Practical Design Considerations for a 3.3kW Bridgeless Totem-pole PFC Using GaN FETs Jim Honea Transphorm Inc
Overview of the Circuit Specifications 3.3kW (max) CCM bridgeless totem-pole PFC, Universal input range: 80VAC-265VAC, 50/60Hz, 15Arms Fixed Frequency Operation, with user-defined switching frequency (45-150kHz) Firmware-programmable VOUT: 373VDC-397VDC Integrated auxiliary power supply, provides second-stage power Applications Automotive on-board chargers (AEC-Q101 qualified GaN FETs now available ) Industrial power supplies 80 PLUS Titanium class power for telecom, data center, server
3 Design Details
Block Diagram AC Line In L N Filter Input Current + Voltage sense PFC Inductor Synchronous Bridge + Vdc out - PE PWM Digital Control - DSP - Firmware Vout Sense Auxiliary DC/DC Converter
The Bridgless Totempole PFC Topology Simplified schematic, CCM operation S2 on S1 on S2 off S1 off Positive Half Cycle (Vac>0) Negative Half Cycle (Vac<0)
6 GaN Synchronous Half Bridge
GaN Cascode Power Switches 3 rd Generation GaN cascode technology. Normally-off 30V Si FET in series with normally-on 650V GaN FET Robust Si gate; standard gate drive; Vth=3.9V Also available: Ron=50, 72, 110 150 290 mω SMD packaging
GaN Cascode Power Switches Qoss is the dominate component of Qrr
AEC-Q101 Qualified GaN Tests and Test Conditions Test Symbol Conditions Sample Pass Criteria TPH3205WSQA: First device with automotive qualification, in-stock and available. Additional devices are now in the qualification process. High Temperature Reverse Bias Highly Accelerated Temp and Humidity Temperature Cycle Temperature Cycling Hot Test HTRB HAST TC TCHT T J =150 C, V DS =650V, 1000 HRS 130 C, 85% RH, 33.3 PSI, Bias=100V, 96 HRS -55 C / 150 C, 2 Cycles / HR, 1000 Cycles 125 C Test After TC Wire Bond Integrity WBI 150 C, 500 HRS 3 lots, 77 parts per lot, 231 total parts 3 lots, 5 parts per lot, 15 total parts 0 Fails PASS 0 Fails PASS 0 Fails PASS 0 Fails PASS 0 Fails PASS Test Specifications Power Cycle PC 25 C / 125 C, T=105 C, 15,000 Cycles 0 Fails PASS Idss Igss Parameter Spec Limit Max Shift Allowed <40µA <100nA Dynamic R(on) 62mΩ <20% Vth 2.6/1.6 V <20% 5x increase (10x increase for environmental testing) Not applicable (low leakage) High Temperature Storage Life High Temperature Gate Bias (Cascode) High Temperature Gate Bias (HEMT only) High Humidity High Temp Reverse Bias Unbiased Accelerated Stress Test HTSL 150 C, 1000 HRS HTGB 150 C, 1000 HRS, V GSS =18V HTGB #2 H3TRB UHAST 150 C, 1000 HRS, V GSS =-35V 85 C/85% RH, 1000 HRS, 100V 130 C, 85% RH, 96 HRS 3 lots, 77 parts per lot, 231 total parts 0 Fails PASS 0 Fails PASS 0 Fails PASS 0 Fails PASS 0 Fails PASS Destructive Physical Analysis DPA Post TC & HAST 3 lots, 2 parts per lot, 6 total parts 0 Fails PASS
Effects of Off State Acceleration Factors Process variability is as important as determining acceleration factors Use plot with extrapolated lifetime for all devices tested ~300 devices from 9 different lots Test conditions ranged: VD from 1150V to 1300V Temperature from -20 C to 150 C Process evaluated at 480V Temperature range for automotive is -40 C to 150 C Nominal temperature expected to be 85 C Process shows 1% failure ++500 years Off state for 480V @ -40 C 480V -40 C 85 C 150 C Process shows excellent extrapolated lifetime with good stability
GaN Half-Bridge Design Details
GaN Half Bridge Design Details Ferrite bead in series with Drain: Damps ringing, overshoot increases. Overshoot is well within the specified transient-voltage limit (800V). http://www.transphormusa.com/document/recommended-external-circuitry-transphorm-gan-fets/
13 PFC Inductor Design
PFC inductor design Two versions of the inductor have been developed, - For use at different switching frequencies - Wound on the same toroidal core Frequency L (typical) Turns AWG Core R (T=25C) 45 khz 577 µh 56 10 CH610060 High Flux 0.017 Ω 100 khz 338 µh 42 10 CH610060 High Flux 0.013 Ω 45 khz 100 khz
PFC inductor design High Flux core permits operation at max current with a single core. Alternatives: - MPP or Sendust would require larger or stacked cores of the same size - Ferrite E core would be larger 15A 2 56Turns = 1188Ampere Turns http://www.changsung.com/_eng/product/goods.php?goods_no=14
16 AC Power Entry: EMI Filter
EMI Filter 8121-RC 8121-RC PFC Inductor
EMI Filter This plot shows Z from the switching inductor node looking back into the AC line, neglecting the LISN terminating impedance. Test result from the TTP4000W066 4kW PFC evaluation board which uses the same EMI filer.
