Electromagnetic Interference (EMI) and filter design for Switched Mode Power Supplies

Electromagnetic Interference (EMI) and filter design for SMPS Centre for Airborne Systems, DRDO

1

TABLE OF CONTENTS

(A). Abstract .................................................................................................................................................................... 3

(B). List of Figures .......................................................................................................................................................... 4

1. Fundamentals of EMI/EMC ..................................................................................................................................... 6

What is EMI/EMC ....................................................................................................................................................... 7

Source of Electromagnetic Interference ................................................................................................................... 7

The three elements of an EMI problem .................................................................................................................... 8

Types of coupling in EMI ........................................................................................................................................... 9 Impedance coupling .............................................................................................................................................. 10 Inductive coupling ................................................................................................................................................ 11 Capacitive coupling ............................................................................................................................................... 11 Radiative coupling ................................................................................................................................................. 11 Crosstalk ................................................................................................................................................................. 12

Modes of coupling in EMI ........................................................................................................................................ 12

Differential Mode .................................................................................................................................................. 12 Common Mode ..................................................................................................................................................... 13

2. Medium and High frequency modeling of components ................................................................................... 14

Capacitors ................................................................................................................................................................... 15

Inductors ..................................................................................................................................................................... 16

Power diode with reverse recovery ......................................................................................................................... 18

Power MOSFET ......................................................................................................................................................... 21

3. Measurement of EMI in DC-DC converters ....................................................................................................... 29

What are DC-DC power converters ....................................................................................................................... 30

Fly-back converter ..................................................................................................................................................... 30

Basic topology of fly-back converter ....................................................................................................................... 31

Line Impedance Stabilization Network (LISN) ..................................................................................................... 32

Measurement of EMI ................................................................................................................................................ 35

4. EMI filter design for DC-DC converters ............................................................................................................. 43


2

Introduction ............................................................................................................................................................... 44

Topology of an EMI filter ......................................................................................................................................... 44

Basis of determining filter component values ....................................................................................................... 45

Common mode ...................................................................................................................................................... 45 Differential mode .................................................................................................................................................. 47

Software based EMI noise separation method ....................................................................................................... 48

Design procedure for EMI filter .............................................................................................................................. 49

Software implementation of EMI filter design ...................................................................................................... 51

SPICE verification of the designed EMI filter ........................................................................................................ 53

Comparison of results obtained with and without filter ...................................................................................... 62

5. Conclusion ................................................................................................................................................................. 63

6. References .................................................................................................................................................................. 64


3

ABSTRACT

The goal of this work was to simulate the Electromagnetic Interference (EMI) generated in a fly-back converter, design a filter based on the generated data and to study the EMI characteristics of the power converter after integration with the filter.

To achieve the designated goals, SPICE models of Power MOSFET and Power diode were improved to simulate the switching characteristics and the reverse recovery characteristics respectively. These improved models are then integrated in the fly-back converter and the EMI data is generated. Based on the data generated, a filter is designed and then integrated to the power converter. The EMI characteristics of the circuit are again generated and a significant improvement in the EMI characteristics is observed.


4

LIST OF FIGURES

S. No Figure Page 1. The three elements of an EMI problem 8 2. Possible modes of coupling in EMI 9 3. Impedance coupling between System A and System B 10 4. Avoiding common impedance between System A and System B 11 5. Differential mode noise 12 6. Common mode noise 13 7. Series R-L-C model for capacitor with parasitic effects 15 8. Impedance response of a series R-L-C model for capacitor 15 9. Impedance response of an ideal capacitor 16 10. Parallel R-L-C model for inductor with parasitic effects 17 11. Impedance response of a parallel R-L-C model for inductor 17 12. Impedance response of an ideal inductor 18 13. Reverse recovery current of a diode 18 14. Input voltage and Output current of a diode 20 15. Close-up view of the reverse recovery characteristic of diode 20 16. Test structure for the proposed MOSFET model 21 17. Internal schematic diagram of the proposed MOSFET model 22 18. Step response of gate-source voltage 27 19. Step response of drain-source voltage 28 20. Step response of drain current 28 21. Ideal fly-back converter schematics 31 22. Output characteristics of an ideal fly-back converter 32 23. Measurement setup for conducted EMI 33 24. Schematic of LISN 33 25. Impedance offered by LISN for the full frequency spectrum (10Hz to 100 MHz) 34 26. Impedance offered by LISN in the high frequency range (10kHz to 100MHz) 34 27. Circuit to measure EMI generated by fly-back converter (with parasitic and realistic

elements) 35

28. Output voltage of the fly-back converter with parasitic elements 39 29. Output voltage ripple 39 30. FFT of the output waveform 40 31. Frequency vs. live voltage (dBμV) 40 32. Frequency vs. neutral voltage (dBμV) 41 33. Common mode noise (in dBμV) 42 34. Differential mode noise (in dBμV) 42 35. Topology of an EMI filter 45 36. Common mode noise equivalent circuit 45 37. Differential mode noise equivalent circuit 45 38. Common mode noise equivalent circuit 46 39. Equivalent circuit of Fig. 38 if ZP >> ( ) and w(Lc + Ld/2) >> 25Ω 46

40. Equivalent circuit of Fig. 39 after applying reciprocity theorem 46 41. Filter attenuation for common-mode noise 46


5

42. Differential mode noise equivalent circuit 47 43. Equivalent circuit of Fig. 42 if ZCX1 >> 100Ω; ZCX2 >> ZP; and wLDM >> 100Ω 47 44. Equivalent circuit of Fig. 43 after applying reciprocity theorem 47 45. Filter attenuation for differential-mode noise 47 46. Circuit diagram for separation of conductive EMI signals 48 47. Flowchart of software based separation of conductive EMI signals 48 48. Design steps of the presented filter design 50 49. Developed MATLAB GUI for conducted EMI filter design 51 50. EMI filter results obtained for the fly-back converter 52 51. EMI filter using the data obtained by the GUI 53 52. Attenuation curve for the EMI filter designed 53 53. LISN followed by EMI filter and fly-back converter 54 54. Output voltage of the fly-back converter with LISN and EMI filter 58 55. Output voltage ripple with EMI filter 59 56. FFT of the output voltage with EMI filter 59 57. Frequency vs. live voltage with EMI filter (in dBμV) 60 58. Frequency vs. neutral voltage with EMI filter (in dBμV) 60 59. Common mode noise with EMI filter (in dBμV) 61 60. Differential mode noise with EMI filter (in dBμV) 61 61(A) Common mode noise without EMI filter 62 61(B) Common mode noise with EMI filter 62 62(A) Differential mode noise without EMI filter 62 62(B) Differential mode noise with EMI filter 62


6

1. Fundamentals of EMI/EMC


7

WHAT IS EMI/EMC

Electromagnetic Interference can be described as the degradation of a device or system caused by an electromagnetic disturbance. An electromagnetic disturbance is any phenomena, which may degrade the performance of a device, equipment or system, or adversely affect living or inert matter. An example of EMI affecting living matter is the current controversy regarding portable cellular telephones causing brain tumours.

Therefore, an electromagnetic disturbance can be an unwanted signal or even a change in the propagation medium itself. A change in the propagation medium can attenuate the signal and have a direct effect on the level of disturbance.

On the other hand, EMC (Electromagnetic Compatibility) can be described as the ability of different pieces of electrically operated equipment to work in close proximity to each other without causing any mutual interference. EMC therefore implies the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to any other equipment in that environment. EMC is a twofold occurrence and consists of emissions and immunity.

First, EMC implies that the equipment will not generate unacceptable interference emission levels, which could cause interference; and second, EMC implies that the equipment’s intrinsic immunity levels are such that it can tolerate ambient levels of interference without degradation of performance.

Therefore, EMC means that a device must be capable of operating in all modes in the environment for which it was designed without degrading its own performance or that of any nearby equipment.

SOURCES OF ELECTROMAGNETIC INTERFERENCE

An electromagnetic environment can be described as the electromagnetic conditions existing at a given location. The EMI environment includes interference emanating from natural sources like lightning and atmospheric static to the various man-made sources of interference such as vacuum cleaners, washing machines, power tools, computers, cellular phones, mobile radios and even electronic toys.

Natural sources can be either terrestrial or extra-terrestrial in nature. Man-made sources include intentional or unintentional radiators. Within the scope of man-made noise sources, we can break it down even further into Inter-system interference and Intra-system interference. Inter-system interference is EMI in a system caused by an electromagnetic disturbance generated by another system; whereas Intra-system interference is self-generated EMI present in a system.

There is very little that can be done to prevent electromagnetic energy generated from natural interference sources. However, natural sources do not create that much of a problem except for perhaps, surges and spikes on power lines induced by lightning strikes. It is also very difficult to prevent EMI from intentional sources of electromagnetic energy. Cellular telephones and two-way radios are a major problem and can


8

create havoc for example in hospital environments. It is therefore crucial that electronic equipment be made immune or less susceptible to environmental interference.

However, the major source of all interference is generated from unintentional manmade sources. This is due to the vast amount of electrical and electronic equipment in use.

THE THREE ELEMENTS OF AN EMI PROBLEM

There are three essential elements to any EMC problem. There must be an EMI source or an electromagnetic disturbance, a receptor or ”victim” that cannot function properly due to the electromagnetic phenomenon, and a path between them that allows the source to interfere with the receptor. Each of these three elements must be present at the same time in order to have an electromagnetic disturbance or EMI. Identifying at least two of these elements and eliminating or attenuating the interference from one of them can solve EMC problems.

