Abstract: This paper presents a simplified toolkit on

conducted electromagnetic interference (EMI) based on

the basic circuits and concepts of power electronics. The

simulated and simplified results of the toolkit is to

introduce the effect of conducted EMI caused by self-

resonant frequency (SRF) of the passive components,

switching characteristic of a switching device such as free

wheeling diode (FWD), gate drive control, snubber circuit

and parasitic of capacitors to ground. The simplified

prototype of line impedance stabilization network (LISN)

is also introduced. Those basic phenomena can lead

designing engineers can understand the EMC concept by

both of simulation and experiment.

Keywords: EMI self-learning, Conducted EMI emission,

Power electronics Noise, Gate control, Snubber circuit,

Self-resonant frequency, LISN.

I. Introduction

EMI is unfamiliar concept for most engineers in most

of universities in Thailand while many companies and

manufactories would like to have engineers who can

ready to serve in those electrical and electronics areas.

The EMI studies in terms of theory and practice are

developed and proposed with the simplified learning

toolkit. Self-learning on EMI studies can help those

engineers to understand the EMI phenomena [1]. Some

EMI issues may not suitable to demonstrate by

experiment such as the operation of without free wheeling

diode on inductive load. This issue can be done by

simulation. Most of learning toolkits are selected based on

the guideline the engineers to understand about the EMI.

The mechanism of LISN operation is necessary to

those engineers to understand. The EMI simulated result

included the LISN is needed due to lacking of LISN and

EMI analyzer for most small and medium companies.

II. The development of a simplified

learning toolkit of EMI issues

The simplified EMI studies focused on power

electronics [1] has been published. This paper is the

extended development of EMI self-learning kit. Key

issues of the toolkits are divided by three main categories.

The first one is noise disturbance or the initiation of EMI

source. This part consists of EMI generation: free

wheeling diode. The second category consists of EMI

controlling such as gate control for decreasing the rise

time and fall time of the switching device, di/dt and dv/dt

are the controlled parameters, and snubber circuit: RLD

and RCD snubber circuit. The third category is conducted

EMI measurement where LISN is focused to maintain the

function of stabilize the 50 ohm impedance during 150

kHz to 30 MHz while avoiding the EMI between the

source and the load.

The three main categories are shown as in figure 1.

and table 1.

Figure 1. Three main basic categories of EMI learning

kits

Table 1 EMI learning contents

EMI

disturbance

EMI

Control

EMI

measurement

1 Free wheeling

diode

Gate Control LISN

2 di/dt RCD Snubber

circuit

3 dv/dt RLD Snubber

circuit

4 Self-resonant

frequency

The basic concept in table 1 is to provide the EMI

phenomena and EMI effects from power converters such

as step down (buck) converter starting from EMI

disturbance, EMI control and following by home-made

EMI measurement: LISN.

EMI

disturbance

ELECTROMAGNETIC INTERFERENCE (EMI) SELF-LEARN KITS

BASED ON POWER ELECTRONICS APPROACH

Werachet Khan-ngern

Research Center for Communications and Information Technology,

Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang

E-mail: kkveerac@kmitl.ac.th.

EMI

measurement

EMI

Control

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III. Proposed of simplified EMI

learning toolkits

EMI disturbace

The free wheeling diode (FWD) should be clearly

understood about the switching operation with inductance

load [2]. The FWD mechanism and operation should be

introduced by simplified simulation shown in figure 2.

(a) PSPICE simulation

(b) Vds and id waveform

Figure 2. Without FWD operation

(a) PSPICE simulation

(b) Vds and id waveform

Figure 3. With snubber circuit operation

Figure 3 shows the FWD phenomena: dv/dt during

switch turn off and di/dt during switch turn on. This is one

of the prime mechanism of EMI noise in power

electronics. The EMI control can be done such as RCD

snubber circuit control shown in the simulated result in

figure 3. The achievement of reduce in spike voltage

during turn off also with the increasing of rise time. Both

reducing in spike voltage and increasing of rise time can

reduce the EMI effect.

One of EMI sources can be generated by impedance

response of inductors and capacitors. The self-resonant

frequency (SFR) of passive components can effect the

EMI phenomena depend upon the frequency response.

Higher SFR is preferred. The SFR effect is shown with

the LISN implementation.

EMI control

Some of the gate control for MOSFET drives can be

controlled using RC time constant shown in figure 4. This

case includes the stray capacitance of the heatsink for

safety reason [3]. The measured results show in figure 5

where the operating conditions and equipment is given in

table 2. The upper trace shows EMI level at without RC

gate control where the lower trace shows the reduction of

EMI level at RC gate control for MOSFET operation. It is

clearly seen that from 2 MHz to 30 MHz, the EMI

reduction is a great achieved about 20 dB in average.

