AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver Application Report

AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver Application Report
Application Report
SNVA429C – August 2010 – Revised May 2013
AN-2034 LM3445 -120VAC, 8W Isolated Flyback
LED Driver
.....................................................................................................................................................
ABSTRACT
This demonstration board highlights the performance of a LM3445 based Flyback LED driver solution that
can be used to power a single LED string consisting of 4 to 8 series connected LEDs from an 90 VRMS to
135 VRMS, 60 Hz input power supply. The key performance characteristics under typical operating
conditions are summarized in this application report.
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Contents
Introduction .................................................................................................................. 3
Key Features ................................................................................................................ 3
Applications .................................................................................................................. 3
Performance Specifications ................................................................................................ 3
LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic ...................................... 5
LM3445 Device Pin-Out .................................................................................................... 7
Bill of Materials .............................................................................................................. 7
Demo Board Wiring Overview ............................................................................................. 9
Demo Board Assembly ................................................................................................... 10
Typical Performance Characteristics .................................................................................... 11
PCB Layout ................................................................................................................. 14
Transformer Design ....................................................................................................... 15
Experimental Results ..................................................................................................... 16
13.1 Non-Dimming Performance ..................................................................................... 16
13.2 Dimming Performance ........................................................................................... 17
13.3 Power Factor Performance ...................................................................................... 19
Circuit Operation With Rotary Forward Phase TRIAC Dimmer ..................................................... 20
Circuit Operation With Reverse Phase TRIAC Dimmer .............................................................. 21
Electromagnetic Interference (EMI) ..................................................................................... 22
Thermal Analysis .......................................................................................................... 24
Circuit Analysis and Explanations ....................................................................................... 26
18.1 Injecting Line Voltage into Filter-2 (Achieving PFC > 0.95) ................................................. 26
List of Figures
1
Demo Board ................................................................................................................. 4
2
LED Current vs. Input Voltage (using Dimmer) ......................................................................... 4
3
Demo Board Schematic .................................................................................................... 6
4
LM3445 Device Pin-Out .................................................................................................... 7
5
Wiring Connection Diagram
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9
10
...............................................................................................
Top View ....................................................................................................................
Bottom View ................................................................................................................
Efficiency vs. Line Voltage Original Circuit .............................................................................
Efficiency vs. Line Voltage Modified Circuits ..........................................................................
LED Current vs. Line Voltage Original Circuit .........................................................................
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All other trademarks are the property of their respective owners.
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AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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11
LED Current vs. Line Voltage Modified Circuits ....................................................................... 11
12
Power Factor vs. Line Voltage Original Circuit ........................................................................ 11
13
Power Factor vs. Line Voltage Modified Circuits ...................................................................... 11
14
Output Power vs. Line Voltage Original Circuit ........................................................................ 12
15
Output Power vs. Line Voltage Modified Circuits
16
Power MOSFET Drain Voltage Waveform (VIN = 120VRMS, 6 LEDs, ILED = 350mA) ............................... 12
17
Current Sense Waveform (VIN = 120VRMS, 6 LEDs, ILED = 350mA) .................................................. 12
18
FLTR2 Waveform (VIN = 120VRMS, 6 LEDs, ILED = 350mA)
19
Top Layer ................................................................................................................... 14
20
Bottom Layer ............................................................................................................... 14
21
LED Current vs. Input Voltage (using Dimmer)
22
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27
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32
33
34
35
36
.....................................................................
...........................................................
.......................................................................
Current Harmonic Performance vs. EN/IEC61000-3-2 Class C Limits .............................................
Forward Phase Circuit at Full Brightness ..............................................................................
Forward Phase Circuit at 90° Firing Angle .............................................................................
Forward Phase Circuit at 150° Firing Angle ...........................................................................
Reverse Phase Circuit at Full Brightness ..............................................................................
Reverse Phase Circuit at 90° Firing Angle .............................................................................
Reverse Phase Circuit at 150° Firing Angle ...........................................................................
Input EMI Filter and Rectifier Circuit ....................................................................................
