Texas Instruments Incorporated LM3445 Application Note

LM3445

Application Note 2069 LM3445 - 230VAC, 6W- 15W Isolated Flyback LED Driver

Literature Number: SNVA447B

LM3445 - 230VAC, 6W- 15W Isolated Flyback LED Driver AN-2069

LM3445 - 230VAC, 6W- 15W
Isolated Flyback LED Driver

Introduction

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 10 series con­nected LEDs from an 180 V
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 LM3445 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.

Performance Specifications

to 265 V

RMS

, 50 Hz input

RMS

National Semiconductor
Application Note 2069
Montu Doshi
November 23, 2010

Key Features

•

Drop-in compatibility with TRIAC dimmers

•

Line injection circuitry enables PFC values greater than

0.94

•

Adjustable LED current and switching frequency

•

Flicker free operation

Applications

•

Retro-fit TRIAC Dimming

•

Solid State Lighting

•

Industrial and Commercial Lighting

•

Residential Lighting

Based on an LED Vf = 3.4V

Symbol Parameter Min Typ Max

V

IN

V

OUT

I

LED

P

OUT

f

sw

Input voltage 180 V

LED string voltage 13 V 20 V 27 V

LED string average current - 350 mA -

Output power - 7.2 W -

Switching frequency - 67 kHz -

Demo Board

30126904

RMS

230 V

RMS

Dimming Characteristics

265 V

RMS

30126924

© 2010 National Semiconductor Corporation 301269 www.national.com

LM3445 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic

AN-2069

Warning:

Warning:

Warning:

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The LM3445 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.

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 evaliation board
(using 1:1 isolation line isolation transformer) rather than the oscilloscope is highly recommended.

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.

30126901

LM3445 Device Pin-Out

30126902

Pin Description 10 Pin MSOP

Pin # Name Description

1 ASNS PWM output of the triac dim 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 V

10 BLDR Bleeder pin. Provides the input signal to the angle detect circuitry as well as a current path through a switched

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.

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Bill of Materials

Designator Description Manufacturer Part Number RoHS

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AA1 Printed Circuit Board - Y

U1 Triac Dimmable Offline LED Driver, PowerWise National

Semiconductor

C1 Ceramic, X7R, 250VAC, 10% Murata Electronics

North America

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

C5 CAP, Film, 0.033µF, 630V, +/-10%, TH EPCOS Inc B32921C3333K Y

C6 CAP, CERM, 0.015µF, 500V, +/-10%, X7R, 1812 Vishay/Vitramon VJ1812Y223KBEAT4X Y

C7-DNP CAP, CERM, 0.1µF, 630V, +/-10%, X7R, 1812 MuRata GRM43DR72J104KW01L Y

C8 CAP, CERM, 0.1µF, 630V, +/-10%, X7R, 1812 MuRata GRM43DR72J104KW01L Y

C9, C11 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

C16 CAP, CERM, 0.47µF, 16V, +/-10%, X7R, 0603 MuRata GRM188R71C474KA88D Y

C17 CAP, CERM, 0.22µF, 16V, +/-10%, X7R, 0603 TDK C1608X7R1C224K 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

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

D5, D10 Diode, Zener, 13V, 200mW, SOD-323 Diodes Inc DDZ13BS-7 Y

D6 Diode, Zener, 36V, 550mW, SMB ON Semiconductor 1SMB5938BT3G Y

D7, D8, D9 Diode, Schottky, 100V, 150 mA, SOD-323 STMicroelectronics BAT46JFILM Y

F1 Fuse, 500mA, 250V, Time-Lag, SMT Littelfuse Inc 0443.500DR Y

H1, H2, H5, H6 Standoff, Hex, 0.5"L #4-40 Nylon Keystone 1902C Y

H3, H4, H7, H8 Machine Screw, Round, #4-40 x 1/4, Nylon, Philips

panhead

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,

LED+, LED-,

TP7, TP8

Q1 MOSFET, N-CH, 600V, 200mA, SOT-223 Fairchild

Q2 Transistor, NPN, 300V, 500mA, SOT-23 Diodes Inc. MMBTA42-7-F Y

Q3 MOSFET, N-CH, 650V, 800mA, IPAK Infineon

Q4 MOSFET N-CH 100V 170MA SOT23-3 Diodes Inc. BSS123-7-F Y

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

Terminal, 22 Gauge Wire, Terminal, 22 Guage Wire 3M 923345-02-C Y

AVX TPSC476K016R0350 Y

B&F Fastener Supply NY PMS 440 0025 PH Y

TDK Corporation TSL0808RA-472JR17-PF Y

Semiconductor

Technologies

LM3445MM Y

DE1E3KX332MA5BA01 Y

GA355DR7GF472KW01L Y

FQT1N60CTF_WS Y

SPU01N60C3 Y

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Designator Description Manufacturer Part Number RoHS

