Electronic product interior contains numerous magnetism element, these parts of an apparatus held the proportion with product more cost. Conveniently looks for a product, we are OK very direct see all sorts of inductance, magnetism bead, transformer wait. However, because magnetics is medium,be complex and changeful probably parameter, because magnetism component looks too simple,perhaps be, most engineer is used to ignoring them in designing a product. We know to be in design of switch power source, to achieve taller changeover efficiency, the design skill that the architect needs to master the parameter such as transformer winding, air gap and PFC inductance adequately. When undertaking EMI filter is designed, we often emphasize particularly on to see the inductance of magnetism component and impedance parameter at going, and the parameter that ignored a lot of keys. This series article aims to make a reader farther know all sorts of character in magnetism component, the hope can help the reader’s more accurate in actual project choice magnetism element, the quicker consideration that analyses a problem.

 

Magnetism bead is a kind of numerous magnetism component, magnetism bead is divided again to wear a heart magnetism bead is mixed stick a magnetism bead. Author individual thinks to wear a heart magnetism bead is more adjacent at inductance, its are relatively scarce also in applying actually, be in especially at present the requirement of product miniaturization trend, stick a magnetism bead to have an advantage more. The article sticks a magnetism bead to spread out around what express production with Yu Yi, hope to be able to be helped somewhat to the reader.

 

1, ferrite magnetism bead

 

Different frequency and the power is characteristic imitate in PCB and digital IC use power supply of different power source network normally. Such conducing to prevent coupling of noise of fast number switch to arrive network of sensitive imitate power source, reduce converter performance, but independent power supply can raise systematic level complexity and production cost. Can choose ferrite normally magnetism bead adopts proper high frequency segregation in the light of power source network. Ferrite magnetism bead it is passive parts of an apparatus, can filter inside wide frequency limits high frequency noise. It has resistor character inside target frequency limits, measure with sound energy of a confusion of voices of caloric form dissipation. Usually, ferrite magnetism bead in basically be being used in network of PDN power source, two side receive magnetism bead rightly to allow the capacitance of the value appropriately normally, form filter wave network, reduce the switch noise of network of PDN power source. Ferrite magnetism bead the circuit that equivalent circuit model is to be comprised by resistor, inductance and capacitance. Following plan institute are shown. RDC is corresponding the dc resistor of magnetism bead. CPAR, LBEAD and RAC state inductance of parasitism capacitance, magnetism bead is mixed respectively with the alternating current block that magnetism bead concerns () of loss of communication magnetism core.

 

Graph 1(a) ferrite of magnetism bead simplify circuit model; Magnetism bead uses graph 1(b) ferrite the ZRX curve that TycoElectronics BMB2A1000LN2 measures

 

Jefferson Eco gave out in its article the result of 4 parameter, its computation procedure is very simple also, here not give uncecessary details. Particular numerical value is RDC=300mΩ , CPAR=1.678pH, LBEAD=1.208μH, RAC=1.082kΩ . From the point of computational result, the equivalent model of magnetism bead is circuit of LCR shunt-wound resonance, the action that RDC place contributes is ignorred. Use CST to build this magnetism bead model, get what impedance parameter shows as follows, can see result whole is consistent.

 

RAC is it is the most important to comprise magnetism bead parameter in 4 parameter, as a result of the existence of RAC, magnetism bead just calls magnetism bead, the model that comprises otherwise can call resistor only, also the existence as a result of RAC, ability can have the impedance curve in next graphs. We know the computation of LC syntonic frequency is formulary, the syntonic circuit that if calculate,CPAR and LBEAD comprise is syntonic frequency, you can discover its resonance frequency just is the apogee of impedance curve. When RLC parallel circuits is syntonic, circuit admittance Y(jω) =G=1/R, that is to say the value that resonance nods corresponding impedance value to be RAC.

 

Graph the 2 magnetism that use CST computation to get bead impedance curve

 

 

Graph 4 The impedance curve of magnetism bead model

 

As a result of of magnetism bead inside electrode whole is lapped by ferrite material, so magnetism bead itself owns complete magnetism screen, its are exterior of magnetic field divulge lesser. When undertaking Layout accordingly, do not need a consideration whether does sensitive circuit exist all round magnetism bead, also do not need sedulous hollow the layer of magnetism bead lower part.

