1. Application information Power supply unit (PSU)
Part 3…PFCs (operation, types, sales guide)
Welcome to this Renesas Interactive course, that covers PSU Power Factor Correction. This course is part 3 in a series of 5 intermediate PSU-specific courses offered by the Renesas General Purpose Systems Division.
Renesas Electronics Corporation
General Purpose Systems Marketing Dept.
General Purpose Systems Division
Marketing Unit
Sep Rev.1.0
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2. Introduction to Part3 Purpose Objectives Contents Learning Time
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
50 minutes
The purpose of this course is to expand your knowledge of Power Supply Units, or PSUs. Specifically, Power Factor Correction, or PFC.
Our objectives are to learn about PFC operation and types of PFCs. This will be followed by some helpful sales guides. 2
©2012. Renesas Electronics Corporation, All rights reserved.

3. Principles of PFC
First, lets examine some principles of Power Factor Correction 3
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4. Boosting voltage to supply current to a smoothing capacitor
AC voltage
The waveforms in the right
figure are of the rectification
and smoothing circuit shown in
Part 1.
Let's supply current into the
boost inductor during these periods.
As a result, the waveform of the input current will be smoothed.
MOSFET is used to supply current to the inductor
Charging current to capacitor
Here we can see an AC voltage waveform and the corresponding spiked current, similar to the example seen in Part 1 of this series of courses.
The black arrows in this figure illustrate the periods where current is not flowing. When the current does flow, it does so in short bursts or peaks, resulting in a low power factor.
To increase the power factor and achieve better efficiency, this current waveform needs to more closely resemble a sinusoidal wave.
To do this, we need to try and supply current during the periods between the voltage peaks.
This can be accomplished by adding an inductor and a MOSFET to the circuit.
PSU Part 1 4
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5. 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.
Here, a boost inductor is inserted between the smoothing capacitor and a diode bridge.
A MOSFET is connected between the inductor and the ground, and the PFC IC performs switching through the MOSFET.
To boost voltage, the PFC IC turns the MOSFET on/off to supply current to the boost inductor, even when current is not flowing to the capacitor.
Given that current in the inductor increases with time, the PFC IC can eliminate current peaks by controlling the on/off switching time of the MOSFET.
This results in an “average ” of the AC current that more closely resembles a sinusoidal wave.
The waveforms of AC current and current through the boost inductor will be described later.
This circuit configuration is the same as that of a boost DC/DC converter.
For more information on the boost DC/DC converter, please refer to Supplement 1.
When making a PSU for the worldwide market, the voltage at the cathode of the diode is usually set to DC 390 V.
The output voltage is set using the resistances shown in red.
*: 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. 5
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6. Reduction of harmonic current by PFC
When there is no PFC (lower right figure, blue)
AC voltage
AC current
* Based on IEC 6
with PFC 5
International Standard *
without PFC 4 3
When PFC is used (green)
Harmonic current [A] 2 1
Here we can see the results of the circuit topology that we’ve just reviewed.
In the example with no PFC, we can see the current spikes, just like in our original example.
However when PFC is used, the current output more closely resembles a sinusoidal wave.
Additionally, we can see how PFC affects harmonic current by studying the graph at the lower right.
The blue bars indicate a PSU with no PFC. In this case, harmonic currents exceed international standards.
However with PFC, the harmonic currents are drastically reduced, as indicated by the green bars.
Joe’s Question:
“Regulation Value” - Is it possible to tell which regulation? IEC61000 ?
A: Yes, but it is international standards (not regulation). Each country has own regulations or standards usually based on IEC
OK – thanks.
Final corrections – changed script to say “In this case, harmonic currents exceed international standards.”
Slide – changed “regulation value” in bar graph to say “International Standard*” with a foot note – “based on IEC specifications”
AC voltage
Funda- mental
wave
3rd order
5th order
7th order
9th order
Harmonic order
AC current
Waveform approaches a sinusoidal wave, and the wave can satisfy the harmonic regulations 6
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7. Critical conduction mode and continuous conduction mode
Now, let's take a look at PFC operation. Specifically, Critical Conduction and Continuous Conduction Modes. 7
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8. 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).
We’ll start with Critical Conduction Mode.