Peak Conductive EMI Scan per CISPR-22, Class B Limits..........................................................
Peak Conductive EMI Scan with Additional 33nF of Input Capacitance ...........................................
Top Side Thermal Scan ..................................................................................................
Bottom Side Thermal Scan...............................................................................................
Line Voltage Injection Circuit .............................................................................................
FLTR2 Waveform with No Dimmer .....................................................................................
Typical Operation of FLTR2 Pin ........................................................................................
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27
List of Tables
2
1
Pin Description 10 Pin VSSOP ............................................................................................ 7
2
Wiring Connection
3
Measured Efficiency and Line Regulation (6 LEDs, No TRIAC Dimmer) .......................................... 16
4
LED Current, Output Power Versus Number of LEDs for Various Circuit Modifications (VIN = 120 VAC , no
TRIAC Dimmer) ............................................................................................................ 16
5
Measured Efficiency and Line Regulation Data (with TRIAC Dimmer) ............................................. 17
..........................................................................................................
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Introduction
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1
Introduction
This is a two-layer board using the bottom and top layer for component placement. The demonstration
board can be modified to adjust the LED forward current, the number of series connected LEDs that are
driven and the switching frequency. For detailed instructions, see Triac Dimmable Offline LED Driver
(SNVS570).
A bill of materials is included that describes the parts used on this demonstration board. A schematic and
layout have also been included along with measured performance characteristics.
2
Key Features
•
•
•
•
3
Applications
•
•
•
•
4
Drop-in compatibility with TRIAC dimmers
Line injection circuitry enables PFC values greater than 0.95
Adjustable LED current and switching frequency
Flicker free operation
Retro-fit TRIAC Dimming
Solid State Lighting
Industrial and Commercial Lighting
Residential Lighting
Performance Specifications
Based on an LED Vf = 3.4V
Symbol
Parameter
Min
Typ
Max
VIN
Input voltage
90 VRMS
120 VRMS
135 VRMS
VOUT
LED string voltage
13 V
20 V
27 V
ILED
LED string average current
-
365 mA
-
POUT
Output power
-
7.3 W
-
fsw
Switching frequency
-
78.5 kHz
-
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Performance Specifications
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Figure 1. Demo Board
400
ILED (mA)
320
240
160
80
0
10
32
54
76
98
120
Input Voltage (Vrms)
Figure 2. LED Current vs. Input Voltage (using Dimmer)
4
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
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LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
WARNING
The LM3445 evaluation board has exposed high voltage
components that present a shock hazard. Care must be taken when
handling the evaluation board. Avoid touching the evaluation
board and removing any cables while the evaluation board is
operating. Isolating the evaluation board rather than the
oscilloscope is highly recommended.
CAUTION
The ground connection on the evaluation board is NOT referenced to earth
ground. If an oscilloscope ground lead is connected to the evaluation board
ground test point for analysis and AC power is applied, the fuse (F1) will fail
open. The oscilloscope should be powered via an isolation transformer before
an oscilloscope ground lead is connected to the evaluation board.
The LM3445 evaluation board should not be powered with an open load. For
proper operation, ensure that the desired number of LEDs are connected at the
output before applying power to the evaluation board.
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LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
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V+
T1
VLED+
D4
C1
R2
R1
D1
C3
R7
R3
+
C4
+
D5
D3
Q1
R22
VLED±
D8
D7
VCC
R8
R9
C7
1
C8
BLDR 10
ASNS
D6
R16
2 FLTR1
C14
VCC
9
GATE
8
4 COFF
ISNS
7
5
GND
6
R12
DIM
3 DIM
Q2
Q4
C12
FLTR2
R15
FLTR2
R13
R20
R14
LM3445
C11
C13
R6
VCC
RT1
L1
LINE
R10
C9
C5
C2
C6
R5
DIM
D2
V+
R11
Q3
R4
C10
F1
NEUTRAL
FLTR2
L2
R24
TRIAC HOLDING
CIRCUIT
INPUT EMI FILTER AND RECTIFIER CIRCUIT
Figure 3. Demo Board Schematic
6
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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LM3445 Device Pin-Out
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6
LM3445 Device Pin-Out
ASNS
1
10 BLDR
FLTR1
2
9 VCC
DIM
3
8 GATE
COFF
4
7 ISNS
FLTR2
5
6 GND
Figure 4. LM3445 Device Pin-Out
Table 1. Pin Description 10 Pin VSSOP
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Pin #
Name
Description
1
ASNS
PWM output of the TRIAC dimmer decoder circuit. Outputs a 0 to 4V PWM signal with a duty cycle proportional
to the TRIAC dimmer on-time.