(a) (b)

Figure 4 Common mode conducted EMI emission

between without and with RC gate control for the

MOSFET

Figure 5 Measured conducted EMI emission between

without and with RC gate control for the MOSFET

Time

580us 584us 588us 592us 596us 600us

V(M2:d,M2:s) I(V4)

-20

0

20

40

Time

580us 584us 588us 592us 596us 600us

I(V4) V(M2:d,M2:s)

-20

0

20

40

Cs

S

G

+Vcc

Cs

S

G

+Vcc

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Table 2 Operation condition and measuring equipment

The Snubber circuit: both of RCD and RLD is shown

in Figure 6 (a). where figure 6 (b) shows a slightly better

in term of EMI level compared to without snubber circuit.

Figure 6 (c) shows a better EMI reduction by the

combination of RCD and RLD snubber circuit.

(a) EMI measurement for RCD and RLD snubber circuit

(b) RCD snubber effect

(d) EMI reduction affected by RCD operation

(c). RCD and RLD combination

Figure 6. The RCD and RLD snubber circuit affect on

EMI reduction

EMI measurement

Line impedance stabilization network (LISN), which

is quite expensive in the market, is developed to use in the

laboratory for economic reason. LCR meter is needed for

modeling the parasitic parameter. EMI analyzer, which

can be related with EMI standard, is preferred. But normal

spectrum analyzer can be complied.

Prototype of LISN is built based on the commercial

LISN: EMCO model 3810/2 where the frequency range is

9 kHz to 30 MHz. The comparison of EMI performance

shows a closed agreement as shown in figure 7. LISN 1 is

the prototype or home-made LISD while LISN 2 is the

commercial LISN. It is shows that it is different by 10 dB

over the conducted EMI range.

Many parasitic components of inductor and

capacitor are involved. The details are not given in this

paper. But the basic material of higher SRF is required. A

lot of winding techniques for inductors are compared and

should be mentioned to reduce parasitic capacitance.

(a) LISN prototype

(b) LISN 1 is prototype compared to commercial

LISN

Figure 7. Conducted EMI measurement: LISN

MOSFET

L

C LoadD

VDS

ID

AC

LS

RLS

DS1

DS1

CS

RS

RLD Snubber

RCD Snubber

LISNC

EMI Receiver

without snubber

w ith RCD+RLD snubber

EN 55011; C lass B Conducted, Group 1 and 2, Q uasi-Peak

EN 55011; Class B C onducted, Group 1 and 2, Average

0

10

20

30

40

50

60

70

80

90

100

1 10

dBuV

without snubber

w ith RCD snubber

EN 55011; C lass B C onducted, G roup 1 and 2, Q uasi-Peak

EN 55011 ; C lass B C onducted, G roup 1 and 2, Average

0

10

20

30

40

50

60

70

80

90

100

1 10

dBuV

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IV. Conclusions

A simplified toolkit on conducted electromagnetic

interference (EMI) based on the basic circuits and

concepts of power electronics is introduced. Three main

categories are presented to understand the basic concept

of EMI phenomena and their effects. Some simulation and

measured results can guide the design engineers and

student to do self-learning based on home-made

equipment and free software such as OrCAD 9.1 student

version. Finally, the goals of EMI self–learning is

concluded and done by the process in table 3.

Table 3. the conclusion of EMI self-learning kits.

Title Process Goals

Free wheeling

diode effect

PSPICE simulation Principle operation

High

frequency

magnetic

concepts

Modeling by

measured result

Stray parameters

effect and SRF of

Inductor and

capacitors

Modeling passive

components

Power

electronics

simulation

PSPICE and

MATLAB

PSPICE tools for

conducted EMI

simulation via Line

Impedance

Stabilization

Network (LISN)

Snubber

circuit

PSPICE simulation

and measurement

RCD, RLD

operation to reduce

spike and reduce

di/dt and dv/dt

Gate control PSPICE simulation

and measurement

To Control rise time

and fall time of

switching device

(MOSFET)

Reference

[1] W. Khan-ngern, “Electromagnetic

Compatibility Experimental Laboratory on

Power Electronics” Proceeding of 2002

International Conference on Electromagnetic

Compatibility, Bangkok, Thailand, July 24-27,

2002, pp. 406-411.

[2] R. Valentine; “Motor Control Electronics

Handbook” .Mc Graw Hill, 1998, pp.418-424.

[3] L. Tihanyi, “Electromagnetic Compatibility in

Power Electronics”, IEEE Press, 1995.

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