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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 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Principles of PFC 3 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A 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 4 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 5 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 6 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Critical conduction mode and continuous conduction mode 7 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A 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). 8 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 9 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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). 10 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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) 11 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 12 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 13 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 14 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 *: 15 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. ©2012. Renesas Electronics Corporation, All rights reserved. CRM Confidential APPED-101054A Single operation and interleaved operation 16 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A 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. 17 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 18 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A PFC modes (summary) CRM: CRitical conduction Mode CCM: Continuous Current Mode Type Continuous (CCM) Critical (CRM) 19 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 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A PFC market and sales guide Applicable to all devices that use AC input 20 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A 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 ©2012. Renesas Electronics Corporation, All rights reserved. 2009 2010 Confidential APPED-101054A 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 22 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 23 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 24 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Supplement 1 Boost converter 25 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A Boost converters (1) When MOSFET is on 26 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Boost converters (2) When MOSFET is off 27 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Supplement 2 Additional functions of PFC ICs 28 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A 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. 29 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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) 30 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 31 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 32 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 33 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 34 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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.) 35 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 36 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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. 37 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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). 38 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Additional functions and major PFC ICs : No corresponding pin *: Also has short detection to GND **: With latch function 39 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A Supplement 3 Power factor correction in inverter air conditioners 40 ©2012. Renesas Electronics Corporation, All rights reserved. APPED-101054A Power factor correction methods in inverter air conditioners 41 ©2012. Renesas Electronics Corporation, All rights reserved. Confidential APPED-101054A 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 42 Single, passive -> interleaved Reasons: Cost, power (3) Single, partial SW -> partial SW, interleaved Reasons: Efficiency, (2) cost 3 kW ©2012. Renesas Electronics Corporation, All rights reserved. Single, passive -> interleaved Reasons: Cost, power High power Confidential APPED-101054A Thank you Thank You Confidential Renesas Electronics Corporation. ©2012. Renesas Electronics Corporation. All rights reserved.