2
FLTR1
First filter input. The 120Hz PWM signal from ASNS is filtered to a DC signal and compared to a 1 to 3V, 5.85
kHz ramp to generate a higher frequency PWM signal with a duty cycle proportional to the TRIAC dimmer firing
angle. Pull above 4.9V (typical) to tri-state DIM.
3
DIM
Input/output dual function dim pin. This pin can be driven with an external PWM signal to dim the LEDs. It may
also be used as an output signal and connected to the DIM pin of other LM3445 or LED drivers to dim multiple
LED circuits simultaneously.
4
COFF
OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant
OFF time of the switching controller.
5
FLTR2
Second filter input. A capacitor tied to this pin filters the PWM dimming signal to supply a DC voltage to control
the LED current. Could also be used as an analog dimming input.
6
GND
Circuit ground connection.
7
ISNS
LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the
maximum LED current.
8
GATE
Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
controller.
9
VCC
10
BLDR
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
Bleeder pin. Provides the input signal to the angle detect circuitry as well as a current path through a switched
230Ω resistor to ensure proper firing of the TRIAC dimmer.
Bill of Materials
Designator
Description
Manufacturer
Part Number
AA1
Printed Circuit Board
-
551600457-001A
C1
CAP .047UF 630V METAL POLYPRO
EPCOS Inc
B32559C6473K000
GA355DR7GB103KY02L
C2
CAP 10000PF X7R 250VAC X2 2220
Murata Electronics North America
C3, C4
CAP 330UF 35V ELECT PW
Nichicon
UPW1V331MPD6
C5
CAP CER .33UF 250V X7R 1812
TDK Corporation
C4532X7R2E334K
C6
CAP .10UF 305VAC EMI SUPPRESSION
EPCOS
B32921C3104M
C7
CAP, CERM, 0.1µF, 16V, +/-10%, X7R,
0805
Kemet
C0805C104K4RACTU
C8
CAP CER 47UF 16V X5R 1210
MuRata
GRM32ER61C476ME15L
C9
CAP CER .10UF 250V X7R 10% 1206
TDK
C3216X7R2E104K
C10
CAP CER .22UF 16V X7R 0603
MuRata
GRM188R71C224KA01D
C11
CAP CER 2200PF 50V 10% X7R 0603
MuRata
GRM188R71H222KA01D
C12
CAP CER 330PF 50V 5% C0G 0603
MuRata
GRM1885C1H331JA01D
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AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Bill of Materials
Designator
8
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Description
Manufacturer
Part Number
C13
CAP CER 2200PF 250VAC X1Y1 RAD
TDK Corporation
CD12-E2GA222MYNS
C14
CAP CERM .47UF 10% 25V X5R 0805
AVX
08053D474KAT2A
D1
DIODE TVS 150V 600W UNI 5% SMB
Littlefuse
SMAJ120A
D2
RECT BRIDGE GP 600V 0.5A MINIDIP
Diodes Inc.
