User's Guide
SNVA462F – November 2010 – Revised May 2013
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED
Driver
1
Introduction
This demonstration board highlights the performance of a LM3444 based Flyback LED driver solution that
can be used to power a single LED string consisting of 4 to 10 series connected LEDs from an 180 VRMS
to 265 VRMS, 50 Hz input power supply. The key performance characteristics under typical operating
conditions are summarized in this application note.
This is a four-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. Refer to the LM3444 datasheet for detailed instructions.
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
Line injection circuitry enables PFC values greater than 0.98
Adjustable LED current and switching frequency
Flicker free operation
Solid State Lighting
Industrial and Commercial Lighting
Residential Lighting
Performance Specifications
Based on an LED Vf = 3.6V
Symbol
Parameter
Min
Typ
Max
VIN
Input voltage
180 VRMS
230 VRMS
265 VRMS
VOUT
LED string voltage
13 V
21.5 V
36 V
ILED
LED string average current
-
350 mA
-
POUT
Output power
-
7.5 W
-
fsw
Switching frequency
-
67 kHz
-
PowerWise is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
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1
LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
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Figure 1. Demo Board
5
LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
C1
V+
R1
R3
1
C2
R2
T1
D1
C3
D3
10
R8
C10
R7
D7
R14
Q1
LED +
D4
3
13
C9
C12 +
C11
D6
6
R15
D8
D5
R13
LED ±
4
Q2
C13
D9
PGND
D10
SGND
VCC
C14
1 NC
NC 10
2 NC
VCC 9
3 NC
GATE 8
+
C15
R23
R19
4 COFF
ISNS 7
5 FILTER
GND 6
C20
FILTER
R20
R22
R21
C18
LINE
RT1
L1
D2
R4
V+
VR1
C4
C5
R12
NEUTRAL
L2
F1
INPUT EMI FILTER AND RECTIFIER
2
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LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
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WARNING
The LM3444 evaluation board has exposed high voltage
components that present a shock hazard. Caution must be taken
when handling the evaluation board. Avoid touching the evaluation
board and removing any cables while the evaluation board is
operating.
WARNING
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 the mains AC
power is applied (without any isolation), the fuse (F1) will fail open.
For bench evaluation, either the input AC power source or the
bench measurement equipment should be isolated from the earth
ground connection. Isolating the evaluation board (using 1:1 line
isolation transformer) rather than the oscilloscope is highly
recommended.
WARNING
The LM3444 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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3
LM3444 Device Pin-Out
6
7
8
LM3444 Device Pin-Out
NC
1
10 NC
NC
2
9 VCC
NC
3
8 GATE
COFF
4
7 ISNS
FILTER
5
6 GND
Pin Descriptions – 10 Pin VSSOP
Pin #
Name
1
NC
No internal connection.
2
NC
No internal connection.
3
NC
No internal connection.
4
COFF
5
FILTER
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
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
10
NC
No internal connection.
Description
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.
Filter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming
input.
