the mains network, magnitude. This is likely to occur and outputs of the equipment, in to which the majority of electrical in case of switching equipment case of radiated interference it equipment is connected. connected to the mains. In general applies to the fi eld strength at a Below 30 MHz this is the main a combination of both types can be certain distance. Often two levels are propagation mode. Suppression present. stated: is done with a high impedance in series (inductor), a low impedance in 2.c. Suppression with ferrites • Class A for commercial and indus- parallel (capacitor) or a combination At RF frequencies a ferrite inductor trial areas. of both (fi lter). shows a high impedance which • Class B for domestic and residen- suppresses unwanted interference. tial areas. Propagation via the mains can The resulting voltage over the take place in two different modes : load impedance will be lower than Class B is always stricter than common and differential mode. Apart without suppression component, the class A. Also immunity is becoming from phase and null which carry the ratio of the two is the insertion loss, subject of regulation. Taking into supply current, there is the safety see Fig. 2. account the severity of the EMC earth connection, which is generally problem, equipment must also be taken as a reference. able to operate without functional degradation in a minimum EMI ambient. The difference between the actual level of emissions or Z Z susceptibility and the EMC limits is G S the required attenuation by fi ltering or shielding. ZL E 2.b. Sources and propagation The source determines whether the interference is a transient or random variation in time (commutation Z motors, broadcast transmitters etc.) G or a periodic signal (e.g. switched- mode power supplies). The frequency Z E spectrum will be continuous in the L o fi rst case and a line spectrum in the second. In practice, the minimum and maximum frequency involved are much more relevant and both types of sources can be broadband. Fig. 2 Insertion loss of an inductor. Random variations are broadband if

4 Ferroxcube level in dB/VdBµV 80 quasi peak 75

average 70

65

60

55

50

45

40 0110f (MHz)

Fig. 1a European generic emission norm 61000-6-3 (residential, commercial, light industry).

level in dB/VdBµV 80 quasi peak 75

average 70

65

60

55

50

45

40 0110f (MHz)

Fig. 1b European generic emission norm 61000-6-1 (industrial environment).

5 Ferroxcube The insertion loss is expressed as : critical interference frequencies; impedance and interference ideally they should coincide with amplifi cation! A resistor cannot . the ferrimagnetic resonance resonate and is reliable independent IL = 20 log10 (Eo/E) [dB] frequency, the top of the impedance of source and load impedances. curve. According to Snoek’s |ZG+ZL+ZS| law, this resonant frequency is • Secondly, a resistance dissipates . interfering signals rather than = 20 log10 [dB] inversely proportional to the initial refl ecting them to the source. |ZG+ZL| permeability, which gives us a guide for material choice. The higher the Small oscillations at high frequency The decibel (dB) as a unit is practical interference frequency, the lower the can damage semiconductors or because interference levels are also material permeability should be. The negatively affect circuit operation expressed in dB. However insertion whole RF spectrum can be covered and therefore it is better to absorb loss de pends on source and load with a few materials if the right them. impedance, so it is not a pure permeability steps are chosen. product parameter like impedance At the resonant frequency and above, • Thirdly, the shape of the impedance (Z). In the application, source and the impedance is largely resistive, curve changes with the material load impedance generally are not 50 which is a favourable characteristic losses. A lossy material will show a Ω resistive. They might be reactive, of ferrites. smooth variation of impedance frequency dependent and quite with frequency and a real wideband different from 50 Ω. • Firstly, a low-loss inductance can attenuation. Interferences often Conclusion : insertion loss is resonate with a capacitance in have a wideband spectrum to a standardized parameter for series (positive and negative suppress. comparison, but it will not predict reactance), leading to almost zero directly the attenuation in the application.

