Solar Powered LED Street Lighting Solar Powered LED Street Lighting Courtesy of BetaLighting www.onsemi.com 2 Agenda • Trends for solar powered LED street lighting • Regulating voltage out of a solar panel – Application overview – Maximum Peak Power Tracking (MPPT) – Reference design • Driving High-Brightness LED (HB-LED) – Selecting a design approach – Reference design www.onsemi.com 3 The Application of Solar Powered LED Street Lighting • LED lighting offers high efficiency, long operating life and low voltage operation which ideal for solar • Solar street lights were initially used in remote locations and disaster prone areas • As LED efficacy and light output have improved, they are becoming mainstream www.onsemi.com 4 LED Performance Over Time Light Source Efficiency Trends 180 Best Announced White LED R&D Capability 160 Lumens/watt 140 (4500-6000K) LED 132-136 L/W High Volume White LED Production 120 HID 100 Linear Fluorescent 80 CFL 60 40 Incandescent 20 0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Source: Cree www.onsemi.com 5 Tipping Point is Close on All the Major Apps… 175 350 150 300 125 250 100 200 75 150 50 100 50 25 0 0 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 www.onsemi.com 6 Expected Lumens per 1W LED Number of 1W LEDs Needed 400 150 W Roadway 400 W HID Met 4x T5 FL Troffer Lumens/1W LED Regulating Voltage out of a Solar Panel www.onsemi.com 7 Solar Power – Block Diagram LED ~24 V Solar Panel www.onsemi.com 8 350 mA ~12 V Charge Controller Battery Comparison of Different Types of Charge Controllers • • Basic Designed to protect the battery from overcharge or undercharge Prevents reverse current www.onsemi.com 9 • • PWM Controls the amount of current charging the battery Trickle charge • • MPPT Optimize the power output from the cell Battery charge to optimal capacity Maximum Peak Power Tracking (MPPT) • Solar panels in general are inefficient – ~30% efficient – Most expensive component in the system • Charge controllers and other electronics need to be as efficiency as possible to maximize the benefits – Typically implemented with a micro-controller • MPPT compensates for the changing Voltage versus Current characteristic of the solar cell to increase the efficiency www.onsemi.com 10 Solar Panel Characteristics Extracting the maximum amount of power from the solar panel is difficult due to the nonlinearity and variability of the Voltage-Current (V-I) characteristic. MPPT fools the panels into outputting a different voltage and current allowing more power to go into the battery by making the solar cell think the load is changing when you really are unable to change the load. www.onsemi.com 11 Power and Voltage for a Solar Panel Voltage Current and Max Power of a Solar Panel Afternoon Sun Output Current (A) Output Current (A) Max power =6.1 w @15.99v 30 Power Panel 20 10 Output Current (A) www.onsemi.com 12 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0 O utput Voltage (V) Voltage Current and Max Power of a Solar Panel in Evening Sun 1.4 1.2 0 1 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 10 0.8 10 Power Panel 20 0.6 Power Panel 0.4 20 30 0.2 30 Max power =17.3 w @15.4v 0 O utput V oltage (V ) Max power =24.3 w @14.3v 0 O u tput V oltage (V ) Voltage Current and Max Power of a Solar Panel Noon Sun Solar Panel Charge Controller • Solution : – • Target Application : – – • CS51221 Solar Panel LED Street Lighting Solar Panel Battery Charger Specification : – – – – – – Input : 12 V – 24 V Output: 12 V @ 2 A Protection: Adj Current Limit, Input UVLO, Input OVLO Maximum peak power tracking required Efficiency: Target >80% Isolation Required: YES – Prevent discharging the batteries www.onsemi.com 13 Component/Topology Justification • • • • • • • The topology was chosen as it can buck down to 12 V from the solar panel in the case of one battery The topology can also boost to 24 V in the case of 2 batteries or more and can be easily changed Aux rail available for remote transmission and monitoring Can accommodate panels as large as 90 W Implement maximum peak power tracking to improve efficiency Need to meet good efficiency, target costs and easy to implement CS51221 offers: – Isolated and non-isolated topology – Adjustable pulse-by-pulse current limit – External voltage reference www.onsemi.com 14 CS51221 - Voltage Mode PWM Controller Value Proposition The CS51221 fixed frequency feed forward voltage mode PWM controller contains all of the features necessary for basic voltage mode operation. This PWM controller has been optimized for high frequency primary side control operation. Unique Features Benefits 1 A sink/source gate drive High efficiency operation Up to 1MHz Fsw Optimize for size or efficiency External voltage reference Reduced component count Application Data Others Features Programmable Max Duty Cycle Limit Programmable Pulse−By−Pulse