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Driving LEDs -AC-DC Power Supplies: LED Fundamentals

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In this presentation on Driving LEDs — AC-DC Power Supplies we will look at the typical circuit structure of AC-DC drivers, the importance of TRIAC dimmability and some standards covering drivers ...

In this presentation on Driving LEDs — AC-DC Power Supplies we will look at the typical circuit structure of AC-DC drivers, the importance of TRIAC dimmability and some standards covering drivers for LED systems.

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Driving LEDs -AC-DC Power Supplies: LED Fundamentals Driving LEDs -AC-DC Power Supplies: LED Fundamentals Presentation Transcript

  • LED Fundamentals F d t lDriving LEDs –AC DCAC-DC PowerSupplies06-26-2012
  • Introduction Normalized Spectrum Behavior at 24, 35, 50, 70 Degree Celsius 1,00 TY INTENSIT 0,80 Proper driving of LEDs is required to 0,60 Spectrum Behavior at 24, 35, 50, 70 Degree Celsius address some of the fundamental INTENSITY 0,40 6,00E-05 variations that all LEDs may have due to y 0,20 5,00E-05 manufacturing tolerances. WAVELENGTH [nm] 4,00E-05 0,00 580 590 600 610 620 630 640 650 660 670 680 3,00E-05 2,00E-05 There are different methods that are 1,00E-05 WAVELENGTH [nm] used to drive LEDs These methods can LEDs. 0,00E+00 , 380 430 480 530 580 630 680 730 780 be very simple or complicated depending on the application. Some of the key parameters needed to choose proper driving include, expected Tj (Junction Temperature), expected Vf mismatch between LEDs, color accuracy needed at the system level and if dimming of LEDs is required.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 2
  • Need for Current Regulation in LED SystemsThe I-V characteristics of an LED plays a keyrole in deciding what type of regulation, currentor voltage is best suited for driving LEDs. g gDue to the fact that there’s a small increase involtage once the threshold is reached, willsignificantly increase current through an LED LED,regulating current is more ideal for drivingLEDs.Also, current regulation is required in LEDsystem to control and maintain: » Color shift VS LED current » Flux or light output VS LED currentThere are three commonly adopted methods ofdriving LEDs; resistor based, linear regulators, g ; , g ,and switching regulators.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 3
  • Driving Options LEDs LEDElectrical characteristics Optical characteristics Thermal characteristics Driving options Discrete based drive Linear drivers Switching drivers - Resistor based - Fixed voltage -DC-DC drivers - Transistor based - constant current -AC-DC driversLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 4
  • Driving Options… Discrete drive Switching drivers can be DC-DC or AC-DC. AC-DC AC DC AC DC is covered in this presentation.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 5
  • AC-DC Drivers Up to 90% efficiency can be achieved Switching regulators offers design flexibility and the when converting AC to DC. advantage of increased power conversion efficiency, especially in high power applications. Compared to linear regulators switching regulator regulators, based drive for LEDs and LED systems, may increase complexity, cost and real estate needed for the driver circuit. Switching drivers can be DC-DC type or AC-DC type. In this presentation AC-DC type switching drivers are examined at a very high level level. Efficiency characteristics of ICL8001GLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 6
  • AC-DC DriversLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 7
  • Importance of Power Factor Correction (PFC)LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 8
  • AC-DC Drivers: 2-Stage Design A two stage AC DC driver will have two separate circuits to control and maintain the AC-DC output. Because there are two separate circuits, they often use two driver IC’s: one for PFC and another for output regulation. Output Regulation PFC Circuit PFC (Constant Current/ OutputVac (Power Factor Correction) output Fixed Voltage) The PFC circuit topology is generally a boost type and would have an output voltage of ~400VdcLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 9
  • Efficiency of a Power System Power system Vac Stage 1 Stage 2 Output Efficiency (Power System) = Efficiency (Stage 1) X Efficiency (Stage 2)LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 10
  • Infineon Technologies’ ICE3B03651 AC inLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 11
  • Some of the Characteristics of a 2-Stage Design A 2-stage design would have more A 2-stage design would have more components compared components compared to a single stage to a single stage design Because of this a 2-stage driver design. design. design Because of this a 2 stage driver will this, 2-stage will have increased cost and PCB area. have increased cost and PCB area. 300kHz Input Voltage vs THD rotion 12 10 Total Harmonic Distr (THD (%)) 8 Peak-Peak 6 ripple of ~10mA 4 H 2 0 0 50 100 150 200 250 300 Vin (ac)LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 12
  • AC-DC Drivers: Single Stage DesignLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 13
  • Some of the Characteristics of a Single Stage Design A single stage design would have less component count compared to a 2-stage design. Because of this, a single stage driver will have improved cost and PCB area. 120Hz Input Voltage vs THD 35 30 THD (%) 25 20 Peak-Peak 15 ripple of ~30mA 10 5 0 0 50 100 150 200 250 300 Input Voltage (Vac)LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 14
  • Single Stage vs 2-Stage Design This table compares 2-stage and single stage designs, if the specification for both were to be kept the same. Two-Stage Design Single Stage Design Efficiency Good Better Component count Higher Lower Output ripple Lower ( 5-15%) 5 15%) Higher (20 40%) (20-40%) Transient response Good Poor PCB area Require more area Less PCB area Cost Higher Lower THD Lower (< 20%) Higher ( > 20%)LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 15
  • TRIAC Dimmable AC-DC DriversFunction of a TRIAC dimmer: A TRIAC dimmer basically keeps the AC voltage to be zerofor a period of time which is determined by how much dimming is required from the TRIAC AC in to the AC Voltage TRIAC driver ~45% dimmedLED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 16
  • Regulatory Requirements of AC-DC DriversThere are many regulatory and standard requirements that need to be taken intoconsideration when designing or selecting an AC-DC driver for an LED application. Typical AC-DC constant current driver specification includes: - Total Power: 25W - Input Voltage: 90-305Vac - Output: 4-72Vdc - Output Current: 620mA - Hi h Effi i High Efficiency - Over current, over voltage, and output short protected - TRIAC didimmable bl - IP66 compliant - UL8750LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 17
  • Summary AC-DC drivers can be single stage or 2-stage design. AC-DC drivers can be Power Factor Corrected or not. A TRIAC dimmable, Power Factor Corrected, AC-DC constant current driver is preferred for LED circuits and systems. AC-DC drivers should be in compliance with some of the standards, such as UL and Energy Star. When designing or selecting a proper AC-DC driver for an LED system, one has to g g g y consider what the target LED application is, in order to make an advised selection.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 18
  • Disclaimer All information contained in this document has been checked with the greatest care. OSRAM Opto Semiconductors GmbH can however, not be made liable for any damage that occurs in connection with the use of these contents. OSRAM Opto Semiconductor GmbH makes no representations and warranties as to a possible interference with third parties intellectual property rights in view of products originating f i i ti from one of OSRAM Opto Semiconductor GmbHs partners, or in view of f O t S i d t G bH t i i f products being a combination of an OSRAM Opto Semiconductor GmbHs product and a product of one of OSRAM Opto Semiconductor GmbHs partners. Furthermore, OSRAM Opto Semiconductors GmbH cannot be made liable for any damage that occurs in p y g connection with the use of a product of one of OSRAM Opto Semiconductor GmbHs partners, or with the use of a combination of an OSRAM Opto Semiconductor GmbHs product and a product of one of OSRAM Opto Semiconductor GmbHs partners.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 19
  • Thank you for your attention.LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 20