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Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter DesignMladen IvankovicInfineon Technologies North America (IFNA) Corp.

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter DesignPublished by Infineon Technologies North America27703 Emperor Blvd, suite 310Durham, NC 27703All Rights Reserved.Attention please!THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDEDAS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITYOF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTEMUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. INFINEONTECHNOLOGIES HEREBY DISCLAIMS ANY AND ALL WARRANTIES AND LIABILITIES OF ANY KIND(INCLUDING WITHOUT LIMITATION WARRANTIES OF NON-INFRINGEMENT OF INTELLECTUALPROPERTY RIGHTS OF ANY THIRD PARTY) WITH RESPECT TO ANY AND ALL INFORMATIONGIVEN IN THIS APPLICATION NOTE.InformationFor further information on technology, delivery terms and conditions and prices please contact yournearest Infineon Technologies Office (www.infineon.com).WarningsDue to technical requirements components may contain dangerous substances. For information on thetypes in question please contact your nearest Infineon Technologies Office. Infineon TechnologiesComponents may only be used in life-support devices or systems with the express written approval ofInfineon Technologies, if a failure of such components can reasonably be expected to cause the failure ofthat life-support device or system, or to affect the safety or effectiveness of that device or system. Lifesupport devices or systems are intended to be implanted in the human body, or to support and/or maintainand sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user orother persons may be endangered.DN 2013-10Subjects: CrCM PFC Boost Converter DesignAuthor: Mladen Ivankovic (IFNA PMM SMD AMR PMD 3)We Listen to Your CommentsAny information within this document that you feel is wrong, unclear or missing at all? Your feedback willhelp us to continuously improve the quality of this document. Please send your proposal (including areference to this document) to: [Mladen.Ivankovic@infineon.com]2

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter DesignTable of contents1 Introduction . 42 Boost topology . 43 PFC Modes of Operation. 54 CrCM PFC Boost Design Equations . 74.1 Rectifier bridge . 74.2 Input Capacitor . 74.3 Input Inductor . 84.4 MOSFET .104.5 Boost diode.134.6 Output Capacitor .134.7 Heatsink .145 References .163

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter Design1IntroductionPower Factor Correction (PFC) shapes the input current of the power supply to be in synchronization withthe mains voltage, in order to maximize the real power drawn from the mains. In a perfect PFC circuit, loadshould look like a pure resistance load. The input current is a clean sine wave and in phase with the voltage,with no input current harmonics. This document is intended to discuss the topology and operational mode forlow power ( 300W) PFC applications, and provide detailed design equations through an example.2Boost topologyActive PFC can be achieved by any basic topology, the boost converter (Figure 2.1) is the most populartopology used in PFC applications.The advantages of boost topology are: Voltage gain 1 works for AC input Only one MOSFET Control Voltage referred to ground capable of high efficiency simple choke, no problems with magnetic coupling CCM provides continuous input current CCM mode with favorable waveform factor for conduction lossThe disadvantages of boost topology are: MOSFET: VDS VO VI no galvanic isolation - short circuit protection a problem Medium ripple current loading of output capacitor CCM Mode requires hard switching of boost diode- SiC required for high efficiencyComments on other topologies: Buck:Lacks voltage gain; pulsating input current Buck/Boost:Complex, output voltage has opposite polarity, pulsating input current Flyback:Easily resistive, but pulsating input current (can be solved with interleaved),but 2x copper losses for given magnetic SEPIC:Step down/step up with continuous input current, but having two inductors,two capacitors, more complex control, only one inductor can be made sinusoidal, more distortion.4

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter DesignBoost Key WaveformsDC BusPFCConverterACVacDC/DCConverterLoadFigure 2.13PFC Modes of OperationThe boost converter can operate in three modes; continuous conduction mode (CCM), discontinuousconduction mode (DCM), and critical conduction mode (CrCM). Fig. 3.1 shows modeled waveforms toillustrate the inductor and input currents in the three operating modes, for the same exact voltage and powerconditions.15151010Iin ( t)15Iin( t)I in( t)IL ( t)I L ( t)50500-4-4-4-4Continuous Conduction Mode (CCM)1 102 3 10t104 1010IL ( t)50-41 10-4-42 103 10-44 10Critical Conduction Mode (CrM)tFigure 3.1Quick comparison between operting modes is given in the table below:500-41 10-42 10-43 10-44 10Discontinuous ConductionMode (DCM)t

