GaN FET-Based High CCM Totem-Pole Bridgeless PFC PSDS ... · Texas Instruments – 2014/15 Power...
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GaN FET-Based High CCM Totem-Pole Bridgeless PFC
Zhong Ye
Alvaro Aguilar Yitzhak Bolurian Brian Daugherty
Agenda
6-2
• AC/DC efficiency standard and PFC efficiency requirement
• Bridgeless PFC topologies and development trend
• GaN ( Gallium Nitride) FET overview
• Totem-pole CCM bridgeless PFC control - UCD3138 control implementation - Ideal diode emulation - AC crossover detection and control
• GaN device test in FET mode and diode mode
• Totem-pole CCM bridgeless PFC test
• Summary
Texas Instruments – 2014/15 Power Supply Design Seminar
AC/DC Efficiency Level Certifications
6-3 Texas Instruments – 2014/15 Power Supply Design Seminar
80 Plus Test Type
115 V Internal Non-Redundant
230 V Internal Redundant
Fraction of rated load
10% 20% 50% 100% 10% 20% 50% 100%
80 Plus 80% 80% 80% 80 Plus Bronze 82% 85% 82% 81% 85% 81% 80 Plus Silver 85% 88% 85% 85% 89% 85% 80 Plus Gold 87% 90% 87% 88% 92% 88% 80 Plus Platinum 90% 92% 89% 90% 94% 91% 80 Plus Titanium 90% 92% 94% 90% 90% 94% 96% 91%
Energy Star Specification
PFC Efficiency Budget
Texas Instruments – 2014/15 Power Supply Design Seminar 6-4
• PFC design becomes more challenging at Platinum level efficiency and much harder at Titanium level efficiency
• Well designed single-phase PFC and interleaved PFC achieve around 97.5% efficiency and are just able to meet Platinum efficiency requirement
• Bridgeless seems to be the only way to reach Titanium efficiency level
80 Plus Test Type
Efficiency at 115 V Internal Non-Redundant
Efficiency at 230 95.5%V Internal Redundant
Fraction of rated load 10% 20% 50% 100% 10% 20% 50% 100%
80 Plus Platinum
PFC 95.8% 95.4% 93.7% 95.7% 97.4% 95.8%
DC/DC 94% 96.5% 95% 94% 96.5% 95%
80 Plus Titanium
PFC 95.5% 95.8% 96.4% 93.8% 95.8% 98% 98.5% 94.8%
DC/DC 94% 96% 97.5% 96% 94% 96% 97.5% 96%
6-5
Existing Bridgeless PFC Application Status Basic Bridgeless PFC + Good efficiency
+ Easy control
- High component count
- Low component utilization
- Low density
Totem-Pole Bridgeless PFC + Good efficiency
+ Fixed frequency
+ Easy control
- DCM only
- For power < 300 W
Texas Instruments – 2014/15 Power Supply Design Seminar
D1
Q1
D2
Q2
D5
D5
D3
D4
+
-
COC1
C2 C3 C4
L2
Lb1
Lb2
Lb
Q1
Q2
D1
D2
D3
D4
+
-
COC1
C2 C3 C4
L2
Line
Line/
Neutral
Earth
Line
Line/
Neutral
Earth
6-6
New PFC Development Trends
Texas Instruments – 2014/15 Power Supply Design Seminar
Transition-Mode Totem-Pole PFC • ZVS operation • Interleaved configuration for high power application (around max 300 W per phase) • Variable frequency control • Phase shedding and adding to optimize light load efficiency • Suitable for MOSFET applications Continuous-Conduction-Mode Totem-Pole PFC • Low component count • Fixed switching frequency, zero reverse recovery switch should be used • GaN is a good candidate for the application • Possible to operate TM and ZVS at light loads