Interference signals are established whenever electrons move. Therefore, any current flow may cause either direct coupling to other circuits or radiated fields, which may in turn couple unwanted signals into other circuits.

Their frequency, bandwidth and amplitude can characterize sources of interference. The propagation medium of EMI below 30 MHz tends to be mains-borne or conducted. The interference travels along the power cord or signal lines from the source to the receptor or victim circuit. The conducted interference is not easily attenuated over distance.

The radiated portion of EMI emissions is borne as an electromagnetic wave, propagating through the air or any other non-conducting media. Generally, the higher the EMI in the frequency spectrum, the more easily it will radiate. EMI and EMC are becoming more of a problem due to the trend to produce equipment in smaller packages operating at very high speeds and processing rates.

The use of higher speed switching logic increases emissions from printed circuit boards. Also the use of devices with low operating voltages and currents, packaged more closely together, increases the potential for intra-system interference and reduced immunity (increased susceptibility).

Coupling Path

Fig. 1- the three elements of an EMI problem

Source (Culprit)

Device (Victim)

Electromagn

TYPES OF C

Any situatcomplemenvictim, whic

Knowledge coupling faperformancemissions waspects are c

Putting souSome of the

The most cowiring andelectromagncoupling belayout and screening pcoupling camaterials mconductors

There are ba

1. Imp

etic Interfere

COUPLING

ion, in whntary aspectsch is suscepti

of how thector is often

ce specificatiwill also imprconsidered s

urce and victe possibilities

ommon culpd mechanicnetic fields, etween equipproximity oflanes will en

an be either cmay also redu

in most prac

asically 5 mo

pedance coup

nce (EMI) and

IN EMI

hich the qus as discusseible to this in

e source emin the only wion. The tworove the susceparately.

im together s are shown i

Fig

prit in EMC sal structurewhich coup

pment is mof interfering

nhance an intcapacitive oruce the fieldctical situatio

odes of coupl

pling

d filter design

uestion of ed above. An

nterference. I

issions are cay to reduceo aspects arceptibility, th

shows the pin the followi

ig. 2 – Possibl

situation is tes. These eple with the odified by th

and victimterfering signr inductive ad by absorptons.

ling, namely

for SMPS

electromagnny such situaIf either of th

coupled to te interferencre frequentlyhough this is

potential intewing figure.

le modes of c

the antenna lelements ca

circuits. Inhe presence o

equipment anal by reflectand depends tion, though

etic compatation must hhese is not pr

the victim isce effects, if y reciprocal s not always

erference rou

coupling in EM

like behavioun transfer practical si

of screening and especialltion or attenon orientati

h this is negl

Centre fo

tibility arisehave a sourcresent, there

s essential, sa product isthat is meatrue. For an

utes that exis

MI

ur of cables, energy via

ituations, intand dielectr

ly their respeuate it by abion, length aligible comp

or Airborne Sy

es, invariabce of interfeis no EMC p

since a redus to continueasures taken n easy analys

st from one t

PCB tracks, electric, m

ntra-system aric materialsective cables

bsorption. Caand proximitpared with th

ystems, DRDO

ly has twoerence and aproblem.

ction in thee to meet its

to improveis, these two

to the other.

and internalmagnetic orand external, and by the

s. Ground orable-to-cablety. Dielectriche effects of

O

9

o a

e s e o

.

l r l e r e c f

Electromagn

2. Ind3. Cap4. Rad5. Cro

1. Impedan

When the vbe coupled the noise pr

Shown belovictim circucurrent withvictim circu

The solutioway that thcommon im

etic Interfere

ductive couplpacitive coupdiative couplosstalk

nce coupling

victim shares to the victim

roduced in th

ow in the figuuit share a ch time in th

uit in series w

n is to avoidhere is no c

mpedance and

nce (EMI) and

ling pling ing

g

common imm and may inhe source can

ure is commocommon grohe source cirwith its own s

Fig. 3 – Imp

d any commocommon imd hence solv

d filter design

mpedance witnterfere withn also couple

on mode impund connect

rcuit producsource.

pedance coup

on path betwpedance. Coes the proble

for SMPS

th the sourceh its workinge either induc

pedance couption. This co

ces a voltage

pling between

ween the souonnection asem.

e, any noise,g. Apart fromctively or cap

pling. As shoonnection is

across this

n System A a

urce and victs shown in

Centre fo

which is prom conductivepacitvely to t

own in the ciinductive in

connection

nd System B

im and connthe followin

or Airborne Sy

oduced in theely coupled tothe victim.

ircuit, the son nature. Thwhich is cou

nect the circung figure av

ystems, DRDO

e source, willo the victim,

urce and thehe change inupled to the

uit in such avoids having

O

10

l ,

e n e

a g

2

3

4

Io

Electromagn

This problePCB.

2. Inductiv

The magneplaced nearconductors.orientation magnetic cowhether or the circuits

3. Capaciti

Changing vinduce a vol

Both mutuaconductors.

4. Radiativ

If the disturbof the instal

etic Interfere

Fig.

m and its so

ve coupling

tic field formrby. The m. The mutuaand separat

oupling is a not there is awere isolated

ive coupling

voltage on onltage on it. T

al capacitanc. An optimal

ve coupling

bance on thelation may a

nce (EMI) and

4 – Avoiding

olution tell th

med around agnitude of al inductanction distance

voltage gena direct connd or connect

g

ne conductorThe magnitud

ce and mutual placement m

e power suppact as antenn

d filter design

g common im

he importanc

a conductof the voltagece depends oe and the prenerator in senection betweed to ground

r creates an ede of this vol

al inductancemust be decid

ply or data nnas and radi

for SMPS

mpedance bet

ce of proper

r when curre developed on the areasesence of anyeries with theen the two cd.

electric field,ltage depend

e are affectedded to minim

network contiate Electrom

tween System

layout of com

rent flows thdepends up

s of the souy magnetic s

he victim circircuits; the i

, which may ds on the mut

d by the phymize the effec

ains high fremagnetic fiel

Centre fo

m A and Syste

mponents wh

hrough it canpon the mu

urce and victscreening. Thrcuit. The coinduced volt

couple with tual capacitan

sical separaticts of these s

equency comld which can

or Airborne Sy

em B

while routing

n couple to utual inducttim current

The equivalenoupling is untage would b

a nearby conce of these

tion of sourcstray impedan

mponents, othn be picked

ystems, DRDO

them on the

a conductortance of the

loops, theirnt circuit fornaffected bye the same if

nductor andconductors.

e and victimnces.

her elementsup by other

O

11

e

r e r r y f

d

m

s r

ctr

5

Electromagn

conductors. towards radiradiate only

5. Crosstal

Apart from PCB traces and closer t

MODES OF

Understandsolving any in the follow

1. Differen

As shown inanother andmode interfown.

etic Interfere

All conductiative couplinwhen their li

lk

inductive anthrough disto reality. Th

F COUPLING

ding how anyEMC proble

wing paragra

ntial Mode

n the figure d returns thference betw

nce (EMI) and

tive parts of ng. It may beinear dimens

nd capacitivetributed indue phenomen

G IN EMI

y stray noiseem. The basiaphs.

below, the curough the o

ween the two

d filter design

f the electrice however nosion exceeds

e coupling atuctance and

non is also cal

e generated c modes of c

urrents carrither. A radiwires; simila

Fig. 5 – D

for SMPS

cal installatiooted that cons approximat

t single poincapacitance.lled as crosst

in a source coupling are

ied in differeiated field caarly, the diff

Differential m

on may servenductive elemtely half of th

t as discusse. This type otalk.

circuit is cothe different

ential mode fan couple toferential curr

mode noise

Centre fo

e as antennaments such ashe wavelength

d above, couf coupling of

upled to thetial and comm

flows in one this system

rent will indu

or Airborne Sy

as and hencs cables and h.

upling also of noise is mo

e victim circmon modes

cable from m and induce

uce a radiate

ystems, DRDO

e contributeslots start to

ccurs on theore common

cuit is key toas explained

one block toe differentialed field of its

O

12

e o

e n

o d

o l s

2

Electromagn

2. Commo

The cable alcurrents vecoupling toequipment susceptible. point and tmode curreEMC point

Although itthere may aoccurs whenexternal grophysical laylayout.

etic Interfere

on Mode

lso carries cury often hav

o the loop foto ground,

Alternativelthe cable conents means th

of view.

