Power Supply Design Seminar Topic 3 Presentation: Designing an LLC Resonant Half-Bridge Power Converter Reproduced from 2010 Texas Instruments Power Supply Design Seminar SEM1900, Topic 3 TI Literature Number: SLUP256 © 2010, 2011 Texas Instruments Incorporated Power Seminar topics and online powertraining modules are available at: power.ti.com/seminars Topic 3 Designing an LLC Resonant Half-Bridge Power Converter Hong Huang SLUP256 Agenda 1 Introduction 1. – Brief review – Advantages 2. Design Prerequisites – – – – Configuration Operation p Modeling Voltage gain function 3 Design 3. D i Considerations C id ti – – – – Voltage gain and switching frequency Line and load regulation Zero voltage switching (ZVS) Steps for designing and a design example 4. Conclusions Texas Instruments—2010 Power Supply Design Seminar 3-2 SLUP256 Introduction • Brief review of resonant converters – Series resonant converter (SRC) – Parallel resonant converter (PRC) Lr Cr Lr RL Cr SRC RL PRC • Single resonant frequency • Resonant point changes with load • Circuit frequency increases with lighter load • Large amount of circulating current Texas Instruments—2010 Power Supply Design Seminar 3-3 SLUP256 Introduction • Brief review of resonant converters – Combination of SRC and PRC LCC • Two resonant frequencies • Requires three elements – LLC: alternative LCC • Lr and Lm integrated in a transformer • Advantages of LLC – High efficiency (ZVS) – Less frequency variation and lower circulating current – ZVS over operating range Lr Cr 1 C r2 LCC Lr RL Texas Instruments—2010 Power Supply Design Seminar Cr Lm LLC RL 3-4 SLUP256 Design Prerequisites • Configuration – Variable-frequency square-wave generator Square-Wave q Generator Resonant Network Q1 Vin = + VD C – – Divider formed by resonant network and RL Vs q Q2 Cr Rectifiers for DC Output D1 n:1:1 Lr Io + Ir Vs o Lm Co RL – D2 – Rectifier to get DC output – Changing frequency varies voltage across RL – Frequency-modulated converter instead of PWM Vo Cr + Ir Vs q Texas Instruments—2010 Power Supply Design Seminar Lr Vs q Im Ios Lm RĹ + Vs o Vs o 3-5 SLUP256 Design Prerequisites • Operation – fsw switching frequency – f0 series resonant frequency (Cr and Lr) – fco circuit resonant frequency (Cr Lr, and Lm, together RL) Vg_Q1 Vg_Q1 Vg_Q1 Vg_Q2 Vg_Q2 Vg_Q2 Vsq Vsq Vsq 0 0 0 Ir 0 Im Ir 0 Is Im Is D1 D2 D2 D1 0 t1 t2 time,, t fsw = f0 t3 t4 Im Is D1 0 t0 Ir 0 D2 0 t0 t1 t2 time,, t fsw < f0 Texas Instruments—2010 Power Supply Design Seminar t3 t4 t0 t1 t2 time,, t t3 t4 fsw > f0 3-6 SLUP256 Design Prerequisites • Modeling M d li – First harmonic approximation (FHA) Cr + Lr I m I os Ir Vs q Cr Lr + + Vs o Vs q Ir Lm RĹ R L – Vge Lm Re Im I oe + Voe – Vs o (a) (b) • Input and output: Square wave voltages • Input and output: Fundamental components to approximate FHA • Sinusoidal current in resonant circuit • Rectifier and RL equivalent to Re Texas Instruments—2010 Power Supply Design Seminar • AC circuit method can be used 3-7 SLUP256 Design Prerequisites • Voltage gain function – Expression from impedance p divider Cr M g _ DC = Lr Ir + – n × Vo Vso Voe M g _DC = ≈ M g _ sw = ≈ M g _ ac = Vin /2 Vsq Vge Vge Lm Re Im Ioe + Voe – = n × Vo V ≈ oe Vin /2 Vge ( jωL m ) || R e ( jωL m ) || R e + jωL r + 1 jω C r where ω = 2πf = 2πfsw and j = −1 Texas Instruments—2010 Power Supply Design Seminar 3-8 SLUP256 Design Prerequisites • Voltage gain function M g _DC = – Expression ((Normalization)) Mg = Normalized Gain Vo Mg = Vin /2 Resonant Frequency f0 = 1 2π L r C r n × Vo V V ≈ M g _ sw = so ≈ M g _ ac = oe Vin /2 Vsq Vge L n × f n2 [(L n + 1) × f n2 − 1] + j[(f n2 − 1) × f n × Qe × L n ] Quality Factor Qe = L r /Cr Re Normalized Frequency Inductor Ratio fsw fn = f0 Lm Ln = Lr Eq. Load R. 8× n2 Re = 2 × RL π Texas Instruments—2010 Power Supply Design Seminar 3-9 SLUP256 Design Prerequisites • Voltage gain function – Plots of gain magnitude, fixed Ln = 5 – Qe (load current) increases ⇒ peak gain decreases ⇒ curves shrink 2 1.8 1.6 Gain 1.4 1.2 Qe Mg_pk Qe = 0.5 1 0.8 Qe = 0.1 Qe = 10 0.6 0.4 0.2 0 0.1 1 Normalized Frequency Texas Instruments—2010 Power Supply Design Seminar 10 3-10 SLUP256 Design Prerequisites • Voltage gain function – Plots of gain magnitude, fixed Qe = 0.5 – Ln decreases ⇒ peak gain increases ⇒ ZVS obtained but conduction losses increase 2 18 1.8 1.6 Gain 1.4 Ln = 10 Ln = 5 Ln Ln = 3 Mg_pk 12 1.2 1 0.8 06 0.6 0.4 0.2 0 0.1 1 Normalized Frequency Texas Instruments—2010 Power Supply Design Seminar 10 3-11 SLUP256 Design Considerations • Where to base a design? – In the vicinity of series resonance, fn = 1 ⇒ narrowest frequency variation ⇒ Mg able to = 1, >1, and <1 – Right side of the resonant peak ⇒ ZVS requirement Frequency in operation 1.6 Qe = 0 Gain, M g 1.4 a3 a2 Q e = max 1.2 a0 1 Qe = 0 0.8 a1 a4 0.6 0.5 1 Normalized Frequency, fn Texas Instruments—2010 Power Supply Design Seminar 2 3-12 SLUP256 Design Considerations • Line and load regulation – Properly set up Mg_max and Mg_min – Frequency limit set up 1.6 Gain n, M g 1.4 1.2 a3 3 Qe = 0 Q e = max at full load a2 M g_ g m a x= n x Vo_ m a x Vin_ m in /2 Q e = max a0 1 Qe = 0 0.8 a1 a4 0.6 f n_min n min 1 Q e = max Normalized Frequency, fn Texas Instruments—2010 Power Supply Design Seminar M g_ m in = n x Vo_ m in Vin_ m a x/2 Q e = 0 at no load fn_max n max 3-13 SLUP256 Design Considerations • Overload O l d currentt operation ti – Qe = max to include and meet the required Mg_max – Operation still on the right side of resonant peak Frequency in operation 1.6 Qe = 0 Gain, M g 1.4 1.2 a3 M g_ m a x= a2 n x Vo_ m a x Vin_ m in /2 Q e = max a0 1 Qe = 0 0.8 M g_ m in i = a1 a4 0.6 f n_min 1 Q e = max Normalized Frequency, fn Texas Instruments—2010 Power Supply Design Seminar n x Vo_ m in Vin_ m a x/2 Qe = 0 fn_max 3-14 SLUP256 Design Considerations • Load short circuit • Protection options – Increase fsw rapidly to reduce Mg to zero – Operation with fn > 1, i.e., fsw > f0 at all times – Independent protection function 2 1.8 Qe = 0 1.6 Gain, M g 1.4 a3 M g_ m a x = a2 n x Vo_ m a x Vin_ m in/2 1.2 a0 1 a1 0.8 a4 0.6 ur ve Curve 1 (Qe = 0) n x Vo_ m in Vin_ m a x/2 2 ( Qe Cu =m r ve ax) 3 C urv e4 0.4 0.2 0 0.1 C M g_ m in = f n_ m in 1 f n_ m a x 10 Normalized Frequency, fn Texas Instruments—2010 Power Supply Design Seminar 3-15 SLUP256 Design Considerations • Zero voltage switching (ZVS) – How ZVS is achieved? Vg_ g Q1 Vg_ Q2 