Transcript PSU_Part3_PFC - Renesas e-Learning

Application information
Power supply unit (PSU)
Part 3…PFCs (operation, types, sales guide)
Renesas Electronics Corporation
General Purpose Systems Marketing Dept.
General Purpose Systems Division
Marketing Unit
Sep. 2011
Rev.1.0
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Introduction to Part3
 Purpose
This course provides basic knowledge of power supply units
 Objectives



Learn about PFC operation
Learn about the types of PFC
Learn about sales guides
 Contents

45 pages
 Learning Time

2
50 minutes
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Principles of PFC
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Boosting voltage to supply current
to a smoothing capacitor
 The waveforms in the right
figure are of the rectification
and smoothing circuit shown in
Part 1.
AC voltage
Charging
current to
capacitor
 Let's supply current into the
boost inductor during these periods.
As a result, the waveform of the
input current will be smoothed.
PSU Part 1
 MOSFET is used to supply current to the inductor
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PFC is a boost converter
 The topology of the boost inductors, MOSFETs, and diodes in
PFCs are the same as that of a boost converter
(see Supplement 1).
 By boosting the voltage, the PFC IC has the MOSFET supply
current to the booster inductor even when current is not
flowing in the capacitor.
*: For a PSUs that are used globally, the output voltage should be higher than 373 V.
240 V (U.K.) x 1.1 (AC voltage variation tolerance) x √2 (peak voltage of sinusoidal wave) = 373 V
If higher boost voltage far from 373 V is set, the cost associated with capacitors and diodes and so on become expensive
rises, so realistically it is usual to set it at 390 V.
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Reduction of harmonic current by PFC
When there is no PFC
(lower right figure, blue)
AC voltage
AC current
AC voltage
Harmonic current [A]
When PFC is used (green)
* Based on IEC6100-3-2
6
with PFC
5
without PFC
4
International
Standard *
3
2
1
0
Fundamental
wave
AC current
3rd
order
5th
order
7th
order
9th
order
Harmonic order
Waveform approaches a sinusoidal wave, and
the wave can satisfy the harmonic regulations
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Critical conduction mode and
continuous conduction mode
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Critical conduction mode (1)
A PFC IC turns the MOSFET on and off repeatedly in order to boost
voltage.
The PFC operating mode is divided depending on the timing at which
the MOSFET is turned on.
 In the method shown in the above figure, the MOSFET is turned on at
the end of period (2) (when the current flowing through the boost
inductor is zero). This is called critical conduction mode (CRM).
 Since the MOSFET is turned on when the inductor current is zero,
there is no loss at the MOSFET (soft switching) and this method is
efficient.
Note: some manufacturers call critical conduction mode TM (transient mode).
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Critical conduction mode (2)
 The detection of when inductor current is zero is called ZCD (zero
current detection). To perform ZCD, usually a secondary winding is
prepared in the boost inductor and this signal is input to the PFC IC
(this is same way as other companies’ products).
 With R2A20113A, the secondary winding of the boost inductor
is unnecessary. The R2A20113A senses the return current in order
to estimate ZCD.
-> inductor costs can be.
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Critical conduction mode (3)
AC voltage
Diode bridge
output voltage
Boost inductor
current
Triangular wave is filtered and averaged ,
and becomes a sinusoidal wave current
Fig. 1. Current flowing through boost inductor
(if voltage applied to boost inductor is
changed)
AC current
 The height of current waveform flowing through
Fig. 2. Current flowing through PFC
an inductor is proportional to the voltage applied
boost inductor
to the inductor.
 Since voltage output from the diode bridge is applied to the inductor, the envelope curve of
the current of the triangular waveform flowing through the boost inductor has the same
waveform as voltage, and the AC current is a sinusoidal wave.
 Other companies also have PFC ICs that change the MOSFET ON time according to the
output voltage of the diode bridge (such PFC ICs have a pin called MULT).
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Critical conduction mode (4)
Boost inductor
current
(light load)
 The height of the current
waveform also changes according
to the ON time of the MOSFET.
Boost inductor
current
(heavy load)
 The PFC IC changes the ON time
of the MOSFET according to the
load and controls the current
flowing to the boost inductor.
 In CRM, the switching frequency changes. (from tens to hundreds
of kHz, frequency is high at light load and low at heavy load)
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Continuous conduction mode (1)
 The method of turning the MOSFET on again before boost inductor
current becomes zero is called continuous conduction mode (CCM).