RH06-T
D3
DIODE RECT GP 1A 1000V MINI-SMA
Comchip Technology
CGRM4007-G
D4
DIODE SCHOTTKY 100V 1A SMA
ST Microelectronics
STPS1H100A
D5
DIODE ZENER 30V 1.5W SMA
ON Semiconductor
1SMA5936BT3G
D6
DIODE ZENER 5.1V 200MW SOD-523F
Fairchild Semiconductor
MM5Z5V1
D7
DIODE ZENER 12V 200MW
Fairchild Semiconductor
MM5Z12V
D8
DIODE SWITCH 200V 200MW
Diode Inc
BAV20WS-7-F
F1
FUSE BRICK 1A 125V FAST 6125FA
Cooper/Bussmann
6125FA
J1, J2, J3, J4,
TP8, TP9, TP10
16 GA WIRE HOLE, 18 GA WIRE HOLE
3M
923345-02-C
J5, J6
Conn Term Block, 2POS, 5.08mm PCB
Phoenix Contact
1715721
L1, L2
INDUCTOR 4700UH .13A RADIAL
TDK Corporation
TSL0808RA-472JR13-PF
Q1
MOSFET N-CH 600V 90MA SOT-89
Infineon Technologies
BSS225 L6327
Q2
MOSFET N-CH 600V 1.8A TO-251
Infineon Technology
SPU02N60S5
Q3
MOSFET N-CH 100V 170MA SC70-3
Diodes Inc
BSS123W-7-F
Q4
TRANS GP SS PNP 40V SOT323
On Semiconductor
MMBT3906WT1G
R1, R3
RES 200K OHM 1/4W 5% 1206 SMD
Vishay-Dale
CRCW1206200KJNEA
R2, R7
RES, 309k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206309KFKEA
R4, R5
RES, 430 ohm, 5%, 0.25W, 1206
Vishay-Dale
CRCW1206430RJNEA
R6, R24
RES, 10.5k ohm, 1%, 0.125W, 0805
Vishay-Dale
CRCW080510K5FKEA
R8, R11
RES 49.9K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW060349K9FKEA
CRCW0603100KFKEA
R9
RES 100K OHM 1/10W 1% 0603 SMD
Vishay-Dale
R10
DNP
-
-
R12
RES 4.7 OHM 1/10W 5% 0603 SMD
Vishay-Dale
CRCW06034R70JNEA
R13
RES 10 OHM 1/8W 5% 0805 SMD
Vishay-Dale
CRCW080510R0JNEA
R14
RES 1.50 OHM 1/4W 1% 1206 SMD
Vishay-Dale
CRCW12061R50FNEA
R15
RES 3.48K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW06033K48FKEA
R16
RES 75.0K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW060375K0FKEA
R20
RES 30.1K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW060330K1FKEA
R22
RES 40.2 OHM 1/8W 1% 0805 SMD
Vishay-Dale
CRCW080540R2FKEA
RT1
CURRENT LIMITOR INRUSH 60OHM
20%
Cantherm
MF72-060D5
T1
Transformer
Wurth Electronics
750311553 Rev. 01
TP2-TP5
Terminal, Turret, TH, Double
Keystone Electronics
1502-2
TP7
TEST POINT ICT
-
-
U1
TRIAC Dimmable Offline LED Driver,
PowerWise™
Texas Instruments
LM3445
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Demo Board Wiring Overview
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Demo Board Wiring Overview
TP3
TP4
LED +
J6
J5
LINE
NEUTRAL
LED TP5
TP2
Figure 5. Wiring Connection Diagram
Table 2. Wiring Connection
Test
Point
Name
I/O
Description
TP3
LED +
Output
LED Constant Current Supply
Supplies voltage and constant-current to anode of LED string.
TP2
LED -
Output
LED Return Connection (not GND)
Connects to cathode of LED string. Do NOT connect to GND.
TP4
LINE
Input
AC Line Voltage
Connects directly to AC line or output of TRIAC dimmer of a 120VAC system.
TP5
NEUTRAL
Input
AC Neutral
Connects directly to AC neutral of a 120VAC system.