At low frequency, a ferrite inductor is a low-loss, constant self-inductance. Interferences occur at elevated frequencies and there the picture changes. Losses start to increase and at a certain frequency, the ferrimagnetic resonant frequency, permeability drops rapidly and the impedance becomes almost completely resistive. At higher frequencies it even behaves like a lossy capacitor. While for most applications the operating frequency should stay well below this resonance, effective interference suppression is achieved up to much higher frequencies. The impedance peaks at the resonant frequency and the ferrite is effective in a wide frequency band around it. The material choice follows from the

6 Ferroxcube 2.d. Current-compensation Ferrite inductors inserted separately in both lines suppress both common and differential mode interference. However, saturation by the supply current can be a problem. Remedies are a low permeability material, a gapped or open circuit core type. Disadvantage is the larger number of turns required to achieve the same inductance, leading to higher copper losses. All this can be overcome with current-compensation. Phase and null supply currents are opposite and have equal magnitude. If both conductors pass through the same holes in the ferrite core, the net current is theoretically zero and no saturation occurs. In other words, these currents generate opposite fl uxes of equal magnitude that cancel out. • A tube or round cable shield shifted In practice, some stray fl ux will occur. on a coaxial cable. The stray fl ux paths will not coincide and these fl uxes do not cancel out. • A fl at cable shield, shifted on a fl at cable. Here the net current of all Examples of current-compen- inductors together is zero. sated inductors : • A ring core with two windings with In case of an I/O cable, such as coax equal number of turns. The winding or fl at cable, the problem will not directions are such that the be saturation by high current. The incoming current through one reason for the current-compensa- winding and the equally large tion is now that the actual signal is outgoing current through the also of RF frequency and it would be other generate opposite fl uxes suppressed together with the inter- of equal magnitude. Current- ference. The current-compensated compensation would be almost inductor has one limitation: it is only ideal with both windings along the active against common-mode inter- total circumference, one over the ference. However the small leakage other. But in practical cases each inductance will also suppress some winding is placed on one half of differential-mode interference. the ring core because of insulation requirements.

• A twisted wire inductor, which is wound with the twisted wire pair as if it were a single wire.

7 Ferroxcube 8 Ferroxcube 3. Material specifications • Iron powder zinc ferrites the same law is valid, Permeability of this material is also but at high frequency the picture is There are different material catego- low but bandwidth is less than for more complex. Apart from resonant ries : nickel-zinc ferrites because of their losses, eddy current losses will play • Manganese-zinc ferrites (MnZn) low resistivity. Their main advantage an important role. They reduce the These ferrites have a high is a saturation fl ux density which impedance at high frequencies for permeability but also a low is much higher than for ferrites, so manganese zinc ferrites. For nickel resistivity and are most effective at they are suitable for very high bias zinc ferrites they are not very low frequencies. The ferrites 3S3 currents. important below 100 MHz due to and 3S4 have a higher resistivity The main material parameters are the much higher resistivity. The 4A15 and are real wideband materials as given in the table while the typical curve in Fig. 3 peaks at 100 MHz well. impedance curves are given in Fig. although permeability is higher than • Nickel-zinc ferrites (NiZn) 3. For manganese zinc ferrites the that of 3B1. A second complicating These materials usually have a frequency at which the impedance factor is parasitic coil capacitance. lower permeability but much peaks, is given in Fig. 4. The 4B1 and 4C65 curves (measured higher electrical resistivity than the on the same ring size and with equal manganese-zinc ferrites and are Main material parameters. number of turns for comparison) are effective up to 1000 MHz. The impedance peak frequency limited by coil capacitance, whereas versus permeability curve clearly the 4S2 curve of Fig. 5 was measured confi rms Snoek’s law. For the nickel on a bead (N=1) and peaks at higher frequency.

µ ρ Type Material i Bsat Tc (mT) (°C) (Ωm) Manganese 3E8 18000 350 100 0.1 Zinc 3E7 15000 400 130 0.1 3E6 12000 400 130 0.1 3E5 10000 400 120 0.5 3E26 7000 450 155 0.5 3E27 6000 400 150 0.5 3C11 4300 400 125 1 3S1 4000 400 125 1 3C90 2300 450 220 5 3S4 1700 350 110 103 3B1 900 400 150 0.2 3S3 250 350 200 104 Nickel 4A15 1200 350 125 105 Zinc 4S2 700 350 125 105 4B1 250 350 250 105 4C65 125 350 350 105 Iron Powder 2P90 90 1600 140 * low

Table 1 : Main material parameters. * Maximum operating temperature

9 Ferroxcube Fig. 3 Impedance versus frequency for several ferrite materials. ( measured on TN12.5/7.5/5 ring cores with 5 turns )

Fig. 4 Frequency of impedance peak for some MnZn ferrite materials.