Overcurrent Protection Overvoltage Protection with Programmable Hysteresis Bidirectional Synchronization Market & Applications Consumer Electronics: PoE PD, … Automotive: Body electronics, Navigation, … Computing: Power supply, … Industrial: Power supplies, Process control, PoE PD, Solar Power Charger… www.onsemi.com 15 Capable of being configured as Forward, Flyback or Boost Ordering & Package Information SOIC-16 CS51221: -40 to +125°C Tj Circuit and Block Diagram Programmable OVLO, UVLO, Vff Adjustable Max Duty Cycle & Fsw Maximum Peak Power Tracking www.onsemi.com 16 Implementing MPPT With the CS51221 Eliminates the need for an expensive microcontroller www.onsemi.com 17 • MPPT is implemented by dynamically adjusting the current limit with the Iset pin • Once the Input voltage drops the pulse by pulse current limit is lowered until the input voltage returns Peak Power Tracking Current and Voltage With Resistive Load and CS51221 Controller will find the peak power point and adjust dynamically to meet changing source characteristics Input Voltage (V) Input Power (W) 25 20 PNL IV 15 PNL PWR 10 PNL CNTRL IV PNL CNTRL PWR 5 0 0 0.5 1 1.5 Input Current (A) Current and Voltage With Resistive Load and CS51221 17.5 Controller tracks the maximum power the panel can produce within -5% error Input Power (W) 17 < 5% Error 16.5 16 PNL PWR PNL CNTRL PWR 15.5 15 14.5 14 0.8 0.9 1 Input Current (A) www.onsemi.com 18 1.1 MPPT – Dynamic Reaction to Full and Partial Sun Sun Returns and Current Limit Adjusted Input Voltage Solar Panel in Partial Shade Current Limit Voltage Full Sun www.onsemi.com 19 Panel in 50% Shade Panel in Full Shade Panel Fails to Provide Minimum Power Fast Moving Shade and Full Sun MPPT Enables Lower System Cost ~30% more charge transferred from the panel to the battery 90 W Panel w/ Basic Charge Controller 60 W Panel w/ MPPT • MPPT enables a smaller size solar panel to be used • ~$4/W for the panel x 30 W = $120 system savings www.onsemi.com 20 Reference Design Device Application CS51221 Solar Panel Battery Charger Input Voltage Output Voltage Output Current Topology 12 V – 24 V 12 V – 14.4 V 2A Flyback CS51221 Characteristic Min Typ Max Output Voltage 12 Output Current 2 A 100 kHz Oscillator Frequency 14.4 Unit V Note: Easily scalable to larger solar panels & multiple batteries www.onsemi.com 21 Driving HB-LED for Street Lighting Applications www.onsemi.com 22 Solar Power – Block Diagram LED ~24 V Solar Panel www.onsemi.com 23 350 mA ~12 V Charge Controller Battery Metal Halide Source Replacement Number of LEDs Required Average Delivered Lumens* Number of LEDs Req’d 2007** Number of LEDs Req’d 2012*** 70 W Metal Halide 2,100 18 12 100 W Metal Halide 3,500 30 20 150 W Metal Halide 5,450 46 31 175 W Metal Halide 7,700 66 44 Coefficient of Utilization 250 W Metal Halide 10,600 90 60 60% 320 W Metal Halide 15,200 130 86 400 W Metal Halide 16,500 141 94 Lamp Type * From HID bulb data sheets, includes 60% typical fixture CU ** Current best-in-class LED technology (Cree XLamp Q4 bin @ 6000K, 700 mA), includes 80% typical fixture CU. Assumes thermal equilibrium of LEDs (65°C Tj) *** Based on DOE projections of LED performance improvement, 80% CU. Assumes thermal equilibrium of LEDs (65°C Tj) • LEDs make clear economic sense in lower wattage applications now, all MH applications in the near future • Tradeoff on lifetime versus operating current should be considered based on ambient conditions www.onsemi.com 24 Strategy #1 for Coping with Rapid Change in LED Performance Modular Approach to MH Source Replacement Driver Circuit Generic LED Strip Fixed Number of LEDs Generation 1 Generation 2 Generation 3 A modular design approach can yield constant photometric output while facilitating ongoing cost reductions each time LED brightness is improved www.onsemi.com 25 Strategy #2 for Coping with Rapid Change in LED Performance Lifetime Analysis - Aim Ahead of the Duck… LF Distribution 0.8*$X $X 0.8*$X 1.2*$X $X 1.2*$X Prototyping with the highest performance LEDs currently available is more expensive, but can yield a more competitive and longer life product over the long term www.onsemi.com 26 Strategy #3 for Coping with Rapid Change in LED Performance Plan for BOM savings Generation 1 Generation 2 25% brighter LEDs can also mean 25% fewer LEDs. Need to plan flexibility in your driver design to accomplish this www.onsemi.com 27 LED Street Light Design What’s important? • • • • • Type III street lighting pattern 4200 initial lumens on target 12 V Battery Source Reasonable optical efficiency; “single layer optics” Manage junction temperature for lifetime What’s less important… • • Uniformity (seeing spots is OK…) Size www.onsemi.com 28 LED Assumptions 1. 2. 3. 4. 