Texas Instruments Incorporated AN-2034 User's Guide
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 V
135 V
, 60 Hz input power supply. The key performance characteristics under typical operating
RMS
conditions are summarized in this application report.
Contents
1 Introduction .................................................................................................................. 3
2 Key Features ................................................................................................................ 3
3 Applications .................................................................................................................. 3
4 Performance Specifications ................................................................................................ 3
5 LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic ...................................... 5
6 LM3445 Device Pin-Out .................................................................................................... 7
7 Bill of Materials .............................................................................................................. 7
8 Demo Board Wiring Overview ............................................................................................. 9
9 Demo Board Assembly ................................................................................................... 10
10 Typical Performance Characteristics .................................................................................... 11
11 PCB Layout ................................................................................................................. 14
12 Transformer Design ....................................................................................................... 15
13 Experimental Results ..................................................................................................... 16
13.1 Non-Dimming Performance ..................................................................................... 16
13.2 Dimming Performance ........................................................................................... 17
13.3 Power Factor Performance ...................................................................................... 19
14 Circuit Operation With Rotary Forward Phase TRIAC Dimmer ..................................................... 20
15 Circuit Operation With Reverse Phase TRIAC Dimmer .............................................................. 21
16 Electromagnetic Interference (EMI) ..................................................................................... 22
17 Thermal Analysis .......................................................................................................... 24
18 Circuit Analysis and Explanations ....................................................................................... 26
18.1 Injecting Line Voltage into Filter-2 (Achieving PFC > 0.95) ................................................. 26
RMS
to
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 ............................................................................................... 9
6 Top View.................................................................................................................... 10
7 Bottom View................................................................................................................ 10
8 Efficiency vs. Line Voltage Original Circuit............................................................................. 11
9 Efficiency vs. Line Voltage Modified Circuits .......................................................................... 11
10 LED Current vs. Line Voltage Original Circuit ......................................................................... 11
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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 ..................................................................... 12
16 Power MOSFET Drain Voltage Waveform (VIN= 120V
17 Current Sense Waveform (VIN= 120V
18 FLTR2 Waveform (VIN= 120V
, 6 LEDs, I
RMS
, 6 LEDs, I
RMS
LED
= 350mA) ........................................................... 12
, 6 LEDs, I
RMS
= 350mA) .................................................. 12
LED
= 350mA)............................... 12
LED
19 Top Layer................................................................................................................... 14
20 Bottom Layer............................................................................................................... 14
21 LED Current vs. Input Voltage (using Dimmer) ....................................................................... 18
22 Current Harmonic Performance vs. EN/IEC61000-3-2 Class C Limits............................................. 19
23 Forward Phase Circuit at Full Brightness .............................................................................. 20
24 Forward Phase Circuit at 90° Firing Angle............................................................................. 20
25 Forward Phase Circuit at 150° Firing Angle ........................................................................... 20
26 Reverse Phase Circuit at Full Brightness .............................................................................. 21
27 Reverse Phase Circuit at 90° Firing Angle............................................................................. 21
28 Reverse Phase Circuit at 150° Firing Angle ........................................................................... 21
29 Input EMI Filter and Rectifier Circuit.................................................................................... 22
30 Peak Conductive EMI Scan per CISPR-22, Class B Limits.......................................................... 22
31 Peak Conductive EMI Scan with Additional 33nF of Input Capacitance........................................... 23
32 Top Side Thermal Scan .................................................................................................. 24
