2. 2
Agenda
• High-brightness LED characteristics
• LED system requirements
• LED driver topologies
- Single-stage vs. two-stage
• LED load control
- Parallel LED strings
• 100 W industrial LED design example
- Power stage calculations
- Test results
• Summary
3. 3
High-Power Industrial LED Fixtures
TypicalApplications
LEDAdvantages
Highway Light
Parking Lot
Streetlight
Tunnel Lighting
High & Low Bay
Airports
Bridges
Manufacturing
Efficiency
Reliability
Maintenance
Instant-on
Dimming
Light Quality
UV-Free
Mercury Free
Typical Power, 50 W<PLED<200 W
Before
After
4. 4
HB-LED Characteristics
VF, Forward Voltage (V)
IF,ForwardCurrent(mA)
0 0.5 1.5 2 2.5 3 3.5 4 4.5
100
200
300
400
500
600
700
800
900
0
200mA (50%)
100 °C
25 °C
200mV
(6%)
• PN junction devices
- Negative temperature coefficient
- T↑, VF↓, IF↑, T↑
- Not easily paralleled
• Steep IF vs. VF curve
• Small ΔVF→Large ΔIF
- LED color shift
- Thermal imbalance
- Decreased reliability
• VF varies with temperature
• VF can vary by 20%~30%
• Operate best from a Constant
Current (CC), Constant
Voltage (CV) power source
(Typical I-V curve for 1 A, HB-LED)
5. 5
CC-CV Characteristic Curve
(Typical CC-CV Curve for 75 W LED Driver)
• Constant Current = 1.5 A
• Constant Voltage = 50 V
• Overvoltage Protection = 60 V
• CC-CV LED Driver Provides:
- Signal Conditioning (PFC)
- Power Conversion
- Load Control
(75 W CC-CV LED Driver)
CC-CV
LED
DRIVER
OUT
GND
VLED=50V
500
mA
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
500
mA
ILED=1.5A
500
mA
ILED, LED Current (A)
VLED,LEDVoltage(V)
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
20
30
40
50
60
70
0
10
Current
Foldback
OVP
6. 6
HB-LED System Requirements
AC-DC DC-DC
CC-CV
LOAD
CONTROL
AC
ANALOG
DIM
PWM
DIM
LED DRIVER
PFC
EMI
BIAS
(OPTIONAL)
• Input voltage range of
85 VRMS<VAC<308 VRMS possible
• 50 W<POUT<200 W
• ILED<2 A per string
• PFC required
• THD: EN61000-3-2, Class C
(Lighting equipment >25 W)
• LED driver
- Single-stage or two-stage (shown)
- DC-DC
- CC-CV load control
- Dimming requirements
- Safety and electrical protection
requirements
• Various LED driver topology choices
(Typical Industrial LED System Block Diagram)
7. 7
Single-Stage: CC-CV PFC Flyback
Advantages
• Best for simple, low-cost fixtures
where POUT<75 W
• Can handle wide VIN range
• Simple “familiar” design
Disadvantages
• High MOSFET VDS stress
• High output voltage ripple
• RCD clamp losses
• Difficult to meet: high PF, low
THD, high efficiency, high VIN
with single-stage
N
N
VVV
S
P
OUTINDS
• Typical VDS for 308 VRMS:
VVVVDS 6754602308
800 V-900 V MOSFET Required
AC-DC
AC
EMI
PFC
FL7930B/C
CC
CVFB
30VDC<VLED<60VDC
8. 8
Two-Stage: PFC and CC-CV LLC
Advantages
• Best for any power level
50 W<POUT<1 kW
• Highest overall efficiency
• VDS = VIN
Disadvantages
• Complex power stage design
• Precise gate drive timing is critical
• Less efficient at low-line for 460 V
PFC output
• Can’t use LLC when operating PFC
in “boost-follower” mode
(NOTE: VBULK = 460 V to boost from 308 VRMS)AC-DC
AC
EMI
PFC
FL7930B/C
FAN7621S
or
FLS Series
CC
CVFB
VBULK=460VDC
30VDC<VLED<60VDC
9. 9