R4, R12 RES, 10k ohm, 5%, 0.25W, 1206 Vishay-Dale CRCW120610K0JNEA Y

R5-DNP RES, 680 ohm, 5%, 1W, 2512 Vishay/Dale CRCW2512680RJNEG Y

R6 RES, 820 ohm, 5%, 1W, 2512 Vishay/Dale CRCW2512820RJNEG Y

R10 RES, 430 ohm, 5%, 1W, 2512 Vishay/Dale CRCW2512430RJNEG Y

R11 RES, 49.9k ohm, 1%, 0.125W, 0805 Vishay-Dale CRCW080549K9FKEA 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

R16 RES, 280k ohm, 1%, 0.1W, 0603 Vishay-Dale CRCW0603280KFKEA Y

R17 RES, 475k ohm, 1%, 0.1W, 0603 Vishay-Dale CRCW0603475KFKEA Y

R18 RES, 49.9k ohm, 1%, 0.1W, 0603 Vishay-Dale CRCW060349K9FKEA 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, RT2 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

TP9, TP10 Terminal, Turret, TH, Double Keystone Electronics 1502-2 Y

VR1 Varistor 275V 55J 10mm DISC EPCOS Inc S10K275E2 Y

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Transformer Design

Mfg: Wurth Electronics, Part #: 750815040 Rev. 01

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Parameter Test Conditions Value

D.C. Resistance (3-1) 20°C

D.C. Resistance (6-4) 20°C

D.C. Resistance (10-13) 20°C

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%

1.91 Ω ± 10%

0.36 Ω ± 10%

0.12 Ω ± 10%

30126909

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Demo Board Wiring Overview

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Wiring Connection Diagram

Test Point Name I/O Description

TP8, TP10 LED + Output LED Constant Current Supply

Supplies voltage and constant-current to anode of LED string.

TP7, TP9 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 or output of TRIAC dimmer of a 230VAC system.

J1-2 NEUTRAL Input AC Neutral

Connects directly to AC neutral of a 230VAC system.

Demo Board Assembly

30126903

Top View

Bottom View

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30126905

30126906

Typical Performance Characteristics (Note 1, Note 2, Note 3)

180 190 200 210 220 230 240 250 260

0.76

0.77

0.78

0.79

0.80

0.81

0.82

0.83

EFFICIENCY

INPUT VOLTAGE (V

RMS

)

10 LEDs

8 LEDs

6 LEDs

4 LEDs

180 190 200 210 220 230 240 250 260

0.60

0.64

0.68

0.73

0.77

0.81

0.85

0.89

0.93

0.97

EFFICIENCY

INPUT VOLTAGE (V

RMS

)

Mod C (10 LEDs)

Mod B (8 LEDs)

Original (6 LEDs)

Mod A (4 LEDs)

180 190 200 210 220 230 240 250 260

50

150

250

350

450

550

650

LED CURRENT (mA)

INPUT VOLTAGE (V

RMS

)

4 LEDs

8 LEDs

10 LEDs

6 LEDs

180 190 200 210 220 230 240 250 260

100

150

200

250

300

350

400

450

500

550

600

LED CURRENT (mA)

INPUT VOLTAGE (V

RMS

)

Mod C (10 LEDs)

Mod B (8 LEDs)

Original (6 LEDs)

Mod A (4 LEDs)

180 190 200 210 220 230 240 250 260

0.920

0.924

0.928

0.932

0.936

0.940

0.944

0.948

0.952

0.956

POWER FACTOR

INPUT VOLTAGE (V

RMS

)

10 LEDs

8 LEDs

4 LEDs

6 LEDs

180 190 200 210 220 230 240 250 260

0.60

0.64

0.68

0.73

0.77

0.81

0.85

0.89

0.93

0.97

POWER FACTOR

INPUT VOLTAGE (V

RMS

)

Mod C (10 LEDs)

Mod B (8 LEDs)

Original (6 LEDs)

Mod A (4 LEDs)

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Efficiency vs. Line Voltage

Original Circuit

LED Current vs. Line Voltage

Original Circuit

30126910

Efficiency vs. Line Voltage

Modified Circuits

30126914

LED Current vs. Line Voltage

Modified Circuits

Power Factor vs. Line Voltage

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Original Circuit

30126911

30126912

30126915

Power Factor vs. Line Voltage

Modified Circuits

30126916

180 190 200 210 220 230 240 250 260

2

3

4

5

6

7

8

9

10

11

12

OUTPUT POWER (W)