Q1 Vg Vin + – CD S1 Lr Vs q Ir Q2 Vg CD S2 Lm n:1:1 1 1 Q1 Turns Off Vs q Vds _ Q2 = 0 0 Ir Im Cr Q2 Turns On Im 0 Q2: Cds Discharge, Body Diode Turns On t de a d t0 Texas Instruments—2010 Power Supply Design Seminar t1 t2 time, t t3 t4 3-16 SLUP256 Design Considerations • Zero voltage switching (ZVS) – Necessary condition • Input impendence of the resonant network inductive • Operation p on the right g side of the resonant p peak – Sufficient condition • Enough energy stored in the magnetic field, mainly Lm • Enough time to discharge the capacitors capacitors, mainly CDS Texas Instruments—2010 Power Supply Design Seminar 3-17 SLUP256 Design Considerations • Why not design on the left side of the resonant peak? – Capacitive current results – ZVS lost Hard switching Switching losses increase – Body diode reverse recovery losses Primary MOSFET failure – Higher EMI noise – Reversed frequency relationship to feedback loop Texas Instruments—2010 Power Supply Design Seminar 3-18 SLUP256 Design Considerations • Design Steps – How to initially select? – fsw, switching it hi ffrequency – n, transformer turns ratio – Ln, inductance ratio – Qe, series resonant quality factor Texas Instruments—2010 Power Supply Design Seminar 3-19 SLUP256 Design Considerations • Design Steps – Switching frequency – Usually selected for particular applications • Example in off-line applications: Typical below 150 kHz – Selecting g the switching g frequency q y • f decrease ⇒ Bulkier converter • f decrease ⇒ Switching losses decrease ⇒ ZVS benefit decrease • f increase ⇒ ZVS benefits increase vs. hard switching converters • Very High f : – Component availability – Additional Addi i l switching i hi llosses – Additional concerns due to parasitic effects Texas Instruments—2010 Power Supply Design Seminar 3-20 SLUP256 Design Considerations • Design Steps – Transformer turns ratio, n – Voltage gain can be larger and smaller than unity – Flexibility in selecting the turns ratio, n – Turns ratio design with Mg =1, initially, and nominal Vin and Vo Vin / 2 Vin _ nom / 2 n = Mg × = Vo Vo_ nom Texas Instruments—2010 Power Supply Design Seminar Mg = 1 3-21 SLUP256 Design Considerations • Design D i St Steps – Ln and d Qe – Ln and Qe to achieve Mg_p g pk > Mg_ g max for maximum load – Initial selection • Ln = 5 • Qe = 0.5 05 – Example: Select Ln and Qe for Mg_max = 1.2 – To achieve design margin – Final selection • Ln - 3.5, Qe = 0.45 Ln = 1.5 Ln = 2.0 Ln = 3.0 Ln = 4.0 Ln = 5.0 Ln = 6.0 60 Ln = 8.0 Ln = 9.0 2.8 Attainable e Peak Gain, M g_ pk – Select Ln and Qe from preplotted peak gain curves 3.0 2.6 Ln = 3.0 2.4 Ln = 3.5 by Interpolation M g_ pk = 1.56 Qe = 0.45 2.2 2.0 18 1.8 Ln = 1.5 1.6 Ln = 5 M g_ pk = 1.2 Qe = 0 0.5 5 1.4 1.2 1.0 0.15 • 30% margin over o er Texas Instruments—2010 Power Supply Design Seminar 0.35 0.55 0.75 0.95 Quality Factor, Qe 1.15 3-22 SLUP256 Design Considerations • Design Steps – Trade-offs to select Ln and Qe – Different requirements for different applications – Fixed Qe, Ln decrease ⇒ peak gain increase ⇒ good for ZVS and a da avoids o ds capacitive capac t e current cu e t – But, Ln decrease ⇒ Lm decrease ⇒ conduction losses increase – Fixed Ln, Qe decrease ⇒ peak gain increase ⇒ frequency variation increase – Recommend starting with Ln = 5, and Qe = 0.5 (from design practice) Texas Instruments—2010 Power Supply Design Seminar 3-23 SLUP256 Design Considerations • Resonant circuit design flow 3.0 Ln = 1.5 Ln = 2.0 Ln = 3.0 Ln = 4.0 Ln = 5.0 Ln = 6.0 Ln = 8.0 Ln = 9.0 Atttainable Peak Gain, Mg_ap 2.8 2.6 Ln = 3.0 24 2.4 Ln = 3.5 by Interpolation Mg_ap = 1.56 Qe = 0.45 2.2 2.0 1.8 Ln = 5 Mg_ap = 1.2 Qe = 0.5 1.4 1.2 1.0 0.15 0.35 n= Mg_min = L n = 1.5 1.6 Converter Specifications 0.55 0.75 0.95 Quality Factor, Qe 1.15 Vin 2Vo Magnetizing Inductance n × Vo _min Vin_ max / 2 L m = Ln × Lr Resonant Inductor n × Vo_ max Mg_max = Vin_ min / 2 Lr = Ch Choose Ln and d Qe 1 .9 L n = 3 .5 f n_m in = 0 .6 5 Gain, Mg 1 .5 Q e = 0 .4 7 M g_m ax = 1 .3 Check M gand f n Against Graph Change L n and Qe 1 .3 M g_m in = 0 .9 9 1 .1 0 .9 Q e = 0 .5 2 0 .7 0 .5 f n_ m aax = 1 .0 2 0 0 .5 1 1 .5 Are Values Within Limits? Mg_m ax Mg_m in i fn_m ax fn_m in Texas Instruments—2010 Power Supply Design Seminar 2 (2 πf sw) × C r Resonant Capacitor Qe = 0 1 .7 1 No Yes Cr = π 1 Calculate R e 2 2 V2 Re = 8 ×2n × R L = 8 ×2n × o π π Pout 3-24 SLUP256 Design Considerations • Design example – Specifications • Rated output power: 300 W p voltage: g 375 to 405 VDC • Input • Output voltage: 12 VDC • Rated output current: 25 A • Efficiency (Vin = 390 VDC and Io = 25 A): >90% • Switching frequency: 70 kHz to 150 kHz • Topology: LLC resonant half-bridge converter Texas Instruments—2010 Power Supply Design Seminar 3-25 SLUP256 Design Considerations • Design example – Proposed converter circuit block diagram DT1 Q1 Lr Cin T1 n:1:1 Ir Vo Io Lm Q2 Co RL Cr ID 1 D1 U1 8 5 7 CB 6 GD1 OC UCC25600 GD 2 VCC GND RT DT SS 3 ID 2 D2 Vs RT1 2 + R o1 U2 1 RT2 4 C SS Cf RD T Rf1 R o2 U3 Texas Instruments—2010 Power Supply Design Seminar 3-26 SLUP256 Design Considerations • Design example – UCC25600 Features – 8-pin SOIC package – Programmable: 8-pin SOIC (D), Top View Drive 1 DT 1 8 GD1 • fmin and fmax RT 2 7 VCC • soft start time OC 3 6 GND SS 4 5 GD2 • dead time – Protection • OCP: hiccup and latch-off Drive 2 • VDD UVLO and OVP • OTP – Burst operation Texas Instruments—2010 Power Supply Design Seminar 3-27 SLUP256 Design Considerations • Resonant circuit design flow 3.0 Ln = 1.5 Ln = 2.0 Ln = 3.0 Ln = 4.0 Ln = 5.0 50 Ln = 6.0 Ln = 8.0 Ln = 9.0 Atttainable Peak Gain, Mgg_ap 2.8 2.6 Ln = 3.0 2.4 Ln = 3.5 by Interpolation Mg_ap = 1.56 Qe = 0.45 2.2 2.0 1.8 L n = 1.5 1.6 1.2 1.0 0.15 0.35 0.55 0.75 0.95 Quality Factor, Qe 1 .9 f n_m in = 0 .6 5 1 .5 Gain, Mg L n = 3 .5 Qe = 0 1 .7 1.15 M g_m ax = 1 .3 Q e = 0 .4 7 M g_m in = 0 .9 9 n × Vo _min Vin_ max / 2 Mg_max = n × Vo_ max Vin_ min / 2 0 .9 Q e = 0 .5 2 0 .7 0 .5 f n_m ax = 1 .0 2 0 0 .5 1 1 .5 L m = Ln × Lr Resonant Inductor Lr = Ch Choose Ln and d Qe Texas Instruments—2010 Power Supply Design Seminar 1 2 (2 πf sw) × C r Resonant Capacitor Check M gand f n Against Graph Are Values Within Limits? Mg_m ax Mg_m g m in fn_m ax fn_m in Lm = 210 µH Lr = 60 µH Cr = 27.3 nF Magnetizing Inductance Mg_min = Change L n and d Qe 1 .3 1 .1 Ln = 3.5 Qe = 0.45 V n = in 2Vo Ln = 5 Mg_ap = 1.2 Qe = 0.5 1.4 n = 16 Converter