Download - Active PFC Boost Rectifier EMC2
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Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost RectifierPower section
CHARACTERISTICS:
Input voltage: Vin = 90-260VRMS
Output voltage: Vo = 380VOutput power: Po = 600WSwitching frequency: fs = 70kHz
ControlPFC
line load
VALUES:
Output capacitor: C = 680 µµFInductor: L = 600 µµHMosfet: IRFP450Diode: RURP1560Controller: L4981A
Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
General Considerations:
MOSFET and DIODE are the main noise generators
• Short wires where high dv/dt
• Small area of fast di/dt loops
• Short paths for return currents
Power section and related EMI aspects
Careful Layout
High di/dt loop
Line Load
High dv/dt wires Common modecapacitive coupling
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Giorgio SpiazziUniversity of Padova
Italy
Circuit Layout (components)Input Output
OutputfilterInput
filter
Control and drive
Power stage
Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Circuit Layout (solder layer)
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Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Circuit Layout (component layer)
Giorgio SpiazziUniversity of Padova
Italy
MOS D
Circuit Layout ConsiderationsActive PFC Boost Rectifier
High dv/dt track is short ...... and shielded between
+Vout and -Vout tracks
Short paths amongswitching components
and filter capacitor
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Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Circuit Layout Considerations
Control
Short (and shielded)track at analog
inputs
Shielding tracksconnected to reference
Small area of the gatecircuit. Snubber close to
gate and source terminals
Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Star connection ofground paths Common mode
filter capacitors
Shield planeconnected to
reference
Circuit Layout Considerations
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Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Coupled inductors show highcommon mode inductance but lowdifferential mode inductance:
Ex: 6.8 mH CM, 70 µµH DM
Power section with EMI Filters
idm
icm
High CM impedance Low CM impedance
Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
Differential mode input noise: 70 kHz, 87 dB µµV (peak values) 140 kHz, 57 dB µµV
210 kHz, 40 dB µµV280 kHz, 26 dB µµV350 kHz, 19 dB µµV420 kHz, 9 dB µµV
a suitable margin (20 dB µµV) is maintained for the commom mode noiseand possible resonances
Input filter design - Differential Mode
vn
1 Fµ 2 Fµ
L = 70 Hµdm
L = 6.8 mHcm
idm50 Ω
50 Ω
Ripple amplitude
triangular waveform
∆IUf L
Aout
smax .= ≅
8113
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Giorgio SpiazziUniversity of Padova
ItalyActive PFC Boost Rectifier
• Several current return paths are present
• The main one is on the output side of the PFC
• High value of filter inductor reduces current term at the input side
• CM input side current generates DM input noise due to asymmetricalconverter topology
• Adding CM capacitors at the input side reduces input CM voltage noise butthe increased CM current causes additional DM noise
Input filter design - Common Mode
50 Ω
1 Fµ 2 Fµ
L = 6.8 mHcm
icm
100 nF
4.7 nF
4.7 nF
icm
Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
v
i
Input behavior
Line current
Line Voltage
100 V/div.
2 A/div.
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Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
v
iL
Line Voltage and Inductor Current(peak to peak sampling)
Inductor currentswitching ripple
Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
vGS
vDS
Gate drive circuit
vG iD
iL
IL+IDthreshold
Voltagedrop
ILthreshold
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Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
vGS
vDS
Gate drive circuit
vG iD
iL
ILthreshold
Commutationis slowed-
down
Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
vDS
vGS
vGiDiG
Gate drive circuit
Drain-Gatecoupling
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Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
vDS
vGS
vGiDiG
Gate drive circuit
Giorgio SpiazziUniversity of Padova
ItalyPrototype Tests
Modulation of Switching FrequencyVDS Spectra
Modulated
Fixed
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Giorgio SpiazziUniversity of Padova
ItalyPrototype EMI TestsConducted noise (peak measure)
Phase Neutral
Giorgio SpiazziUniversity of Padova
ItalyPrototype EMI Tests
Introducing input-side common-modefilter capacitors
• Differential noise increases (circuit isnot symmetrical) and low-frequencybehavior is worse
• A resonance, between input andoutput CM filter capacitors and theinductances of their connections,appears, modifying the high-frequency behavior
Conducted noise (peak measure)
Line PFC
Added
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Giorgio SpiazziUniversity of Padova
ItalyPrototype EMI Tests
Increased output-side common-modecapacitors
• Common mode currents are closed onthe output side (no additional voltagedrop on the input filter occurs)
• Low-frequency behavior is improved
• High-frequency behavior becomesworse due to resonance of two CMfilter capacitors and their connections
Conducted noise (peak measure)
LoadPFC
Added
Giorgio SpiazziUniversity of Padova
Italy
By connecting the heatsink to thenegative rail (capacitive currents areclosed “near” to the Mosfet source):
•Low-frequency behaviour is improved
•High-frequency behavior is good (theheatsink shields all circuitry)
Prototype EMI TestsConducted noise (peak measure)
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Giorgio SpiazziUniversity of Padova
Italy
By inserting a shield, between Mosfetand heatsink, connected to Mosfetsource (drain coupled capacitivecurrents are closed directly to the Mosfetsource)•Low-frequency behavior is improved(common mode noise is reduced)•High-frequency behavior is good (Usingthe heatsink as shield of the whole circuitgives however better results)
Shield
Prototype EMI TestsConducted noise (peak measure)
Giorgio SpiazziUniversity of Padova
Italy
Switching Frequency Modulation
Switching frequency harmoniccomponents disappear
• Measured peak noise remainsunchanged
• Measured average noise isconsiderably reduced
Peak
Average
Prototype EMI TestsConducted noise (peak measure)
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Giorgio SpiazziUniversity of Padova
Italy
Effect of Diode Reverse Recovery(Disconnecting gate snubber)
• Low-frequency behavior is almostunchanged
• High-frequency behavior is heavilyworsened
vG iD
iL
Prototype EMI TestsConducted noise (peak measure)
Giorgio SpiazziUniversity of Padova
Italy
Increasing gate resistor
• Low-frequency behavior remainsunchanged
• High-frequency behavior is improved(MOSFET commutation slows down)
vGiDiG
33 72 Ω
Prototype EMI TestsConducted noise (peak measure)
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Giorgio SpiazziUniversity of Padova
Italy
By spreading the ac wires close to theinput filter (filter inductors inside plasticcan)
•Low-frequency behavior becomesworse (input wires capture leakagemagnetic field of filter inductor)
•High-frequency behavior remainsunchanged
Line PFCEMIFilter
Increased Area
Prototype EMI Tests