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Demo Board Assembly
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Demo Board Assembly
Figure 6. Top View
Figure 7. Bottom View
10
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Typical Performance Characteristics
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Typical Performance Characteristics
Original Circuit: R14 = 1.50Ω; Modification A: R14 = 1.20Ω; Modification B: R14 = 1.00Ω; Modification C:
R14 = 0.75Ω
82
82
8 LEDs
80
78
EFFICIENCY (%)
EFFICIENCY (%)
Original
Mod A
80
6 LEDs
76
4 LEDs
78
Mod B
76
74
Mod C
74
72
72
80
90
100
110
120
130
140
80
LINE VOLTAGE (VRMS)
90
100
110
120
130
140
LINE VOLTAGE (VRMS)
Figure 8. Efficiency vs. Line Voltage
Original Circuit
Figure 9. Efficiency vs. Line Voltage
Modified Circuits
1.0
1.0
0.8
0.8
0.7
ILED(A)
ILED(A)
Mod C
6 LEDs
4 LEDs
0.4
0.2
0.7
Mod B
0.4
0.2
Mod A
8 LEDs
Original
0.0
0.0
80
90
100
110
120
130
140
80
LINE VOLTAGE (VRMS)
Figure 10. LED Current vs. Line Voltage
Original Circuit
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90
100
110
120
130
140
LINE VOLTAGE (VRMS)
Figure 11. LED Current vs. Line Voltage
Modified Circuits
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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100
100
98
98
POWER FACTOR
POWER FACTOR
Typical Performance Characteristics
4 LEDs
6 LEDs
96
94
8 LEDs
92
Mod B
Mod A
96
94
Original
Mod C
92
90
90
80
90
100
110
120
130
140
80
90
LINE VOLTAGE (VRMS)
100
110
120
130
140
LINE VOLTAGE (VRMS)
Figure 12. Power Factor vs. Line Voltage
Original Circuit
Figure 13. Power Factor vs. Line Voltage
Modified Circuits
15
15
Mod C
12
POUT(W)
POUT(W)
12
8 LEDs
9
6 LEDs
6
Mod B
9
6
4 LEDs
3
Mod A
Original
3
80
90
100
110
120
130
140
80
90
LINE VOLTAGE (VRMS)
12
100
110
120
130
140
LINE VOLTAGE (VRMS)
Figure 14. Output Power vs. Line Voltage
Original Circuit
Figure 15. Output Power vs. Line Voltage
Modified Circuits
Figure 16. Power MOSFET Drain Voltage Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
Figure 17. Current Sense Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Typical Performance Characteristics
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Figure 18. FLTR2 Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
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PCB Layout
11
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PCB Layout
Figure 19. Top Layer
Figure 20. Bottom Layer
14
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Transformer Design
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12
Transformer Design
Mfg: Wurth Electronics, Part #: 750311553 Rev. 01
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Experimental Results
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Experimental Results
The LED driver is designed to accurately emulate an incandescent light bulb and therefore behave as an
emulated resistor. The resistor value is determined based on the LED string configuration and the desired
output power. The circuit then operates in open-loop, with a fixed duty cycle based on a constant on-time
and constant off-time that is set by selecting appropriate circuit components. Like an incandescent lamp,
the driver is compatible with both forward and reverse phase dimmers.
13.1 Non-Dimming Performance
In steady state, the LED string voltage is measured to be 20.1 V and the average LED current is
measured as 365 mA. The 120 Hz current ripple flowing through the LED string was measured to be 182
mApk-pk at full load. The magnitude of the ripple is a function of the value of energy storage capacitors
connected across the output port and the TRIAC firing angle. The ripple current can be reduced by
increasing the value of energy storage capacitor or by increasing the LED string voltage. With TRIAC
dimmers, the ripple magnitude is directly proportional to the input power and therefore reduces at lower
LED current.
The LED driver switching frequency is measured to be close to the specified 78.5 kHz. The circuit
operates with a constant duty cycle of 0.28 and consumes near 9.2 W of input power. The driver steady
state performance for an LED string consisting of 6 series LEDs without using a TRIAC dimmer is
summarized in Table 3.