Bill of Materials
Designator
Description
Manufacturer
Part Number
RoHS
U1
Offline LED Driver, PowerWise™
Texas Instruments
LM3444
Y
C1
Ceramic, X7R, 250VAC, 10%
Murata Electronics
North America
DE1E3KX332MA5BA01
Y
C2
Ceramic, Polypropylene, 400VDC, 10%
WIMA
MKP10-.033/400/5P10
Y
C3
CAP, CERM, 330pF, 630V, +/-5%, C0G/NP0, 1206
TDK
C3216C0G2J331J
Y
C4
Ceramic, X7R, 250V, X2, 10%, 2220
Murata Electronics
North America
GA355DR7GF472KW01L
Y
C5
CAP, Film, 0.033µF, 630V, +/-10%, TH
EPCOS Inc
B32921C3333K
Y
CAP, CERM, 1µF, 50V, +/-10%, X7R, 1210
MuRata
GRM32RR71H105KA01L
Y
C10
CAP, CERM, 0.47µF, 50V, +/-10%, X7R, 0805
MuRata
GRM21BR71H474KA88L
Y
C12
Aluminium Electrolytic, 680uF, 35V, 20%,
Nichicon
UHE1V681MHD6
Y
C13
CAP, CERM, 1µF, 35V, +/-10%, X7R, 0805
Taiyo Yuden
GMK212B7105KG-T
Y
C14
CAP, CERM, 0.1µF, 25V, +/-10%, X7R, 0603
MuRata
GRM188R71E104KA01D
Y
C15
CAP, TANT, 47uF, 16V, +/-10%, 0.35 ohm, 6032-28
SMD
AVX
TPSC476K016R0350
Y
C18
CAP, CERM, 2200pF, 50V, +/-10%, X7R, 0603
MuRata
GRM188R71H222KA01D
Y
C20
CAP, CERM, 330pF, 50V, +/-5%, C0G/NP0, 0603
MuRata
GRM1885C1H331JA01D
Y
D1
DIODE TVS 250V 600W UNI 5% SMD
Littelfuse
P6SMB250A
Y
C9, C11
4
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Bill of Materials
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Designator
Description
Manufacturer
Part Number
RoHS
D2
Diode, Switching-Bridge, 600V, 0.8A, MiniDIP
Diodes Inc.
HD06-T
Y
D3
Diode, Silicon, 1000V, 1A, SOD-123
Comchip
Technology
CGRM4007-G
Y
D4
Diode, Schottky, 100V, 1A, SMA
STMicroelectronics
STPS1H100A
Y
Diode, Zener, 13V, 200mW, SOD-323
Diodes Inc
DDZ13BS-7
Y
Diode, Zener, 36V, 550mW, SMB
ON Semiconductor
1SMB5938BT3G
Y
Diode, Schottky, 100V, 150 mA, SOD-323
STMicroelectronics
BAT46JFILM
Y
Fuse, 500mA, 250V, Time-Lag, SMT
D5, D10
D6
D7, D8, D9
Littelfuse Inc
0443.500DR
Y
H1, H2, H5, H6 Standoff, Hex, 0.5"L #4-40 Nylon
F1
Keystone
1902C
Y
H3, H4, H7, H8 Machine Screw, Round, #4-40 x 1/4, Nylon, Philips
panhead
B&F Fastener
Supply
NY PMS 440 0025 PH
Y
J1, J2
Conn Term Block, 2POS, 5.08mm PCB
Phoenix Contact
1715721
Y
L1, L2
Inductor, Radial Lead Inductors, Shielded, 4.7mH,
130mA, 12.20ohm, 7.5mm Radial,
TDK Corporation
TSL080RA-472JR13-PF
Y
Terminal, 22 Gauge Wire, Terminal, 22 Guage Wire
3M
923345-02-C
Y
Q1
MOSFET, N-CH, 600V, 200mA, SOT-223
Fairchild
Semiconductor
FQT1N60CTF_WS
Y
Q2
Transistor, NPN, 300V, 500mA, SOT-23
Diodes Inc.