GaN Versus Silicon and SiC Eg: Wide band-gap energy EBR: Critical field break down voltage VS: Saturation velocity µ: Electron mobility
6-7 Texas Instruments – 2014/15 Power Supply Design Seminar
Properties GaN Si SiC EG(eV) 3.4 1.12 3.2 EBR(MV/cm) 3.3 0.3 3.5 VS(x 107cm/s) 2.5 1.0 2.0 µ(cm2Vs) 990-2000 1500 650
Theoretical on-resistance vs blocking voltage
101
100
10-1
10-2
10-3
10-4
101 102 103 104
RO
N �ȍ
PP
2)
Breakdown Voltage (V)
6L�/LPLW
6L&�/LPLW
*D1�/LPLWReference: EPC, Gallium Nitride (GaN) technology overview
rONα1
µ × EBR3
Key electrical properties of three semiconductor materials
100
10
1
0.1
0.01
7000
6000
5000
4000
3000
2000
1000
0
0 400 800 1200 1600 2000 2400
0 50 100 150 200
Ke
y F
igu
re
of
Me
rit
(R
ON
x Q
G�>ȍ
�Q&@
VDSS�>9@
6ZLWFKLQJ�)LJXUH�RI�0HULW�±�6L�YV��6L&�YV��*D1
}
}
1200 V GaN cascode
performance range
600/650 V GaN cascode
performance range
LV GaN FET
(Enhancement)
RF GaN FET
(Depletion)
Si FETs
GaN 66 V/µmGaN 66 V/µmSilicon transistors
6LOLFRQ *D1
6L&Cree
Infineon
ST
International Rectifier
Toshiba
6L&�&DVFRGHAOS/SemiSouth
EPC-CO
International Rectifier
Micro GaN
GaN Systems 2012 rON x QG�>ȍ x S&@R
ON
x &
OS
S�>P
ȍ x
S)@
Power Electronics Technology Feb. 2013
Figure of Merit Comparison
Figure of Merit depicts fundamental characteristics of switching devices – Rds_on, Qg, COSS and breakdown voltage
6-8 Texas Instruments – 2014/15 Power Supply Design Seminar
6-9
Cascode GaN FET Structure
Texas Instruments – 2014/15 Power Supply Design Seminar
Cascode GaN FET internal structure Example of a boost configuration
Advantages: • Depletion-mode GaN: low cost and
better performance (compared to enhancement-mode GaN)
• Same MOSFET driver used • Low forward voltage drop in diode mode
Disadvantages: • Same reverse recovery of the
cascode MOSFET body diode • Potential MOSFET avalanche at high Vds slew rate • Large gate charge (same as the MOSFET)
Normally-onHV GaNHEMT
Normally-offLV NMOS SS
G
D
SSS
G
D
G
S
SCN
+
–
+
–
VO
CO
Q1
Q2
L
iL
Vin
PWM
Dmode-GaN + Safety FET Structure
6-10 Texas Instruments – 2014/15 Power Supply Design Seminar
PWM
D
GND
VCC
S
Normally onHV GaN
StartupMOSFET
GateDriver
StartupLogic
Advantages: • Zero reverse recovery • Low gate charge • No LV MOSFET switching loss • Suitable for high switching frequency applications • Integrated gate driver circuit to ease applications
Disadvantages: • High forward voltage drop in
diode mode • Complicated gate driver circuit (IC design)
+
–
VO
CO
Q1
Q2
Q3
Q4
PWM
GND
VCC D
S
PWM
GND
ZCD
VCC D
S
StartupLogic
StartupLogic
IsolatedPower
DigitalISO
HallSensor
AC1
AC2
Earth
Iac
12 V
Vg3
12 V12 V
Vg1
Vg2
Vg4
Driv
er
6-11
GaN-Based CCM Totem-Pole Bridgeless PFC Power Stage
Texas Instruments – 2014/15 Power Supply Design Seminar
Positive switching cycle § Active switching stage
• Q1 and Q2 are low frequency switches.
• Q3 and Q4 are an active switch and a SyncFET.