As was described in Part 1, the current flowing into the inductor increases in proportion to time. In addition, when the applied voltage is lost, the inductor will use the energy that was accumulated in the form of magnetic flux to generate voltage.
Although this voltage charges the capacitor, the accumulated energy will eventually run out, and current will become zero.
Thus, the current flowing into the boost inductor has a triangular waveform, as shown in the left figure.
This method of turning the MOSFET on when current flowing into the inductor becomes zero, is called critical conduction mode, or CRM.
AC current is observed as the average current of the triangular wave.
Because CRM turns the MOSFET on when the current is zero, there is almost no power loss at the MOSFET and switching is efficient.
This type of switching is called soft switching. 8
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9. 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.
In order to tell the timing at which current flowing into the inductor becomes zero, a secondary winding for zero current detection (ZCD) is attached to the inductor.
The PFC IC turns the MOSFET on if zero current is detected.
The Renesas R2A20113A detects zero current by detecting the return current, as shown in the left figure. Therefore, there is no need for a winding for zero current detection in the inductor.
This is one of the features of the R2A20113A.
-- SLIDE --
Joe’s question: Can you re-word this?
“…. and detection of break in the wiring of the secondary winding is also unnecessary”
The way it is written sounds like it detects a “physical break” – example = no continuity
Answer: Please eliminate the phrase after “, and detection of break in…” because this is not essential explanation on this page, and this text is not for explanation of each PFC IC.
If pressed I would say,
if wiring between the secondary winding and PFC IC is broken down by any reasons (for example, some physical forces, corrosions, incomplete soldering, etc.), PFC IC can not decide the timing to turn on the MOSFET. Therefore usually, designers have to add some circuits which detect the breaking down.
R2A20113A does not need the secondary winding on the boost inductor, so it is not necessary to consider the cost for such detection circuits.
Ok thanks – I used your first suggestion. - joe 9
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10. 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 an inductor is proportional to the voltage applied to the inductor.
Fig. 2. Current flowing through PFC
boost inductor
As stated earlier, current flowing into an inductor increases in proportion to the applied voltage.
Renesas PFC ICs turn the MOSFET on and off with a constant ON time when the load is constant.
Consequently, when the diode bridge output voltage in the right figure is added to the inductor, the current flowing through the inductor is a triangular waveform with an average that is the same as the output voltage of the diode bridge. This can be seen in the orange highlighted area in the right figure.
The triangular wave component is removed by a filter inside the PSU, and at the AC plug the AC current becomes a sinusoidal wave, like the one shown at the bottom of the right figure.
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). 10
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11. 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.
The PFC IC changes the ON time of the MOSFET according to the load and controls the current flowing to the boost inductor.
Boost inductor current
(heavy load)
The volume of current flowing through the inductor is proportional to conduction time - that is to say, it is also proportional to the ON time of the MOSFET.
When the load changes, the PFC IC changes the ON time of the MOSFET and controls the current flowing to the boost inductor. That is, when the load is heavy the ON time is lengthened, and when the load is light the ON time is shortened.
On the other hand, as soon as the MOSFET turns off, current flows according to the electromotive force generated by the inductor, and it eventually becomes zero. The timing at which the current becomes zero changes depending on the load and the current of the inductor just before the MOSFET turned off.
For this reason, in CRM the switching frequency changes dynamically , relative to the load. That is, when the load is light the switching frequency is high, and when the load is heavy the switching frequency is low.
In CRM, the switching frequency changes. (from tens to hundreds of kHz, frequency is high at light load and low at heavy load) 11
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12. 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.
Now that we’ve learned about Critical Conduction Mode (CRM), lets have a look at Continuous Conduction Mode, or CCM.
In CCM, as shown in the left figure, the MOSFET is turned on before the inductor current becomes zero, and voltage is applied to the inductor.
Since the MOSFET is turned on from a state where inductor current is present, there is more power loss due to MOSFET switching when compared to CRM.
This type of switching, which is performed when current or voltage is not zero is called hard switching.
When the MOSFET turns on, the diode is reverse bias so it switches off. However, while the diode is switching, a reverse current flows from the capacitor to the MOSFET as shown by the red arrow in the right figure. This current results in power loss. Consequently, CCM requires a high-speed diode, that is, an FRD (fast recovery diode). For more information on FRDs, please refer to part 5 of this series of courses.
