Design Considerations of Highly-Efficient Active Clamp Flyback Converter Using GaNFast Power ICs Lingxiao (Lincoln) Xue March 29 th 2017
How to Improve Power Adapter Density? Traditional Travel Adapter and Chargers USB PD and Quick Charge 5 W/in 3 7 W/in 3 Samsung 25 W Apple 45 W > 20 W/in 3 Added power in USB PD and Quick Charge requires dramatically higher power density (>20 W/in 3 ) Higher efficiency and lower power loss are required in high density adapters How to dramatically improve the power density? 2
ACF Enables ZVS and High Frequency Switching Lossless snubber Zero-voltage switching ilm S2 S1 Vsw V sw i Lm Zero-current switching No snubber losses, all leakage energy is recovered ZVS soft switching over entire operation range ZCS soft turn-off for output rectifier Clean waveforms reduce EMI Enable small adapter design with high-frequency switching 3
Towards Highly Efficient ACF n:1 i D S1 ON S2 ON V IN C r S2 i Lm S1 V sw V O Energy from source V sw Energy circulated to source i Lm Soft-switching is achieved, conduction loss dominates Circulating energy to the input source and clamping capacitor Cr, increasing current RMS Reduce both parts of circulating energy for highly efficient ACF i D Energy circulated within Cr Energy to load 4
Minimizing Energy Circulated Back to Source Minimize negative i Lm for ZVS Depending on C o (tr) GaN has only ½ C o (tr) even with ½ R DS(ON) GaN needs less circulating energy V sw S1 ON S2 ON IPA60R299CP IPA60R385CP NV6115 Voltage Rating (V) 650 650 650 Energy circulated to source i Lm R DS(ON) 270 350 160 C o (tr) (pf) 120 96 50 Q g (nc) 22 17 2.5 Q rr (nc) 3900 3100 0 i D 5
GaN ACF Minimized Negative i Lm GaN: NV6115-0.2A (1 A/div) Si: IPA60R299CP V SR (20 V/div) (RMS) = 0.9A V SW (100 V/div) -0.5A 1 μs/div GaN ACF needs only 0.2A negative current for ZVS vs. Si s 0.5A GaN ACF RMS is only 0.9A vs. Si s 1.1A Besides, GaN has no body diode loss Low high-frequency gate-charge loss (1 A/div) V SR (20 V/div) V SW (100 V/div) (RMS) = 1.1A 1 μs/div 6
Minimizing Energy Circulated in Cr Minimizing the shaded area Two methods identified Creating deeper current dip Using secondary resonant scheme V sw i Lm S1 ON S2 ON Energy circulated within Cr i D 7
Method 1 GaN Increases Current Dip C oss ilr ilm C j ilr less dip ilr SR double turn-on SR single turn-on SR single turn-on C oss ilr More dip Current dip RMS value (RMS) Less SR double turn-on C j /C oss = 0.5 C j /C oss = 1 C j /C oss = 2 ilm Cj Coss Circulating Energy Use better device: GaN 8
Method 2 Secondary Resonance Scheme* Big Cr, small Co n:1 i D S1 ON S2 ON V IN C r S2 i Lm S1 V sw C o V O I O V Cr Lr Lm C o /n 2 - + I o /n V sw i Lm Output capacitor to resonate with transformer leakage Clamping capacitor Cr has low voltage ripple More current pushed to the secondary side i D V Cr *Navitas Patent Pending nv o 9
Method 2 Secondary Resonance Reduces Circulating Energy Pri. Resonant Pri. Resonant Sec. Resonant i D Sec. Resonant Current (A) 1.1 1 0.9 0.8 0.7 0.6 TX Primary Current (rms)* Pri. Resonant Sec. Resonant 24% reduction 100 150 200 250 300 350 100 150 200 250 300 350 Input Voltage (V) Input Voltage (V) *Measured results of 45W ACF Cuurent (A) 4.2 3.9 3.6 3.3 3 2.7 TX Secondary Current i D (rms)* Pri. Resonant Sec. Resonant 11% reduction 10
65W USB-PD ACF Using GaNFast Power ICs 38 mm 15.5 mm 46 mm Input Output Frequency Universal AC (85-265V AC, 47-63Hz) Type C, USB-PD 2.0 (5-20V) 250-350 khz Power Density 2.4 W/cc (39 W/in 3 ) uncased 1.5 W/cc (24 W/in 3 ) cased Construction 4-layer, 2-oz Cu PCB, No heatsink design 11
Efficiency Meets CoC Tier 2 and DOE LV VI Efficiency: 4-Points Average Efficiency: 10% Load 94.0% 92.0% 115 V AC 230 V AC 95.0% 90.0% 115 V AC 90.0% CoC Tier 2 85.0% 230 V AC 88.0% 86.0% 80.0% 75.0% CoC Tier 2 84.0% 70.0% 82.0% 65.0% 80.0% 5V/3A 9V/3A 15V/3A 20V/3.25A 60.0% 5V/3A 9V/3A 15V/3A 20V/3.25A 12
Integration Eases ACF Design Powertrain ON/OFF Bootstrap Level-Shift High Side Switch Low Side Switch Saved PCB space Avoided powertrain layout mistakes -> Noise confined Reduces standby loss 13
Efficiency Meets CoC Tier 2 and DOE LV VI Efficiency: 4-Points Average Efficiency: 10% Load 94.0% 115 V AC 95.0% 92.0% 90.0% 88.0% 86.0% 230 V AC CoC Tier 2 90.0% 85.0% 80.0% 115 V AC 230 V AC CoC Tier 2 84.0% 82.0% 75.0% 80.0% 5V/3A 9V/3A 15V/3A 20V/3.25A 70.0% 5V/3A 9V/3A 15V/3A 20V/3.25A 14
27W USB-PD 3.0 Using GaNFast HB Power IC 39 mm 37 mm Input Output Frequency Universal AC (85-265V AC, 47-63Hz) Type C, USB-PD 3.0 (27W) 200-400 khz Power Density 1.2 W/cc (19 W/in 3 ) uncased 0.7 W/cc (11 W/in 3 ) cased Construction 4-layer, 2-oz Cu PCB, No heatsink design 16 mm 15
Efficiency: Meets CoC Tier 2 and DOE LV VI Efficiency: 4-Points Average Efficiency: 10% Load Efficiency 0.94 0.92 0.9 0.88 0.86 0.84 0.82 0.8 0.5 1 1.5 2 2.5 3 3.5 Vo=5V Vo=9V Vo=11V 115V ac 230V ac CoC Tier 2 Efficiency 0.9 0.88 0.86 0.84 0.82 0.8 0.78 0.76 0.74 0.72 0.7 Vo=5V Vo=9V Vo=11V 115Vac 230Vac CoC Tier 2 0.5 1 1.5 2 2.5 3 3.5 16
High Frequency 65W ACF with GaN ICs 0.96 12.5mm 0.95 Efficiency 0.94 0.93 Full Load F SW : 500-600 khz Power Density: 47 W/ in 3 (Uncased) 26 W/ in 3 (2.5mm case) 0.92 90 110 130 150 170 190 210 230 V ac (V) Average Efficiency= 93.4% @115 V AC, 92% @230 V AC 17
Conclusion Highly-efficient ACF should minimize the circulating energy GaN is uniquely suitable for high frequency ACF operation Half-Bridge GaNFast Power IC simplifies ACF design and improves density Examples of 27W and 65W PD designs are given showing high efficiency/density 18