Design Considerations of Highly-Efficient Active Clamp Flyback Converter Using GaNFast Power ICs

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1 Design Considerations of Highly-Efficient Active Clamp Flyback Converter Using GaNFast Power ICs Lingxiao (Lincoln) Xue March 29 th 2017

2 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

3 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

4 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

5 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) Energy circulated to source i Lm R DS(ON) C o (tr) (pf) Q g (nc) Q rr (nc) i D 5

GaN ACF Minimized Negative i Lm GaN: NV6115-0.

5A 1 μs/div GaN ACF needs only 0.2A negative current for ZVS vs. Si s 0.

6 GaN ACF Minimized Negative i Lm GaN: NV A (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

7 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

8 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

9 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 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

10 Method 2 Secondary Resonance Reduces Circulating Energy Pri. Resonant Pri. Resonant Sec. Resonant i D Sec. Resonant Current (A) TX Primary Current (rms)* Pri. Resonant Sec. Resonant 24% reduction Input Voltage (V) Input Voltage (V) *Measured results of 45W ACF Cuurent (A) TX Secondary Current i D (rms)* Pri. Resonant Sec. Resonant 11% reduction 10

65W USB-PD ACF Using GaNFast Power ICs 38 mm 15.

11 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) 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

12 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 % 230 V AC 88.0% 86.0% 80.0% 75.0% CoC Tier % 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

13 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

14 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 % 85.0% 80.0% 115 V AC 230 V AC CoC Tier % 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

15 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) 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

16 Efficiency: Meets CoC Tier 2 and DOE LV VI Efficiency: 4-Points Average Efficiency: 10% Load Efficiency Vo=5V Vo=9V Vo=11V 115V ac 230V ac CoC Tier 2 Efficiency Vo=5V Vo=9V Vo=11V 115Vac 230Vac CoC Tier

17 High Frequency 65W ACF with GaN ICs mm 0.95 Efficiency Full Load F SW : khz Power Density: 47 W/ in 3 (Uncased) 26 W/ in 3 (2.5mm case) V ac (V) Average Efficiency= V AC, V AC 17

18 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

GaN Power IC Enable Next Generation Power

GaN Power IC Enable Next Generation Power Adaptor Design Peter Huang, Director, FAE & Technical Marketing peter.huang@navitassemi.com 2018 前瞻電源設計與功率元件技術論壇 Jan -30 th Navitas Semiconductor Inc. World s