10 Ferroxcube 100 3S1 Zs (Ω)

no DC 50 100 mA 300 mA 1A

2A

0 1 10 100 1000 f(MHz)

Fig. 5 Effect of bias current on the impedance of a 3S1 bead. ( measured on BD5/2/10 beads on a single wire )

150 4S2 Zs (Ω)

100 no DC

0.3A 1A 3A 50

0 1 10 100 1000 f(MHz)

Fig. 6 Effect of bias current on the impedance of a 4S2 bead. ( measured on BD5/2/10 beads on a single wire )

11 Ferroxcube 4. EMI suppression can be custom designed to fi t are certifi ed to ISO 9001 and ISO aspecifi c application. Solderability 14001. For detailed information product lines and taping are in accordance with on product lines, ask for the accepted IEC and EIA norms. appropriate product brochure, A variety of shapes is used for EMI A thorough quality control is see at the back. Sample boxes are available to support the designer. suppression (see the table below). maintained in all stages of the For most of these product types production process : raw materials Ferroxcube have defi ned a standard inspection, powder batch control, range with balanced size distribution statistical process control (SPC) and and logical material selection. Apart production batch control as fi nal from the standard range, products inspection. Our production facilities

Type Shape Main applications

magnetically closed cores ferrite ring cores mains filters iron powder rings lamp dimmers tubes round cable shielding beads wire & component lead filtering multihole cores wire filtering (multi-turn) cable shields round & flat cable shielding plate with holes flat cable connector shielding magnetically open cores rods commutation motors in cars bobbin cores power line chokes inductors beads-on-wire PCB supply line / RF filtering SMD beads & chokes PCB supply line / RF filtering wideband chokes domestic appliances, various multilayer suppressors PCB supply line / RF filtering integrated inductive components PCB supply line / RF filtering Table 2 : Product shapes with their main applications

Range of SMD beads and chokes

12 Ferroxcube 13 Ferroxcube 5. EMI suppression and / or number of shields. confi guration of the above Impedance depends linearly on mentioned cable shields. applications length and only logarithmically on the outside dimensions. The product 5.b. Intermediate applications Whereas the material choice is can be in one piece for mounting • Component lead filtering derived from the EMI frequency during manufacturing or split for (beads) band, the core shape and way of retrofi t solution. A split product uses Beads are small tubes especially winding are largely determined special clamps to prevent a parasitic designed for suppression. If a specific by practical considerations and air gap with loss of impedance. A known component is the source, possible saturation by the load very simple (temporal) retrofi t e.g. a diode causing overshoot current. According to the last solution for fl exible cable is winding oscillations when entering the non- criterion, three application groups a few turns on a ring core of large conductive state, then the bead is can be distinguished : small signal, diameter. The large inner diameter shifted directly over the leads of this intermediate and power. and short length (small impedance) component. are compensated by using more than 5.a. Small signal applications one turn. The suppression is only • PCB inductors • Coaxial cable shielding common mode. (beads-on-wire, SMD beads & (round cable shield, tubes, ring chokes, multilayer suppressors, cores) • Cable connector shielding integrated inductive components) • Flat cable shielding (plate with holes) If the source is not known, but the (rectangular cable shield) A built-in suppression for the propagation path can be identified, If the cable carries an information connector of a fl at cable is a ferrite e.g. the DC power supply lines or a signal, either analog or digital, plate with holes fi tting over the fast digital clock line, then this line saturation will be no issue. This separate pins. The material must should be blocked. The bead has two is typically the case with cable be nickel-zinc to prevent short- equivalents : shielding. Inside diameter is fi xed by circuit. Because the holes are • for through-hole mounting a bead- the cable dimensions and impedance close together, this confi guration on-wire (bead glued on a wire, adjusted mainly by the length approximates the common mode axially taped and reeled). • for surface mounting an SMD bead (bead with flat wire, blister taped and reeled).