Two-Stage: PFC and Two-Switch Flyback
Advantages
• Best for 50 W<POUT<150 W
• High overall efficiency
• Quasi-resonant (QR) flyback offers
valley switching
• Can handle wide VIN range
• Good choice for boost follower PFC
• Gate drive timing less critical
• Simple “familiar” design
• VDS = VIN
Disadvantages
• High-side gate drive required
• Less efficient compared to
PFC+LLC at high input
(NOTE: VBULK varies (Boost-Follower) according to VAC)
FLYBACK
FAN6300
HVIC
FAN7382
CC
CVFB
250VDC<VBULK<460VDC
30VDC<VLED<60VDC
AC-DC
AC
EMI
PFC
FL7930B/C
10. 10
LED Load Control
Single Series String Control
VCS
VBUS
IF
VF
VF
VF
VF
CC LED
DRIVER
OUT
FB
GND
Advantages
• Can drive 100s of series LEDs
• IF is same for every LED
- No current sharing necessary
• Easy to control in CC or CV
Disadvantages
• HIGH STRING VOLTAGE
• Efficiency impact due to high voltage
power stage components
• LED shunts needed to account for
open LED failure
• UL 1310 safety→VBUS<60 V
The greater the number of required LEDs, the more thought should be given to a series-parallel configuration
11. 11
LED Load Control
Linear Regulator Control
VOLTAGE
PRE-REG
OUT
FB
GND
VBUSIF1
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
IF2 IFN
ILED
CC
REG
CC
REG
CC
REG
Disadvantages
• VBUS> ∑VF +VREG
• Additional VBUS margin voltage is
dropped across linear regulator
• Increase in regulator
voltage→increase power
dissipation→lower efficiency
• Max current and power dissipation
limit the use of linear regulators for
high-power industrial LED lighting
• Matched VF (Binning) can increase
efficiency but increase LED cost
Advantages
• Driver operates in CV
• Each string independently regulated
• Single string can fail while remaining
strings regulate in CC
• Low EMI
12. 12
LED Load Control
Switching Buck Regulator Control
VOLTAGE
PRE-REG
OUT
FB
GND
VBUS
IF1
VF
VF
VF
VF
ILED
SW
CS
VIN
GND
RCS1
CC BUCK
IF2
VF
VF
VF
VF
SW
CS
VIN
GND
RCS2
CC BUCK
IFN
VF
VF
VF
VF
SW
CS
VIN
GND
RCSN
CC BUCK
Advantages
• Driver operates in CV
• Each string independently regulated
• Single string can fail while remaining
strings regulate in CC
• Typical 20%-30% efficiency
improvement over linear regulators
Disadvantages
• High component count
• Must operate at high frequency to
minimize inductor size
- EMI impact
• Current sharing accuracy
tolerances→5% considered good
13. 13
LED Load Control
FAN7346, 4-Channel LED Controller
FAN7346
CURRENT
BALANCE
OVR
FB1
GND VCS1
VBUS
IF1
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
VF
IF2 IFN
ILED
VCS2 VCSN
FB2
FBN
CC-CV
LED
DRIVER
OUT
GND
FB FB OUT1
OUT2
OUTN
CH1
CH2
CHN
ADIM
PWMN
FO
Q1
Q2
QN
Advantages
• Driver operates in CC-CV
• VLED minimized→higher efficiency
• Each string independently
regulated
• Single string can fail while
remaining strings regulate in CC
• Low EMI
• Analog and PWM dimming
• Used with any LED driver topology
• Master/slave configurable for
additional LED channels
• Secondary (shown) or primary
(opto) side control
• Fault output (FO)
• ±1.5% current sharing accuracy
14. 14
100 W, LED Design Specification
Two-Stage, BCM PFC and Two-Switch Flyback
Parameter Min. Typ. Max.