Although CCM relies on hard switching, which results in power loss, the peak of the triangular wave current flowing through the inductor is lower when compared to CRM, so there is less ripple. This makes CCM more suitable for large power PSUs. 12
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13. 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.
As with CRM, since voltage output from the diode bridge is applied to the boost inductor, the averaged waveform of the boost inductor current is a sinusoidal wave, as shown in this figure.
A PFC IC changes the duty of the MOSFET gate signal according to the load, changing the current flowing through the boost inductor.
However, unlike CRM which alters the switching frequency relative to the load, with CCM the switching frequency of the MOSFET does not change, even if the load changes. 13
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14. 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.
Its worth mentioning one other method of know as DCM, or discontinuous conduction mode which is a method containing a period when there is zero current flowing through the inductor.
Since power factor is not so improved, DCM is not a very commonly used method of PFC.
It is possible to go into DCM from a transient state of a CCM PFC IC.
Additionally, there are also some manufacturers who refer to CRM as DCM. 14
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15. CRM or CCM?
Advantage
Disadvantage
CRM
Critical Conduction Mode
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
Continuous Conduction Mode
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.
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
CCM
CRM
Average current
This slide lists the advantages and disadvantages of both modes. Namely,
CRM has better efficiency because it uses soft switching when the MOSFET is on, but the peak of the inductor current is higher than that of CCM, so a larger boost inductor is required.
CCM uses hard switching and is less efficient than CRM, and it also requires an FRD, but it can use a smaller inductor than CRM.
For these reasons, in general CRM is used for low-to-mid-range PSUs and CCM is used for mid-to-high-power PSUs.
*: Which method to use in the 200 to 600 W range also depends on the customer's experience, habits, cost of procuring peripherals, etc. 15
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16. Single operation and interleaved operation
CRM and CCM were differentiated by how the current flowing into the inductor is controlled.
Both modes can also perform either single operation or interleaved operation, and their PFC ICs differ. 16
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17. 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.
The PFC examples shown up to now have used a single set consisting of a MOSFET, a boost inductor, and a diode, as shown in the upper figure. This configuration is referred to as single operation.
In addition to single operation, there is also interleaved operation, which uses two sets of MOSFETs, boost inductors, and diodes. 17
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18. 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
Since the current path in interleaved operation is divided in two, twice the power can be output when compared to single operation. This makes interleaved operation a good choice for high power PSUs.
Interleaved operation is also suitable for reducing component size. For example, to achieve the same output power as with a single operation, the specs of the single operation’s MOSFET, boost inductor, and diode can be halved and the component count doubled to make a smaller interleaved PSU. Ultra-thin televisions are one product example that use interleaved operation.
In this figure we can see an example of CRM interleaved. Two inductor currents with a phase difference of 180 degrees are combined at the output. Although each line is CRM, the waveform of the combined current does not return to zero and, similar to CCM, there is little AC current ripple so small input filters can be used. This is another advantage that contributes to smaller PSUs. 18
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19. PFC modes (summary) CRM: CRitical conduction Mode
CCM: Continuous Current Mode
Type
Power range/mode
Applications
PFC products
Related products
Continuous
(CCM)
Inter-leaved
High-power (over 1 kW)
Small ripple current
Circuit is complex
Air-con, IH
R2A20114A
IGBT
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
Critical
(CRM)
Mid-range (0.2 to 3 kW)
Air-con, plasma/LCD TVs, computers, office equipment
R2A20112A
Low-power (under 300 W)
LCD monitor, AC adaptor, LCD projector
R2A20113A
R2A20133A
R2A20133B
R2A20133D
This table summarizes CCM, CRM, single, and interleaved PFC.
PSUs in the 200 W to several hundred W range can use either CCM single or CRM interleaved operation. Which method to use is selected depending on the customer's habits and cost of components, etc.
In terms of applications, televisions mostly use CRM, and computers mostly use CCM.
This concludes the explanation of the basic operation of PFC. Actual PFC ICs contain protection circuits and functions for improving efficiency, etc., in addition to functions for basic operation.
For more information on these additional functions of PFC ICs, please refer to Supplement 2. 19
©2012. Renesas Electronics Corporation, All rights reserved. 19

20. PFC market and sales guide
Applicable to all devices that use AC input
Now for a look at the PFC Market and Sales Guide.