Table 3. Measured Efficiency and Line Regulation (6 LEDs, No TRIAC Dimmer)
VIN (VRMS)
IIN (mARMS)
PIN(W)
VOUT (V)
ILED (mA)
POUT (W)
Efficiency (%) Power Factor
89.98
64
5.44
19.24
222
4.27
78.5
94.7
95.03
67
6.03
19.40
244
4.73
78.5
94.8
100.00
70
6.62
19.55
267
5.22
78.8
94.9
104.97
73
7.24
19.69
291
5.73
79.1
95.0
110.03
76
7.90
19.83
315
6.25
79.1
95.0
115.00
78
8.55
19.95
340
6.78
79.3
95.1
120.05
81
9.21
20.06
365
7.32
79.5
95.1
125.02
83
9.84
20.14
389
7.83
79.6
95.0
129.99
85
10.44
20.22
412
8.33
79.8
94.9
135.04
86
11.02
20.29
433
8.79
79.7
94.8
Table 4. LED Current, Output Power Versus Number of LEDs for Various Circuit Modifications
(VIN = 120 VAC , no TRIAC Dimmer)
# of LEDs
(1)
16
Original Circuit
(1)
Modification A
(1)
Modification B
(1)
Modification C
(1)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
4
513
7.11
627
8.83
683
10.03
805
11.91
6
365
7.32
435
9.09
481
10.22
566
12.23
8
276
7.34
334
9.16
367
10.16
431
12.12
Original Circuit: R14 = 1.50Ω; Modification A: R14 = 1.20Ω; Modification B: R14 = 1.00Ω; Modification C: R14 = 0.75Ω
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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13.2 Dimming Performance
The LED driver is capable of matching or exceeding the dimming performance of an incandescent lamp.
Using a simple rotary TRIAC dimmer, smooth and near logarithmic dimming performance is achieved. By
varying the firing angle of the TRIAC dimmer and measuring the corresponding input and output
parameters, the dimming performance of the demonstration board driving 6 LEDs is summarized in
Table 5.
Table 5. Measured Efficiency and Line Regulation Data (with TRIAC Dimmer)
VIN (VRMS)
VO (V)
IO (mA)
POUT (W)
115.0
19.9
351
7.0
110.1
19.8
323
6.4
105.2
19.7
295
5.8
100.4
19.6
269
5.3
95.5
19.6
258
5.0
90.7
19.5
248
4.8
85.2
19.4
222
4.3
80.2
19.3
199
3.8
75.1
19.2
176
3.4
70.8
19.1
159
3.0
65.5
18.7
138
2.6
60.5
18.8
120
2.3
55.2
18.6
101
1.9
50.6
18.5
86
1.6
45.7
18.3
72
1.3
39.4
18.0
54
1.0
34.2
17.8
42
0.7
30.3
17.6
33
0.6
26.0
17.4
25
0.4
20.0
17.0
15
0.3
15.2
16.6
9
0.1
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Experimental Results
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400
ILED (mA)
320
240
160
80
0
10
32
54
76
98
120
Input Voltage (Vrms)
Figure 21. LED Current vs. Input Voltage (using Dimmer)
18
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13.3 Power Factor Performance
The LED driver is able to achieve close to unity power factor (P.F. ~ 0.95) which meets Energy Star
requirements. This design also exhibits low current harmonics as a percentage of the fundamental current
(as shown in the following figure) and therefore meets the requirements of the IEC 61000-3-2 Class-3
standard.
Figure 22. Current Harmonic Performance vs. EN/IEC61000-3-2 Class C Limits
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Circuit Operation With Rotary Forward Phase TRIAC Dimmer
14
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Circuit Operation With Rotary Forward Phase TRIAC Dimmer
The dimming operation of the circuit was verified using a forward phase rotary TRIAC dimmer. Waveforms
captured at different dimmer settings are shown in the following figures.
Figure 23. Forward Phase Circuit at Full Brightness
Figure 24. Forward Phase Circuit at 90° Firing Angle
Figure 25. Forward Phase Circuit at 150° Firing Angle
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Circuit Operation With Reverse Phase TRIAC Dimmer
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15
Circuit Operation With Reverse Phase TRIAC Dimmer
The circuit operation was also verified using a reverse phase dimmer and waveforms captured at different
dimmer settings are shown in the following figures.