5. Output: 100 lm Typical at 350 mA @ Tj = 25 deg C Drive current = 350 mA Optical losses of 12% due to single layer, well coupled optics Max ambient = 40 deg C Driver losses = 10% (90% efficiency target) Many LED Options Available www.onsemi.com 29 Sizing the # of LEDs for the Application First order estimate: – Number of emitters – Total wattage Emitter output = 100 lm @ Tj 25. Derate for elevated Tj; assume Tj = 90 deg C. At 90 deg C, emitter output is down 20% = 80 lumens per emitter. Optical losses – 12% Æ 71 Lumens per emitter. 4200 lumens required/71 lm per emitter = 60 emitters Vf= 3.6 volts * .350 A = 1.26 W (60 emitters x 1.26 W = 76 W) Worst Case driver losses: = 15% => Total fixture wattage is ~89 W www.onsemi.com 30 LED Street Light • Solution : – – • Target Application : – – • NCP3066 Configured as a Boost Controller Solar Panel LED Street Lighting LED Light Bar Specification : – – – – – Input : 12 V battery Output : 350 mA Protection: Current Limit, Under Voltage Lockout (UVLO) Efficiency: Target >90% Isolation Required: NO www.onsemi.com 31 Component/Topology Justification • • • • • Supports modular Constant current architecture Configurable output LED current from 350 mA to 1 A Able to drive 5-10 LEDs in series Cost effective system approach Easy to implement • NCP3066 offers: – – – – – Dedicated ENABLE pin for low standby power Average current sense (current accuracy independent of LED Vf) 0.2 V reference for small / low cost sense resistor User adjustable peak current limit to maximize battery lifetime No loop compensation required www.onsemi.com 32 NCP3066 – Constant Current Multi-mode Regulator Value Proposition The NCP3066 is a switching regulator designed to deliver constant current to high power LEDs. The device has a very low feedback voltage of 235 mV (nominal) which is used to regulate the average current of the LED string. Typical Application diagram & Package info Unique Features Benefits • Fsw from 52 to 250 kHz • Optimize component size and efficiency • Wide Vin from 3 to 40 V • Allows use in many • Multi-topology versatile applications • ENABLE pin • <100 uA standby Others Features • 1.5 A peak current • Ability to add external transistor to increase output current in buck mode or increase voltage in boost mode • 2% accurate internal reference over temperature Market & Applications ENABLE Pin - PWM dimming - Low power standby • Consumer Electronics: CRT, LCD TVs, STB, DVD, … • Automotive: Airbag, Body electronics, Brake systems, Infotainment, Navigation, … Power supply, Peripherals (Printer, Scanner, Graphic card, …) • Industrial: Power supplies, Process control, Home energy and control, Security systems, … • Computing: www.onsemi.com 33 Ordering info & Support PDIP-8, SOIC-8, DFN-8 NCP3066: -40 to +125°C Tj NCP3066 as a Controller – – – – Boost: Higher output voltage and/or current is desired Buck and SEPIC topologies also supported Controller efficiency can be optimized for highest performance Simple drive circuit to support external MOSFET or Bipolar Boost example with 100 V External N-FET From a 24 V Source www.onsemi.com 34 Boost Controller Schematic Programmable Maximum Duty Cycle Limit Programmable Current Limit Open LED Clamp Optional: Ramp Injection For enhanced performance With high line and load variation • Supports a variety of different applications from 4-30 W • Options for different MOSFETS (Gate Clamp) www.onsemi.com 35 Iout vs. Vin of NCP3066 Boost Driving 8 CREE XRE 100.00% 0.450 ÅAccurate Current Regulation 0.400 98.00% 96.00% 0.350 94.00% 0.300 Iout (A) 92.00% 0.250 90.00% Æ Efficiency > 90% 0.200 88.00% 0.150 86.00% 0.100 84.00% Automatic LED dimming under Low battery conditions 0.050 82.00% 0.000 80.00% 6 7 8 9 10 Vin (V) www.onsemi.com 36 11 12 13 14 Reference Design LED Street Light Device Application Input Voltage Output Voltage Output Current Topology NCP3066 LED Street Light +12 V Battery ~25 V 350 mA Boost NCP3066 Characteristic Typ Max Unit Output Voltage 25 V Output Current 350 mA Oscillator Frequency 250 kHz Output Voltage Ripple 8 % www.onsemi.com 37 Min Conclusion • Highly efficient solutions like the CS51221 with MPPT are needed to maximize the efficiency from solar panels • The NCP3066 provides a flexible/expandable solution for driving LEDs from a battery source • Expectations are increasing for solarpowered LED lighting to become the environmentally friendly outdoor lighting solution for the 21st century www.onsemi.com 38 Backup www.onsemi.com 39 Guangzhou, China Courtesy of Multi-Cell Semiconductor Lighting Technology Co., Ltd. Hybrid Solar/Grid Powered Street Lamps www.onsemi.com 40 Split, Croatia Courtesy of Schréder Warm White Street Lamps www.onsemi.com 41 For More Information • View the extensive portfolio of power management products from ON Semiconductor at www.onsemi.com • View reference designs, design notes, and other material supporting the design of highly efficient power supplies at www.onsemi.com/powersupplies www.onsemi.com 42