LINE VOLTAGE (V

RMS

)

10 LEDs

8 LEDs

4 LEDs

6 LEDs

180 190 200 210 220 230 240 250 260

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

OUTPUT POWER (W)

INPUT VOLTAGE (V

RMS

)

Mod C (10 LEDs)

Mod B (8 LEDs)

Original (6 LEDs)

Mod A (4 LEDs)

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Output Power vs. Line Voltage

Original Circuit

Line Voltage and Line Current

(VIN = 230V

, 6 LEDs, I

RMS

LED

= 350mA)

30126913

Output Power vs. Line Voltage

Modified Circuits

Output Voltage and LED Current

(VIN = 230V

, 6 LEDs, I

RMS

= 350mA)

LED

30126917

Ch1: Line Voltage (100 V/div); Ch3: Line Current

(20 mA/div); Time (4 ms/div)

Power MOSFET Drain and ISNS (Pin-7) Voltage

(VIN = 230V

Ch1: Drain Voltage (100V/div); Ch4: ISNS Voltage

Note 1: 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

Note 2: The output power can be varied to acheive desired LED current by interpolating R14 values between the maximum of 3.9 Ω and minimum of 1.8 Ω

Note 3: The maximum output voltage is clamped to 36 V. For operating LED string voltage > 36 V, replace D6 with suitable alternative

(500 mV/div); Time (4 µs/div)

, 6 LEDs, I

RMS

LED

= 350mA)

30126918

30126921

Ch1: Output Voltage (10 V/div); Ch3: LED Current

(100 mA/div); Time (4 ms/div)

FLTR2 (Pin-5) and ISNS (Pin-7) Voltage

(VIN=230V

, 6 LEDs, I

RMS

= 350mA

LED

Ch1: FLTR2 Voltage (200 mV/div); ISNS Voltage

(200 mV/div); Time (4 µs/div)

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30126920

30126922

PCB Layout

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Top Layer

Bottom Layer

30126907

30126908

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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.

NON-DIMMING PERFORMANCE

In steady state, the LED string voltage is measured to be 20.5
V and the average LED current is measured as 350 mA. The

measured to be 194 mA
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 67 kHz. The circuit operates with a constant
duty cycle of 0.21 and consumes near 8.75 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 the following table.

at full load. The magnitude of the

pk-pk

100 Hz current ripple flowing through the LED string was

MEASURED EFFICIENCY AND LINE REGULATION (6 LEDS, NO TRIAC DIMMER)

VIN (V

) IIN (mA

RMS

) PIN(W) V

RMS

(V) I

OUT

(mA) P

LED

(W) Efficiency (%) Power Factor

OUT

180 31.73 5.35 19.67 221.64 4.36 81.4 0.9375

190 33.39 5.96 19.85 244.82 4.86 81.5 0.9394

200 35.11 6.61 20.04 269.16 5.39 81.6 0.9493

210 36.85 7.30 20.22 294.82 5.96 81.6 0.9493

220 38.53 8.01 20.40 321.26 6.55 81.8 0.9451

230 40.18 8.75 20.56 348.70 7.17 82.0 0.9463

240 41.75 9.50 20.74 375.70 7.79 82.0 0.9477

250 43..39 10.30 20.90 404.82 8.46 82.1 0.9490

260 45.07 11.14 21.05 434.48 9.15 82.0 0.9500

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

MEASURED DIMMING PERFORMANCE

VIN (V

) VO (V) I

RMS

229.39 20.51 343.1 7.04

220.47 20.35 320.8 6.53

210.24 20.16 294.8 5.94

199.05 19.98 266.8 5.33

190.32 19.80 245.8 4.87

180.33 19.61 222.7 4.37

170.51 19.42 200.1 3.89

156.39 19.31 187.4 3.62

149.11 19.15 171.6 3.29

140.35 18.97 154.0 2.92

129.61 18.75 133.1 2.50

119.7 18.53 115.3 2.14

110.17 18.33 99.1 1.82

100.55 18.11 83.5 1.51

90.75 17.87 68.8 1.23

79.72 17.59 53.1 0.93

70.42 17.34 40.8 0.71

60.91 17.08 30.1 0.81

49.94 16.77 19.8 0.33

45.04 16.64 16.0 0.27

TRIAC dimmer and measuring the corresponding input and
output parameters, the dimming performance of the demon­stration board driving 6 LEDs is summarized in the table
below.