t was said abalso be a comn the two-sigound. These

yout, and are

nce (EMI) and

urrent in comve nothing tormed by th

and may tly, they maynnection, anhat no cable,

bove that commponent of gnal conducte impedances

only under t

d filter design

mmon modeto do with the cable, the then cause

y be generatend be respon, whatever si

Fig. 6 –

mmon modecommon m

tors present ds are dominthe circuit de

for SMPS

, that is, all fthe signal cu ground plainternal dif

ed by internnsible for radignals it may

Common mo

e currents mmode current

differing impnated at RF besigner’s con

flowing in thurrents. Theane and the fferential cunal noise voldiated emiss

y be intended

ode noise

may be unrelawhich is du

pedance to thby stray cap

ntrol if that p

Centre fo

e same direcy may be invarious imp

urrents to wtages betwee

sions. The exd to carry can

ated to the iue to the sigheir environm

pacitance andperson is also

or Airborne Sy

ction on eachnduced by epedances conwhich the eqen the grounxistence of Rn be viewed

intended signgnal current. ment, represd inductanceo responsible

ystems, DRDO

h wire. Thesexternal fieldnnecting thequipment isnd referenceRF commonas safe from

nal currents,Conversion

sented by thees related to

e for physical

O

13

e d e s e n

m

, n e o l


14

2. Medium and High frequency modelling of components

Electromagn

CAPACITO

An actual cainternal strufrequency wtypes of resian effectivefrequency. Aof the dielewhere the cchosen to m

etic Interfere

RS

apacitor inclucture. This

where it ringsistive effects

e series resisA parallel res

ectric materiaapacitor is u

model the filte

F

nce (EMI) and

ludes several inductance

s with the capin a capacito

stance (ESR)sistance mayal. This para

used as a low er capacitors

Fig. 7 – Seri

C

Fig. 8 – Imped

d filter design

parasitic effemay dominapacitance unor. Dielectric). Dielectric y be used to mallel resistancimpedance e

s and their pa

es R-L-C mod

Cmain = 1μF,

dance respon

for SMPS

fects. One of ate the impenless sufficienc losses and tlosses, whic

model the lece is negligibelement. Thearasitic effec

del for capac

, Ls = 22.5nH

nse of a series

these is the sdance of thently dampedthe non-zeroch dominateakage of the ble, howevere series R-L-ts.

citor with par

H, Rs = 0.025

R-L-C mode

Centre fo

series inductae component

by resistive o resistance o

the ESR, cacapacitor du

r, at the EMC model sho

rasitic effects;

5Ω

el for capacito

or Airborne Sy

tance of the lt above the seffects. Ther

of the leads ccause it to inue to the fini

MI frequencieown in Fig. 7

;

or

ystems, DRDO

eads and theself-resonantre are severalcontribute toncrease withite resistivityes of interest7 is therefore

O

15

e t l

o h y t e

Electromagn

INDUCTOR

The parasitthroughout parasitic capof the filterdamped or

The resistivfrequency. Aof the inducseries resistfrequenciesand the depis negligiblehand, is direcore loss, becore materiand flux lev

etic Interfere

RS

tic effects ofthe compo

pacitance mar, giving the even domina

ve impedanceAt low frequctive reactantance becom, the skin de

pendence of te below the kectly proportecomes impoal, may be m

vel.

nce (EMI) and

Fig. 9

f inductors nent. For siay resonate wcomponent

ated, howeve

e of an induuencies, lossence at the lowmes less impepth is only the resistanckHz range fotional to freqortant. Core

modelled by a

d filter design

9 – Impedanc

are quite complicity, thiwith the maicapacitive c

er, by lossy p

uctor, compris are determ

w frequenciesportant. Alta weak func

ce on this skior the wire dquency. As thlosses, inclu

a shunt resist

for SMPS

ce response of

omplex. Anis effect is min inductor acharacteristicarasitic effec

ising both wmined by the

s of power trthough the ction of freqin depth, althdimension ohe reactive im

uding both hytance; howev

f an ideal cap

n inductor hmodelled wiat a frequenccs above thiscts.

wire and coreseries wire rransmission.skin effect uency, inver

hough inversof interest. Thmpedance riysteresis effever this resist

Centre fo

pacitor

has winding th a parasiticy well withins frequency.

e losses, is a esistance wh At higher frincreases th

rsely proportsely proportiohe inductiveses, howevercts and eddytance is a fun

or Airborne Sy

capacitanceic shunt capin the range

This resona

complicatedhich may be frequencies, hhis resistanctional to its ional at high e reactance, or, the secondy currents innction of bot

ystems, DRDO

e distributedpacitor. Thisof operationance may be

d function ofon the orderhowever, thece at highersquare root,frequencies,

on the otherd type of loss,

duced in theth frequency

O

16

d s n e

f r e r , , r , e y

Electromagn

In addition densities duhowever, thindependenaccurate moR-L-C modrepresents t

etic Interfere

F

to these parue to skin effehese effects wnt of frequenodel for indudel, Cw reprthe core loss

Fig

nce (EMI) and

Fig. 10 – Para

Lm

rasitic effectsfects may chawere neglecte

cy. The circuuctors over thresents the eeffects.

g. 11 – Imped

d filter design

allel R-L-C m

main = 3.3mH

s, variations ange the actued in modelliuit shown in he measurabeffects of th

dance respon

for SMPS

model for indu

H, Cw = 30p

of core permual inductancing the induc Fig. 10 was

ble EMI frequhe distribute

nse of a parall

uctor with pa

pF, Rc = 22.3k

meability ovece of a compoctors. The cotherefore chuency range ed winding

lel R-L-C mo

Centre fo

arasitic effect

kΩ

er frequencyonent over fr

ore resistancehosen as a con

(10 kHz to 3capacitance

del for induc

or Airborne Sy

ts;

y and changefrequency. Foe was also asnvenient and30 MHz). In

and Rc pre

ctor

ystems, DRDO

es in currentor simplicity,ssumed to bed reasonably

n this paralleledominantly

O

17

t , e y l y

Electromagn

POWER DI

Reverse recooccurs whetransient rev

The diode mmodel whicreverse recoduring comdiode is sho

The diode mrecovery ch

etic Interfere

ODE WITH

overy plays aen a forwardverse curren

models widech includes thovery of the

mmutation toown in Fig. 1

model availaaracteristics.

nce (EMI) and

Fig. 12

REVERSE R

an importantd conducting

nt to flow at h

ely used in cihe effects of cdiode. Thus,

o the no-con3.

Fig

able in SPIC. The SPICE

d filter design

2 – Impedan

RECOVERY

t role in the ag diode is t

high reverse v

ircuit simulacharge storag, these diodenducting stat

g. 13 – Revers

CE is extendemacro-mod

for SMPS

nce response o

accuracy of sturned off ravoltage.

ators such asge during reve models alwte. The reve

se recovery cu

ed by providel code used

of an ideal in

simulation ofapidly, and

s SPICE are bverse recover

ways exhibit aerse recovery

urrent of a di

ding additionto model th

Centre fo

ductor

f a dc-dc conthe internal

based on thery operation an instantaney current cha

iode

nal data so ae diode is as

or Airborne Sy

nverter. Revelly stored ch

e original chbut does noeous or snaparacteristic o

as to includefollows:

ystems, DRDO

erse recoveryharge causes

harge controlt provide forppy recoveryof a realistic

e the reverse

O

18

y s

l r y c

e


19

Reverse recovery diode *reverse recovery Vin 1 0 pulse (-10 10 600n 0 0 600n 1200n) Rin 1 2 10 Xd1 2 0 40EPS08 .SUBCKT 40EPS08 A K D1 A K 40EPS08 .MODEL 40EPS08 d ( +IS=1e-15 RS=0.00426912 N=0.926332 EG=0.6 +XTI=0.5 BV=800 IBV=0.0001 CJO=1e-11 +VJ=0.7 M=0.5 FC=0.5 TT=1e-09 +KF=0 AF=1 ) .ENDS *reverse recovery .tran 1n 5600n 0 1n .probe

.end

Diode Model Parameters

Model Parameter Description Unit Value Specified IS Saturation current A 1E-15 RS Parasitic resistance Ohm 0.00426912 N Emission coefficient - 0.926332 EG Bandgap voltage (barrier height) eV 0.6 XTI IS temperature exponent - 0.5 BV Reverse breakdown knee voltage V 800 IBV Reverse breakdown knee current A 0.0001 CJO Zero-bias p-n capacitance F 1E-11 VJ p-n potential V 0.7 M p-n grading coefficient - 0.5 FC Forward-bias depletion capacitance coefficient - 0.5 TT Transit time Sec 1E-9 KF Flicker noise coefficient - 0 AF Flicker noise exponent - 1

Electromagn

etic Interfere

Fig

nce (EMI) and

Fig. 14

g. 15 – Close-

d filter design

4 – Input volt

up view of th

for SMPS

tage and Outp

he reverse rec

tput current o

overy charac

Centre fo

of diode

cteristics of di

or Airborne Sy

iode

ystems, DRDOO

20

Electromagn

POWER M

The commoit also has itthe drain-tolinearity of t

In this sectmentioned drain-sourcwhere it cor

etic Interfere

OSFET

on PSpice mts lacks for so-source resithe MOS cap

tion, a Poweparameters.

ce voltage, drrrectly predic

nce (EMI) and

odel for the some critical istance relatepacitor again

er MOSFET The chosen

rain current cts the EMI g

Fig. 16 –

d filter design

power MOSsimulating p

ed to the simnst applied vo

is modelled approach suand gate-sou

generated by

Test Structur

for SMPS

SFET devicesproblems. Th

mulation tempoltage.

taking intouccessfully reurce voltage

y the converte

re for the pro

is satisfyinghese lacks coperature and

account theeproduces th. The modeler.