MMBTA42-7-F
Y
Q3
MOSFET, N-CH, 650V, 800mA, IPAK
Infineon
Technologies
SPU01N60C3
Y
LED+, LED-,
TP7, TP8
R1
RES, 221 ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206221RFKEA
Y
R2, R7
RES, 200k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206200KFKEA
Y
R3, R8
RES, 309k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206309KFKEA
Y
R4, R12
RES, 10k ohm, 5%, 0.25W, 1206
Vishay-Dale
CRCW120610K0JNEA
Y
R13
RES, 33.0 ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW120633R0FKEA
Y
R14
RES, 10 ohm, 5%, 0.125W, 0805
Vishay-Dale
CRCW080510R0JNEA
Y
R15
RES, 10.0k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW060310K0FKEA
Y
R19
RES, 10 ohm, 5%, 0.1W, 0603
Vishay-Dale
CRCW060310R0JNEA
Y
R20
RES, 1.91k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW06031K91FKEA
Y
R21
RES, 2.70 ohm, 1%, 0.25W, 1206
Panasonic
ERJ-8RQF2R7V
Y
R22
RES, 10.7 ohm, 1%, 0.125W, 0805
Vishay-Dale
CRCW080510R7FKEA
Y
R23
RES, 324k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW0603324KFKEA
Y
RT1
Current Limitor Inrush, 60Ohm, 20%, 5mm Raidal
Cantherm
MF72-060D5
Y
T1
FLBK TFR, 2.07 mH, Np=140T, Ns=26T, Na= 20T
Wurth Elektornik
750815040 REV 1
Y
Terminal, Turret, TH, Double
Keystone
Electronics
1502-2
Y
Varistor 275V 55J 10mm DISC
EPCOS Inc
S10K275E2
Y
TP9, TP10
VR1
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Transformer Design
9
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Transformer Design
Mfg: Wurth Electronics, Part #: 750815040 Rev. 01
6
Parameter
Test Conditions
Value
D.C. Resistance (3-1)
20°C
1.91 Ω ± 10%
0.36 Ω ± 10%
D.C. Resistance (6-4)
20°C
D.C. Resistance (10-13)
20°C
0.12 Ω ± 10%
Inductance (3-1)
10 kHz, 100 mVAC
2.12 mH ± 10%
Inductance (6-4)
10 kHz, 100 mVAC
46.50 µH ± 10%
Inductance (10-13)
10 kHz, 100 mVAC
74.00 µH ± 10%
Leakage Inductance (3-1)
100 kHz, 100 mAVAC (tie 6+4, 10+13)
18.0 µH Typ., 22.60 µH Max.
Dielectric (1-13)
tie (3+4), 4500 VAC, 1 second
4500 VAC, 1 minute
Turns Ratio
(3-1):(6-4)
7:1 ± 1%
Turns Ratio
(3-1):(10:13)
5.384:1 ± 1%
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
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Demo Board Wiring Overview
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10
Demo Board Wiring Overview
TP9
J1
J2
LED -
LINE
NEUTRAL
LED +
TP10
Figure 2. Wiring Connection Diagram
11
Test
Point
Name
I/O
Description
TP10, J21
LED +
Output
LED Constant Current Supply
Supplies voltage and constant-current to anode of LED string.
TP9, J2-2
LED -
Output
LED Return Connection (not GND)
Connects to cathode of LED string. Do NOT connect to GND.
J1-1
LINE
Input
AC Line Voltage
Connects directly to AC line of a 230VAC system.
J1-2
NEUTRAL
Input
AC Neutral
Connects directly to AC neutral of a 230VAC system.
Demo Board Assembly
Figure 3. Top View
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Demo Board Assembly
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Figure 4. Bottom View
8
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
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Typical Performance Characteristics
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12
Typical Performance Characteristics
Original Circuit (6 LEDs operating at 350mA): R21 = 2.7Ω; Modification A (10 LEDs operating at 375mA):
R21 = 1.8Ω; Modification B (8 LEDs operating at 350mA): R21 = 2.2Ω; Modification C (4 LEDs operating
at 315mA): R21 = 3.9Ω
The output power can be varied to achieve desired LED current by interpolating R21 values between the
maximum of 3.9 Ω and minimum of 1.8 Ω
The maximum output voltage is clamped to 36 V. For operating LED string voltage > 36 V, replace D6
with suitable alternative
0.97
10 LEDs
0.87
8 LEDs
Mod B (8 LEDs)
0.89
0.85
6 LEDs
0.82
EFFICIENCY
EFFICIENCY
Mod C (10 LEDs)
0.93
0.85
0.81
0.77
Original (6 LEDs)
Mod A (4 LEDs)
0.73
4 LEDs
0.68
0.80
0.64
0.78
180 190 200 210 220 230 240 250 260
0.60
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
INPUT VOLTAGE (VRMS)
Figure 5. Efficiency vs. Line Voltage
Original Circuit
Figure 6. Efficiency vs. Line Voltage
Modified Circuits
600
650
Mod C (10 LEDs)
550
LED CURRENT (mA)
450
LED CURRENT (mA)
4 LEDs
550
6 LEDs
350
250
8 LEDs
150
10 LEDs
50
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
