Active PFC Boost Rectifier
Giorgio Spiazzi
University of Padova
Italy
Power section
PFC
Control
line
VALUES:
CHARACTERISTICS:
Input voltage:
Output voltage:
Output power:
Switching frequency:
load
Vin = 90-260VRMS
Vo = 380V
Po = 600W
fs = 70kHz
Output capacitor:
Inductor:
Mosfet:
Diode:
Controller:
C = 680 µF
L = 600 µH
IRFP450
RURP1560
L4981A
Active PFC Boost Rectifier
Giorgio Spiazzi
University of Padova
Italy
Power section and related EMI aspects
High dv/dt wires
Line
Common mode
capacitive coupling
Load
High di/dt loop
General Considerations:
MOSFET and DIODE are the main noise generators
• Short wires where high dv/dt
• Small area of fast di/dt loops
Careful Layout
• Short paths for return currents
1
Circuit Layout (components)
Giorgio Spiazzi
University of Padova
Italy
Output
Input
Power stage
Output
filter
Input
filter
Control and drive
Active PFC Boost Rectifier
Circuit Layout (solder layer)
Giorgio Spiazzi
University of Padova
Italy
2
Active PFC Boost Rectifier
Circuit Layout (component layer)
Active PFC Boost Rectifier
Circuit Layout Considerations
Giorgio Spiazzi
University of Padova
Italy
Giorgio Spiazzi
University of Padova
Italy
Short paths among
switching components
and filter capacitor
MOS
High dv/dt track is short ...
D
... and shielded between
+Vout and -Vout tracks
3
Active PFC Boost Rectifier
Circuit Layout Considerations
Giorgio Spiazzi
University of Padova
Italy
Shielding tracks
connected to reference
Small area of the gate
circuit. Snubber close to
gate and source terminals
Control
Short (and shielded)
track at analog
inputs
Active PFC Boost Rectifier
Circuit Layout Considerations
Giorgio Spiazzi
University of Padova
Italy
Shield plane
connected to
reference
Star connection of
ground paths
Common mode
filter capacitors
4
Active PFC Boost Rectifier
Giorgio Spiazzi
University of Padova
Italy
Power section with EMI Filters
Low CM impedance
High CM impedance
i cm
Coupled inductors show high
common mode inductance but low
differential mode inductance:
i dm
Ex: 6.8 mH CM, 70 µH DM
Active PFC Boost Rectifier
Giorgio Spiazzi
University of Padova
Italy
Input filter design - Differential Mode
Lcm = 6.8 mH
Ripple amplitude
∆I max =
U out
≅ 113
. A
8 fs L
L dm = 70 µH
vn
50 Ω
i dm
50 Ω
triangular waveform
Differential mode input noise: 70 kHz,
(peak values)
140 kHz,
210 kHz,
280 kHz,
350 kHz,
420 kHz,
1 µF
2 µF
87 dB µV
57 dB µV
40 dB µV
26 dB µV
19 dB µV
9 dB µV
a suitable margin (20 dB µV) is maintained for the commom mode noise
and possible resonances
5
Active PFC Boost Rectifier
Giorgio Spiazzi
University of Padova
Italy
Input filter design - Common Mode
i cm
i cm
L cm = 6.8 mH
100 nF
4.7 nF
50 Ω
4.7 nF
1 µF
2 µF
•
•
•
•
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 asymmetrical
converter topology
• Adding CM capacitors at the input side reduces input CM voltage noise but
the increased CM current causes additional DM noise
Prototype Tests
Giorgio Spiazzi
University of Padova
Italy
Input behavior
Line Voltage
v
i
100 V/div.
2 A/div.
Line current
6
Giorgio Spiazzi
University of Padova
Italy
Prototype Tests
Line Voltage and Inductor Current
(peak to peak sampling)
Inductor current
switching ripple
v
iL
Giorgio Spiazzi
University of Padova
Italy
Prototype Tests
Gate drive circuit
IL+ID
threshold
iL
Voltage
drop
vDS
vG
iD
vGS
IL
threshold
7
Giorgio Spiazzi
University of Padova
Italy
Prototype Tests
Gate drive circuit
iL
vG
iD
vDS
vGS
IL
threshold
Commutation
is sloweddown
Giorgio Spiazzi
University of Padova
Italy
Prototype Tests
Gate drive circuit
vDS
Drain-Gate
coupling
iG
vG
iD
vGS
8
Giorgio Spiazzi
University of Padova
Italy
Prototype Tests
Gate drive circuit
vDS
iG
vG
iD
vGS
Prototype Tests
Giorgio Spiazzi
University of Padova
Italy
Modulation of Switching Frequency
VDS Spectra
Modulated
Fixed
9
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
Neutral
Phase
Prototype EMI Tests
Conducted noise (peak measure)
Giorgio Spiazzi
University of Padova
Italy
Introducing input-side common-mode
filter capacitors
• Differential noise increases (circuit is
not symmetrical) and low-frequency
behavior is worse
• A resonance, between input and
output CM filter capacitors and the
inductances of their connections,
appears, modifying the highfrequency behavior
Added
Line
PFC
10
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
Increased output-side common-mode
capacitors
• Common mode currents are closed on
the output side (no additional voltage
drop on the input filter occurs)
• Low-frequency behavior is improved
• High-frequency behavior becomes
worse due to resonance of two CM
filter capacitors and their connections
Added
PFC
Load
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
By connecting the heatsink to the
negative rail (capacitive currents are
closed “near” to the Mosfet source):
•Low-frequency behaviour is improved
•High-frequency behavior is good (the
heatsink shields all circuitry)
11
Prototype EMI Tests
Conducted noise (peak measure)
Giorgio Spiazzi
University of Padova
Italy
By inserting a shield, between Mosfet
and heatsink, connected to Mosfet
source (drain coupled capacitive
currents are closed directly to the Mosfet
source)
•Low-frequency behavior is improved
(common mode noise is reduced)
•High-frequency behavior is good (Using
the heatsink as shield of the whole circuit
gives however better results)
Shield
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
Switching Frequency Modulation
Switching frequency harmonic
components disappear
• Measured peak noise remains
unchanged
• Measured average noise is
considerably reduced
Peak
Average
12
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
Effect of Diode Reverse Recovery
(Disconnecting gate snubber)
• Low-frequency behavior is almost
unchanged
• High-frequency behavior is heavily
worsened
iL
vG
iD
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
Conducted noise (peak measure)
Increasing gate resistor
• Low-frequency behavior remains
unchanged
• High-frequency behavior is improved
(MOSFET commutation slows down)
iG
33
vG
iD
72 Ω
13
Prototype EMI Tests
Giorgio Spiazzi
University of Padova
Italy
By spreading the ac wires close to the
input filter (filter inductors inside plastic
can)
•Low-frequency behavior becomes
worse (input wires capture leakage
magnetic field of filter inductor)
•High-frequency behavior remains
unchanged
Line
EMI
Filter
PFC
Increased Area
14