oposed MOSF

Centre fo

g for most of onsist especiad in almost n

e non-lineare step respon is employed

FET model

or Airborne Sy

f the designerally in poor m

no-modelling

rity aspects onse characted in a fly-bac

ystems, DRDO

r’s needs butmodelling ofg of the non-

of the aboveristics of theck converter

O

21

t f -

e e r

Electromagn

The SPICE

POWER M .OPTION Vcc 1 0Vin 10 l1 1 2 r1 2 3 r2 10 1ls 13 0 Xm1 3 1

.subckt* * 10 = * ******** *------* PACKA

etic Interfere

Fig

macro-mode

MOSFET Mod

NS METHOD=

0 dc 50 0 pulse(0

51n 5

11 56 0 3n

11 13 mtp6

t mtp6n60/

Drain 20

**********

----------AGE INDUCT

nce (EMI) and

g. 17 – Interna

el code for th

del

=GEAR

10 0 20n

6n60/mc

mc 10 20 3

= Gate 30

**********

---------- TANCE

d filter design

al schematic

he above sho

20n 510n

30

= Source

**********

EXTERNAL

for SMPS

diagram of t

own schemati

4u)

***********

PARASITICS

the proposed

ic is as follow

**********

S --------

Centre fo

MOSFET mo

ws:

***********

-----------

or Airborne Sy

odel

**********

----------

ystems, DRDO

*****

-----

O

22


23

* LDRAIN 10 11 4.5e-09 LGATE 20 21 7.5e-09 LSOURCE 30 31 7.5e-09 * * RESISTANCES * RDRAIN1 4 11 RDRAIN 0.8036 RDRAIN2 4 5 RDRAIN 0.0084 RSOURCE 31 6 RSOURCE 0.02018 RDBODY 8 30 RDBODY 0.0135 * RGATE 21 2 5 * *-------------------------------------------------------------------------- * *--------------- CAPACITANCES AND BODY DIODE ------------------------------ * DBODY 8 11 DBODY DGD 3 11 DGD CGDMAX 2 3 2.7e-09 RGDMAX 2 3 1e+08 CGS 2 6 1.31e-09 * *-------------------------------------------------------------------------- * *----------------------- CORE MOSFET -------------------------------------- * M1 5 2 6 6 MAIN * *-------------------------------------------------------------------------- * .MODEL RDRAIN R( +TC1 = 0.008891 +TC2 = 3.056e-05) * .MODEL RSOURCE R( +TC1 = -0.003198 +TC2 = 2.60004e-05) * .MODEL RDBODY R( +TC1 = 0.003945 +TC2 = 9.54752e-06) * * .MODEL MAIN NMOS ( +LEVEL = 3 +VTO = 3.8 +KP = 13 +GAMMA = 2.6 +PHI = 0.6 +RD = 0 +RS = 0 +CBD = 0 +CBS = 0 +IS = 1e-14 +PB = 0.8 +CGSO = 0 +CGDO = 0 +CGBO = 0 +RSH = 0 +CJ = 0 +MJ = 0.5 +CJSW = 0 +MJSW = 0.33 +JS = 1e-14 +TOX = 1e-07 +NSUB = 1e+15


24

+NSS = 0 +NFS = 6.59e+11 +TPG = 1 +XJ = 0 +LD = 0 +UO = 600 +VMAX = 0 *+NEFF = 1 +KF = 0 +AF = 1 +FC = 0.5 +DELTA = 0 +THETA = 0 +ETA = 0 +KAPPA = 0.2) * *-------------------------------------------------------------------------- * .MODEL DGD D ( +IS = 1e-15 +RS = 0 +N = 1000 +TT = 0 +CJO = 1.129e-09 +VJ = 1.943 +M = 1.476 +EG = 1.11 +XTI = 3 +KF = 0 +AF = 1 +FC = 0.5 +BV = 10000 +IBV = 0.001) * *-------------------------------------------------------------------------- * .MODEL DBODY D ( +IS = 1.532e-11 +RS = 0 +N = 1.062 +TT = 2.5e-07 +CJO = 9.725e-10 +VJ = 1.127 +M = 0.6627 +EG = 1.11 +XTI = 5 +KF = 0 +AF = 1 +FC = 0.5 +BV = 671 +IBV = 0.00025) .ENDS .tran 1n 1u 0 1n .plot tran v(11,13) V(3,13) .probe .plot tran i(Xm1.ld) .end


25

Resistor Model Parameters (RDRAIN)

Model Parameter Description Unit Value Specified TC1 Linear temperature coefficient oC-1 0.008891 TC2 Quadratic temperature coefficient oC-1 3.056E-5

Resistor Model Parameter (RSOURCE)

Model Parameter Description Unit Value Specified TC1 Linear temperature coefficient oC-1 -0.003198 TC2 Quadratic temperature coefficient oC-1 2.60004E-5

Resistor Model Parameter (RDBODY)

Model Parameter Description Unit Value Specified TC1 Linear temperature coefficient oC-1 0.003945 TC2 Quadratic temperature coefficient oC-1 9.54752E-6

NMOS MOSFET Model Parameter

Model Parameter Description Unit Value Specified LEVEL Model index - 3 VTO Zero bias threshold voltage V 3.8 KP Transconductance coefficient amp/v2 13 GAMMA Bulk threshold parameter Volt1/2 2.6 PHI Surface potential V 0.6 RD Drain ohmic resistance Ohm 0 RS Source ohmic resistance Ohm 0 CBD Zero-bias bulk drain p-n capacitance Farad 0 CBS Zero-bias bulk source p-n capacitance Farad 0 IS Bulk p-n saturation current A 1E-14 PB Bulk p-n bottom potential V 0.8 CGS0 Gate-source overlap capacitance/channel width Farad/meter 0 CGD0 Gate-drain overlap capacitance/channel width Farad/meter 0 CGB0 Gate-drain overlap capacitance/channel length Farad/meter 0 RSH Drain, source diffusion sheet resistance Ohm/square 0 CJ Bulk p-n zero-bias bottom capacitance/area Farad/meter2 0 MJ Bulk p-n bottom grading coefficient - 0.5 CJSW Bulk p-n zero-bias sidewall capacitance/length Farad/meter 0


26

MJSW Bulk p-n sidewall grading coefficient - 0.33 JS Bulk p-n saturation current/area Amp/meter2 1E-14 TOX Oxide thickness Meter 1E-7 NSUB Substrate doping density 1/cm3 1E15 NSS Surface state density 1/cm2 0 NFS Fast surface state density 1/cm2 6.59E11 TPG Gate material type:

+1 = opposite of substrate -1 = same as substrate 0 = aluminium

- 1

XJ Metallurgical junction depth Meter 0 LD Lateral diffusion Meter 0 UO Surface mobility cm2/v-sec 600 VMAX Maximum drift velocity m/s 0 KF Flicker noise coefficient - 0 AF Flicker noise exponent - 1 FC Bulk p-n forward bias capacitance coefficient - 0.5 DELTA Width effect on threshold - 0 THETA Mobility modulation Volt-1 0 ETA Static feedback - 0 KAPPA Saturation field factor - 0.2

Diode Model Parameters (DGD)

Model Parameter Description Unit Value Specified IS Saturation current A 1E-15 RS Parasitic resistance Ohm 0 N Emission coefficient - 1000 TT Transit time Sec 0 CJO Zero-bias p-n capacitance Farad 1.129E-9 VJ p-n potential V 1.943 M p-n grading coefficient - 1.476 EG Bandgap voltage (barrier height) eV 1.11 XTI IS temperature exponent - 3 KF Flicker noise coefficient - 0 AF Flicker noise exponent - 1 FC Forward-bias depletion capacitance coefficient - 0.5 BV Reverse breakdown knee voltage V 10000 IBV Reverse breakdown knee current A 0.001

Electromagn

Diode Mod

Model Para IS RS N TT CJO VJ M EG XTI KF AF FC BV IBV

etic Interfere

del Paramete

ameter D SaPaEmTZep-p-BaISFlFlFoRR

nce (EMI) and

ers (DBODY

Description

aturation curarasitic resistmission coefransit time ero-bias p-n -n potential -n grading coandgap volta

S temperaturlicker noise clicker noise eorward-bias everse breakeverse break

Fig.

d filter design

Y)

rrent tance fficient

capacitance

oefficient age (barrier he exponentcoefficient exponent depletion ca

kdown knee vkdown knee c

18 – Step res

for SMPS

height)

apacitance covoltage current

sponse of Ga

oefficient

te-Source vol

Centre fo

U A

V

e

VA

ltage

or Airborne Sy

Unit Valu A 1.53Ohm 0 - 1.06Sec 2.5EFarad 9.72V 1.12- 0.66eV 1.11- 5 - 0 - 1 - 0.5 V 671 A 0.00

ystems, DRDO

ue Specified

32E-11

62 E-7 25E-10 27 627

0025

O

27

Electromagn

etic Interference (EMI) and

Fig.

F

d filter design

19 – Step res

Fig. 20 – Step

for SMPS

sponse of dra

p response of

ain-source vo

f drain curren

Centre fo

ltage

nt

or Airborne Syystems, DRDO

O

28


29

3. Measurement of EMI in DC-DC converters


30

WHAT ARE DC-DC POWER CONVERTERS

DC-DC power converters are employed in a variety of applications, including power supplies for personal computers, office equipment, aircraft power systems, laptop computers, and telecommunications equipment, as well as dc motor drives. The input to a dc-dc converter is an unregulated dc voltage Vg. The converter produces a regulated output voltage V, having a magnitude (and possibly polarity) that differs from Vg. For example, in the power supply system of the Airborne Early Warning & Control Systems (AEW&CS) the input supply of 200V/400Hz from the aircraft is rectified to 270V DC by a rectifier unit. This 270V DC is then supplied to a Multi-output power supply which converts this 270V DC into a number of smaller outputs using a DC-DC converter.

