National Semiconductor Application Note 2097 Clinton Jensen May 3, 2011 Introduction Key Features 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. • • • Line injection circuitry enables PFC values greater than 0.98 Adjustable LED current and switching frequency Flicker free operation Applications • • • 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 - LM3444 - 230VAC, 8W Isolated Flyback LED Driver LM3444 - 230VAC, 8W Isolated Flyback LED Driver Demo Board AN-2097 30139704 © 2011 National Semiconductor Corporation 301397 www.national.com AN-2097 LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic 30139701 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 evaliation 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. www.national.com 2 AN-2097 LM3444 Device Pin-Out 30139702 Pin Descriptions – 10 Pin MSOP Pin # Name Description 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. 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. 3 www.national.com AN-2097 Bill of Materials Designator Description Manufacturer Part Number RoHS U1 Offline LED Driver, PowerWise National Semiconductor LM3444MM 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 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 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 B&F Fastener Supply NY PMS 440 0025 PH Y C9, C11 D5, D10 D6 D7, D8, D9 F1 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 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 LED+, LED-, TP7, TP8 www.national.com 4 Description Manufacturer Part Number RoHS 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 Y TP9, TP10 VR1 5 S10K275E2 www.national.com AN-2097 Designator AN-2097 Transformer Design Mfg: Wurth Electronics, Part #: 750815040 Rev. 01 30139709 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 Inductance (3-1) 10 kHz, 100 mVAC 0.12 Ω ± 10% 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 www.national.com Turns Ratio (3-1):(6-4) 7:1 ± 1% Turns Ratio (3-1):(10:13) 5.384:1 ± 1% 6 AN-2097 Demo Board Wiring Overview 30139703 Wiring Connection Diagram Test Point Name I/O Description TP10, J2-1 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 30139705 Top View 30139706 Bottom View 7 www.national.com (Note 1, Note 2, Note 3) Efficiency vs. Line Voltage Original Circuit Efficiency vs. Line Voltage Modified Circuits 0.97 10 LEDs 0.93 8 LEDs EFFICIENCY EFFICIENCY 0.87 0.85 6 LEDs 0.82 0.89 Mod C (10 LEDs) Mod B (8 LEDs) 0.85 0.81 0.77 0.73 4 LEDs 0.80 Original (6 LEDs) Mod A (4 LEDs) 0.68 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) 30139710 30139714 LED Current vs. Line Voltage Original Circuit LED Current vs. Line Voltage Modified Circuits 600 650 LED CURRENT (mA) 450 550 4 LEDs 550 LED CURRENT (mA) AN-2097 Typical Performance Characteristics 6 LEDs 350 250 8 LEDs 150 450 Mod B (8 LEDs) 400 350 300 250 200 150 10 LEDs Original (6 LEDs) Mod A (4 LEDs) 100 180 190 200 210 220 230 240 250 260 50 180 190 200 210 220 230 240 250 260 INPUT VOLTAGE (VRMS) INPUT VOLTAGE (VRMS) 30139711 www.national.com 500 Mod C (10 LEDs) 30139715 8 AN-2097 Power Factor vs. Line Voltage Output Power vs. Line Voltage Original Circuit 1.000 12 0.995 11 0.990 POWER FACTOR OUTPUT POWER (W) 0.985 0.980 0.975 0.970 0.965 0.960 10 9 8 10 LEDs 8 LEDs 4 LEDs 7 6 LEDs 6 5 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) 30139713 30139712 Output Power vs. Line Voltage Modified Circuits Line Voltage and Line Current (VIN = 230VRMS, 6 LEDs, ILED = 350mA) 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 30139718 Ch1: Line Voltage (100 V/div); Ch3: Line Current (20 mA/div); Time (4 ms/div) INPUT VOLTAGE (VRMS) 30139717 Output Voltage and LED Current (VIN = 230VRMS, 6 LEDs, ILED = 350mA) Power MOSFET Drain and ISNS (Pin-7) Voltage (VIN = 230VRMS, 6 LEDs, ILED = 350mA) 30139720 30139721 Ch1: Output Voltage (10 V/div); Ch3: LED Current (100 mA/div); Time (4 ms/div) Ch1: Drain Voltage (100V/div); Ch4: ISNS Voltage (500 mV/div); Time (4 µs/div) 9 www.national.com AN-2097 FILTER (Pin-5) and ISNS (Pin-7) Voltage (VIN=230VRMS, 6 LEDs, ILED = 350mA 30139722 Ch1: FILTER Voltage (200 mV/div); ISNS Voltage (200 mV/div); Time (4 µs/div) 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 achieve desired LED current by interpolating R21 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 PCB Layout 30139707 Top Layer www.national.com 10 AN-2097 30139740 Top Middle Layer 30139741 Bottom Middle Layer 11 www.national.com AN-2097 30139708 Bottom Layer www.national.com 12 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. 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 MEASURED EFFICIENCY AND LINE REGULATION (6 LEDS) VIN (VRMS) IIN (mARMS) PIN(W) VOUT (V) ILED (mA) POUT (W) Efficiency (%) Power Factor 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 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%. 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 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 13 www.national.com AN-2097 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. Experimental Results AN-2097 Electromagnetic Interference (EMI) The EMI input filter of this evaluation board is configured as shown in the following circuit diagram. 30139731 FIGURE 1. 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.(Note 4) 30139732 FIGURE 2. Peak Conductive EMI scan per CISPR-22, Class B Limits Note 4: CISPR 15 compliance pending www.national.com 14 AN-2097 ILED = 348 mA # of LEDs = 6 POUT = 7.2 W The results are shown in the following figures. Thermal Analysis The board temperature was measured using an IR camera (HIS-3000, Wahl) while running under the following conditions: VIN = 230 VRMS 30139733 FIGURE 3. Top Side Thermal Scan 30139734 FIGURE 4. Bottom Side Thermal Scan 15 www.national.com AN-2097 TER 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 FILTER pin has the voltage wave shape shown in Figure 6 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 7 how (by adding the rectified voltage) the on-time is adjusted. Circuit Analysis and Explanations 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 5. 30139737 FIGURE 6. FILTER Waveform 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. 30139735 FIGURE 5. Line Voltage Injection Circuit The LM3444 works as a constant off-time controller normally, but by injecting the 1.0VPk rectified AC voltage into the FIL- 30139736 FIGURE 7. Typical Operation of FILTER Pin www.national.com 16 AN-2097 Notes 17 www.national.com LM3444 - 230VAC, 8W Isolated Flyback LED Driver Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes 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 LVDS www.national.com/lvds Packaging www.national.com/packaging 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 www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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