A larger impedance can be achieved with a multi-turn choke. For even higher attenuation either a multilayer suppressor or a complete filter can be made by adding capacitors. SMD ceramic multi-layer capacitors (CMC) are best suited for this purpose because of their very small lead inductance and excellent high- frequency characteristics.

14 Ferroxcube A

L D a b A

B c C C B d SMD bead (BD) SMD wideband choke (WBS) SMD common mode choke (CMS2) EMI-suppression bead (BD)

40 D A 10 40 d ± 5 ± 5 6

C ∅0.6 L B 14 l max SMD common mode choke (CMS4) Wideband choke (WBC) Bead on wire (BDW)

D

d d H d H

LD LD L Multihole core (MHC6) Multihole core (MHR2) Multihole core (MHF4)

d d d H D H

L D L H LD Multihole core (MHB2) Multihole core (MHR6) Multihole core (MHC2) E

B

L D C D B A E B A C

d D A Tubular cable shield (CST) Bisected arcade shaped cable shield (CSA) Flat cable shield (CSF) C Bisected flat cable shield (CSU)

E

E

E B C C B A A B D A B E B B D C A C D D C A C D A Bisected arcade shaped cable shield Bisected flat cable shield Bisected tubular cable shield with with plastic case (CSA-EN) plastic case (CSC-EN) with plastic case (CSU-EN)

B A C D C D B E

A I F G H Multilayer Integrated Inductive Component (IIC) Suppressor (MLS)

Fig. 7 Overview of small signal suppression products

15 Ferroxcube 5.c. Power applications L • Current-compensated chokes P P in mains filters Cy (ferrite ring cores) Mains Cx E Load Most equipment nowadays has Cy switched-mode power supplies N N L to reduce volume and weight. P = phase Electronic circuits have been N = null miniaturised constantly and the remaining subsystems set the size E = earth limits. A television set is not much more than a picture tube and a Fig. 8 Typical mains filter configuration. power supply. For EMC purposes, a mains filter is necessary. The same • Wire filtering • Wideband chokes holds for the electronic ballast of (beads, two-hole cores) Wideband chokes are mounted on energy-saving fluorescent lamps. If only the printed circuit board different places, often not on circuit Mains filters are also manufactured that generates the interference is boards. Their main advantage is as separate components. known, then the wires connecting it a combination of high impedance with other system boards should be and large bandwidth. The wires are The following components can be filtered. Wires can be filtered with wound through holes in the core, found in mains filters : a bead like component leads. To thus separating them physically and achieve more impedance, multihole reducing parasitic coil capacitance. • two inductors L on the same core cores are a good solution. The wire Several insulated types are available for low-frequency attenuation is simply drawn through several to prevent short-circuit between (harmonics of the switching holes until sufficient impedance is wire bends or of wire bends with frequency) achieved. The system parts are not other metallic parts. • two Cy capacitors for additional necessarily boards. In an electric common-mode attenuation (at shaver for instance you will find a higher frequencies) filter between mains plug and motor • a Cx capacitor for differential- consisting often of a bead on either mode attenuation lead, combined with 3 capacitors.

DH D D L d L d

d Tube (TUB) Rod (ROD) Ring core (T, TN, TX, TL, TC)

B D C D L d a c B D AE s d F C E b A Bobbin core (BC) U core (U) Impeder core (IMP) E core (E)

Fig. 9 Some products used in power applications.