High efficiency is invariably required, since cooling of inefficient power converters is difficult and expensive. The ideal dc-dc converter exhibits 100% efficiency; in practice, efficiencies of 70% to 95% are typically obtained. This is achieved using switched-mode, or chopper, circuits whose elements dissipate negligible power. Pulse-width modulation (PWM) allows control and regulation of the total output voltage. This approach is also employed in applications involving alternating current, including high-efficiency dc-ac power converters (inverters and power amplifiers), ac-ac power converters, and some ac-dc power converters (low-harmonic rectifiers).

FLYBACK CONVERTER

Fly-back converter is the most commonly used SMPS circuit for low output power applications where the output voltage needs to be isolated from the input main supply. The output power of fly-back type SMPS circuits may vary from few watts to less than 100 watts. The overall circuit topology of this converter is considerably simpler than other SMPS circuits. Input to the circuit is generally unregulated dc voltage obtained by rectifying the utility ac voltage followed by a simple capacitor filter. The circuit can offer single or multiple isolated output voltages and can operate over wide range of input voltage variation. In respect of energy-efficiency, fly-back power supplies are inferior to many other SMPS circuits but it’s simple topology and low cost makes it popular in low output power range.

The commonly used fly-back converter requires a single controllable switch like, MOSFET and the usual switching frequency is in the range of 100 kHz. A two-switch topology exists that offers better energy efficiency and less voltage stress across the switches but costs more and the circuit complexity also increases slightly.

Electromagn

BASIC TOP

Fig. 21 showderived fromgenerally ofSince the SMspite of beinA fast switcthe desired between intransformerbe noted tsimultaneounormal tranampere turnSince primamore like transformerdone like threctificationAs can be sdiode and a

etic Interfere

POLOGY OF

ws the basicm the utility f low frequenMPS circuit ng unregulatching device,

output voltput and our are wound that the priusly and in nsformer, unns of primaryary and secotwo magnet

r as inductorhat for an in

n and filterinseen from tha capacitor. V

nce (EMI) and

FLYBACK C

c topology oac supply af

ncy and the is operated aed, may be clike a MOSF

tage. The trutput voltage

to have goodimary and sthis sense flnder load, py winding is

ondary windtically coupr-transformenductor. Th

ng, is considehe circuit (FigVoltage acros

Fig

d filter design

CONVERTER

f a fly-back fter rectificatoverall ripplat much highconsidered toFET, is used ansformer ise and currend coupling sosecondary wly-back trans

primary and nearly balanings of the fled inductorer. Accordine output secerably simplg.21), the secss this filter c

g.21 – Ideal f

for SMPS

R

circuit. Inpution and somle voltage waher frequenco have a cons

with fast dyns used for vnt requiremo that they a

windings of sformer worsecondary w

nced by the ofly-back tranrs and it m

ngly the magction of the ler than in mcondary win

capacitor is th

fly-back conv

ut to the cirme filtering. Taveform repecy (in the ranstant magnitunamic contrvoltage isola

ments. Primaare linked by

the fly-bacrks differentwindings co

opposing ampnsformer donmay be morgnetic circuit

fly-back tramost other swnding voltagehe SMPS out

verter schema

Centre fo

rcuit may beThe ripple ineats at twice nge of 100 kHude during aol over switction as well

ary and seconearly samek transformly from a nonduct simulpere-turns ofn’t conduct re appropriat design of ansformer, w

witched mode is rectified tput voltage.

atic

or Airborne Sy

e unregulatedn dc voltage the ac main

Hz) the inpuany high freqch duty ratiol as for bettondary winde magnetic flumer don’t ca

ormal transfltaneously suf the secondsimultaneou

ate to call ta fly-back trawhich consistde power sup

and filtered

ystems, DRDO

d dc voltagewaveform is

ns frequency.ut voltage, inquency cycle. to maintainer matching

dings of theux. It shouldarry currentformer. In auch that theary winding.

usly they arethe fly-backansformer ists of voltagepply circuits.

using just a

O

31

e s .

n .

n g e d t a e . e k s e . a

Electromagn

LINE IMPE

LISN is an converter insituation is

An LISN rea

1. It al2. It fe3. It p4. It p

rep

etic Interfere

DANCE STA

industrial encluding loadshown in Fig

alizes four im

llows supplyeeds and con

prevents exterpresents a croducibility

nce (EMI) and

Fig. 22 – Ou

ABILIZATION

element offed as an interfg. 23.

mportant task

ying the equipncentrates disrnal noise toonstant impfrom site to

d filter design

utput charac

N NETWOR

ered by stanface to make

ks

pment with Asturbance thr modify mea

pedance of 5site.

for SMPS

cteristics of an

K

ndards to ple it possible m

AC power (lorough the m

asurements 50Ω with re

n ideal fly-ba

lace betweenmeasuring th

ow frequencymeasurement

espect to fre

Centre fo

ack converter

n the supplyhe conducted

y behaviour)points.

equency whi

or Airborne Sy

y and powerd interference

) from the po

ich allows m

ystems, DRDO

r electronicse. The stated

ower mains.

measurement

O

32

s d

t

Electromagn

The adopted

etic Interfere

d LISN topol

nce (EMI) and

Fig. 2

logy is shown

Fig. 24 – Sc

d filter design

23 – Measure

n in Fig. 24.

hematic of L

for SMPS

ement setup f

ine Impedan

for conducted

nce Stabilizat

Centre fo

d EMI

ion Network

or Airborne Sy

ystems, DRDOO

33

Electromagn

It is evidentthus allowin

etic Interfere

Fig. 25 – Imp

Fig. 26 – Im

t from the Imng standardiz

nce (EMI) and

pedance offer

mpedance offe

mpedance cuzed measure

d filter design

red by LISN f

ered by LISN

urves that a Lment of EMI

for SMPS

for the full fr

in the high fr

LISN offers aI component

requency spec

frequency ran

a constant imt (10 kHz to

Centre fo

ctrum (10Hz

nge. (10 kHz t

mpedance of 30 MHz).

or Airborne Sy

to 100 MHz)

to 100 MHz)

50Ω at high

ystems, DRDO

)

)

frequencies,

O

34

,

Electromagn

MEASUREM

Fig. 27 –

The SPICE

REALIST .OPTION ******** INPUT Vinput Vgate 7 ******* * LISN Clisn1_Rlisn1_ Llisn1 Clisn1_Rlisn1_Rlisn1_ ******* * LISN Clisn2_Rlisn2_ Llisn2 Clisn2_

etic Interfere

MENT OF E

Circuit to me

net-list for th

TIC FLYBAC

N METHOD=G

**********T VOLTAGE

1 2 dc 307 8 pulse(

**********

1

_1 1 12 8u_1 12 0 5

1 3 50uH

_2 3 11 0._2 11 0 1k_3 11 0 50

**********

2

_1 2 10 8u_1 10 0 5

2 8 50uH

_2 8 9 0.2

nce (EMI) and

MI

easure EMI g

he above sho

CK CONVERTE

GEAR LVLTIM

**********

0V 0 10 0 10n

**********

u

25u k

**********

u

5u

d filter design

generated by

own schemat

ER

M=1

**********

n 10n 0.58

**********

**********

for SMPS

the fly-back

tic is as show

***********

8u 1u)

***********

***********

converter (w

wn below:

**********

**********

**********

Centre fo

ith parasitic

***********

***********

***********

or Airborne Sy

and realistic

******

******

******

ystems, DRDO

c elements)

O

35


36

Rlisn2_2 9 0 1k Rlisn2_3 9 0 50 ********************************************************************* * primary side of flyback converter R1 3 4 0.014 Cpar1 4 5 2.73nF Lpar1 5 6 1.58uH Xm1 6 7 8 mtp6n60/mc ********************************************************************* * flyback transformer LFPRIMARY 4 5 14u LFSECONDARY 0 13 0.6u KTX LFPRIMARY LFSECONDARY 0.99 ********************************************************************* * capacitor parasitics of flyback transformer CtxPar1 4 13 0.29nF CtxPar2 5 0 0.29nF ********************************************************************* * secondary side of transformer Cpar2 13 0 4.46nF Xd1 13 14 40EPS08 Cfilter 14 0 50uF Rload 14 0 3.2 ********************************************************************* * MOSFET subcircuit .subckt mtp6n60/mc 10 20 30 * * 10 = Drain 20 = Gate 30 = Source * ********************************************************************* * *------------------------ EXTERNAL PARASITICS ----------------------- * PACKAGE INDUCTANCE * LDRAIN 10 11 4.5e-09 LGATE 20 21 7.5e-09 LSOURCE 30 31 7.5e-09 * * RESISTANCES * RDRAIN1 4 11 RDRAIN 0.8036 RDRAIN2 4 5 RDRAIN 0.0084 RSOURCE 31 6 RSOURCE 0.02018 RDBODY 8 30 RDBODY 0.0135 * RGATE 21 2 5