 

Graph 5 Magnetism bead distributings in the magnetic field below highest impedance frequency

 

2, of magnetism bead insert caustic

 

In design of filter wave circuit, inserting caustic is the parameter that can reflect character of filter wave circuit most. In the product in rectifying and reform, when consideration parts of an apparatus chooses, we can see the character inserting caustic of parts of an apparatus above all. Insert caustic to be able to mirror circuit system integratedly to be opposite of electromagnetism energy use up ability, this kind is used up can be to reflex the end that answer a source already, the means that also can give out heat through oneself of parts of an apparatus is its changeover another kind of energy. The damp that insert caustic parameter however and can not reflect a circuit system is characteristic, this also is the thing that most design personnel headaches most, often the application of parts of an apparatus of correct parameter is in circuit, the result is mixed however below of carry on of a few intermediary similar, circuit noise did not fall to rise instead.

 

Next graphs are the test system of Chang Hui appearance, use network analyzer and tailor-made clamping apparatus, use at checking the S parameter of the parts of an apparatus such as magnetism bead. When what use a 600R magnetism bead has a test when, its are shown like plan institute as a result.

 

Graph 6 Use network analyzer to check magnetism bead to insert caustic

 

Graph 7 magnetism bead the curve that insert caustic

 

Because of the impedance curve that give out insufficient clarity, here is approximate estimation LBEAD=1.59μH, CPAR=0.7pF, RDC=600mΩ , RAC=680Ω , following plan institute show the curve inserting caustic that uses this parameter computation to get. Can see, the result that computation gives and test photograph are compared, in high frequency insert caustic a few lower, we checked equipment to pass accurate calibration suppose, the difference that causes test result so is curve of product impedance parameter not accurate! It is 90.74MHz according to the nadir inserting caustic of the test, the 18.188dB that insert caustic, write the parameter in testing a system software, through recount, get this the LBEAD=1.59μH of magnetism bead, CPAR=2.1pF, RDC=600mΩ , RAC=715Ω . The curve inserting caustic after amending and impedance curve distributing as follows plan institute is shown. We see the curve inserting caustic after amending, agree almost completely of the parameter inserting caustic that Mark nods and real test.

 

Graph 8 According to the curve inserting caustic that computation of product impedance curve gets

 

Graph 9 The curve inserting caustic after amending

 

Graph the 10 impedance curves after amending

 

Opposite at inductance, the insertion of magnetism bead loss character is to slant small, LC filter wave is used alone in circuit, can realize the greater value that insert caustic, 80dB can accomplish even in actual measurement insert caustic. But use LC filter wave alone, when syntonic frequency of LC of frequency tower above, its insert damage value to will be reduced quickly, we are not willing to see this, can cooperate magnetism bead to improve high frequency character right now.

 

Graph 11 Ferrite is used in circuit of L filter wave the character inserting caustic of magnetism bead (computational value)

 

3, the magnetism in power source bead

 

There is the case that magnetism bead has use ferrite noise is restrained and be improved in the data of Murata company. Following plan institute are shown, can see, magnetism bead has apparent segregation effect to IC noise.

 

Graph 12 Use magnetism bead to undertake noise restrains the example with improvement

 

ANSYS Simplorer is used to build circuit of a Buck below, input 10V, output 3.5V, switch frequency is 200khz, occupy sky comparing 50% , the weaveform that we need to examine each parts of an apparatus and switch canal are in those who input end to conduct noise.

 

Graph 13 Buck circuit emulates a model

 

Graph 14 The voltage on each parts of an apparatus is undee

 

Next graphs are what LISN receives to conduct noise, the harmonic that can see itself of switch power source is richer. The switch frequency of 200Khz, its harmonic is outspread all the time still see apparently to 20MHz. Mains switch canal occupies sky comparing for 50% , theoretic 50% occupy sky comparing to fall occasionally second harmonic amplitude should is 0, it is however here be not 0 values, is this why? This problem leaves a reader to think.