16 Ferroxcube The choke has to fulfil contradicting • Electric commutation motors requirements : high inductance in cars (rods) as well as high rated current. To In a modern car, many electric com- prevent an unpractical choke size, mutation motors are applied. There current-compensation is applied to are a starter motor, a fuel pump, a ring core in a high-permeability small ventilators, screen wiper material (see also section 2.d.). motors, window lift motors, sun Many variations exist according to roof motors etc. The commutation the specific equipment type, e.g. the is accompanied by high-frequency compensated choke alone can be sparks which cause RF interference. moulded in the plug of TV supply This will be picked up by the FM cables. radio, but if motor functions are regulated electronically, also safety is • Lamp dimmers at stake. Large currents are involved, (iron powder ring cores) starter motor current can be as high Fluorescent lamps cannot be as 40 A. Due to the frequency (FM dimmed like incandescent lamps band around 100 MHz) the induc- simply by decreasing voltage, tance does not have to be very large because below their threshold they and a rod with a single layer winding turn off. Electronic dimmers use a is the right choice. Motor tempera- variable part of the supply voltage tures can reach 150 °C, so the Curie period by means of delayed thyristor temperature of the ferrite should ignition. The harmonics of the mains be well over 200 °C, in combination frequency require iron powder i.s.o. with good HF impedance behaviour. laminated silicon iron to reduce The low permeability is no problem eddy current losses. On the ignition in a rod shape. 3S3 is the ideal mate- instant a parasitic ringing can be rial for this application. observed, of which the frequency (a few MHz) is determined by parasitic inductances and capacitances in the circuit. At MHz frequencies the losses of iron powder are large and the ringing is dissipated in a few periods. Ferrites have much less losses and would reflect a large part of the ringing energy, which could damage the semiconductors of the control circuitry. Range of multilayer suppressors in standard EIA sizes 0402 to 1812 • Power line chokes (bobbin cores) If chokes operate on separate power lines and current-compensation is not possible, then an open core type must be chosen. To reach a high inductance, hundreds of turns can be necessary and a bobbin core is the appropriate shape.

17 Ferroxcube 6. Design rods and bobbin cores, the stray part to the losses. flux can be a problem. Bobbin cores ω considerations are better than rods. Apart from Z = j . (µ’-jµ”) . Lo keeping distance to other circuit ω ω Even without any trials or parts, the positioning is important. = . µ” . Lo + j . µ’ . Lo calculations, a lot of problems can be For long thin rods a horizontal Z = R + jX → avoided beforehand by good design position is the best. The core axis practices. In order of priority they is horizontal, so the magnetic field ω R = . µ” . Lo , are : is almost parallel to the PCB and ω ω π the induced electric field almost X = . µ’ . Lo ( = 2 . . f) • avoid generating interference perpendicular. This results in only (minimize clock rate, smoothen low induced voltages in PCB tracks. |Z| = √(R2 + X2) pulse shape), • For inductors with many turns, the ω √ 2 2 • keep it far away (separate power winding method influences the = . Lo . (µ’ + µ” ) components and circuits from the parasitic coil capacitance. Too rest) much capacitance causes early Where Lo is the inductance if initial • impede its propagation (minimize frequency roll-off of the impedance. permeability were equal to 1 : conductor path length and Ways to reduce parasitic L = µ . n2 . A / l component lead length), capacitance are multi-chamber o o e e • suppress with ferrites and winding (separation of turns in (µ = 4 π x 10-7 = 1.2566 x 10-6 capacitors. groups), and 90 degree cross- o winding (electrical decoupling of [H/m]) The following points should be con- adjacent turns). sidered while taking EMI-suppression • Capacitors should always be For the calculation of effective mag- measures : connected with leads as short as netic dimensions Ae and le, see next possible, because the leads have paragraph. • The insertion of ferrite parasitic inductance (in the order components lowers equally of 10 nH/cm) which causes early emission and susceptibility, the frequency roll-off in the attenuation µ' µ'' essence is blocking the propagation curve. In general filters should be path. The ferrite should always be layed-out as compact as possible. µ' located as close to the source as possible. All intermediate circuitry and cable length acts as antenna Appendix A. µ" and produces radiated interference. Impedance concept The same holds for capacitors frequency or any type of suppression fr A.1. Material component. The impedance curve can be • The ferrite and the conductor Z translated to a pure material curve, should be close together. the so-called complex permeability Beads, tubes and cable shields curve. As impedance consists of should fit close around the wire or |Z| a reactive and a resistive part, cable and other core shapes should permeability should have two parts be wound tightly. If not, then stray too to represent this. The real flux is present, which converts into part corresponds to the reactance, f frequency mutual inductance if other circuit r positive for an inductance, negative parts are close enough to be in the for a capacitance, and the imaginary stray field. Fig. 10 Complex permeability • Especially for open core types like and impedance.