37

* *-------------------------------------------------------------------- * *--------------- CAPACITANCES AND BODY DIODE ------------------------ * DBODY 8 11 DBODY DGD 3 11 DGD CGDMAX 2 3 2.7e-09 RGDMAX 2 3 1e+08 CGS 2 6 1.31e-09 * *-------------------------------------------------------------------- * *----------------------- CORE MOSFET -------------------------------- * M1 5 2 6 6 MAIN * *-------------------------------------------------------------------- * .MODEL RDRAIN R( +TC1 = 0.008891 +TC2 = 3.056e-05) * .MODEL RSOURCE R( +TC1 = -0.003198 +TC2 = 2.60004e-05) * .MODEL RDBODY R( +TC1 = 0.003945 +TC2 = 9.54752e-06) * * .MODEL MAIN NMOS ( +LEVEL = 3 +VTO = 3.8 +KP = 13 +GAMMA = 2.6 +PHI = 0.6 +RD = 0 +RS = 0 +CBD = 0 +CBS = 0 +IS = 1e-14 +PB = 0.8 +CGSO = 0 +CGDO = 0 +CGBO = 0 +RSH = 0 +CJ = 0 +MJ = 0.5 +CJSW = 0 +MJSW = 0.33 +JS = 1e-14 +TOX = 1e-07 +NSUB = 1e+15 +NSS = 0 +NFS = 6.59e+11 +TPG = 1 +XJ = 0 +LD = 0 +UO = 600 +VMAX = 0 +KF = 0 +AF = 1 +FC = 0.5 +DELTA = 0 +THETA = 0 +ETA = 0


38

+KAPPA = 0.2) * *-------------------------------------------------------------------- * .MODEL DGD D ( +IS = 1e-15 +RS = 0 +N = 1000 +TT = 0 +CJO = 1.129e-09 +VJ = 1.943 +M = 1.476 +EG = 1.11 +XTI = 3 +KF = 0 +AF = 1 +FC = 0.5 +BV = 10000 +IBV = 0.001) * *-------------------------------------------------------------------- * .MODEL DBODY D ( +IS = 1.532e-11 +RS = 0 +N = 1.062 +TT = 2.5e-07 +CJO = 9.725e-10 +VJ = 1.127 +M = 0.6627 +EG = 1.11 +XTI = 5 +KF = 0 +AF = 1 +FC = 0.5 +BV = 671 +IBV = 0.00025) .ENDS ********************************************************************* * diode subcircuit .SUBCKT 40EPS08 A K D1 A K 40EPS08 .MODEL 40EPS08 d ( +IS=1e-15 RS=0.00426912 N=0.926332 EG=0.6 +XTI=0.5 BV=800 IBV=0.0001 CJO=1e-11 +VJ=0.7 M=0.5 FC=0.5 TT=1e-09 +KF=0 AF=1 ) .ENDS ********************************************************************* .tran 1ms 10ms .plot tran V(10,0) .FOUR 10kHz 100 V(10,0) .probe .end

The results obtained from the simulation of the above circuit are shown below:

Electromagn

etic Interfere

Fig.2

nce (EMI) and

28 – Output v

d filter design

voltage of the

Fig. 29 –

for SMPS

e fly-back con

Output volta

nverter with p

age ripple

Centre fo

parasitic elem

or Airborne Sy

ments

ystems, DRDOO

39

Electromagn


Fi

d filter design

Fig. 30 – FF

ig. 31 – frequ

for SMPS

T of the outp

uency vs. live

put waveform

voltage (dBμ

Centre fo

m

V)

or Airborne Sy

ystems, DRDOO

40

Electromagn


Fig.

d filter design

32 – frequen

for SMPS

ncy vs. neutra

al voltage (dB

Centre fo

BμV)

or Airborne Sy

ystems, DRDOO

41

Electromagn


F

Fig

d filter design

ig. 33 – Com

g. 34 – Differ

for SMPS

mmon mode n

rential mode

noise (in dBμ

noise (in dBμ

Centre fo

V)

μV)

or Airborne Sy

ystems, DRDOO

42


43

4. EMI filter design for DC-DC converters


44

INTRODUCTION

The main purpose of the EMI filter is to limit the interference that is conducted or radiated from the power circuit. Excessive conducted or radiated interference can cause erratic behaviour in other systems that are in close proximity of, or that share an input source with, the power circuit. If this interference affects the power circuit, it can cause erratic operation, excessive ripple, or degraded regulation, which can lead to system level problems. Input EMI filters may also be used to limit inrush current, reduce conducted susceptibility, and suppress spikes. The specifications for the allowable interference are generally driven by the power circuit specification. The most common specifications include MIL-STD-461 for military applications and FCC for commercial applications. Many other EMI specifications also exist.

The basic requirements for an EMI filter are

The filter must provide the power converter with lower output impedance than the negative input resistance of the power circuit.

The input filter attenuation must be sufficient to limit the resulting interference to a level that is below the imposed specification.

This section deals with the design and analysis of EMI filters that will reduce conducted interference and conducted susceptibility.

TOPOLOGY OF AN EMI FILTER

The noise voltage, measured from the 50Ω LISN contains both common-mode (CM) noise and differential-mode (DM) noise. Each mode of noise is dealt with by the respective section of an EM1 filter. Fig. 33 shows a commonly used filter network topology, and Fig. 34 and 35 shows, respectively, the equivalent circuit of the CM section and the DM section of the filter. Referring to Fig. 34 and 35, it is noticed that some elements of the filter affect DM (or CM) noise only and some affect both DM and CM noise. The capacitors CX1 and CX2 affect DM noise only. An ideal common-mode choke LC affects CM noise only, but the leakage inductance Lleakage between the two windings of LC affects DM noise. CY suppresses both CM noise and DM noise, but its effect on DM noise suppression is practically very little because of the relatively large value of CX2. Similarly, LD suppresses both DM noise and CM noise, but its effect on CM noise is practically very little because of the relatively large value of Lc. The two modes of noise collectively contribute to the total EMI noise.

Electromagn

BASIS OF D

1. Comm

The commassumption

etic Interfere

DETERMINI

mon Mode

mon mode ens and theore

nce (EMI) and

Fig. 3

Fig. 37

NG FILTER C

quivalent cirems as show

d filter design

Fig. 35 – T

36 – Commo

7 – Differenti

COMPONEN

rcuit of Fig.wn in Fig. 36 –

for SMPS

Topology of a

n Mode nois

ial Mode noi

NT VALUES

. 34 is reduc– 39.

an EMI filter

e equivalent

ise equivalent

S

ced to an L

Centre fo

circuit

t circuit

C series circ

or Airborne Sy

cuit through

ystems, DRDO

h a series of

O

45

f

Electromagn

etic Interfere

Fig. 39

nce (EMI) and

Fig. 3

– Equivalent

Fig.40 –Equ

Fig. 41

d filter design

38 – Commo

t circuit of Fig

uivalent circu

1 – Filter atte

for SMPS

on mode noise

ig. 38 if ZP >>

uit of Fig. 39

enuation for c

If

w

App

CM

=

e equivalent

> ( ) and w

after recipro

common-mo

ZP >> ((LC + LD/2)

lying Recipro

M Attenuatio

, ∗, ∗ ≈

f

≈

Centre fo

circuit

w(Lc + Ld/2)

ocity theorem

de noise

) and

>> 25Ω

ocity theorem

on = ( (,,

fR,CM = √≈ .

or Airborne Sy

) >> 25Ω

m

m

) )

= ( If LC >> LD/

ystems, DRDO

)

/2

O

46

Electromagn

2. Differe

The differeassumption

etic Interfere

ential Mode

ential mode ns and theore

Fig. 43 – Eq

Fig

nce (EMI) and

equivalent cems as show

Fig

quivalent circ

g. 44 – Equiv

F

d filter design

circuit of Figwn in Fig. 40 –

g. 42 – Differe

cuit of Fig. 42

valent circuit

Fig. 45 – Filte

for SMPS

g. 35 is redu– 43.

ential Mode e

2 if ZCX1 >> 1

of Fig. 43 by

er attenuatio

Re

If C

uced to an L

equivalent ci

100Ω; ZCX2 >

applying rec

n for DM no

If >>

wLDM >> 10

ciprocity the

CX1 = CX2 = CD

f

=

Centre fo

LC series cir

rcuit

>> ZP; and wL

ciprocity theo

ise

100Ω,

00Ω

eorem

DM

fR,DM = √= (

or Airborne Sy

rcuit through

LDM >> 100Ω

orem

>> ZP

)

ystems, DRDO

h a series of

Ω

O

47

f

Electromagn

SOFTWAR

Fig. 44 shofollowing e

VL = VCM +

VN = VCM -

Therefore,

VDM = (VL

Fig. 46 –

etic Interfere

E BASED EM

ows the circequations can

+ VDM

- VDM

VCM = (VL +

– VN) / 2

Circuit diag

nce (EMI) and

MI NOISE SE

uit diagram n be derived.

+ VN) / 2, and

gram for sepa

signals

d filter design

EPARATION

for separati.

d

aration of con

for SMPS

N METHOD

ion of condu

nductive EMI

uctive EMI s

I

Fig.sep

C

Centre fo

signals. As s

47 – Flow charation of co

Measu

Measur

Conversion

Calculation oabove def

Conversion

or Airborne Sy

shown in th

hart of softwaonductive EM

Start

urement of V

rement of VN

n of VL & VN

of VCM & VDM

fined equatio

n of VCM & VdBμV

End

ystems, DRDO

e figure, the

are based MI signals

VL

N

in μV

M by the ons

VDM in

O

48

e


49

DESIGN PROCEDURE FOR EMI FILTER

Step 1: Accurately measure the base-line of common mode EMI noise spectrum VCM and differential mode EMI noise spectrum VDM.