BCM PFC Stage
VAC 85VRMS 308VRMS
fVIN(AC_ 50Hz 60Hz 65Hz
VOUT_PFC
Fixed Regulation
440V 450V 465V
VOUT_PFC
Boost Follower
245V VIN(PK)+30V 465V
POUT_PFC 120W
tSOFT_START 50ms
tON_OVERSHOOT 10V
η_PFC 0.9 0.95
Two-Switch Flyback DC-DC LED Stage
VIN 250V 460V
VOUT_LED 30V 60V
IOUT_LED
Single Channel
2A
IOUT_LED
4-Channel (Per Channel)
350mA
POUT_LED 100W
fSW_LED 50kHz 150kHz
η_LED 0.9 0.95
Total System
η_120V 0.90
η_230V 0.90
PF_120V 0.95 0.99
PF_230V 0.95
Mechanical and Thermal
Height 30mm
TJ 60⁰C
Primary Design Goals
1. Wide input 85 VRMS<VAC<308 VRMS
2. Maximize wide range efficiency
3. Configurable for single-channel or
4-channel LED operation
4. Compatible with 0 V-10 V analog
dimming and 0%-100% PWM
dimming
5. Lowest possible design profile
Intended Applications
1. Streetlight, parking lot & highway
lighting
2. Industrial high-bay & low-bay
lighting
15. 15
BCM, PFC Design
FL7930C
1
2
3
4 5
6
7
8
OUT
VCC
GND
ZCDCS
COMP
RDY
INV PBIAS
ZCD
ZCD
AC
EMI
FILTER
RDY
(TO FLYBACK)
BF
ON
OFF
VOUT
(TO FLYBACK)
1
2
3
R5
R6
C4
C5
R7
R8
R9
R10 R11
D6
D7 Q3
Q4
Q5
L1
D8
C6
C7
NB
NAUX
VIN
RZCD
RCS
J1
0V
VDS
tREStOFF tON
TS
0V
VAUX
0V
VZCD
0.65V
0A
IL
0V
VGS
VIN
VOUT
2x(VIN – VOUT)
1.4V
t
ZCD Delay
(150ns)
NAUX
NB
x (VOUT – VIN)
NAUX
NB
x VIN
1.5V
IL(PK)
• Constant on-time, variable frequency
• Switching period, TS = tOFF + tRES + tON
• Inductor current switches from 0A (ZCS)
• VDS
- ZVS→VOUT<2×VIN
- Valley switch→otherwise
• Boost follower modes set by J1
16. 16
BCM, PFC Design
Boost Follower Operation
Time (ms)
Voltage(V)
0 20 40 60 80 100 120 140 160
50
100
150
200
250
300
350
400
450
0
500
180 200
VOUT=465V
250V<VOUT<475V
85VRMS<VAC<308VRMS
• Rectified AC shown for
85 VRMS<VAC<308 VRMS
• J1 boost follower setting:
- ON: 250 V<VOUT<460 V
- OFF: VOUT = 465 V
- OPEN: VOUT = 250 V
• Flyback DC-DC handles
~2:1 input range instead
of ~4:1
27. 27
• Can be used with any power
topology
• Constant current, U1a
- Set V-, initially to ~200 mV
- ILED through R12 will reach -200 mV
- U1a output goes high→regulates ILED
- ILED regulates CC as long as VLED<50 V
• Constant voltage, U1b
- Set R16, R17 divider to 2.5 V when
VLED = 50 V
- For VLED≥50 V, U1b output goes
high→regulates CV
LED Load Control Design
CC-CV Single-String Control
VL
SBIAS
2.5VREF
FB
R12
R13
R14
R15
R16
R17
R18
R19
R20R21
R22
D8
D9
30V<VLED<50V
C8
C9
ILED=2A
U1a
U1b
FAN4274
FAN4274
FOD817A
U2
VAO
29. 29
• Constant current, ICHx
- ICHx sensed by RSx (FBx)
- FBx compared to VADIM/10
- 4 V<VADIM<5 V for full brightness
- FBx>1 V for 20 µs→OCP (latching)
for string x
• Constant voltage, VLED
- Qx drain sensed by CHx
- CHx compared to Gm amplifier, 1 V
reference
- Gm amplifier output drives FB pin
- Regulates VLED to minimum value to
maintain Qx drain to 1 V
• Over Voltage Regulation (OVR)