PFC is used in on devices over 75 W and lighting equipment over 25 W running on AC power. 20
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21. PFC roadmap (as of Feb. /2012)
Evolving
for each application
Air-con., server, industrial equipment
Power
range
Large power range
10kW
R2A20114
R2A20114A
R2A20104
Improved characteristics
Mid. power range
CCM interleave
CRM interleave
1kW
General PSU, DT-PC
R2A20132
CCM single
High efficiency
at light load
R2A20111
R2A20115
R2A20131
Improved characteristics
FPD-TV
High efficiency at light load
CRM interleave
300W
R2A20112
R2A20117
R2A20118A
R2A20112A
Protection functions
Abundant protection functions
16pin version of R2A20118A
CRM single
This figure shows the product roadmap as of April 2011.
When sharing this information with customers, please be sure that you are referencing the newest version.
100W
Small FPD-TV, monitor, lighting
Small power range
R2A20133A/B/D
R2A20113
R2A20113A
2nd OVP
CCM PFC
Enhanced version
R2A20134
CRM PFC
50W
LED lighting
2008
2009
2010
2011 21
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22. Selection guide R2A20133A～D R2A20112A R2A20131 R2A20104 R2A20114A
Start
Power range?
LCD monitors,
Desk-top PCs,
Office equipment
Small servers,
Large TV,
MFP with IH for
fixation
Servers,
Base stations,
Air con.
LCD-TV,
Desk-top PCs,
Office equipment
Under 200W W
300-1kW
Over 1kW
Yes
CRM is preferred ? No
Yes
For slim applications No
When determining part requirements for TV sets, the primary considerations are the power requirements and the TV set-type (ultra-slim or not).
When determining requirements for PCs the key consideration is power.
For air-conditioners, the key points are the power, efficiency, and the PF (or harmonic currents).
In general, R2A20114A can cover numerous air-conditioner applications.
When the power is under 3kW and the MCU used for controlling the inverter has a margin, a good way might be to adopt the partial switching method.
However, if the harmonic current regulations are strict, a PFC IC is better.
CRM
single
CRM
interleaved
CCM
single
CCM
interleaved
R2A20133A～D
R2A20112A
R2A20131
R2A20104
Servers
Base stations
R2A20114A
Air con. 22
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23. 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
Here is a list of Tools and documents that are available to help with your sales promotion.
All evaluation boards are for lending use only. Requests for boards should be submitted through COMPASS. 23
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24. 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
This table shows the major manufacturers of PFC ICs.
EU: Europe, US: United States, JP: Japan, TW: Taiwan 24
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25. Supplement 1 Boost converter25
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26. Boost converters (1) When MOSFET is on
A boost converter is used when voltage higher than the input is required.
When the MOSFET is turned on, current flows in the path shown by the red line.
The current flowing through the inductor increases with time, and power is stored as magnetism in the inductor (Fig. 2).
During this time, the voltage on both sides of the inductor are as shown in Fig. 1: VIN is high and the voltage at point A is almost GND.
The diode is reverse bias, so current does not flow into the diode.
The electric charge stored in the capacitor flows to the load. 26
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27. Boost converters (2) When MOSFET is off
When the MOSFET is turned off, the inductor generates voltage as shown in fig. 1, in order to continue sending current in the direction it was flowing.
The source of this energy the magnetism generated by the inductor.
The voltage at A =
VIN + voltage generated by inductor,
so it is greater than VIN.
The diode is forward bias and current flows in the paths shown by the blue lines.
Eventually, the current flowing through the inductor will become zero and the MOSFET is repeatedly turned on and off in order to maintain output voltage. 27
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28. Supplement 2 Additional functions of PFC ICs28
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29. 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*.
OVP (Over Voltage Protection) is a function that stops the PFC IC if the PFC output voltage exceeds a set value (becomes overvoltage).
If output voltage rises above the set voltage for some reason (sudden loss of load, etc.) and exceeds the voltage tolerance of the capacitor, diode, MOSFET, etc., it can damage these components but may also cause fire or smoke.
For this reason, OVP is an essential function for a boost circuit.
*: May differ according to product. Please check the datasheet. 29
©2012. Renesas Electronics Corporation, All rights reserved.