Positive switching cycle – active switching stage
6-12 Texas Instruments – 2014/15 Power Supply Design Seminar
GaN-Based CCM Totem-Pole Bridgeless PFC Power Stage
Positive switching cycle § Active switching stage
+
–
VOCO
Q1
Q2
Q3
Q4
PWM
GND
VCC D
S
PWM
GND
VCC D
S
StartupLogic
StartupLogic
IsolatedPower
DigitalISO
HallSensor
AC1
AC2
Earth
Iac
12 V
Vg3
12 V12 V
Vg1
Vg2
Vg4
Driv
er
ZCD
+
–
VOCO
Q1
Q2
Q3
Q4
PWM
GND
VCC D
S
PWM
GND
ZCD
VCC D
S
StartupLogic
StartupLogic
IsolatedPower
DigitalISO
HallSensor
AC1
AC2
Earth
Iac
12 V
Vg3
12 V12 V
Vg1
Vg2
Vg4
Driv
er
6-13 Texas Instruments – 2014/15 Power Supply Design Seminar
Positive switching cycle – freewheel stage
GaN-Based CCM Totem-Pole Bridgeless PFC Power Stage
Positive switching cycle § Freewheeling stage
+
–
+
–
VO
CO
Q3
PWM1A
PWM1B
iL
Q4
PWM
GNDL
VCC
VCC
D
S
PWM
GND
D
S
Startup
Logic
Startup
Logic
100
80
60
40
20
0
-20
-40
-60
-80
-100
-3.0 -2.0 -1.0 0 1.0 2.0 3.0
VD
VGS
I D
0 V
-1 V
-1.5 V
-2 V
-2.5 V
-3.3 V
VDS of Q3
-iQ3iQ4 -iQ3iQ4
Vg of Q4
VDS of Q3
Vg of Q4 Vg of Q3
GaN FET Forward Voltage Drop and Ideal Diode Emulation Control
6-14 Texas Instruments – 2014/15 Power Supply Design Seminar
Output characteristics of a typical depletion mode GaN FET Ref: Transphorm datasheet
GaN FET operates at diode mode GaN FET operates at ideal diode mode
Adaptive Dead-Time Control for SyncFET to Turn On
6-15 Texas Instruments – 2014/15 Power Supply Design Seminar
Csub_d, Csd and Crss add to form Coss Current sampling point
td =2Coss × VO
IL_peak
Da Db Da Db Da DaDb
DbDa Da
ZCD
Hardware-Assisted IDE Control
6-16 Texas Instruments – 2014/15 Power Supply Design Seminar
• Difficulty of volt-second control for ideal diode emulation
CCM Load increasing Stuck at CCM
Negative current detection and SyncFET soft off control is needed
• Freewheel stage current sensing for zero current detection
Db is chopped off at ZCD point
DCM Load decreasing
UDC3138 Digital Controller
Q3 Q4Q2Q1
VO
Vref
Iref
AB
C
+
-+
-
IS
SyncFET
Programmable NCD Ref
Main FET
Comparator
Iac
AC1
AC2
Current Loop
Voltage Loop
Main FET and SyncFET
Selection
EADC + CLA + DPWM
GVKmABC
ZCD
1/Vrms2Vrms
Kf|x|ADC
ADC
Crossover
Detection
UCD3138 – Based Control Circuit
6-17 Texas Instruments – 2014/15 Power Supply Design Seminar
Test Results – GaN FET Performance in FET Mode
6-18 Texas Instruments – 2014/15 Power Supply Design Seminar
Test Conditions: • Vin = 200 VDC, Iin = 2 ADC, VO = 400 V • Q4: 600 V 150 mΩ depletion-mode GaN power transistor • D3: Cree SiC diode C3D04060A • Gate turn-off resistance = 2.2 Ω, turn-on resistance=15 Ω Test Results: • Turn-on time = 9 nS • Max turn-on dV/dt = 79 V/nS • Coss is linearly charged up to VO at turn-off • About 18 V ringing when freewheel diode conducts
+
–
VO
CO
Q3
Q4
SiC
D3
PWM
GND
VCCD
S
Startup
Logic
12 V
Vg4Vin
+
–
IL
6-19 Texas Instruments – 2014/15 Power Supply Design Seminar
Test Results – GaN FET Forward Voltage Drop in Diode Mode
Test Conditions: • Current = 0.1 A – 3 A, dead-time = 100 nS Test Results: • Forward voltage drop varies from 4.3 V to 7.3 V device-to-device when GaN is off
