apped-101054a confidential part 3…pfcs (operation, types, sales guide) sep. 2011rev.1.0 general...

APPED-101054AConfidential

Part 3…PFCs (operation, types, sales guide)

Sep. 2011 Rev.1.0

General Purpose Systems Marketing Dept.General Purpose Systems DivisionMarketing Unit

Renesas Electronics Corporation

Application information

Power supply unit (PSU)

©2012. Renesas Electronics Corporation, All rights reserved.


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 50 minutes

2 ©2012. Renesas Electronics Corporation, All rights reserved.

APPED-101054A

Principles of PFC



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

AC voltage

Boosting voltage to supply current to a smoothing capacitor

4

PSU Part 1



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 VIf 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.

PFC is a boost converter



AC voltage

AC current

0

1

2

3

4

5

6

3rd order

5th order

7th order

9th order

Harmonic order

Harm

onic

curr

ent

[A]

AC voltage

AC current

When there is no PFC (lower right figure, blue)

When PFC is used (green)

International Standard *

Funda-mentalwave

Waveform approaches a sinusoidal wave, and the wave can satisfy the harmonic regulations

without PFC

with PFC

Reduction of harmonic current by PFC


* Based on IEC6100-3-2

APPED-101054A

Critical conduction mode and continuous conduction mode



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).

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.

Critical conduction mode (1)



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.




The height of current waveform flowing through an inductor is proportional to the voltage applied to the inductor.

Fig. 1. Current flowing through boost inductor(if voltage applied to boost inductor is changed)

AC voltage

Diode bridgeoutput voltage

Boost inductor current

AC current

Triangular wave is filtered and averaged , and becomes a sinusoidal wave current

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).

Fig. 2. Current flowing through PFC boost inductor




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.


(light load)


(heavy load)

In CRM, the switching frequency changes. (from tens to hundreds of kHz, frequency is high at light load and low at heavy load)




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.

Continuous conduction mode (1)



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.

Continuous conduction mode (2)



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.

Discontinuous conduction mode



CCM

CRM

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.

CRM or CCM?

15

Advantage Disadvantage

CRMCritical 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.

CCMContinuous

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


APPED-101054A

Single operation and interleaved operation



Single and 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

Advantages of interleaved operation



Type Power range/mode Applications PFC products

Related products

Continuous(CCM)

Inter-leaved

High-power (over 1 kW)Small ripple currentCircuit is complex

Air-con, IH R2A20114A IGBT

ServerBase station

R2A20104 R2A20124A,High-voltage

MOS

Single Mid-range (0.3 to 1 kW)Large ripple currentCircuit is simple

Plasma TV, office equipment, computer

R2A20131 High-voltage MOS

Critical(CRM)

Inter-leaved

Mid-range (0.2 to 3 kW) Small ripple currentCircuit is complex

Air-con, plasma/LCD TVs, computers, office equipment

R2A20112A High-voltage MOS

Single Low-power (under 300 W)Large ripple currentCircuit is simple

LCD monitor, AC adaptor, LCD projector

R2A20113AR2A20133AR2A20133BR2A20133D

High-voltage MOS

CRM: CRitical conduction ModeCCM: Continuous Current Mode

PFC modes (summary)


APPED-101054A

PFC market and sales guide

Applicable to all devices that use AC input



1kW

10kW

100W

50W

300W

2008 2009

Power range

CCM PFC

CRM PFC

2010

Large power range Large power range

Small power range Small power range

Mid. power range Mid. power range

R2A20113

2011

R2A20114

R2A20111

Protection functions Abundant protection functions

R2A20115

FPD-TV

General PSU, DT-PC

High efficiency at light load

R2A20132

R2A20131

Air-con., server, industrial equipment

Small FPD-TV, monitor, lighting

CRM interleave

CRM single

CCM single

Evolving for each application

CRM interleave

Enhanced version

Improved characteristics

R2A20134LED lighting

High efficiencyat light load

PFC roadmap (as of Feb. /2012)

R2A20114A

R2A20112 R2A20117 R2A20112AR2A20118A

R2A20104CCM interleave

Improved characteristics

16pin version of R2A20118A

R2A20133A/B/DR2A20113A

2nd OVP



Selection guide

Power range?

R2A20133A ～D

R2A20131R2A20112A

NoYes

Under 200W 200-300W 300-1kW

Servers,Base stations,Air con.

Over 1kW

CRMsingle

CCMsingle

CRMinterleaved

LCD-TV,Desk-top PCs,Office equipment

Small servers,Large TV,MFP with IH forfixation

LCD monitors,Desk-top PCs,Office equipment

R2A20104

CCMinterleaved

CRM is preferred ?

For slim applications

NoYes

R2A20114A

ServersBase stations

Air con.

Start

©2012. Renesas Electronics Corporation, All rights reserved.22


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

Sales guide (documents and tools)



In each application and area, competitors are different Renesas covers all power range with abundant products

Competitors analysis

24

◎:has strong products, ○:competitive, △:poor, -:no product

EU: Europe, US: United States, JP: Japan, TW: Taiwan


APPED-101054A

Supplement 1 Boost converter



Boost converters (1)

When MOSFET is on



Boost converters (2)

When MOSFET is off


APPED-101054A

Supplement 2 Additional functionsof PFC ICs



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.

OVP (Over Voltage Protection)



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.

Acoustic noise and dynamic OVP (1)

Countermeasures against acoustic noise are as follows.1) Change the boost inductor and filter to ones hardened with varnish2) Change the capacitor to one which does no generate noise easily3) 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)



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.

When output voltage exceeds dynamic OVP set voltage, dynamic OVP gently restricts inductor current

inductor current

Output voltage

inductor current

Output voltage

Enlarged view

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.

Acoustic noise and dynamic OVP (2)



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.

Second OVP (2nd OVP)



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.

OCP (Over Current Protection)



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.

Open (circuit) detection function/FB pin, ZCD pin, and others



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.)

Brown-out and UVLO (Under Voltage Lockout)



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.

Efficiency

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.

Slave drop/phase drop



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.

LTB (Load Tracing Boost)



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).



: No corresponding pin

*: Also has short detection to GND**: With latch function

Additional functions and major PFC ICs


APPED-101054A

Supplement 3 Power factor correction in inverter air

conditioners



Power factor correction methods in inverter air conditioners



Passive,Partial SWReason: CostAC 100 V

systems

AC 220 to 230 V systems

Packaged air conditioner (PAC)

Partial SW-> partial SW,interleaved

Reason: Cost

Low power

Single, partial SW-> interleaved

Reason: Cost

3 kW

Room air conditioner (RAC)

Single, passive-> interleaved

Reasons: Cost, power

High power

Possibility of entry of PFC IC is lowPossibility of entry of PFC ICPossibility of entry of PFC IC is high

(1)

(2) (3)

(2)

Single, passive-> interleaved

Reasons: Cost, power

The focus of all manufacturers is shifting from 2.8 kW (conventional) to 4-5 kW. high-power models are expected to increase.

Single, partial SW-> partial SW,interleaved

Reasons: Efficiency, cost

Power factor correction methods in inverter air conditioners


apped-101054a confidential part 3…pfcs (operation, types, sales guide) sep. 2011rev.1.0 general...

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