33 Bottom Side Thermal Scan............................................................................................... 25
34 Line Voltage Injection Circuit............................................................................................. 26
35 FLTR2 Waveform with No Dimmer ..................................................................................... 26
36 Typical Operation of FLTR2 Pin ........................................................................................ 27
List of Tables
1 Pin Description 10 Pin VSSOP............................................................................................ 7
2 Wiring Connection .......................................................................................................... 9
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
2
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver SNVA429C–August 2010–Revised May 2013
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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
• 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
3 Applications
• Retro-fit TRIAC Dimming
• Solid State Lighting
• Industrial and Commercial Lighting
• Residential Lighting
Introduction
4 Performance Specifications
Based on an LED Vf= 3.4V
Symbol Parameter Min Typ Max
V
IN
V
OUT
I
LED
P
OUT
f
sw
Input voltage 90 V
LED string voltage 13 V 20 V 27 V
LED string average current - 365 mA -
Output power - 7.3 W -
Switching frequency - 78.5 kHz -
RMS
120 V
RMS
135 V
RMS
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Input Voltage (V
rms
)
I
LED
(mA)
400
320
240
160
80
0
10 32 54 76 98 120
Performance Specifications
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Figure 1. Demo Board
4
AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver SNVA429C–August 2010–Revised May 2013
Figure 2. LED Current vs. Input Voltage (using Dimmer)
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LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
5 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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R15
C11
FLTR2
R2
R7
DIM
R9
C14
R1
R3
D7
Q1
R8
ASNS
FLTR1
DIM
COFF
FLTR2
BLDR
VCC
GND
GATE
ISNS
LM3445
1
2
3
4
5
10
9
8
7
6
V+
C7 C8
V
CC
R22 D8
R12
R13 R14
+
VLED+
VLED±
L1
C5
R4
V+
LINE
NEUTRAL
INPUT EMI FILTER AND RECTIFIER CIRCUIT
Q2
D1
D3
D4
D5C3
C4
DIM
V
CC
FLTR2
R11
C10
R10
TRIAC HOLDING
CIRCUIT
R16
C12
Q3
Q4
R20
C1
D6
C6
L2
R6
R24
C9
R5
C2
RT1
D2
F1
T1
C13
+
LM3445 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
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AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver SNVA429C–August 2010–Revised May 2013
Figure 3. Demo Board Schematic
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1
4
3
2
10
7
8
9
I
SNS
FLTR1
GATE
BLDR
COFF
V
CC
ASNS
DIM
5 6FLTR2 GND
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6 LM3445 Device Pin-Out
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
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
3 DIM Input/output dual function dim pin. This pin can be driven with an external PWM signal to dim the LEDs. It may
4 COFF OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant
5 FLTR2 Second filter input. A capacitor tied to this pin filters the PWM dimming signal to supply a DC voltage to control
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
8 GATE Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
9 V
10 BLDR Bleeder pin. Provides the input signal to the angle detect circuitry as well as a current path through a switched
to the TRIAC dimmer on-time.
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.
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.
OFF time of the switching controller.
the LED current. Could also be used as an analog dimming input.
maximum LED current.
controller.
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
CC
230Ω resistor to ensure proper firing of the TRIAC dimmer.
LM3445 Device Pin-Out
Figure 4. LM3445 Device Pin-Out
Table 1. Pin Description 10 Pin VSSOP
7 Bill of Materials
Designator Description Manufacturer Part Number
AA1 Printed Circuit Board - 551600457-001A
C1 CAP .047UF 630V METAL POLYPRO EPCOS Inc B32559C6473K000
C2 CAP 10000PF X7R 250VAC X2 2220 Murata Electronics North America GA355DR7GB103KY02L
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, Kemet C0805C104K4RACTU
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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
0805
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Bill of Materials
Designator Description Manufacturer Part Number
J1, J2, J3, J4, 16 GA WIRE HOLE, 18 GA WIRE HOLE 3M 923345-02-C
TP8, TP9, TP10
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
TP2-TP5 Terminal, Turret, TH, Double Keystone Electronics 1502-2
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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
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
R9 RES 100K OHM 1/10W 1% 0603 SMD Vishay-Dale CRCW0603100KFKEA
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 Cantherm MF72-060D5
20%
T1 Transformer Wurth Electronics 750311553 Rev. 01
TP7 TEST POINT ICT - -
U1 TRIAC Dimmable Offline LED Driver, Texas Instruments LM3445
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AN-2034 LM3445 -120VAC, 8W Isolated Flyback LED Driver SNVA429C–August 2010–Revised May 2013
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LED +
LED -
LINE
NEUTRAL
J5
J6
TP3
TP2
TP4
TP5
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8 Demo Board Wiring Overview
Figure 5. Wiring Connection Diagram
Test Name I/O Description
Point
TP3 LED + Output LED Constant Current Supply
TP2 LED - Output LED Return Connection (not GND)
TP4 LINE Input AC Line Voltage
TP5 NEUTRAL Input AC Neutral
Demo Board Wiring Overview
Table 2. Wiring Connection
Supplies voltage and constant-current to anode of LED string.
Connects to cathode of LED string. Do NOT connect to GND.
Connects directly to AC line or output of TRIAC dimmer of a 120VAC system.
Connects directly to AC neutral of a 120VAC system.
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