Figure 26. Reverse Phase Circuit at Full Brightness
Figure 27. Reverse Phase Circuit at 90° Firing Angle
Figure 28. Reverse Phase Circuit at 150° Firing Angle
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Electromagnetic Interference (EMI)
16
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Electromagnetic Interference (EMI)
The EMI input filter of this evaluation board is configured as shown in Figure 29.
R6
RT1
L1
LINE
C9
C5
V+
C2
C6
R5
D2
R4
F1
NEUTRAL
L2
R24
Figure 29. Input EMI Filter and Rectifier Circuit
In order to get a quick estimate of the EMI filter performance, only the PEAK conductive EMI scan was
measured and the data was compared to the Class B conducted EMI limits published in FCC – 47,
section 15.
Figure 30. Peak Conductive EMI Scan per CISPR-22, Class B Limits
If an additional 33nF of input capacitance (that is, C6) is utilized in the input filter, the EMI conductive
performance is further improved as shown in Figure 31.
22
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Electromagnetic Interference (EMI)
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Figure 31. Peak Conductive EMI Scan with Additional 33nF of Input Capacitance
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Thermal Analysis
17
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Thermal Analysis
The board temperature was measured using an IR camera (HIS-3000, Wahl) while running under the
following conditions:
• VIN = 120 VRMS
• ILED = 365 mA
• Number of LEDs = 6
• POUT = 7.3 W
The results are shown in the following figures.
Figure 32. Top Side Thermal Scan
24
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver
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Figure 33. Bottom Side Thermal Scan
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Circuit Analysis and Explanations
18
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Circuit Analysis and Explanations
18.1 Injecting Line Voltage into Filter-2 (Achieving PFC > 0.95)
If a small portion (750mV to 1.00V) of line voltage is injected at FLTR2 of the LM3445, the circuit is
essentially turned into a constant power flyback as shown in Figure 34.
The LM3445 works as a constant off-time controller normally, but by injecting the 1.0V rectified AC voltage
into the FLTR2 pin, the on-time can be made to be constant. With a DCM Flyback, Δi needs to increase
as the input voltage line increases. Therefore a constant on-time (since inductor L is constant) can be
obtained.
By using the line voltage injection technique, the FLTR2 pin has the voltage wave shape shown in
Figure 35 on it with no TRIAC dimmer in-line. Voltage at VFLTR2 peak should be kept below 1.25V. At 1.25V
current limit is tripped. C11 is small enough not to distort the AC signal but adds a little filtering.
Although the on-time is probably never truly constant, it can be observed in Figure 36 how (by adding the
rectified voltage) the on-time is adjusted.
V+
VFLTR2
R2
LM3445
t
R9
1 ASNS
BLDR 10
2 FLTR1
VCC 9
R7
3 DIM
GATE 8
4 COFF
ISNS
7
5 FLTR2
GND
6
DIM
COFF
FLTR2
R15
C11
Figure 34. Line Voltage Injection Circuit
Figure 35. FLTR2 Waveform with No Dimmer
For this evaluation board, the following resistor values are used:
R2 = R7 = 309kΩ
R15 = 3.48kΩ
Therefore the voltages observed on the FLTR2 pin will be as follows for listed input voltages:
For VIN = 90VRMS, VFLTR2 = 0.71V
For VIN = 120VRMS, VFLTR2 = 0.95V
For VIN = 135VRMS, VFLTR2 = 1.07V
Using this technique, a power factor greater than 0.95 can be achieved without additional passive active
power factor control (PFC) circuitry.
26
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750 mV
ASNS
As line voltage increases, the voltage across the
inductor increases, and the peak current increases.
50k
DIM DECODER
333k
4.5V
RFLTR1
Nearly a constant ontime as the line varies
PWM
I-LIM
FLTR1
Tri-State
D x LED Current
1.25V
CFLTR1
RAMP GEN.
5.5 kHz
3V
1V
1k
ISNS
1V
DIM
FLTR2
1V
LEADING EDGE BLANKING
The PWM reference increases
as the line voltage increases.
PGND
RSNS
110 ns
CFLTR2
Figure 36. Typical Operation of FLTR2 Pin
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