LM3445 Application Note 2069 LM3445 - 230VAC, 6W- 15W Isolated Flyback LED Driver Literature Number: SNVA447B
National Semiconductor Application Note 2069 Montu Doshi November 23, 2010 Introduction Key Features 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 VRMS to 265 VRMS, 50 Hz input power supply. The key performance characteristics under typical operating conditions are summarized in this application note.
AN-2069 LM3445 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic 30126901 Warning: 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. Warning: The ground connection on the evaluation board is NOT referenced to earth ground.
AN-2069 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.
AN-2069 Bill of Materials Designator AA1 Description Manufacturer Printed Circuit Board Part Number RoHS - Y U1 Triac Dimmable Offline LED Driver, PowerWise National Semiconductor LM3445MM Y C1 Ceramic, X7R, 250VAC, 10% Murata Electronics North America DE1E3KX332MA5BA01 Y C2 Ceramic, Polypropylene, 400VDC, 10% WIMA MKP10-.
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.
AN-2069 Transformer Design Mfg: Wurth Electronics, Part #: 750815040 Rev. 01 30126909 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.
AN-2069 Demo Board Wiring Overview 30126903 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.
(Note 1, Note 2, Note 3) Efficiency vs. Line Voltage Original Circuit 0.83 8 LEDs Efficiency vs. Line Voltage Modified Circuits 10 LEDs 0.97 0.81 EFFICIENCY EFFICIENCY 0.82 6 LEDs 0.80 0.79 4 LEDs 0.93 Mod C (10 LEDs) 0.89 Mod B (8 LEDs) 0.85 0.81 0.77 0.73 0.78 0.68 Original (6 LEDs) Mod A (4 LEDs) 0.77 0.64 0.76 180 190 200 210 220 230 240 250 260 0.60 180 190 200 210 220 230 240 250 260 INPUT VOLTAGE (VRMS) INPUT VOLTAGE (VRMS) 30126910 30126914 LED Current vs.
Output Power vs. Line Voltage Modified Circuits 12 10 9 8 25.0 22.5 10 LEDs 8 LEDs OUTPUT POWER (W) OUTPUT POWER (W) 11 AN-2069 Output Power vs. Line Voltage Original Circuit 4 LEDs 7 6 LEDs 6 5 4 20.0 Mod B (8 LEDs) 17.5 15.0 Mod C (10 LEDs) 12.5 10.0 7.5 5.0 3 2.5 2 180 190 200 210 220 230 240 250 260 Original (6 LEDs) 0.
AN-2069 PCB Layout 30126907 Top Layer 30126908 Bottom Layer www.national.
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.
AN-2069 30126924 Dimming Characteristics CURRENT THD of the fundamental current (as shown in the following figure) and therefore meets the requirements of the IEC 61000-3-2 The LED driver is able to achieve close to unity power factor Class-3 standard. (P.F. ~ 0.94) which meets Energy Star requirements. This design also exhibits low current harmonics as a percentage 30126923 Current Harmonic vs. EN/IEC61000-3-2 Class C Limits www.national.
AN-2069 Circuit Operation With Rotary Forward Phase Triac Dimmer Input waveforms at full brightness setting Output waveforms at full brightness setting 30126925 30126928 Ch1: Input Voltage (100 V/div); Ch3: Input Current (20 mA/div); Time (4 ms/div) Ch1: Output Voltage (10 V/div); LED Current (100 mA/div); Time (4 ms/div) Input waveforms at half brightness setting (90° firing angle) Output waveforms at half brightness setting (90° firing angle) 30126926 30126929 Ch1: Input Voltage (100 V/div); Ch3
AN-2069 Electromagnetic Interference (EMI) The EMI input filter of this evaluation board is configured as shown in the following circuit diagram. 30126931 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) 30126932 FIGURE 2.
AN-2069 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 30126933 FIGURE 3. Top Side Thermal Scan 30126934 FIGURE 4. Bottom Side Thermal Scan 15 www.national.
AN-2069 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 VFLTR2 peak should be kept below 1.25V. At 1.25V current limit is tripped.
AN-2069 Notes 17 www.national.
LM3445 - 230VAC, 6W- 15W 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.
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