Texas Instruments Incorporated AN-2097 User's Guide

AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED

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 V to 265 V 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

• Line injection circuitry enables PFC values greater than 0.98

• Adjustable LED current and switching frequency

• Flicker free operation

, 50 Hz input power supply. The key performance characteristics under typical operating

RMS

User's Guide

SNVA462F–November 2010–Revised May 2013

Driver

RMS

3 Applications

• Solid State Lighting

• Industrial and Commercial Lighting

• Residential Lighting

4 Performance Specifications

Based on an LED Vf= 3.6V

Symbol Parameter Min Typ Max

OUT

LED

OUT

Input voltage 180 V

LED string voltage 13 V 21.5 V 36 V

LED string average current - 350 mA -

Output power - 7.5 W -

Switching frequency - 67 kHz -

RMS

230 V

RMS

265 V

RMS

PowerWise is a trademark of Texas Instruments. All other trademarks are the property of their respective owners.

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FILTER

VCC

COFF

FILTER

VCC

GATE

ISNS

GND

V+

LED +

LED ±

LINE

NEUTRAL

V+

VR1

RT1

C4 C5

R12

INPUT EMI FILTER AND RECTIFIER

R3R8R2

R13

C10

C11

C12

R14

C13

R15

D10

C15C14

C18R20

R19

R22 R21

R23

C20

PGND SGND

LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic

Figure 1. Demo Board

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5 LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic

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LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic

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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SNS

GATE

COFF

5 6FILTER GND

LM3444 Device Pin-Out

6 LM3444 Device Pin-Out

7 Pin Descriptions – 10 Pin VSSOP

Pin # Name Description

1 NC No internal connection. 2 NC No internal connection. 3 NC No internal connection. 4 COFF OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant

5 FILTER Filter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming

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 NC No internal connection.

OFF time of the switching controller.

input.

maximum LED current.

controller. Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.

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8 Bill of Materials

Designator Description Manufacturer Part Number RoHS

AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver SNVA462F–November 2010–Revised May 2013

U1 Offline LED Driver, PowerWise™ Texas Instruments LM3444 Y C1 Ceramic, X7R, 250VAC, 10% Murata Electronics 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 GA355DR7GF472KW01L Y

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

SMD

North America

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Bill of Materials

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 CGRM4007-G Y

Technology

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 B&F Fastener NY PMS 440 0025 PH Y

panhead Supply J1, J2 Conn Term Block, 2POS, 5.08mm PCB Phoenix Contact 1715721 Y L1, L2 Inductor, Radial Lead Inductors, Shielded, 4.7mH, TDK Corporation TSL080RA-472JR13-PF Y

130mA, 12.20ohm, 7.5mm Radial,

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

TP7, TP8

Q1 MOSFET, N-CH, 600V, 200mA, SOT-223 Fairchild FQT1N60CTF_WS Y

Semiconductor Q2 Transistor, NPN, 300V, 500mA, SOT-23 Diodes Inc. MMBTA42-7-F Y Q3 MOSFET, N-CH, 650V, 800mA, IPAK Infineon SPU01N60C3 Y

Technologies 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

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

Electronics

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

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Transformer Design

9 Transformer Design

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

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Parameter Test Conditions Value

D.C. Resistance (3-1) 20°C 1.91 Ω ± 10% D.C. Resistance (6-4) 20°C 0.36 Ω ± 10%

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%

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TP9

TP10

LED -

LED +

LINE

NEUTRAL

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10 Demo Board Wiring Overview

Figure 2. Wiring Connection Diagram

Test Name I/O Description

Point

TP10, J2- LED + Output LED Constant Current Supply

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

TP9, J2-2 LED - Output LED Return Connection (not GND)

J1-1 LINE Input AC Line Voltage

J1-2 NEUTRAL Input AC Neutral

Demo Board Wiring Overview

Connects to cathode of LED string. Do NOT connect to GND.

Connects directly to AC line of a 230VAC system.

Connects directly to AC neutral of a 230VAC system.

11 Demo Board Assembly

Figure 3. Top View

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Demo Board Assembly

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Figure 4. Bottom View

AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver SNVA462F–November 2010–Revised May 2013

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180 190 200 210 220 230 240 250 260

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

0.78

0.80

0.82

0.85

0.87

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 B (8 LEDs)

Mod C (10 LEDs)

Mod A (4 LEDs)

Original (6 LEDs)

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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

Typical Performance Characteristics

Figure 5. Efficiency vs. Line Voltage Figure 6. Efficiency vs. Line Voltage

Original Circuit Modified Circuits

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Figure 7. LED Current vs. Line Voltage Figure 8. LED Current vs. Line Voltage

Original Circuit Modified Circuits

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)