18 Ferroxcube A.2. Core size A.3. Bias current First, bias current is translated to the The choice of a suppression product Often a DC supply or AC mains current that would induce the same is made in two steps. First the current is passing through the fi eld strength in the reference core, material choice corresponding to the inductor to allow normal operation which means the same state of core interference frequencies occurring of the connected equipment. This saturation : and afterwards the right core size current induces a high fi eld strength and turns for the impedance level in the ferrite core, which can lead Io = I . (n/no) . (leo/le) required. to saturation. Impedance then The simplest way of calculation decreases along with permeability, For a ring core, tube or bead the is taking the impedance curve especially for low frequencies. The effective length is of a reference core of the same infl uence of a bias current can be π material. Calculation from complex calculated. The induced fi eld strength le = . ln(OD/ID) / (1/ID-1/OD) permeability is another possibility, is directly proportional to the but it’s more bothersome. Two current : Now the relative impedance factors have to be corrected : decrease will be the same : effective magnetic dimensions and H = n . I / le turns. Zbias = Z . (Zo bias / Zo) Whether this fi eld causes a 2 → signifi cant saturation or not, can be Z :: N . Ae / le seen in the curve of permeability 2 2 versus bias fi eld. However, this only Z = Zo . (N / No ) . (Ae/Aeo) . indicates the decrease of inductance (leo / le) at low frequency. The impedance The parameters with index o at high frequency decreases less. correspond to the reference core. Again, impedance can be calculated The number of turns N is always from reference curves if they show an integer number. Half a turn impedance versus frequency with geometrically is 1 turn magnetically. bias current as a parameter. For a bead with a single wire going Literature, Software and Sample Boxes through, N = 1 turn. The effective magnetic dimensions A (area) e General catalogues & Software and le (length) are calculated from Data Handbook : Soft ferrites and Accessories geometric dimensions according Product Selection Guide to IEC 205. For complicated Soft Ferrites and Accessories Design Tools Disk geometries this involves complex formulas. Therefore the suppliers Specifi c brochures usually specify these data in their SMD Beads and Chokes handbooks. For a cylindrical Wideband Chokes geometry (ring core, tube, bead, Cable Shielding bead-on-wire) a simple formula Power Inductors applies : Multilayer Suppressors and Inductors IIC Integrated Inductive Components A / l = h / (2 . π) . ln(OD/ID) 3S4 a new Soft Ferrite for EMI suppression e e 3S3 a new Soft Ferrite for EMI suppression

OD = outer diameter Sample boxes ID = inner diameter SAMPLEBOX9 SMD Beads and Chokes h = height SAMPLEBOX10 Cable Shielding SAMPLEBOX11 EMI-suppression Products

19 Ferroxcube If you require impedance graphs or other detailed product data, which are not presented in this brochure, please visit our website at :

www.ferroxcube.com

20 Ferroxcube FERROXCUBE America Sales Offices

State Sales Office Phone Fax E-mail/Website

Arizona Harper and 2, Tempe, AZ (480) 804-1290 (480) 804-1291 www.harperandtwo.com Arkansas PEI, Richardson, TX (972) 479-9777 (972) 479-9778 [email protected] Brazil - Rio De Janeiro Richardson Electronics do Brazil 55 21 521-4004 55 21 521-5193 www.rell.com Brazil - Sao Paulo Richardson Electronics do Brazil 55 11 3845-6199 55 11 3845-6199 www.rell.com California - San Diego Harper and 2, San Diego, CA (858) 391-1940 (858) 391-1945 www.harperandtwo.com California - South Harper and 2, Signal Hill, CA (562) 424-3030 (562) 424-6622 www.harperandtwo.com Colombia Richardson Electronics Colombia 57-1 636-1028 57-1 636-1005 www.rell.com Hawaii Harper and 2, Signal Hill, CA (562) 424-3030 (562) 424-6622 www.harperandtwo.com Louisiana PEI, Richardson, TX (972) 479-9777 (972) 479-9778 [email protected] Minnesota ECS, Eden Prairie, MN (952) 946-9510 (952) 946-9052 [email protected] Nevada (Clark County) Harper and 2, Tempe, AZ (480) 804-1290 (480) 804-1291 www.harperandtwo.com New Mexico Harper and 2, Tempe, AZ (480) 804-1290 (480) 804-1291 www.harperandtwo.com North Dakota ECS, Eden Prairie, MN (952) 946-9510 (952) 946-9052 [email protected] Oklahoma PEI, Richardson, TX (972) 479-9777 (972) 479-9778 [email protected] South Dakota ECS, Eden Prairie, MN (952) 946-9510 (952) 946-9052 [email protected] Texas PEI, Richardson, TX (972) 479-9777 (972) 479-9778 [email protected] Wisconsin (Western) ECS, Eden Prairie, MN (952) 946-9510 (952) 946-9052 [email protected]