30. 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.
Change the boost inductor and filter to ones hardened with varnish
Change the capacitor to one which does no generate noise easily
Hermetically seal the set so that sound doesn't leak (cost rises, and heat dissipation is difficult).
Insert a countermeasure circuit on the PFC IC side (dynamic OVP --- see next page)
Hum or acoustic noise, etc. is a phenomenon that causes circuit components to vibrate, generating audible noise.
Although the PFC IC itself does not generate sound, sound may be generated by the filter, inductor, or capacitor, etc.
This sound would be an annoyance in devices ( like TVs) that are used in homes. So a countermeasure against acoustic noise is needed.
There are a variety of sources of acoustic noise. Here we'll focus on noise caused by the repeated operation of OVP caused by output overvoltage.
If overvoltage occurs for some reason, OVP operates and PFC output stops. Due to this, PFC output voltage drops, so OVP is released and PFC operation resumes.
If the source of overvoltage is not removed, overvoltage will occur again, and reactivate OVP. The repetition of this causes PFC to operate intermittently. If the period of repetition enters the audible range, acoustic noise will be generated.
Countermeasures against acoustic noise include hardening the filter and inductor, insulating the sound, and so on.
Renesas employs a dynamic OVP function to PFC ICs to prevent acoustic noise. 30
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31. 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
Enlarged view
Output voltage
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.
Instead of stopping PFC IC output after overvoltage occurs like the OVP function, the dynamic OVP function gradually restricts the output of the PFC IC before overvoltage is reached.
This prevents a cycle of overvoltage -> OVP stops PFC operation -> output voltage drops -> PFC operation resumes -> overvoltage, preventing the generation of audible noise by intermittent operation of PFC. 31
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32. 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
The 2nd OVP function provides additional OVP functions beyond the standard OVP. This is required by applications demanding high safety.
The OVP function uses the FB pin to monitor output voltage. However, if for example wiring between the resistor divider and the FB pin is partially broken or deteriorates, both the control of output voltage and the OVP function may stop working.
So, the output voltage of a separate resistor divider is monitored, and input to the OVP2 pin. Safety increases because this OVP circuit is on a separate line from the OVP function monitored by the FB pin.
--SLIDE—
First bullet point: When you say “doubled OVP function, do you mean “redundant” google translate “ 冗長な “
-> no, not for “redundant”. Our intention is “an additional OVP function on standard OVP”. Please change the words at the first bullet point with proper words.
OK Final Correction - The 2nd OVP function provides additional OVP functions beyond the standard OVP.
Thanks - Joe
*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. 32
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33. 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.
The OCP function stops driving the MOSFET when load current is too high to prevent damage to the MOSFET and diode, etc.
Overcurrent is detected by monitoring the voltage of the resistor connected to the source of the MOSFET, or the voltage on both sides of the resistor that measures return current.
Some ICs have an OCP timer latch function that stops PFC operation if an overcurrent state continues for a certain period of time (PFC operation will resume when power is turned on again). 33
©2012. Renesas Electronics Corporation, All rights reserved.

34. 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.
This function detects abnormalities, such as open circuit of a feedback signal (FB signal, ZCD signal, or CS signal), and stops PFC operation.
The FB signal monitors the PFC output voltage. If the FB signal is not taken into the PFC IC normally, output voltage will become abnormal and may damage the element.
The ZCD (zero current detection) pin is found in CRM PFC ICs and is a signal input pin that's used for finding the timing at which boost inductor current becomes zero.
The signal of the secondary ZCD winding for zero current detection of the boost inductor is input to this pin.
The CS pin is for measuring current, but it is also used by the OCP function. If a CS signal is open circuit (disconnected), the OCP function doesn't operate and overcurrent protection is disabled.
The CS pin is not available in any CRM PFC ICs except the R2A20113A. 34
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35. 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.)
The brown-out function prevents damage due to continued use of the MOSFET by stopping PFC operation when the AC voltage is too low.
The UVLO function prevents malfunction by stopping PFC operation when the Vcc pin voltage of the PFC IC is too low. 35
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36. 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 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.
Efficiency
Although interleaved operation is more efficient than single operation at heavy loads, switching loss is high at light loads due to switching between two lines.