Figure 7. LED Current vs. Line Voltage
Original Circuit
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500
Mod B (8 LEDs)
450
400
350
300
250
Original (6 LEDs)
200
Mod A (4 LEDs)
150
100
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
Figure 8. LED Current vs. Line Voltage
Modified Circuits
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
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9
Typical Performance Characteristics
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12
0.995
11
0.990
10
POWER FACTOR
OUTPUT POWER (W)
1.000
0.985
0.980
0.975
0.970
0.965
10 LEDs
8 LEDs
9
4 LEDs
8
7
6 LEDs
6
5
0.960
4
0.955
3
0.950
180 190 200 210 220 230 240 250 260
2
180 190 200 210 220 230 240 250 260
LINE VOLTAGE (VRMS)
INPUT VOLTAGE (VRMS)
Figure 9. Power Factor vs. Line Voltage
Figure 10. Output Power vs. Line Voltage
Original Circuit
25.0
OUTPUT POWER (W)
22.5
20.0
Mod B (8 LEDs)
17.5
15.0
Mod C (10 LEDs)
12.5
10.0
7.5
5.0
2.5
Mod A (4 LEDs)
Original (6 LEDs)
0.0
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
Figure 11. Output Power vs. Line Voltage
Modified Circuits
10
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Typical Performance Characteristics
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Line Voltage and Line Current
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
Output Voltage and LED Current
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
Figure 12. Ch1: Line Voltage (100 V/div);
Ch3: Line Current
(20 mA/div); Time (4 ms/div)
Figure 13. Ch1: Output Voltage (10 V/div);
Ch3: LED Current
(100 mA/div); Time (4 ms/div)
Power MOSFET Drain and ISNS (Pin-7) Voltage
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
FILTER (Pin-5) and ISNS (Pin-7) Voltage
(VIN=230VRMS, 6 LEDs, ILED = 350mA
Figure 14. Ch1: Drain Voltage (100V/div);
Ch4: ISNS Voltage
(500 mV/div); Time (4 µs/div)
Figure 15. Ch1: FILTER Voltage (200 mV/div);
ISNS Voltage
(200 mV/div); Time (4 µs/div)
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PCB Layout
13
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PCB Layout
Figure 16. Top Layer
Figure 17. Top Middle Layer
12
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Experimental Results
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Figure 18. Bottom Middle Layer
Figure 19. Bottom Layer
14
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.
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Experimental Results
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14.1 Performance
In steady state, the LED string voltage is measured to be 21.55 V and the average LED current is
measured as 347.5 mA. The 100 Hz current ripple flowing through the LED string was measured to be
194 mApk-pk at full load. The magnitude of the ripple is a function of the value of energy storage capacitors
connected across the output. The ripple current can be reduced by increasing the value of energy storage
capacitor or by increasing the LED string voltage.
The LED driver switching frequency is measured to be close to the specified 67 kHz. The circuit operates
with a constant duty cycle of 0.21 and consumes near 9W of input power. The driver steady state
performance for an LED string consisting of 6 series LEDs is summarized in the following table.
Table 1. Measured Efficiency and Line Regulation (6 LEDS)
VIN (VRMS)
IIN (mARMS)
PIN(W)
VOUT (V)
ILED (mA)
POUT (W)
180
30.65
5.42
20.59
219.40
4.52
Efficiency (%) Power Factor
83.3
0.9867
190
32.35
6.06
20.80
242.55
5.05
83.3
0.9869
200
34.21
6.75
21.00
267.37
5.62
83.2
0.9870
210
36.01
7.47
21.18
293.39
6.21
83.2
0.9871
220
37.74
8.20
21.37
320.18
6.84
83.3
0.9872
230
39.44
8.96
21.55
347.51
7.49
83.6
0.9873
240
41.22
9.76
21.72
375.52
8.15
83.6
0.9874
250
43..29
10.62
21.90
404.82
8.86
83.5
0.9875
260
45.06
11.57
22.07
436.75
9.64
83.3
0.9877
14.2 Current THD
The LED driver is able to achieve close to unity power factor (PF ~ 0.98) which meets Energy Star
requirements. This design also exhibits low current harmonics as a percentage of the fundamental current
(as shown in the following table) and therefore meets the requirements of the IEC 61000-3-2 Class-3
standard. Total harmonic distortion was measured to be less than 1.2%.