180 190 200 210 220 230 240 250 260

0.950

0.955

0.960

0.965

0.970

0.975

0.980

0.985

0.990

0.995

1.000

POWER FACTOR

INPUT VOLTAGE (V

RMS

)

180 190 200 210 220 230 240 250 260

OUTPUT POWER (W)

LINE VOLTAGE (V

RMS

)

10 LEDs

8 LEDs 4 LEDs

6 LEDs

Typical Performance Characteristics

Figure 9. Power Factor vs. Line Voltage Figure 10. Output Power vs. Line Voltage

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Original Circuit

AN-2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver SNVA462F–November 2010–Revised May 2013

Figure 11. Output Power vs. Line Voltage

Modified Circuits

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Typical Performance Characteristics

Line Voltage and Line Current Output Voltage and LED Current

(VIN= 230V

, 6 LEDs, I

RMS

= 350mA) (VIN= 230V

LED

, 6 LEDs, I

RMS

= 350mA)

LED

Figure 12. Ch1: Line Voltage (100 V/div); Figure 13. Ch1: Output Voltage (10 V/div);

Ch3: Line Current Ch3: LED Current

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

Power MOSFET Drain and ISNS (Pin-7) Voltage FILTER (Pin-5) and ISNS (Pin-7) Voltage

(VIN= 230V

, 6 LEDs, I

RMS

= 350mA) (VIN=230V

LED

, 6 LEDs, I

RMS

= 350mA

LED

Figure 14. Ch1: Drain Voltage (100V/div); Figure 15. Ch1: FILTER Voltage (200 mV/div);

Ch4: ISNS Voltage ISNS Voltage

(500 mV/div); Time (4 µs/div) (200 mV/div); Time (4 µs/div)

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PCB Layout

13 PCB Layout

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Figure 16. Top Layer

Figure 17. Top Middle Layer

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Experimental Results

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

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 mA 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.

VIN(V

at full load. The magnitude of the ripple is a function of the value of energy storage capacitors

pk-pk

) IIN(mA

RMS

180 30.65 5.42 20.59 219.40 4.52 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

Table 1. Measured Efficiency and Line Regulation (6 LEDS)

) PIN(W) V

RMS

(V) I

OUT

(mA) P

LED

(W) Efficiency (%) Power Factor

OUT

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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

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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LINE

NEUTRAL

V+

VR1

RT1

C4 C5

R12

INPUT EMI FILTER AND RECTIFIER

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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.

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.

Electromagnetic Interference (EMI)

CISPR 15 compliance pending

Figure 21. Peak Conductive EMI scan per CISPR-22, Class B Limits

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Thermal Analysis

16 Thermal Analysis

The board temperature was measured using an IR camera (HIS-3000, Wahl) while running under the following conditions:

VIN= 230 V I

= 348 mA

LED

# of LEDs = 6 P

OUT

The results are shown in the following figures.

RMS

= 7.2 W

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Figure 22. Top Side Thermal Scan

Figure 23. Bottom Side Thermal Scan

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FILTER

R15 C11

FILTER

COFF

FILTER

VCC

GND

GATE

ISNS

LM3444

V+

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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.

Circuit Analysis and Explanations

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. ThereforePka 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 V

peak should be kept below 1.25V. At 1.25V current limit is tripped. C11

FILTER

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.

Figure 25. FILTER Waveform

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SNS

PWM

I-LIM

1.27V

SNS

PGND

FILTER

750 mV

125 ns

LEADING EDGE BLANKING

Nearly a constant ontime as the line varies

The PWM reference increases

as the line voltage increases.

As line voltage increases, the voltage across the

inductor increases, and the peak current increases.

D x LED Current

Circuit Analysis and Explanations

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 = 180V For VIN = 230V For VIN = 265V

RMS

, V , V , V

FILTER, Pk

Using this technique, a power factor greater than 0.98 can be achieved without additional passive active power factor control (PFC) circuitry.

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= 0.78V = 1.00V = 1.15V

Figure 26. Typical Operation of FILTER Pin

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Texas Instruments Incorporated AN-2097 User's Guide

Specifications and Main Features

Frequently Asked Questions

User Manual

1 Introduction

2 Key Features

3 Applications

4 Performance Specifications

5 LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic

6 LM3444 Device Pin-Out

7 Pin Descriptions – 10 Pin VSSOP

8 Bill of Materials

9 Transformer Design

10 Demo Board Wiring Overview

11 Demo Board Assembly

12 Typical Performance Characteristics

13 PCB Layout

14 Experimental Results

14.1 Performance

14.2 Current THD

15 Electromagnetic Interference (EMI)

16 Thermal Analysis

17 Circuit Analysis and Explanations

17.1 Injecting Line Voltage Into Filter (Achieving PFC > 0.98)