 

Graph 15 LISN carries those who receive to conduct noise

 

Go up a medium magnetism bead equivalent circuit joins power source to input end, following plan institute are shown, examine magnetism bead to be opposite in circuit the filter wave effect of switch noise. Affirmative somebody should ask here, why to choose high frequency (the magnetism with 100MHz) highest impedance bead noise of low frequency of manage of place to go, the reader that holds similar opinion asks the heart below Xian Jing to continue oversee. Can see from inside the result even if high frequency magnetism bead, also have certain attenuation to power source noise, in pursueing below, can see, inductance electrify presses ripple to be reduced apparently, LISN receives conduct noise to also certain level drops (line value is here, drop at this o’clock when changeover is logarithm to be worth negligible not plan) .

 

Graph 16 Join the BUCK circuit after circuit of magnetism bead equivalent

 

Graph 17 The on each component voltage after joining circuit of magnetism bead equivalent is undee

 

Graph 18 Join what LISN of magnetism bead around receives to conduct noise to contrast

 

The person that always have some of good work uses magnetism bead to replace inductance, put in power source to input end, comprise filter wave circuit with capacitance, following plan institute are shown. Use similar way to be able to produce a kind of problem, end of input of power source input is in low frequency paragraph can have very large antiresonance generation. Place of following graph LISN result are shown, 1MHz the following noise all has apparent fall. However the power source noise that the noise amplitude before 0.6MHz does not have filter wave measure to fall to prep above very. Those who make a person disappointed is, because be opposite,a certain quantity of engineer is met of inductance do not understand and choose to increase capacitance to hold a cost directly, right now capacitance look value jumps over little imagine big, low frequency noise is louder, rectifying and reform a contact to go to is water of a mist.

 

Graph 19 In the input end adds 10nF capacitance and magnetism bead (equivalent circuit is replaced) the BUCK circuit when

 

Graph 20 3 kinds of circumstances issue what LISN receives to conduct noise

 

When low connect filter network (by ferrite magnetism bead inductance and tall Q go occasionally capacitance is comprised) syntonic frequency under magnetism bead hand in when jumping over frequency, produce aiguille. Filter wave eventuate owes damp. Issueing what the graph shows is the relation curve that TDK MPZ1608S101A measures impedance and frequency (document offers) . Block sex component (concern with the dissipation that disturbs energy) in achieve about 20 MHz arrives before 30MHz limits the impact is not big. Under this magnetism bead still has frequency criterion ferrite extremely high Q cost, and use as ideal inductance. The LC resonance frequency of magnetism bead filter is located in typical ferrite commonly 0.1MHz arrives inside 10MHz limits. Arrive to 300kHz the typical switch frequency inside 5MHz limits, need more damp to reduce filter Q cost.

 

Curve of graph 21(a) A TDK MPZ1608S101A ZRX; Graph 21(b) ferrite magnetism bead and electric capacity are small the S21 that connects filter is answered

 

A give a demonstration of this effect showed on; In the graph, the S21 frequency of magnetism bead is answered and electric capacity is small connected filter to show peak value effect. The ferrite that this uses in the exemple is magnetism bead TDK MPZ1608S101A(100? , 3A, 0603) , use go Ou capacitance is capacitance of pottery and porcelain of Murata GRM188R71H103KA01 low ESR (10 NF, x7R, 0603) . Load current is microamper level.

 

Without damp ferrite magnetism bead filter may be shown from make an appointment with 10dB to arrive the aiguille that makes an appointment with 15dB, specific depend on value of filter circuit Q. In graph 4b, aiguille appears in 2.5MHz to control, gain is as high as 10dB.

 

In addition, signal gain arrives in 1MHz inside 3.5MHz limits visible. If this aiguille appears in the working frequency of switch manostat paragraph inside, may have a problem so. It can magnify interference switch bogus resembles, affect the performance of sensitive load badly, lock up photograph annulus for instance (PLL) , pressure accuse an oscillator (VCO) and converter of high resolution modulus (ADC) . The eventuate that shows in graph 4b uses imponderability load (microamper level) , but arrive to needing to count microamper only the circuit part of 1mA load current perhaps is below certain work mode close the share with saving power comsumption, this is a practical application. This potential aiguille produced additional noise in the system, may bring about undesirable string together faze.