 Since the MOSFET is turned on again while current is flowing (hard
switching), more heat is generated using this method compared to CRM.
 Although CCM is less efficient than CRM, the peak of the boost inductor
current in CCM is lower than the peak in CRM, so there is less voltage
ripple observed at AC plug.
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Continuous conduction mode (2)
 Since the output voltage of the
diode bridge is applied to the
boost inductor, the waveform of
the current flowing through the
boost inductor is as shown in the
right figure.
 In continuous conduction mode,
switching frequency is fixed, the
ratio (duty) of the ON time
and OFF time of the MOSFET
are changed, and current flowing
to the boost inductor is
controlled.
 In CCM, the switching frequency
does not change even if the load
changes.
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Discontinuous conduction mode
 The operation shown in the above figure is called
discontinuous conduction mode (DCM).
 It is not very popular method of PFC.
 There are also some manufacturers who refer to critical
conduction mode (CRM) as DCM.
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CRM or CCM?
Advantage
Disadvantage
CRM
Since it uses soft switching, it
generates less heat at the MOSFET
than CCM, so higher efficiency can
be achieved.
When supplying the same average
current, CRM has the larger triangular
wave, and requires a larger boost
inductor.
CCM
Since the height of the triangular
wave is lower and ripples are
smaller, the size of the boost
inductor and input filter can be
reduced.
Since it uses hard switching, much heat
is generated at the MOSFET and also
the diode has recovery loss, decreasing
efficiency.
Critical Conduction
Mode
Continuous
Conduction Mode
Due to the above, the use of CCM PFC ICs and CRM PFC ICs is usually
divided as follows:*
CCM: Mid-to-high-power 200 W and above
CRM: Low-to-mid-range 300 W and below
*:
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CCM
Average current
Which method to use in the 200 to 600 W range
also depends on the customer's experience,
habits, cost of procuring peripherals, etc.
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Single operation and
interleaved operation
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Single and Interleaved Operation
 Single Operation utilizes a MOSFET, a boost inductor and a diode.
 Interleaved Operation alternates between two sets of MOSFETS, boost
inductors and diodes.
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Advantages of interleaved
operation
(1) In interleaved operation, two lines each use half of the available current.
Twice the power of a single system using the same components (MOSFET,
boost inductor, etc.) can be obtained
(2) Lower current ripple decreases as a continuous mode waveform
Smaller input filters can be used -> smaller and slimmer PSUs can be realized
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PFC modes (summary)
CRM: CRitical conduction Mode
CCM: Continuous Current Mode
Type
Continuous
(CCM)
Critical
(CRM)
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Power range/mode
Applications
PFC
products
Related
products
IGBT
Interleaved
High-power (over 1 kW)
Small ripple current
Circuit is complex
Air-con, IH
R2A20114A
Server
Base station
R2A20104
R2A20124A,
High-voltage
MOS
Single
Mid-range (0.3 to 1 kW)
Large ripple current
Circuit is simple
Plasma TV,
office
equipment,
computer
R2A20131
High-voltage
MOS
Interleaved
Mid-range (0.2 to 3 kW)
Small ripple current
Circuit is complex
Air-con,
plasma/LCD
TVs,
computers,
office
equipment
R2A20112A
High-voltage
MOS
Single
Low-power (under 300
W)
Large ripple current
Circuit is simple
LCD monitor,
AC adaptor,
LCD projector
R2A20113A
R2A20133A
R2A20133B
R2A20133D
High-voltage
MOS
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PFC market and sales guide
Applicable to all devices that use AC input
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PFC roadmap (as of Feb. /2012)
Power
range
10kW
Evolving
for each
application
Air-con., server, industrial equipment
Large power range
R2A20114
R2A20104
Mid. power range
CCM interleave
1kW
300W
R2A20112
Small power
range
High efficiency
at light load
R2A20117
R2A20118A
R2A20112A
16pin version of
R2A20118A
Small FPD-TV, monitor, lighting
R2A20113A
R2A20113
Enhanced version
CRM single
R2A20133A/B/D
2nd OVP
R2A20134
CRM PFC
LED lighting
2008
21
CRM interleave
Abundant protection
functions
CCM PFC
50W
CCM single
R2A20131
Improved
characteristics
Protection functions
100W
CRM interleave
High efficiency
at light load
R2A20115
FPD-TV
Improved
characteristics
R2A20132
General PSU, DT-PC
R2A20111
R2A20114A
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2011
Selection guide
Start
Power range?
