Inductor Selection for LED Driver Designs Introduction MPI4040 Series Light Emitting Diodes (LEDs) are semiconductor devices that contain no moving parts. This makes LEDs very reliable in demanding applications with high vibration and shock. These properties, along with high efficiency and long life, also make LEDs very attractive in lighting applications. The typical operating life of an LED is one hundred thousand (100,000) hours. LEDs are available in a wide range of colors making them ideal for a variety of applications such as backlighting, instrument panel, liquid crystal display, automobile lighting and general illumination. DR Series: DR1030, DR1040, DR1050, DR73, DR74, DR124, DR125, The LED needs to be properly driven to ensure optimal performance and long life. Designing and implementing an effective driver with suitable topology is the key to successful LED lighting circuits. The topologies used in present day LED drivers are: • Buck • SEPIC • Boost • Flyback • Forward • Buck-Boost Each topology is selected according to the required power level and cost. Semiconductor companies have developed Integrated Circuits (ICs) to drive LEDs. Controlling the current is the most important consideration in designing circuits that drive LEDs. Increasing current will result in higher intensity/brighter lighting, but with considerably reduced LED life. DR127 LDS Series: LDS0705 SD Series: SD3110, SD3112, SD3114, SD3118, SD3812, SD3814, SDH3812, SD10, SD12, SD14, SD18, SD20, SD25, SD52, SD53, SD6020, SD6030, SD7030, SD8328, SD8350 SDH Series: SDH2812, SDH3812 Uni-Pac Series: UP2.8B, UP0.4C, UP2C, UP1B, UP2B, UP3B, UP4B LD Series: LD1, LD2 For more information go to: • Data sheets at www.cooperbussmann.com/datasheets/Elx • Parametric search engine at: www.cooperbussmann.com/powerinductorsearch.aspx Buck-Boost The Buck-Boost circuit generates an output voltage that is either higher or lower than the input voltage. The polarity of the output is opposite to that of the input. C Vin D Low wattage LEDs can be driven directly from the IC and higher power LED drivers using Pulse Width Modulation (PWM). Q Buck Circuit A buck circuit regulates input DC voltage down to a desired DC voltage. C D LED D Most LED driver circuits need an inductor or transformer to drive the LED. Cooper Bussmann has a large selection of Coiltronics® inductors and transformer in various sizes, inductance values and current ratings to satisfy a particular LED driver circuit requirement. Typical Circuits for LED Driver Applications Inductor L Controller Buck-Boost circuits generally require one inductor. The following part number series are typical Coiltronics inductors used in buck circuits. DR Series: DR1030, DR1040, DR1050, DR73, DR74, DR124, DR125, DR127 LDS Series: LDS0705 Vin MPI4040 Series D Controller Q C D D LED L Inductor SD Series: SD3110, SD3112, SD3114, SD3118, SD3812, SD3814, SDH3812, SD10, SD12, SD14, SD18, SD20, SD25, SD52, SD53, SD6020, SD6030, SD7030, SD8328, SD8350 SDH Series: SDH2812, SDH3812 Uni-Pac Series: UP2.8B, UP0.4C, UP2C, UP1B, UP2B, UP3B, UP4B R Buck circuits generally require one inductor. The following part number series are typical Coiltronics inductors used in buck circuits. 1 LD Series: LD1, LD2 For more information go to: • Data sheets at www.cooperbussmann.com/datasheets/Elx • Parametric search engine at: www.cooperbussmann.com/powerinductorsearch.aspx Single Ended Primary Inductance Converter (SEPIC) Circuit Flyback Circuits The SEPIC circuit is a popular Buck-Boost topology that allows the output voltage to be higher or lower than the input voltage. The SEPIC output polarity is the same as the input. The Flyback transformer combines isolation, energy storage, and voltage scaling. The Flyback allows multiple output voltages as well as can provide plus and minus outputs by using tapped windings. D C Vin L Inductor Flyback circuits require a custom-designed flyback transformer. C L D D Controller LED Coiltronics designs and makes custom and semi-custom transformers to match flyback circuit design requirements. Transformer Q Vin D D T R C D LED D Q SEPIC circuits generally require two identical inductors that can be individController ual inductors or a dual-winding inductor. Dual winding inductors that are R bifilar wound are preferred because the technique uses less space, reduces leakage inductance, and increases the coupling of the windings which results in overall increased circuit efficiency. Forward Circuits DRQ Series: DRQ73, DRQ74, DRQ125, DRQ127 The Forward transformer only provides isolation and voltage scaling. The SDQ Series: SDQ12, SDQ25 Forward allows multiple output voltages as well as can provide plus and minus outputs by using tapped windings. A separate energy storage device For more information go to: • Data sheets at www.cooperbussmann.com/datasheets/Elx (inductor) is needed. • Parametric search engine at: Transformer L www.cooperbussmann.com/powerinductorsearch.aspx Vin Boost Circuits D D T C D Boost circuits are power converters with an output DC voltage greater than its input DC voltage. LED D