Step 2: Determine the required common mode noise attenuation & differential mode noise attenuation at various sampled frequencies.

(Vreq-cm)dB = (VCM)dB – (Vlim)dB + 6dB

(Vreq-dm)dB = (VDM)dB – (Vlim)dB + 6dB

To avoid design error, +6dB is added because both the measured DM noise and CM noise are 3dB above the actual values, and because the measured CM & DM noise voltages may be in phase, which will cause a total error of 6dB in estimating the required attenuation.

Step 3: Determine filter corner frequencies The filter corner frequencies can be determined by searching the minimum values of fc-cm and fc-dm from the required attenuation from all sampled frequencies.

(Vreqd-CM))dB = 40log fc-cm = common mode corner frequency

(Vreqd-DM))dB = 40log fc-dm = differential mode corner frequency

Step 4: Determine filter component values a. CM components LC and CY:

Since there is a safety leakage current requirement, CY is normally limited to 3300pF. LC and 2CY should have a resonant frequency of fC-CM obtained in Step 3. Therefore

LC = ( ) ×

b. DM components LD, CX1 and CX2:

Based on the assumption made for Fig. 43, CX1 and CX2 are selected to be the same value CDM and are related to LDM through corner frequency fc-dm requirement as shown below

CX1 = CX2 = CDM = ( ) ×

CX1, CX2, LD are unknowns. There exists a degree of freedom for trade-off. Since the leakage inductance due to the coupling imperfection of a practical CM choke also has a filtering effect on the DM noise, thus to reduce the EMI filter design cost and size, the effect of the DM inductance LD can be totally replaced by the leakage inductance Lleakage of the CM choke. Practically, Lleakage is generally in the range of 0.5-2% of the Lc value.


50

Fig. 48 – Design steps of the presented filter design

Start

Separated CM and DM components

Limit line

Calculate the required CM and DM attenuation

Compute the CM and DM corner frequencies

Calculate the CM inductor value given that the Y-capacitor is fixed at 3300pF

Calculate the leakage inductance of the CM inductor

Calculate the value of CX1= CX2=CDM.

End

Electromagn

SOFTWAR

A MATLAdeterminati

Some of the

1. Req2. Allo3. Allo

For an expeconverter [SEMI filter isvoltage to 4has been ext

The results

etic Interfere

E IMPLEME

AB GUI wasion of EMI fi

e features of t

quires live voows pre-selecows design oa. FCC Clb. FCC Clc. MIL ST

Fi

erimental verSee Page – 4s chosen to c

45dBμV for atended over

obtained fro

nce (EMI) and

ENTATION O

s developed ilter compon

the GUI are

oltage and thecting the Y-C

of EMI filter alass A lass B, and

TD

ig. 49 –Devel

rification of t41] is used. Tcomply with a frequency rthe full cond

om the GUI a

d filter design

OF EMI FILT

using the nent values.

e neutral lineCapacitor valaccording to

loped MATL

the developeThe live volta

FCC Class Arange of 450 ducted EMI s

are shown be

for SMPS

TER DESIGN

above descr

e voltage as ilue and the l

o 3 standards

LAB GUI for

ed GUI, the dage and the A standard. F kHz to 30Mspectrum i.e.

elow.

ribed metho

inputs to comeakage induc

conducted EM

data obtainedneutral volta

FCC Class AMHz, but for

. 10 kHz to 3

Centre fo

ods and algo

mpute the filtctance of the

MI filter desig

d from the siage are loade

A standard limthis simulati0MHz.

or Airborne Sy

orithms to

ter componee CM inducto

ign

imulation ofed into the Gmits the condtion, the freq

ystems, DRDO

help in the

ent values. or.

f the fly-backGUI and theducted noise

quency range

O

51

e

k e e e

Electromagn

The values f

Common M

C

Differentia

C

etic Interfere

for the EMI f

Mode filter

CY = 3300 nF

al Mode filter

CX = 10.223 μF

nce (EMI) and

Fig. 50 – EM

filter as sugg

F

r

F

d filter design

MI filter resu

gested by the

for SMPS

lts obtained f

GUI are

LC = 0.2949

LD =2.949 m

for the fly-ba

H

mH

Centre fo

ack converter

Corne

Corne

or Airborne Sy

er freq. = 0.1

er freq. = 0.9

ystems, DRDO

1408 kHz

1662 kHz

O

52

Electromagn

SPICE VERI

With the daand it was in

It can be see

etic Interfere

IFICATION O

ata obtainedntegrated wi

en that the fi

nce (EMI) and

OF THE DES

d from the Gith the fly-ba

Fig. 51 –

Fig. 52 –

ilter effective

d filter design

SIGNED EM

GUI, an EMIck converter

– EMI filter u

– Attenuation

ly attenuates

for SMPS

I FILTER

I filter was dr earlier desig

using the data

n curve for th

s signals with

designed. Its gned, and the

a obtained by

he EMI filter

h frequency o

Centre fo

attenuation e EMI charac

y the GUI

designed.

over 10kHz i

or Airborne Sy

properties wcteristics wer

i.e. EMI nois

ystems, DRDO

were derivedre studied.

e.

O

53

d

Electromagn

To study thand neutral

The SPICE

LISN FO .OPTION ******** INPUT Vinput Vgate 7 ******* * LISN Clisn1_Rlisn1_ Llisn1 Clisn1_Rlisn1_Rlisn1_ ******* * LISN Clisn2_Rlisn2_ Llisn2 Clisn2_Rlisn2_

etic Interfere

e effectiveneline voltages

net list for th

OLLOWED BY

N METHOD=G

**********T VOLTAGE

1 2 dc 307 18 pulse

**********

1

_1 1 12 8u_1 12 0 5

1 3 50uH

_2 3 11 0._2 11 0 1k_3 11 0 50

**********

2

_1 2 10 8u_1 10 0 5

2 8 50uH

_2 8 9 0.2_2 9 0 1k

nce (EMI) and

ess of the EMs are again co

Fig. 53 – LI

he above sho

Y EMI FILTE

GEAR LVLTIM

**********

0V e(0 10 0 10

**********

u

25u k

**********

u

5u

d filter design

MI filter desigollected and

ISN followed

wn schemati

ER AND FLY

M=1

**********

0n 10n 0.5

**********

**********

for SMPS

gned, it is intestudied.

d by EMI filte

ic is as follow

YBACK CONVE

***********

58u 1u)

***********

***********

egrated with

er and fly-bac

ws:

ERTER

**********

**********

**********

Centre fo

the fly-back

ck converter

***********

***********

***********

or Airborne Sy

k converter an

******

******

******

ystems, DRDO

nd the live

O

54


55

Rlisn2_3 9 0 50 ********************************************************************* * EMI filter CX1 3 8 10.223u LC1 3 15 0.2949H LC2 8 16 0.2949H KEMI LC1 LC2 0.99 LD1 15 17 2.949mH LD2 16 18 2.949mH CX2 17 18 10.223u CY1 17 0 3300n CY2 18 0 3300n ********************************************************************* * primary side of flyback converter R1 17 4 0.014 Cpar1 4 5 2.73nF Lpar1 5 6 1.58uH Xm1 6 7 18 mtp6n60/mc ********************************************************************* * flyback transformer LFPRIMARY 4 5 14u LFSECONDARY 0 13 0.08u KTX LFPRIMARY LFSECONDARY 0.99 ********************************************************************* * capacitor parasitics of flyback transformer CtxPar1 4 13 0.29nF CtxPar2 5 0 0.29nF ********************************************************************* * secondary side of transformer Cpar2 13 0 4.46nF Xd1 13 14 40EPS08 Cfilter 14 0 50uF Rload 14 0 3.2 ********************************************************************* * MOSFET subcircuit .subckt mtp6n60/mc 10 20 30 * * 10 = Drain 20 = Gate 30 = Source


56

* ********************************************************************* * *------------------------ EXTERNAL PARASITICS ----------------------- * PACKAGE INDUCTANCE * LDRAIN 10 11 4.5e-09 LGATE 20 21 7.5e-09 LSOURCE 30 31 7.5e-09 * * RESISTANCES * RDRAIN1 4 11 RDRAIN 0.8036 RDRAIN2 4 5 RDRAIN 0.0084 RSOURCE 31 6 RSOURCE 0.02018 RDBODY 8 30 RDBODY 0.0135 * RGATE 21 2 5 * *-------------------------------------------------------------------- * *--------------- CAPACITANCES AND BODY DIODE ------------------------ * DBODY 8 11 DBODY DGD 3 11 DGD CGDMAX 2 3 2.7e-09 RGDMAX 2 3 1e+08 CGS 2 6 1.31e-09 * *-------------------------------------------------------------------- * *----------------------- CORE MOSFET -------------------------------- * M1 5 2 6 6 MAIN * *-------------------------------------------------------------------- * .MODEL RDRAIN R( +TC1 = 0.008891 +TC2 = 3.056e-05) * .MODEL RSOURCE R( +TC1 = -0.003198 +TC2 = 2.60004e-05) * .MODEL RDBODY R( +TC1 = 0.003945 +TC2 = 9.54752e-06) * * .MODEL MAIN NMOS ( +LEVEL = 3 +VTO = 3.8 +KP = 13 +GAMMA = 2.6 +PHI = 0.6 +RD = 0 +RS = 0 +CBD = 0 +CBS = 0 +IS = 1e-14 +PB = 0.8 +CGSO = 0 +CGDO = 0 +CGBO = 0 +RSH = 0 +CJ = 0 +MJ = 0.5