LCD monitors,
Desk-top PCs,
Office equipment
Under 200W
Small servers,
Large TV,
MFP with IH for
fixation
LCD-TV,
Desk-top PCs,
Office equipment
200-300W
300-1kW
Yes
Yes
CRM
single
R2A20133A～D
For slim
applications
Servers,
Base stations,
Air con.
Over 1kW
CRM is
preferred ?
No
No
CRM
interleaved
R2A20112A
CCM
single
R2A20131
CCM
interleaved
R2A20104
R2A20114A
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Servers
Base stations
Air con.
Sales guide (documents and tools)
Items shown below are available for each product.
 One page information: Introduction of the ICs’ features in one
page
 Presentation material: Introduction and explanation of the ICs
 Data sheet:
Specifications
 Application note:
Explanation of built-in functions,
examples of board design,
design guide, etc.
 Excel sheet:
Worksheet to calculate the value of
external components value
 Technical Q&A:
FAQ
 Evaluation board:
Not for sale, for lending only
 IC sample:
For evaluation
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Competitors analysis
 In each application and area, competitors are different
 Renesas covers all power range with abundant products
◎:has strong products, ○:competitive, △:poor, -:no product
EU: Europe, US: United States, JP: Japan, TW: Taiwan
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Supplement 1 Boost converter
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Boost converters (1)
When MOSFET is on
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Boost converters (2)
When MOSFET is off
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Supplement 2 Additional functions
of PFC ICs
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OVP (Over Voltage Protection)
 A PFC IC uses the FB pin to monitor the output voltage. If the
output voltage exceeds 390 V, the MOSFET's ON time is
shortened (the duty of the gate signal is reduced) in order to
lower the output voltage.
 For Renesas PFC ICs, OVP is triggered when output voltage
hits the set value of 109% or more*.
*: May differ according to product. Please check the datasheet.
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Acoustic noise and dynamic OVP (1)
 Hum or acoustic noise is a phenomenon
that is caused by vibration of circuit
components generating audible noise.
This can be cause by overvoltage.
 If the cause of the overvoltage is not
removed, it may result in
overvoltage -> OVP operation ->
PFC stops-> output voltage drops ->
PFC operation resumes
This cycle continues and the PFC IC repeatedly turns on and off.
 In such cases, since voltage is repeatedly applied to the boost inductor, filter,
and capacitor, sound may be generated.
 Countermeasures against acoustic noise are as follows.
1) Change the boost inductor and filter to ones hardened with varnish
2) Change the capacitor to one which does no generate noise easily
3) Hermetically seal the set so that sound doesn't leak (cost rises, and heat
dissipation is difficult).
4) Insert a countermeasure circuit on the PFC IC side (dynamic OVP --- see
next page)
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Acoustic noise and dynamic OVP (2)
 Dynamic OVP is a function
that prevents hum or acoustic
noise.
 If the output of a PFC IC can
be gradually restricted before
reaching OVP voltage, the
previously mentioned
repetitive on/off operation can
be prevented along with
acoustic noise.
Output
voltage
inductor
current
Output
voltage
Enlarged view
inductor
current
When output voltage exceeds dynamic OVP
set voltage, dynamic OVP gently restricts
inductor current
 This is achieved by dynamic OVP. The function activates when
output voltage reaches the set value of 104%.
 Similar to the OVP function, the dynamic OVP function
monitors the FB pin voltage.
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Second OVP (2nd OVP)
 The 2nd OVP function provides
additional OVP functions beyond
the standard OVP.
 If wiring to the FB pin is partially
broken or the resistance that
makes the FB signal deteriorates,
both the control of output voltage
and the OVP function don’t work
correctly
 To prevent this, sometimes an additional OVP function is required. This is
called 2nd OVP.
 The OVP2 pin is placed on a resistor divider on a separate line from the FB pin,
PFC IC stops when the OVP2 pin voltage exceeds the set voltage.
 The relationship between each OVP set voltage is as follows.
 Normal output voltage < dynamic OVP < OVP, 2nd OVP*1 < Maximum rating
of elements*2
*1: The operating voltages of OVP and 2nd OVP can be set independently.
*2: The lowest voltage among the absolute maximum ratings of the capacitor, diode, and
MOSFET, etc.