The slave drop function allows high efficiency to be achieved at light load by stopping the slave channel (or phase 2 channel) and switching to single operation.
For the same power rating, interleaved operation uses components whose rating values are less than the those required by single operation.
By employing the slave drop function at light load, higher efficiency can be achieved through single operation.
This function is effective when AC voltage is 200 V.
Joe, “fewer components” in third paragraph is not my meaning.
I want to say “components with smaller specification” like “MOSFET which max. spec. is Id=2A” is smaller than MOSFET of Id = 4A“.
I don’t know proper expression. Please change the word with proper word. Is it good now?
Thanks for the clarification – final edit “components whose rating values are less than the those required by single operation. “ 36
©2012. Renesas Electronics Corporation, All rights reserved.

37. 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.
The LTB function changes output voltage (boost voltage) relative to the load.
It reduces output voltage when the load is light. The boosted voltage reduces loss in efficiency.
LTB functions may change output voltage in steps or linearly.
Renesas PFC ICs employ the linear method because the step method makes sudden changes to the output voltage that can cause instability in the PSU.
LTB is effective when AC voltage is 100 V. 37
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38. 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).
The soft start function prevents excessive AC current when Vcc of the PFC IC is supplied.
When PFC starts, for example when AC voltage is 100 V, the voltage of the output capacitor is about 141 V.
Once PFC starts, the MOSFET is almost continuously in an ON state in order to boost voltage towards the set PFC output voltage. Thus, current flow is large, which may damage the MOSFET.
Therefore, we have a function that squeezes the gate pulse width (ON time) of the MOSFET when PFC starts to prevent the flow of excessive current. 38
©2012. Renesas Electronics Corporation, All rights reserved.

39. Additional functions and major PFC ICs
: No corresponding pin
Additional PFC functions and Renesas' main PFC ICs are shown in this table.
The latest PFC ICs may contain functions in addition to those shown here.
Please check the latest datasheets for the most current information.
*: Also has short detection to GND
**: With latch function 39
©2012. Renesas Electronics Corporation, All rights reserved. 39

40. Supplement 3 Power factor correction in inverter air conditioners40
©2012. Renesas Electronics Corporation, All rights reserved.

41. Power factor correction methods in inverter air conditioners
This slide shows power factor correction methods used in inverter air conditioners. Although the passive method is mainly used in 100 V air conditioners of 2 kW or less power, this method is becoming less common because it requires a large reactor (inductor). In addition, the AC current waveform is also considerably removed from a sinusoidal wave, so harmonic current is not sufficiently reduced.
When the MCU in the inverter section has power to spare, the partial switching method shown in fig. 2 is often used.
In partial switching, the MCU turns on the MOSFET or IGBT several times in the first half of each half-cycle of AC voltage to boost voltage. Although the AC current waveform is greatly improved compared to the passive method, since it is considerably removed from a sinusoidal wave, it is difficult for air conditioners over 3 kW (power consumption) to meet harmonic regulations.
Air conditioners over 3 kW need PFC using the active filter method to meet harmonic regulations. An example of the PFC IC for this method is shown in fig. 3. Although this figure shows single PFC, in general high-power air conditioners use CCM-Interleave PFC ICs.
When the MCU in the inverter section has several tens of MIPS of more of power to spare, it is also possible to implement an active filter using an MCU instead of a PFC IC. 41
©2012. Renesas Electronics Corporation, All rights reserved.

42. 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
Reason: Cost
Single, partial SW
-> interleaved
Reason: Cost
Single, passive
-> interleaved
Reasons: Cost, power
AC 220 to 230 V systems
(2)
(3)
Passive,
Partial SW
Reason: Cost
Single, partial SW
-> partial SW,
interleaved
Reasons: Efficiency, cost
Single, passive
-> interleaved
Reasons: Cost, power
The relationship between AC voltage, the power of the air conditioner, and PFC method is shown.
The focus of all air conditioner manufacturers is gradually shifting from 2.8 kW to 4-5 kW, so we can expect an increase in demand for CCM-Interleave PFC ICs.
AC 100 V systems
(2)
(1)
3 kW
Low power
High power 42
©2012. Renesas Electronics Corporation, All rights reserved.

43. Thank you
Thank You
Confidential 43