19 PCB
PCB 388mm Fabrication Notes: 4 Layers 92mm Board Thickness: 93 mils Copper Thickness: a) Outer Layers: 2oz (70µm) b) Inner Layers: 1oz (35µm) Material: a) Base material: FR4 140 Tg as per IPC-4101 b) Prepreg material: FR4 as per IPC-4101 Minimum track thickness: 6 mil Minimum spacing: 6 mil
PCB Vdc out Top Layer Agnd Dgnd Pgnd Mid Layer 2 +3V3 Vdc out Mid Layer 1 Pgnd Bottom Layer
22 Control: Algorithm, Firmware Implementation
Digital Signal Controller TMS320F28335PGFA Texas Instruments Digital Signal Controller (DSC). QFP package was used to accommodate small production runs. BGA is significantly smaller. Use of a vertical, fixed (soldered/no-connector) daughter board for the DSP would improve power density.
Control Diagram for the Totempole PFC 24
25 Test Results
Efficiency vs Load 99% Load Efficiency 50kHz 99% Load Efficiency 100kHz 98% 98% 97% 97% 96% Efficiency (%) 96% 95% 90 VAC 115 VAC 180 VAC 230 VAC 260 VAC Efficiency (%) 95% 94% 93% 92% 90 VAC 115 VAC 180 VAC 230 VAC 94% 91% 260 VAC 93% 0 500 1000 1500 2000 2500 3000 Input Power (W) [15Arms rated] 90% 0 500 1000 1500 2000 2500 3000 Input Power (W) [15Arms rated]
Power Factor vs Load 1 POWER FACTOR versus Input Power, 50kHz 1 POWER FACTOR versus Input Power, 100kHz 0,98 Power Factor 0,96 0,94 90VAC 115 VAC 180 VAC 230 VAC 260 VAC Power Factor 0,98 0,96 90VAC 115 VAC 180 VAC 230 VAC 260 VAC 0,92 0,9 0 500 1000 1500 2000 2500 3000 Input Power (W) 0,94 0 500 1000 1500 2000 2500 3000 Input Power (W)
Current and Voltage Waveforms 90 VAC, 50% Load. 90 VAC, 100% Load. Red: Vin, 100V/div Gold: Iin, 5A/div 5ms/div Red: Vin, 100V/div Gold: Iin, 10A/div 5ms/div 230 VAC, 50% Load. 230 VAC, 100% Load. Red: Vin, 200V/div Gold: Iin, 5A/div 5ms/div Red: Vin, 200V/div Gold: Iin, 10A/div 5ms/div
Start up Operation 90 VAC, 0% Load. Red: VIN, 100 V / div. Gold: IIN, 5 A / div. Green: Vout, 100 V / div., 200 ms / div. 90 VAC, 100% Load. Red: VIN, 100 V / div. Gold: IIN, 10 A / div. Green: Vout, 100 V / div., 200 ms / div.
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