- Compares VLED to 1.42 V reference
- VLED set point>1.42 V→FB
proportionally pulled low
- ICHx is reduced, VLED clamped to
OVR set voltage level
RSx
VADIM/10
1V
Vf
VDS
VS
Gm
OVR
DCDC
OUT
FB
CMP
FB
CHx
OUTx
FBxFAN7346
ICHx
1.42V
ILED
50mV<VREF(LED)<400mV
Qx
VLED
VF
VF
VF
VF
(NOTE: One of four LED strings shown)
LED Load Control Design
CC-CV 4-Channel, Control Block Diagram
30. 30
Power Board Schematic
PFC, Boost Follower Enable, Inrush Limit
BOOST FOLLOWER
1. OFF = 450 V
2. ON = BF
3. OPEN = 250 V
32. 32
Power Board Schematic
High-Voltage Flyback Bias Power Supply
• 85 VRMS<VAC<308 VRMS
• Primary referenced, PBIAS~15 V, 0.5 A
• Secondary referenced, SBIAS = 12 V, 0.5 A
33. 33
Controller Daughter Card Schematic
Single String CC-CV LED Controller
• Sources current into optocoupler anode (OPTO_A)
• Constant LED current set to 2 A
• Constant LED voltage set to 50 V
34. 34
Controller Daughter Card Schematic
4-Channel LED Controller
• Sinks current through optocoupler cathode
(OPTO_C)
• Constant LED current set to 350 mA
• OVR set to 62 V
PDIM
1. OFF = 5 V
2. ON = PWM DIM
37. 37
LED CC-CV Controller Cards
OR
4-Channel, 50 V, 350 mA per Channel Single Channel, 50 V, 2 A
J19
J23
38. 38
• VIN = 120 VAC
• VOUT = 450 V vs. boost follower
• POUT = 120 W = 100%
• Δη = 1.8%, @ 20% POUT
• ηPK = 97%, @ 90% POUT
BCM PFC Measured Efficiency & PF
• VIN = 120 VAC, 230 VAC
• VOUT = 450 V
• POUT = 120 W = 100%
• PF = 0.994
• LED power is constant so PFC should
operate within 50%<POUT<90%
Δƞ=1.8%,
@20% POUT
LED Power Range
39. 39
• Measured
- 80 VRMS<VAC<308 VRMS
- POUT = 120 W
BCM PFC, Boost Follower Mode
Measured vs. Predicted
• Predicted
- 80 VRMS<VAC<308 VRMS
- VOUT(BF) tracks VAC >150 VRMS
when boost follower is used
- Downstream DC-DC converter
designed for 250 V<VIN<460 V
time (ms)
Voltage(V)
0 20 40 60 80 100 120 140 160
50
100
150
200
250
300
350
400
450
0
500
180 200
VOUT=465V
250V<VOUT<475V
85VRMS<VAC<308VRMS
40. 40
• VIN = step 115 VRMS to 300 VRMS
• VOUT(BF) = 250 V to 450 V
• POUT = 60 W
BCM PFC Boost Follower Voltage Tracking
CH1 = VIN(AC), CH2 = VOUT(BF)
• VIN = step 300 VRMS to 115 VRMS
• VOUT(BF) = 450 V to 250 V
• POUT = 60 W
41. 41
2-Switch Flyback
CH1 = VGS(HO), CH2 = VGS(LO), CH3 = V(CBOOT)
• Boost Follower Benefit
- η = 94.75% peak @ 300 VDC
- VIN = VOUT(BF) = 250 V to 470 V
- 250 VIN corresponds to 120 VAC
- Without boost follower, VIN = 450 V
for 85 VRMS<VAC<308 VRMS
• FAN7382 Gate Drive Start-Up
94.02%,
250V
93.34%,
450V
Δη=0.68%
Δη=1.41%
42. 42
2-Switch Flyback
CH1 = VDS(LO), CH3 = VGS(LO)
• Extended valley switching
- VIN = VOUT(BF) = 250 V
- D = 11%
- fS = 68 kHz
- POUT = 24 W (Dim, 60 V, 4 x 100 mA)
• VDS valley switching on first valley
- VIN = VOUT(BF)=250 V
- D = 42%
- fS = 63kHz
- POUT = 85 W (60 V, 4 x 350 mA)
44. 44
System Performance