57

+CJSW = 0 +MJSW = 0.33 +JS = 1e-14 +TOX = 1e-07 +NSUB = 1e+15 +NSS = 0 +NFS = 6.59e+11 +TPG = 1 +XJ = 0 +LD = 0 +UO = 600 +VMAX = 0 +KF = 0 +AF = 1 +FC = 0.5 +DELTA = 0 +THETA = 0 +ETA = 0 +KAPPA = 0.2) * *-------------------------------------------------------------------- * .MODEL DGD D ( +IS = 1e-15 +RS = 0 +N = 1000 +TT = 0 +CJO = 1.129e-09 +VJ = 1.943 +M = 1.476 +EG = 1.11 +XTI = 3 +KF = 0 +AF = 1 +FC = 0.5 +BV = 10000 +IBV = 0.001) * *-------------------------------------------------------------------- * .MODEL DBODY D ( +IS = 1.532e-11 +RS = 0 +N = 1.062 +TT = 2.5e-07 +CJO = 9.725e-10 +VJ = 1.127 +M = 0.6627 +EG = 1.11 +XTI = 5 +KF = 0 +AF = 1 +FC = 0.5 +BV = 671 +IBV = 0.00025) .ENDS ********************************************************************* * diode subcircuit .SUBCKT 40EPS08 A K D1 A K 40EPS08 .MODEL 40EPS08 d ( +IS=1e-15 RS=0.00426912 N=0.926332 EG=0.6 +XTI=0.5 BV=800 IBV=0.0001 CJO=1e-11 +VJ=0.7 M=0.5 FC=0.5 TT=1e-09 +KF=0 AF=1 )

Electromagn

.ENDS ******* .TRAN 1.probe .end

The results

etic Interfere

**********

10E-004 0.

obtained fro

Fig. 54

nce (EMI) and

**********

01 7E-3

om the simul

4 – Output v

d filter design

**********

ation of the a

voltage of the f

for SMPS

***********

above circuit

fly-back con

**********

t are shown b

verter with L

Centre fo

***********

below:

LISN and EM

or Airborne Sy

******

MI filter

ystems, DRDOO

58

Electromagn


Fig.

Fig. 56

d filter design

55 – Output

6 – FFT of th

for SMPS

t voltage ripp

he output volt

ple with EMI f

tage with EM

Centre fo

filter

MI filter

or Airborne Sy

ystems, DRDOO

59

Electromagn


Fig. 57 – f

Fig. 58 – fre

d filter design

frequency vs.

equency vs. n

for SMPS

live voltage

neutral voltag

with EMI filt

ge with EMI f

Centre fo

ter (dBμV)

filter (dBμV)

or Airborne Sy

ystems, DRDOO

60

Electromagn


Fig. 59 –

Fig. 60 –

d filter design

– Common m

Differential

for SMPS

mode noise w

mode noise w

ith EMI filter

with EMI filte

Centre fo

r (dBμV)

er (dBμV)

or Airborne Sy

ystems, DRDOO

61

Electromagn

COMPARIS

On comparimprovemeintegration

Fig. 61 (A)

Fig. 62 (A

etic Interfere

SON OF RES

ring the comnt can be seeof the EMI f

Withou

– common m

A) – different

nce (EMI) and

SULTS OBTA

mon and difen. The commfilter thus, va

ut EMI filter

mode noise w

tial mode noifilter

d filter design

AINED WITH

fferential momon and dif

alidating the f

r

without EMI f

se without EM

for SMPS

H AND WIT

ode noise levfferential mofilter as effec

filter F

MI Fig

THOUT FILTE

vels with andode noises shctive.

Fig. 61(B) – co

g. 62 (B) – diff

Centre fo

ER

d without theow a signific

With EMI

ommon mode

fferential mo

or Airborne Sy

e EMI filter, cant attenuat

I filter

e noise with E

de noise with

ystems, DRDO

a significanttion after the

EMI filter

h EMI filter

O

62

t e


63

5. CONCLUSION

The switching characteristics of a Power MOSFET and the reverse recovery characteristics of a diode are the main contributors to EMI generated in a power converter. Both the characteristics were successfully modelled, tested and integrated in the converter and the EMI data was generated. An EMI filter was developed using the data generated by the converter. This filter was then integrated into the converter schematic and the EMI characteristics were simulated. A significant improvement in the EMI attenuation was observed.

In chapter 1, a basic overview of EMI/EMC was provided. The foundation stone for further EMI studies was laid down in the chapter. The reasons for occurrence of EMI and the modes of occurrence were discussed.

In chapter 2, high frequency models of components used in power converters were modelled. These included basic components such as the capacitor and inductor and switching components like the MOSFET. SPICE models for a diode and a MOSFET were developed to be used in the EMI simulation of a power converter.

In chapter 3, the basic concepts of a fly-back converter were discussed. Also the high frequency models of MOSFET and diodes were integrated into the converter and the circuit was simulated to determine the EMI characteristics of the converter.

In chapter 4, the data generated from the simulation in chapter 3 was used to design an EMI filter. A MATLAB GUI was developed for the purpose. The attenuation properties of the designed filter were studied and it was integrated in the fly-back converter. Thus a complete fly-back converter was simulated and the EMI data was again generated. The data so obtained (after the filter was integrated) was compared to the data previously obtained for the same converter and a significant improvement in the EMI characteristics was observed.

On the whole, a model for EMI simulation in a fly-back converter was developed bottom up. A complete SPICE program for the same has also been provided that can be used in further studies.


64

6. REFERENCES

[1] Dong-Young Lee, J.H. Lee, S.H. Min, B.H. Cho, B.H. Lee. “Exact Simulation of Conducted EMI in Switched Mode Power Supplies”, SAE ’98.

[2] Fu-Yuan Shih, Dan Y. Chen, Yan-Pei Wu, Yei-Ton Chen. “A Procedure for Designing EMI Filters for AC Line Applications”, IEEE transactions on Power Electronics, Vol. 11, No. 1, January ’96.

[3] Po-Shen Chen, Yen-Shin Lai. “New EMI Filter Design Method for Single Phase Power Converter using Software-based Noise Separation Method”, IEEE ’07.

[4] Himanshu K. Patel. “Critical Considerations for EMI Filter Design in Switch Mode Power Supply”. [5] Jukka-Pekka SjÖroos. “Conducted EMI filter design for SMPS”, IEEE ’06. [6] Hsin-Lung Su, Ken-Huang Lin. “Computer-Aided Design of Power Line Filters with a Low Cost

Common- and Differential-Mode Noise Diagnostic Circuit”, IEEE ’01. [7] A. Farhadi, A. Jalilian. “Modelling and Simulation of Electromagnetic Conduced Emission Due to

Power Electronics Converters”, IEEE ’06. [8] Thomas Farkas. “A Scientific Approach to EMI Reduction in Switching Power Supplies”, MS Thesis,

Massachusetts Institute of Technology, September ’91. [9] MIL-STD-462. Military Standard: Measurement of Electromagnetic Interference Characteristics.

[10] Andreas Karvonen. “MOSFET Modelling Aimed at Minimizing EMI in Switched DC/DC Converters Using Active Gate Control”, Engineering Thesis, Chalmers University of Technology, 2009.

[11] Liyu Yang. “Modelling and Characterization of a PFC Converter in the Medium and High Frequency Ranges for Predicting the Conducted EMI”, MS Thesis, Virginia Polytechnic Institute and State University, September ’03.

[12] C.H. Xu, D. Schroder. “Modelling and Simulation of Power MOSFET’S and Power Diodes”, IEEE PESC ’88.

[13] Gabriel Chindris, Ovidiu Pop, Grama Elin, Florin Hurgui. “New PSpice model for Power MOSFET devices”, IEEE International Spring Seminar on Electronics Technology, May ’01.

[14] Hong Man Leung. “SPICE Simulation and Modelling of DC-DC Flyback Converter”, MS Thesis, Massachusetts Institute of Technology, August ’95.

[15] Peter O. Lauritzen. “A Simple Diode Model with Reverse Recovery”, IEEE transaction on Power Electronics, Vol. 6, No.2, April ’91.

[16] C. Chang, H. Teng, J. Chen, H. Chiu. “Computerized conducted EMI filter design system using labVIEW and its applications”.

[17] Mohit Kumar, Vivek Agarwal. “Power Line Filter Design for Conducted Electromagnetic Interference Using Time-Domain Measurements”, IEEE transaction on Electromagnetic Compatibility, Vol. 48, No. 1, February ’06.

[18] Mohannad Lutfi Nayfah, Ali Keyvan Ekbatani, Abdullah Albisher. “Power Line Filter Design for Conducted Electromagnetic Interference Using Time-Domain Measurements”,

[19] Supratim Basu. “EMI-EMC Notes”. [20] “Fly-Back Type Switched Mode Power Supply”, Module-3, Lecture-22, Power Electronics, IIT

Kharagpur, NPTEL. [21] MicroSim Application Notes, MicroSim. [22] Reference Manual, OrCAD PSpice A/D, OrCAD Inc.

Electromagnetic Interference (EMI) and filter design for Switched Mode Power Supplies

Documents

Transcript of Electromagnetic Interference (EMI) and filter design for Switched Mode Power Supplies