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OCP (Over Current Protection)
 This function stops driving the
MOSFET when load current is
too large to prevent damage to
the MOSFET and diode, etc.
 The OCP pin is used to monitor
the voltage of the resistor
connected to the source of the
MOSFET, to detect over current
(Fig. 1).
R2A20113A uses the return
current to detect over current,
as shown in Fig. 2.
 Over current is checked for at
every switching, and driving of
the MOSFET is resumed once
the over current state is
resolved.
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Open (circuit) detection function/FB pin,
ZCD pin, and others
 This function detects abnormalities, such as open circuit of a
feedback signal (FB signal, ZCD signal, or CS signal), and
stops PFC operation.
 PFC operation resumes once the open state of the FB pin is
resolved.
 The FB pin also has short detection with regards to GND.
 Some ICs have a ZCD pin and CS pin with open detection.
 When the ZCD pin or CS pin is in an open state, PFC stops
until the power is turned on again.
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Brown-out and UVLO
(Under Voltage Lockout)
Brown-out function
 This function prevents damage to the MOSFET by stopping PFC operation when
the AC voltage is too low.
 AC voltage is monitored by the brown-out pin.
 The brown-out function stops PFC operation until AC voltage recovers to a high
enough level. (The brown-out activate/cancel voltage has hysteresis.)
UVLO (Under Voltage Lockout)
stops PFC under low AC voltage
 This function prevents malfunction by stopping PFC operation when the Vcc pin
voltage of the PFC IC is too low.
 The Vcc of the PFC IC is usually supplied from an auxiliary power supply.
 The UVLO function stops PFC operation until Vcc rises to a high enough level
again. (The UVLO activate/cancel voltage has hysteresis.)
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Slave drop/phase drop
 Slave drop (called phase drop in CCM PFC) is a function that stops
interleaved operation at light load and switches to single operation.
 Although interleaving realizes higher efficiency at heavy loads, switching loss at
the MOSFETs are conspicuous at light loads and the efficiency is less than single.
Therefore, efficiency can be improved by stopping interleaved operation at light
load and switching to single operation.
 When designing PSUs of the
same power rating with
interleaved PFC, smaller
component values than single
PFC can be used, the slave drop
function can achieve higher
Efficiency
efficiency than single PFC at
light load.
 This function is especially
effective when AC voltage is in
the 200 V range.
 The power at which a slave
channel stops can be set by an
external component.
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LTB (Load Tracing Boost)
 The LTB function changes
output voltage (boost voltage)
relative to the load.
 The boosted voltage reduces
loss in efficiency.
 Renesas PFC ICs use a system
of changing output voltage
linearly according to load.
 This facilitates the
development of PSUs
satisfying 80 PLUS and CSCI
Gold class, which are required
for computers and servers.
 LTB is effective when AC
voltage is 100 V.
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Soft start
 The soft start function prevents
excessive AC current when PFC is
on.
 Since the voltage of the capacitor is
low when PFC is on, even at no load
large AC current flows toward the
capacitor (OCP repeatedly operates
and stops and acoustic noise may be
generated) (upper right figure).
 The soft start function squeezes the
gate pulse width (ON time) of the
MOSFET when power is on to prevent
the flow of excessive current (lower
right figure).
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Additional functions and major PFC
ICs
: No corresponding pin
*: Also has short detection to GND
**: With latch function
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Supplement 3 Power factor correction
in inverter air
conditioners
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Power factor correction methods in
inverter air conditioners
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Power factor correction methods in
inverter air conditioners
The focus of all manufacturers is shifting from 2.8 kW (conventional) to
4-5 kW. high-power models are expected to increase.
Possibility of entry of PFC IC is low
Possibility of entry of PFC IC
Possibility of entry of PFC IC is high
Packaged air conditioner
(PAC)
Room air conditioner (RAC)
Partial SW
-> partial SW,
interleaved
AC 220 to 230 V
systems Reason: Cost
Single, partial SW
-> interleaved
Reason: Cost
(2)
Passive,
Partial SW
AC 100 V Reason: Cost
systems
(1)
Low power
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Single, passive
-> interleaved
Reasons: Cost, power
(3)
Single, partial SW
-> partial SW,
interleaved
Reasons: Efficiency,
(2)
cost
3 kW
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Single, passive
-> interleaved
Reasons: Cost, power
High power
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Thank you
Thank You
Confidential
Renesas Electronics Corporation.
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