Table 2. Measured Harmonic Current
14
Harmonic
Class C Limit (mA)
Measured (mA)
2
0.78
0.022
3
11.61
0.125
5
3.90
0.11
7
2.73
0.105
9
1.95
0.11
11
1.73
0.15
13
1.73
0.093
15
1.73
0.071
17
1.73
0.154
19
1.73
0.165
21
1.73
0.065
23
1.73
0.065
25
1.73
0.08
27
1.73
0.084
29
1.73
0.065
31
1.73
0.07
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Electromagnetic Interference (EMI)
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15
Electromagnetic Interference (EMI)
The EMI input filter of this evaluation board is configured as shown in the following circuit diagram.
LINE
RT1
L1
D2
R4
V+
VR1
C4
C5
R12
NEUTRAL
F1
L2
INPUT EMI FILTER AND RECTIFIER
Figure 20. 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.
CISPR 15 compliance pending
Figure 21. Peak Conductive EMI scan per CISPR-22, Class B Limits
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Thermal Analysis
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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 = 230 VRMS
ILED = 348 mA
# of LEDs = 6
POUT = 7.2 W
The results are shown in the following figures.
Figure 22. Top Side Thermal Scan
Figure 23. Bottom Side Thermal Scan
16
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Circuit Analysis and Explanations
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17
Circuit Analysis and Explanations
17.1 Injecting Line Voltage Into Filter (Achieving PFC > 0.98)
If a small portion (750mV to 1.00V) of line voltage is injected at FILTER of the LM3444, the circuit is
essentially turned into a constant power flyback as shown in Figure 24.
V+
R2
LM3444
NC
NC 10
2 NC
VCC 9
3 NC
GATE 8
4 COFF
ISNS
7
5 FILTER
GND
6
1
R7
COFF
FILTER
R15
C11
Figure 24. Line Voltage Injection Circuit
The LM3444 works as a constant off-time controller normally, but by injecting the 1.0V rectified AC voltage
into the FILTER pin, the on-time can be made to be constant. With a DCM Flyback, Δi needs to increase
as the input voltage line increases. ThereforePk a constant on-time (since inductor L is constant) can be
obtained.
By using the line voltage injection technique, the FILTER pin has the voltage wave shape shown in
Figure 25 on it. Voltage at VFILTER 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 26 how (by adding the
rectified voltage) the on-time is adjusted.
VFILTER
t
Figure 25. FILTER Waveform
SNVA462F – November 2010 – Revised May 2013
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AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
Copyright © 2010–2013, Texas Instruments Incorporated
17
Circuit Analysis and Explanations
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For this evaluation board, the following resistor values are used:
R3 = R8 = 309 kΩ
R20 = 1.91 kΩ
Therefore the voltages observed on the FILTER pin will be as follows for listed input voltages:
For VIN = 180VRMS, VFILTER, Pk = 0.78V
For VIN = 230VRMS, VFILTER, Pk = 1.00V
For VIN = 265VRMS, VFILTER, Pk = 1.15V
Using this technique, a power factor greater than 0.98 can be achieved without additional passive active
power factor control (PFC) circuitry.
As line voltage increases, the voltage across the
inductor increases, and the peak current increases.
750 mV
1M
Nearly a constant ontime as the line varies
PWM
I-LIM
D x LED Current
1.27V
1k
ISNS
1V
1V
LEADING EDGE BLANKING
FILTER
The PWM reference increases
as the line voltage increases.
PGND
RSNS
125 ns
CFILTER
Figure 26. Typical Operation of FILTER Pin
18
AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
SNVA462F – November 2010 – Revised May 2013
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Copyright © 2010–2013, Texas Instruments Incorporated
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