+
–
VO
CO
Q3
Q4
PWM
GND
VCCD
S
PWM
GND
VCCD
S
Startup
Logic
Startup
Logic
Isolated
Power
Digital
ISO
12 V
Vg3
12 V
Vg4
Vin
+
–
IL
GaN
Si: STTH8R06D
SiC
+
–
VO
CO
Q3
Q4
PWM
GND
VCC D
S
PWM
GND
VCC D
S
StartupLogic
StartupLogic
IsolatedPower
DigitalISO
12 V
Vg3
12 V
Vg4Vin
IL
+–
6-20 Texas Instruments – 2014/15 Power Supply Design Seminar
Test Results – GaN FET Reverse Recovery in Diode Mode
Test Conditions: • Q3 uses GaN FET, C3D04060E and
STTH8R06D
• di/dt is about 368 A/µS
Test Results and Conclusions: • Both GaN FET and SiC diode just have ringing
current – no reverse current was observed
• STTH8R06D has a significant reverse current
• GaN FET has a larger ringing than SiC, but at lower frequency, as a result of larger output capacitance of the two GaN FETs
6-21 Texas Instruments – 2014/15 Power Supply Design Seminar
AC Current Crossover Control
115 Vac
230 Vac|Vac_L – Vac_N|
0
|Vac|
VT_H
VT_L
Vg_Q1 Vg_Q2
Vg_Q3 Vg_Q4
RectifierFETs
ActiveGaN FETs
Integrator Running Integrator RunningIntegrator Stall
Turn-on Delay
Soft Turning On
Negative Half Cycle Positive Half Cycle
6-22 Texas Instruments – 2014/15 Power Supply Design Seminar
Current Spike Root Causes and Solutions
Root Causes: • Inaccurate a.c. voltage sensing • Turning on rectifier FET too early
cause a.c. line short sircuit • Current loop disturbed by current spike • Rectifier FET hard switching • Current loop compensation not
optimized
Solutions: • Differential a.c. voltage sensing with low
phase offset • Using different a.c. crossover voltage
thresholds for high line and low line • Sufficient blanking time • Disable PWM and stall integrator during
blanking time • Rectifier FET soft switching on • Inserting PWM turn-on delay time • Optimize current loop compensation
6-23 Texas Instruments – 2014/15 Power Supply Design Seminar
AC Current Waveforms
115 Vac input at 450 W PF= 0.999 THD = 3.3%
230 Vac input at 750W PF= 0.995 THD = 4.0%
6-24 Texas Instruments – 2014/15 Power Supply Design Seminar
Totem-Pole Bridgeless PFC Efficiency
38 76 114
152
190
228
266
304
342
380
418
456
494
532
570
608
646
684
722
760
100.00%
98.00%
96.00%
94.00%
92.00%
90.00%
88.00%
86.00%
84.00%
82.00%
80.00%
98.5%
230 Vac 115 Vac
Partial ZVS at low line input and light loads
Po/W
6-25 Texas Instruments – 2014/15 Power Supply Design Seminar
750 W Totem-Pole Bridgeless PFC Prototype
6-26 Texas Instruments – 2014/15 Power Supply Design Seminar
Summary • GaN FET exhibits superior switching characteristics • Safety GaN FETs has zero reverse recovery
• Suitable for high-frequency hard-switching applications
• Relative high “body diode” forward drop • Sophisticated ideal-diode-emulation is the key to the success of Safety
GaN FET applications
• Enables Totem-Pole PFC CCM operation • AC crossover current spike root causes were analyzed and solutions
provided
• High efficiency potential
• Possible TM ZVS control to optimize light loads efficiency
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