(mA) P

LED

OUT

(W)

11 www.national.com

AN-2069

CURRENT THD

Dimming Characteristics

The LED driver is able to achieve close to unity power factor
(P.F. ~ 0.94) which meets Energy Star requirements. This
design also exhibits low current harmonics as a percentage

Current Harmonic vs. EN/IEC61000-3-2 Class C Limits

30126924

of the fundamental current (as shown in the following figure)
and therefore meets the requirements of the IEC 61000-3-2
Class-3 standard.

30126923

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Circuit Operation With Rotary Forward Phase Triac Dimmer

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Input waveforms at full brightness setting

Ch1: Input Voltage (100 V/div); Ch3: Input Current

30126925

(20 mA/div); Time (4 ms/div)

Input waveforms at half brightness setting (90° firing angle)

Output waveforms at full brightness setting

Ch1: Output Voltage (10 V/div); LED Current

30126928

(100 mA/div); Time (4 ms/div)

Output waveforms at half brightness setting (90° firing angle)

Ch1: Input Voltage (100 V/div); Ch3: Input Current

30126926

(20 mA/div); Time (4 ms/div)

Input waveforms at minimum brightness setting

Ch1: Input Voltage (100 V/div); Ch3: Input Current

30126927

(20 mA/div); Time (4 ms/div)

Ch1: Output Voltage (10 V/div); LED Current

30126929

(100 mA/div); Time (4 ms/div)

Output waveforms at minimum brightness setting

Ch1: Output Voltage (10 V/div); LED Current

30126930

(100 mA/div); Time (4 ms/div)

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Electromagnetic Interference (EMI)

The EMI input filter of this evaluation board is configured as

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shown in the following circuit diagram.

FIGURE 1. Input EMI Filter and Rectifier Circuit

30126931

In order to get a quick estimate of the EMI filter performance,
only the PEAK conductive EMI scan was measured and the

FIGURE 2. Peak Conductive EMI scan per CISPR-22, Class B Limits

Note 4: CISPR 15 compliance pending

data was compared to the Class B conducted EMI limits pub­lished in FCC – 47, section 15.(Note 4)

30126932

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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 V

RMS

I

= 348 mA

LED

# of LEDs = 6
P

= 7.2 W

OUT

The results are shown in the following figures.

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FIGURE 3. Top Side Thermal Scan

30126933

FIGURE 4. Bottom Side Thermal Scan

15 www.national.com

30126934

Circuit Analysis and Explanations

INJECTING LINE VOLTAGE INTO FILTER-2 (ACHIEVING

AN-2069

PFC > 0.94)

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 5.

FIGURE 5. Line Voltage Injection Circuit

The LM3445 works as a constant off-time controller normally,
but by injecting the 1.0VPk rectified AC voltage into the FLTR2

30126935

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 6 on it with no
triac dimmer in-line. Voltage at V
below 1.25V. At 1.25V current limit is tripped. C11 is small

peak should be kept

FLTR2

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 7 how (by adding the rectified voltage)
the on-time is adjusted.

30126937

FIGURE 6. FLTR2 Waveform with No Dimmer

For this evaluation board, the following resistor values are
used:

R3 = R8 = 309 kΩ
R20 = 1.91 kΩ
Therefore the voltages observed on the FLTR2 pin will be as

follows for listed input voltages:
For VIN = 180V
For VIN = 230V
For VIN = 265V

RMS

RMS

RMS

, V

FLTR2, Pk

, V

FLTR2, Pk

, V

FLTR2, Pk

= 0.78V
= 1.00V
= 1.15V

Using this technique, a power factor greater than 0.94 can be
achieved without additional passive active power factor con­trol (PFC) circuitry.

FIGURE 7. Typical Operation of FLTR2 Pin

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30126936

Notes

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17 www.national.com

Notes

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Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns

Data Converters www.national.com/adc Samples www.national.com/samples

Interface www.national.com/interface Eval Boards www.national.com/evalboards

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Power Management www.national.com/power Green Compliance www.national.com/quality/green

Switching Regulators www.national.com/switchers Distributors www.national.com/contacts

LDOs www.national.com/ldo Quality and Reliability www.national.com/quality

LED Lighting www.national.com/led Feedback/Support www.national.com/feedback

Voltage References www.national.com/vref Design Made Easy www.national.com/easy

PowerWise® Solutions www.national.com/powerwise Applications & Markets www.national.com/solutions

Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero

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Products Applications

Audio www.ti.com/audio Communications and Telecom www.ti.com/communications
Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers
Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps
DLP® Products www.dlp.com Energy and Lighting www.ti.com/energy
DSP dsp.ti.com Industrial www.ti.com/industrial
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Interface interface.ti.com Security www.ti.com/security
Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense
Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive
Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video
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