Specifications No Yes Cr = π 1 Calculate R e 2 2 Vo2 8 × n 8 × n Re = × RL = × π2 π2 Pout 3-28 SLUP256 Design Considerations • Design check 1.9 Ln = 3.5 Qe = 0 1.7 Gain, Mg 1.5 f n_ m in = 0.65 (80 9 kHz) (80.9 70 kHz Q e = 0.47 Mg_ m a x = 1.3 1.3 11 1.1 Q e = 0.52 M g_ m in = 0.99 0.9 0.7 0.5 124.4 kHz 0 fn_ 1 02 n m a x = 1.02 (126.9 kHz) 0.5 1 Normalized Frequency, fn Texas Instruments—2010 Power Supply Design Seminar 150 kHz 1.5 3-29 SLUP256 Design Considerations • Design g check – – – – – – Verification with computer-based circuit simulation Design reiteration, if needed Size/select components Build the board Verification with bench tests Re-spin Re spin the board/design board/design, if needed Texas Instruments—2010 Power Supply Design Seminar 3-30 SLUP256 Design Considerations • Experiment results (Lm = 280 µH µH, Lr = 60 µH µH, Cr = 24 nF) Efficiency Efficiency (%) 95 90 mV 405 V 390 V 375 V 75 65 1 5 10 15 Load Current ( A ) VCr (200 V/div) Resonant N Network k Voltages (full load) Output Ripple Voltage (50 mV/div) Input Voltage, Vin 85 1 3 4 2 20 25 Time (5 µs/div) Vgs _ Q2 (20 V/div) 1 Ir (200 V/div) VL (1.2 A/div) 3 r VL m (200 V/div) VC r (100 V/div) Vds _ Q2 (500 V/div) Output Ripple Voltage (full load) 4 2 Time (5 µs/div) Texas Instruments—2010 Power Supply Design Seminar Resonant Network C Current t and Voltage ((full load)) Vds _ Q2 (500 V/div) Time (1 µs/div) 3-31 SLUP256 Test Result versus FHA from the Design • In the vicinity of f0, FHAbased result very accurate to the final test resultlt (Lr = 60 µH H and d Cr = 24 nF) ( 60, 60 1.57 1 57) 1.4 0.6 • Equation Eq ation (18) Mg = = jX Lm || R e Voe = Vge ( jjX Lm || R e ) + j(X j( Lr − X Cr ) ( jωL m ) || R e ( jωL m ) || R e + jωL r + ( 65, 1.90) (55, 1.27) Gain, Mg ay from o f0, less ess • Away accuracy from FHAbased result 2.0 Bench Test Measurements (80, 1.58) Plot Based on E Equation ti 18 ( 100, 1.21) (135, 0.99) (170, 0.87) ( 40, 0.70) ( 30, 0.51) 0.0 10 ( 200, 0.78) ( 240, 0.72) ( 400, 0.56) f 0 = 135 kHz 100 Frequency, fs w (kHz) 1000 1 jω C r Texas Instruments—2010 Power Supply Design Seminar 3-32 SLUP256 Conclusions • FHA-based method approximately, while effectively, converted complicated LLC resonant-converter circuit to standard AC circuit – greatly simplified its analysis and design •M Method th d results lt effective ff ti ffor LLC converter t d design, i especially for initial parameters determination • Design example with comprehensive design considerations in procedural design steps g method effectiveness demonstrating • Possibility of FHA-based approach for other resonant converters Texas Instruments—2010 Power Supply Design Seminar 3-33 SLUP256 TI Worldwide Technical Support Internet TI Semiconductor Product Information Center Home Page support.ti.com TI E2E™ Community Home Page e2e.ti.com Product Information Centers Americas Phone +1(972) 644-5580 Japan Asia Brazil Phone 0800-891-2616 Mexico Phone 0800-670-7544 Phone Domestic 0120-92-3326 Fax International +81-3-3344-5317 Domestic 0120-81-0036 Phone International +91-80-41381665 Domestic Toll-Free Number Note: Toll-free numbers do not support mobile and IP phones. 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