Transcript Document

PowereLab
Explanation of Electromagnetic Interference
(EMI) in Switching Power Supply
Speakers
Dr. Franki Poon, Dr. Joe Liu
Power eLab
The PowerELab Limited
© copyright 2006
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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EMI solutions: Passive filter
 Conventional EMI solutions depend on passive filter using
inductors and capacitors:
 Inductors: CMC, DMC
 Capacitors: X-cap, Y-cap
 There are limitations when using passive filters:
 Inductors: Large size and high conduction loss
 Capacitors: leakage current specifications
Designing a 90% efficiency 150W power supply with PFC in hours
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PowerELab Limited
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Active EMI cancellation IC WT6001:
An effective EMI solution – Y-cap booster
WT6001
 A patented technology developed in PowerELab.
 An SO-8 IC WT6001 developed with W2.
 Equivalent to a Y-cap with very large value within the EMI concerned
frequency range only.
 No boosting effect in the leakage current test concerned frequency
range (50 – 800Hz).
 Greatly reduce the common mode inductor size and requirements.
 Reduce converter size and improve conversion efficiency.
 Provide effective and efficient EMI solution.
 Built-in electrical surge protection which can easily pass the EN610004-4 and EN61000-4-5 immunity standard.
Designing a 90% efficiency 150W power supply with PFC in hours
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Applications: Replace passive Y-cap
Replaced by Y-cap booster
LISN
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Effect measurable by oscilloscope
when using Y-cap booster
Noise voltage across Y-cap in
switching converter
Noise voltage across Y-cap booster
in switching converter
More application examples can be found in the datasheet of WT6001
Designing a 90% efficiency 150W power supply with PFC in hours
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Practical application examples
 The original EMI filter design cannot pass the EN55022 class B limit.
 Filter component:
 2 x 20mm high mu toroid for common mode filters
 2 x 0.15uF X – cap
 1 x 1n Y1-cap connected between primary and secondary
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Practical application examples:
Original filter schematic
P1
TH1
L1B
F1
L2B
4
3
4
3
1
2
C2
1
2
1
C1
P2
1
• It is a commonly used filter configuration
• L2B is wound with many turns which intends to suppress the low to
mid-frequency common mode noise. Its leakage inductance together
with C1 also provides differential mode noise filtering
• L1B is a single layer, bi-filer wound common mode choke for high
frequency common mode noise filtering
Designing a 90% efficiency 150W power supply with PFC in hours
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Practical application examples:
EMI measurement
DM noise
dBuV
80
Y-cap: From 1n to 3n3
Improved but not enough
dBuV
CM noise
80
70
70
230V pri-sec Y1n U shielded original
230V pri-sec Y3n3 U shielded original
60
60
EN 55022; Class B Conducted, Quasi-Peak
50
40
40
30
30
20
20
10
10
0
EN 55022; Class B Conducted, Average
0
1
10/3/200510:55:40
EN 55022; Class B Conducted, Quasi-Peak
50
EN 55022; Class B Conducted, Average
10
(Start = 0.15, Stop= 30.00) MHz
1
10/3/200516:08:11
10
(Start = 0.15, Stop= 30.00) MHz
Failure was identified to be caused by:
• Insufficient leakage inductance of the common mode choke for DM noise
attenuation.
• The two common mode choke cannot effectively block out the common mode
current.
• Further increase of Y-cap can reduce CM noise but fail to meet leakage
current specifications.
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Practical application examples:
Solution using Y-cap booster
dBuV
80
70
60
50
EN 55022; Class B Conducted, Quasi-Peak
230V CB U shield SDMC SCMC .33uF
EN 55022; Class B Conducted, Average
40
30
20
10
0
1
10/3/200516:39:55
10
(Start = 0.15, Stop= 30.00) MHz
 Y-cap booster is used to replace the primary to secondary Y-cap
 After using the Y-cap booster, L2B is replaced by a small differential
mode filter and L1B is reduced to a 9mm toroid with only a few turns
to tackle the high frequency common node noise. The test results pass
the required limit lines
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Practical application examples:
Filter comparison: Before and After...
Failed design even with more
cost, loss and bigger size for the
filter
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
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Passed design using Y-cap booster
with much smaller filter size that
saves cost, power and space
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Another practical application examples:
Filter comparison: Before and After...
Original EMI solution using passive filter
in ATX converter
Designing a 90% efficiency 150W power supply with PFC in hours
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New EMI solution using Y-cap booster
in ATX converter
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Conclusion
 Y-cap booster breaks the relationship between the Y-cap values and
leakage current requirement.
 Greatly reduce product design period and resources.
 It can be applied to any position with conventional Y-cap.
 Significantly reduce the size and loss of common mode choke implies
higher power density and efficiency.
 EMI less sensitive to transformer winding capacitance implies more
rooms for improving transformer coupling.
 Very suitable for equipment required low leakage current like medical
equipment.
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Active Diode – An easy to use and high
efficiency rectifier suitable for all converters
Stringent requirements of nowadays converters:





Compact size
Low heat generation and high conversion efficiency
High output power and output current
Low cost
………!!!
Conventional technologies cannot meet the requirements!!
Designing a 90% efficiency 150W power supply with PFC in hours
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PowerELab Limited
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Synchronous rectifier
 Use MOSFETs to replace diode rectifiers.
0.24 V
K
9 m
A
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K
7.8 m
A
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Synchronous rectifier
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 Provides low conduction loss.
 Can operate at higher high current without heatsink.
SCK 2.8W losses @ 10A
3
2.5
W
2
1.5
1
MOSFET 0.7W losses @ 10A
0.5
0
0
2
4
6
8
10
A
STP S30 L30
SO8 Act iv e Di o de
Lo sses comp ari so n b etw een SCK and AD
Designing a 90% efficiency 150W power supply with PFC in hours
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Synchronous rectifier
 Usage not limited to converters with high profit margin.
 Price of nowadays low RDSon MOSFETs comparable to
schottky diodes using the state of the art technology.
 Provide even lower converter cost because of reduced
heatsink, more output power, higher conversion efficiency…..
 Emerge in low cost converter like adaptors, standard open
frame converters, ATX …… .
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Synchronous rectifier
AD
AD
 Problematic for some conventional topologies
 Special and sometimes complicated driving circuits SR
are needed for different topologies
 Performance sensitive to transformer leakage
inductance and operating conditions
 Converter cannot be paralleled – Reverse current
 Poor efficiency at low load
 Simple circuit
 Discontinuous mode is allowed
 Good low load efficiency
 Converter can be paralleled
 High conversion efficiency
 Works just like a diode
 Limited input voltage range
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Active diode – Operating principle
A
K
A1
N1
N2
N3
D1
N4
D2





N1 is the current sense winding
N2 provides MOSFET driving signals
A1 driver circuit (IC WT6002)
N1 N3 & D1 form energy recovery circuit
N4 & D2 form reset circuit
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
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Active diode – Operating principle
Voltage across winding N2 or
gate drive voltage Von of SR
depends on ratio of N2 to N3
and voltage Vo
Toff
N
Von  Vo 2
N3
A
K
Ii
Von
VN2
A1
N1
Voltage source Vo
can be any voltage
source in a converter,
e.g. output voltage
Vo
N2
VN3
Vo
N3
D1
VN4
N4
D2
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
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Application of Active Diode in different
topologies
Lf
+
+
+
Co
Vo
+
Vin
-
S
-
Freewheel
SR
Magnetic
Reset
Vin
Flyback SR
Co Vo
-
S
Forward SR
-
Flyback
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Forward
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Application of Active Diode in different
topologies
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Lf1
Lf
+
S1
C1
SR1
Vin
-
S2
C2
+
Co Vo
-
SR2
Half Bridge centre tap
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S1
C1
S2
C2
SR1
Co
Vin
+
Vo -
SR2
Lf2
Current Doubler
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Application of Active Diode in different
topologies
SR1
Co
+
Vo
-
ISIN
SR2
and many others….
Resonant converter
Designing a 90% efficiency 150W power supply with PFC in hours
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Successful application of Active Diode
in converter products
AD on 150W ACDC
AD on 50W ACDC
AD on 120W ACDC
AD on 300W ACDC
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AD on 1.5 V 200 A ACDC
AD on 60W ACDC
AD on 100W DCDC
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Conclusion
 A new “Active Diode” technology is presented.
 A kind of current driven synchronous rectifier technology that
provides high conversion efficiency and eliminates many
conventional synchronous rectifier application problems.
 Patented technologies.
 An Active Diode driver IC WT6002 for easy implementation of the
technology.
 Well proven by many converter product design.
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
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References
•
Liu, J.C.P.; Poon, F.N.K.; Xuefei Xie; Pong, M.H.; current driven synchronous rectifier with energy recovery sensor Power
Electronics and Motion Control Conference, 2000. Proceedings. PIEMC 2000. The Third International , Volume: 1 , 2000, page(s):
375 -380 vol.1
•
Xuefei Xie; Liu, J.C.P.L.; Poon, F.N.K.; Man Hay Pong; Current-driven synchronous rectification technique for flyback
topology, Power Electronics Specialists Conference, 2001. PESC. 2001 IEEE 32nd Annual , Volume: 1 , 2001, Page(s): 345 350 vol. 1
•
Xuefei Xie; Liu, J.C.P.; Poon, F.N.K.; Man Hay Pong; A novel high frequency current-driven synchronous rectifier for low
voltage high current applications, Applied Power Electronics Conference and Exposition, 2001. APEC 2001. Sixteenth Annual
IEEE , Volume: 1 , 2001, Page(s): 469 -475 vol.1
•
Liu, J.C.P.; Xuefei Xie; Poon, F.N.K.; Pong, B.M.H.; Practical solutions to the design of current-driven synchronous rectifier
with energy recovery from current sensing, Applied Power Electronics Conference and Exposition, 2002. APEC 2002.
Seventeenth Annual IEEE , Volume: 2 , 2002, Page(s): 878 -884 vol.2
•
Xuefei Xie; Joe Chui Pong Liu; Poon, F.N.K.; Man Hay Pong; A novel high frequency current-driven synchronous rectifier
applicable to most switching topologies, Power Electronics, IEEE Transactions on , Volume: 16 Issue: 5 , Sep 2001, Page(s):
635 -648
•
Xie Xuefei; Liu, J.C.P.; Poon, F.N.K.; Pong, B.M.H.; Two methods to drive synchronous rectifiers during dead time in
forward topologies, Applied Power Electronics Conference and Exposition, 2000. APEC 2000. Fifteenth Annual IEEE , Volume:
2 , 2000, Page(s): 993 -999 vol.2
•
US patent "Current driven synchronous rectifier with energy recovery" patent number 6,134,131
•
US patent “Self-driven synchronous rectifier by retention of gate charge” patent number 6,377,477
•
US patent “Current driven synchronous rectifier with energy recovery using hysterisis driver”, patent number 6,597,587
Designing a 90% efficiency 150W power supply with PFC in hours
Prepared by Dr. Franki Poon & Dr. Joe Liu
PowerELab Limited
www.powerEsim.com
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