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter DesignPart /CharacteristicInput CurrentCrCM Variable FrequencyHigh Ripple current - largeEMI filter2High conduction loss: 9-12%I XR MOSFET loss penaltyVariable Frequency CCMLower Ripple Currentsmaller EMILower Ripple Current smaller EMITrapezoidal waveformlower lossTrapezoidal waveformlower lossMOSFET tONQuasi resonant Ton possibleHigh- dependent on BoostdiodeHigh- dependent onboost diodeMOSFET tOFFToff at 2x input current- highlossHigh fSW higher lossesLower - Toff dependent ondesignLower- Toff dependenton designBoost DiodeSlow, cheap type OK- selectfor QRBest performance with SiCor GaNBest performance withSiC or GaNDesign for high ripple- gappedsoft ferrite usually best choice;combine with Litz wire; lowertemp rangeDesign for high average LFcurrent and lower ripplecurrent; powdered core:Kool Mu, High FluxDesign for high averageLF current and lowerripple current; powderedcore: Kool Mu, High FluxSized for fAC input current,very HF RMS ripple currentSized for fAC input current,HF RMS ripple currentSized for fAC inputcurrent, HF RMS ripplecurrentPF/DistortionController and designdependent; can be quite goodController and designdependent; fixed CCMinherently higher distortiondue to current loopController and designdependent; very lowdistortion possible; fewoff the shelf controllersolutionsPower DensityDesign dependent on inductorand semiconductorsDesign dependent oninductor andsemiconductorsDesign dependent oninductor andsemiconductorsLow for lower power levels;EMI filter a limitBetter at higher powerlevelsBetter at higher powerlevelsInductorOutput CapacitorCost4Fixed Frequency CCMCrCM PFC Boost Design EquationsThe following are design equations for the CrCM operated boost, also a design example is integrated tofurther clarify the usage of all equations. The boost converter encounters the maximum current stress and6

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter Designpower losses at the minimum line voltage condition (will be using the low line voltage condition.), hence, all design equations and power lossesTable 1 SpecificationsInput voltage90-270 Vac 60 HzOutput voltage420 VMaximum power150 WMinimum frequency25 kHzOutput voltage ripple10 Vp-pHold-up time16.6 ms @ Vo.min 350 VEstimated efficiency η0.94.1 Rectifier BridgeThe bridge total power loss is calculated using the average input current flowing through two of the bridgerectifying diodes.4.2 Input CapacitorThe input high frequency filter Cin has to attenuate the switching noise due to the high frequency inductorcurrent ripple (twice of average line current). The worst conditions will occur on the peak of the minimuminput voltage.The maximum high frequency voltage ripple is usually imposed between 1% and 10% of the minimum ratedinput voltage. This is expresses by a coefficient r (typically, r 0.01 to 0.1).High values of Cin helps EMI filter but causes lower power factor to decrease (higher displacemetcomponent), especially at high input voltage and low load. Low values of Cin improve power factor (lowerdisplacement component) but require larger EMI filter.4.3 Input InductorLets define following parameters:a - ratio between peak input voltage and output voltage (DC bus voltage)a max 1.41 VinmaxVo-1a max 9.064 10a min 1.41 VinminVo- 1 load (resistance)Ro- equivalentoutputa min 3.021 107

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter Design2Ro VoPinRo 1.058 103Switching frequency is changing with input voltage amplitude and angle. Amplitude varies from minimum(90V*1.41 ) to maximum (270*1.41) value. Angle is changing from o to π during each half grid cycle.Switching frequency as function of these two variable is represented on graph below:f ( x y) 1 1 2 y ( 1 - y sin( x) )2 2normalized operating frequencyOne can notice that during each cycle (angle axis) switchingfrequency start with maximum value travels through minimumvalue at peak voltage (angle π/2) and goes back tomaximum. See details below:foperating frequency versus line voltage angle0.25f ( x a max )f x 0.5 0.20.15f ( x a min) 0.10.0500123xAlso, when amplitudechanges from minimum value (90*1.41) to the maximum value (270*1.41) frequency travel from oneminimum through maximum to another minimum value. One needs to choose smaller of these two and useto calculate inductance value. Details are given below:8

Design Note DN 2013-10V1.0 January 2013CrCM PFC Boost Converter Designoperating frequency versus peak input voltage0.04f 2 y 0.030.020.010.4 -2f a max 1.922 10 2 a min 1.593 10- 2 2 f 0.6y0.8Frequency multiplier atmax input voltage.Frequency multiplier at max input voltageOne needs to select condiotion at overall minimum frequency, so:boost inductor value is:Lin Ro min f a min f a max fswmin 2 2 -4Lin 6.743 109