Mexico (excl. Baja) R.V. Componentes, Guadalajara, MX 52-33-3122-2325 52-33-3122-2332 [email protected] Mexico (Baja) Harper and 2, San Diego, CA (858) 391-1940 (858) 391-1945 www.harperandtwo.com All others in America Ferroxcube USA Inc., (915) 8603289 (915) 8603270 [email protected] El Paso (Tx)

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France: Ferroxcube France, NANTERRE Taiwan: Ferroxcube Taiwan, TAIPEI Tel: +33 (01) 5551 8422, Fax: +33 (01) 5551 8423 Tel. +886 2 86650099, Fax: +886 2 86650145

Germany: Ferroxcube Germany, HAMBURG Turkey: Contact Ferroxcube Italy Tel: +49 (040) 527 28 302, Fax: +49 (040) 527 28 306 Tel: +39 02 241131 1 , Fax: +39 02 241131 11

Greece: Contact Ferroxcube Italy United Kingdom: Ferroxcube UK, DORKING Tel: +39 02 241131 1 , Fax: +39 02 241131 11 Tel: +44 1306 646200, Fax: +44 1306 646222

Hungary: Contact Ferroxcube Poland United States: Ferroxcube USA, EL PASO (TX) Tel: +48 46 834 00 07, Fax: +48 46 834 00 35 Tel: +1 915 8603289, Fax: +1 915 8603270

Hong Kong: Ferroxcube Hong Kong, HONG KONG For all other countries apply to closest regional sales office: Tel: +852 2319 2740, Fax: +852 2319 2757 ■ HAMBURG, Germany Indonesia: Contact Ferroxcube Singapore Tel: +49 (040) 527 28 302, Fax: +49 (040) 527 28 306 Tel: +65 6244 7815, Fax: +65 6449 0446 e-mail: [email protected] ■ EL PASO (TX), USA Ireland: Contact Ferroxcube UK Tel: +1 915 8603289, Fax: +1 915 8603270 Tel: +44 1306 646200, Fax: +44 1306 646222 e-mail: [email protected] Israel: Arrow\Rapac Ltd., PETACH TIKVA ■ TAIPEI, Taiwan Tel: +972 3 9203480, Fax: +972 3 9203443 Tel. +886 2 86650099, Fax: +886 2 86650145 e-mail: [email protected] Italy: Ferroxcube Italy, SESTO S. GIOVANNI (MI) Tel: +39 02 241131 1 , Fax: +39 02 241131 11 © Ferroxcube International Holding B.V. 2002 Malaysia: Contact Ferroxcube Singapore All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. Tel: +65 6244 7815, Fax: +65 6449 0446 The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. Mexico: Contact Ferroxcube USA No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial or Tel: +1 915 8603289, Fax: +1 915 8603270 intellectual property rights.

New Zealand: Contact Ferroxcube Taiwan Visit our web-site for the latest information on new products, application info Tel. +886 2 86650099, Fax: +886 2 86650145 as well as updated phone- and fax numbers Internet: www.ferroxcube.com Norway: Contact Ferroxcube Sweden Tel: +46 8 580 119 76, Fax: +46 8 580 121 60 Printed in The Netherlands 9398 088 00511 Date of release: 07/02