Q Vin Controller D R L Inductor Controller C D D LED Q R Boost circuits generally require one inductor. The following part number series are typical Coiltronics inductors used in boost circuits. MPI4040 Series DR Series: DR1030, DR1040, DR1050, DR73, DR74, DR124, DR125, DR127 LDS Series: LDS0705 SD Series: SD3110, SD3112, SD3114, SD3118, SD3812, SD3814, SD10, SD12, SD14, SD18, SD20, SD25, SD52, SD53, SD6020, SD6030, SD7030, SD8328, SD8350 SDH Series: SDH3812, SDH2812 Uni-Pac Series: UP2.8B, UP0.4C, UP2C, UP1B, UP2B, UP3B, UP4B LD Series: LD1, LD2 For more information go to: • Data sheets at www.cooperbussmann.com/datasheets/Elx • Parametric search engine at: www.cooperbussmann.com/powerinductorsearch.aspx 2 Forward circuits require a custom-designed forward transformer and an output inductor. Coiltronics designs and makes custom and semi-custom transformers to match forward circuit design requirements as well as has a number of output inductor offerings. Inductor Selection and Design Process Design Guide for SEPIC Topology and Inductor Selection Inductors are energy storage devices. Energy is stored in the inductor during the ON time and delivered to the LED during the OFF time. f = frequency The rule of thumb to design the inductor is to set the peak-to-peak ripple current in the inductor to 30 percent of the nominal LED current. It is a good practice to calculate the total volt drop across the LED string. For example: An LED string consist of five LEDs with each having a forward voltage drop of 3.0 volts resulting in a total LED voltage of 15 Volts. Inductance value is calculated using formulas below. D= Vled Vin Ton = D Fosc Ton = L= Vled Vin (Vin − Vled ) * Ton (0.3 * I led ) Duty Cycle = D Inductance = L in mH Frequency = Fosc Dmax = maximum duty cycle Iout = output current Iin = input current Dmax = L≥ Vout Vout + Vin (min) Dmin = Vout Vout + Vin (max) Vin (max) × Dmin ⎛ Vout ⎞ + 1⎟ ⎜ f × I out (min) ⎜ Vin (max) ⎟ ⎜ ⎟ ⎝ ⎠ I in (max) = I in (max) = I out (max) × Dmax 1 − Dmax I out (max) × Dmax 1 − Dmax 2 Iout max2 × D max + Iin max × (1 − D max) Total inductor current is the sum of the required LED current plus half the ripple current. RMSripplecurrent = The inductance value and the maximum current requirement lead us to the selection of the correct Cooper Bussmann Coiltronics part number from the catalog. The saturation current is also taken into consideration when selecting the inductor. The DC resistance of the inductor is also an important parameter. Lower DC resistance will yield better efficiency. The calculated inductor value and the Irms current enable the engineer to select the correct inductor. For SEPIC application, the dual inductor must be bifiliar wound on a single core. This will reduce the leakage inductance. This in turn reduces the losses and improves efficiency. Care must be taken to implement the power factor correction for circuits on the offline LED application circuits. This will give a leg up on passing the AC line harmonic limits of EN61000-3-2 standard for Class C equipment. 3 Inductor Data Sheets DR Series The following data sheets are available online at www.cooperbussmann/datasheets/elx. Inductor Series Data Sheet MPI4040 Series 4086 DR Series • • • • DR73, DR74, DR125, DR127 DR1030 DR1040 DR1050 4315 DR1030 DR1040 DR1050 LD Series 4310 LDS Series LDS0705 Series LD Series SD Series • SD3110 • SD3112 • SD3114 • SD3118 • SD3812 • SD3814 • SD10, SD12, SD14, SD18, SD20, SD25 • SD52 • SD53 • SD6020 • SD6030 • SD7030 • SD8328 • SD8350 SD3110 Series SD3112 Series SD3114 Series 4084 SD38 Series SD38 Series SD Series SD52 Series SD53 Series SD6020 Series 4314 4330 SD8328 Series SD8350 Series SD Series Uni-Pac Series SDH Series • SDH3812 • SDH2812 SDH3812 Series 4354 Uni-Pac Series • UP1B, UP2B, UP3B, UP4B • UP0.4C • UP2.8B • UP2C • UP2UC Uni-Pac Uni-Pac 0.4C Uni-Pac 2.8B Uni-Pac 2C 4369 The Cooper Bussmann Coiltronics® brand of magnetics specializes in standard and custom solutions, offering the latest in state-of-the-art low-profile, high power density magnetic components. We remain at the forefront of innovation and new technology to deliver the optimal mix of packaging, high efficiency and unbeatable reliability. Our designs utilize high frequency, low core loss materials, and new and custom core shapes in combination with innovative construction and packaging to provide designers with the highest performance parts available. The Coiltronics product line of power magnetics continually expands to satisfy shifts in technology and related market needs. Standard Product Categories include: • Shielded & Unshielded Drum Inductors • High Current Inductors • Toroidal Inductors • Specialty Magnetics For our Inductor Parametric Search Engine: www.cooperbussmann.com/powerinductorsearch.asp For product data sheets: www.cooperbussmann.com/datasheets/elx For technical inquiries e-mail: [email protected] For availability inquiries e-mail: [email protected] Order samples online: www.cooperbussmann.com © 2010 Cooper Bussmann www.cooperbussmann.com 4 Reorder # 4062 0910 PDF Only • Custom Magnetics