CH1 = VIN(AC), CH2 = IIN(AC)
• VIN(AC) = 300 VRMS
- PF = 0.915
- POUT = 85 W (LED load)
• VIN(AC) = 85 VRMS
- PF = 0.994
- POUT = 85 W (LED load)
45. 45
• Inrush current limiting
- NTC R7 and R12 limit inrush to 3.18 A during startup
- RDY signal (12 V) applied to U1-3, comparator output is HIGH, relay shorts
across R7 + R12 to maintain high efficiency during steady state operation
- Relay shorting time can be further adjusted by R16, C10
- Relay short is removed during power supply turn-off
System Performance
CH1 = VIN(AC), CH2 = IIN(AC), CH3 = VLED
47. 47
• PWM Dimming “chops” LED DC current
• FPWM = 250 Hz
• DCH1 = DCH2 = 50%, DCH3 = 10%, DCH4 = 100%
• ILEDCH1 = ILEDCH2 = 35 mA
• ILEDCH3 = 176 mA
• ILEDCH4 = 350 mA
• η = 87.02%
• PF =.971 during dimming
System Performance
CH1=PWMCH3, CH2=PWMCH1_CH2, CH3=ILEDCH3, CH4=ILEDCH1_CH2
• 2,on-board PWM dimmers
• PDIM1 controls channels 1, 2
• PDIM2 control channels 3, 4
• FPWM = 250 Hz, 1%<D<99.9%
• VPWM = 5 V
• Set J17, J21 to “OFF” to disable PWM
dimming or apply external PWM dimming
signal
48. 48
System Performance
Dimming
• FAN7346 analog dimming
- All four strings dim simultaneously
- 0.5 V<VADIM<4 V
- 12% minimum dimming
- Cannot dim to 0% (full-off) due to minimum
internal analog dimming voltage clamped at
0.5 V
• FAN7346 PWM Dimming
- PWM dim each LED string independently
- 2 V<VDIM(PWM)<5 V
- 100 Hz<FPWM<500 Hz
- PWM dimming is linear from 0% (barely on)
to 100% (full brightness)
49. 49
System Performance
EN61000-3-2, Class C (PIN>25 W)
• VIN(AC) = 115 VRMS
- VOUT(PFC) = 250 V
- POUT = 85.41 W (60 V, 4×350 mA)
- η = 91.05%
- THD = 8.91%
- Passes EN61000-3-2,Class C
• VIN(AC) = 230 VRMS
- VOUT(PFC) = 400 V
- POUT = 86.2 W (60 V, 4×350 mA)
- η = 91.51%
- THD = 21.52%
- Passes EN61000-3-2,Class C
50. 50
System Performance
Efficiency
• POUT comparison
- POUT = 70 W vs. 85 W
- η>90% over entire range for
85 W<POUT<100 W
- Both cases shown operating
with PFC boost follower
• Boost follower comparison
- Greater benefit at low-line
- ~1.2% overall efficiency
improvement at low-line
- 91.8% peak efficiency includes
EMI filter and bias supply
51. 51
System Performance
Power Factor & CC-CV
• System PF
• PF>90% for 85 W<POUT<100 W
• Peak PF = .996 for low-line
• Fixed 450 V and boost follower PFC
output shows identical PF
• CC-CV
• OVR set to ~52 V for 50 V, 4 x 350 mA
(70 W) operation to meet 50 V
specification
• VLED(MIN) = 31 V
52. 52
Summary
• High-power, industrial LED lighting requirements were
reviewed
• Several power solutions for CC-CV LED load control were
introduced
• 100 W, dual-stage, QR flyback, LED driver was designed
- Wide AC input voltage range
- High efficiency
- Configurable for single-string or 4-string CC-CV LED
operation
• Techniques for maximizing efficiency were verified
