Welcome to the training module on Texas Instruments LED General Illumination Solutions - Po wer Supply Control . This training module introduces the LED general illumination applications, the benefits of the UCC28810/11 lighting power controllers, and 2 reference designs.
Here are applications for which TI is developing LED driver solutions. In each of these applications, the input voltage is AC mains voltage with some isolated and non isolated requirements. Each of these applications has its own unique challenges. For example, residential and light commercial applications such as the light bulb and down lighting are very space constrained. They have very difficult thermal management challenges and are very cost sensitive. This space is currently dominated by incandescent, halogen and CFL type lighting sources. The next application is lighting in the outdoor and industrial space, such as street or roadway lighting. The power range in these applications if using LEDs is from 20 to 75W. The main driving force behind the adoption of LED based lighting systems is the increased reliability. LED based lighting systems have life expectancies upwards to 50 thousand hours or more. The longer life significantly reduces costly maintenance recurrences which can save cities and municipalities significant budgetary expense. Other applications, such as large infrastructure lighting applications are in the 65W to 500W range, applications including high bay and stadium lighting. Other areas include airport, and night construction type lighting systems. One of the main differentiators for LED lighting is its inherent simplicity to dim for energy conservation. We can now envision smart light sources that react to changing environmental conditions. Another growing requirement for lighting is Power Factor Correction. PFC requirements may go down to power levels below 25W.
Here list some factors that are driving the adoption of LED lighting. One reason is the movement to the green economy. Adoption of LED lighting can save significant energy on a global scale and cut down on the production of greenhouse gasses. The high cost of energy is another factor, which is gently persuading residents and business to adopt technologies that will mitigate these increased costs. Pending legislation is such countries like Australia, Canada and Taiwan are planning to ban the use of incandescent lights.
Another driver is saving maintenance costs. Just imagine the effort required to change out a bulb for a street light lamp, its cost is measured in hundreds of dollars because of the man hours and equipment needs. With the much longer life LED based lighting systems, much of these maintenance costs can be measurable reduced. It is just a matter of time when the cost of a light engine for an LED based system is in the range of a CFL lamp. As the adoption increases, the economies of scale will start producing significant downward price pressure, lowering the costs. Finally, LEDs are advancing, both in efficiency and cost. They work exceptionally well in cold weather and they lend themselves to easy control. In the future, adaptive lighting will be the norm, not just for esthetics but as a strategy to energy savings.
TI recently released some ICs that address the general LED lighting space. Here we will overview the UCC28810 and UCC28811 LED lighting power controllers specified specifically for off-line LED lighting. They are transition mode controllers, which operate similarly as hysteretic controllers. The difference between the two is that the 28810 has enhances slew rate correction for undershoot while the 28811 has a lower UVLO and is better suited when a separate bias supply is available. They can both be used as stand alone PFC controllers or primary side switching current sources for LED current regulation or even in a single stage design that provides both PFC with LED current regulation. They are low cost, are only 8 pins and require few external components. They can also be configured to allow triac dimmer compatibility and have open over voltage protection and have low start-up current requirements. Generally, these are good device for many LED lighting applications. You will see some of the potential uses in the coming reference design solutions that we will be talking about shortly.
Here is the block diagram of the devices. It features a transconductance voltage error amplifier, a simple current reference generator for generating a current command proportional to the input voltage, a current-sense (PWM) comparator, PWM logic and a totem-pole driver for driving an external MOSFETs directly. The reference circuit generates a precision reference voltage used to obtain a tightly controlled UVLO threshold. In addition to generating a 2.5-V reference for the non-inverting terminal of the transconductance amplifier, it generates the reference voltages for OVP, enable, zero energy detect and the current reference generator circuits.
You can see here a list of 2 reference designs that have been developed for all the various applications previously shown. We will go into more detail in the coming slides. These reference designs cover a power range that can cover 90% these applications. They go from 19W on the low end to 100W on the high end. Also, these solutions can all be scaled to other power levels, a few changes to the power train and some passive component vales changes and you have a solution. The current output can also be changed as well, so, if there is a specific design that looks like it would support your application but at a different LED current, just some minor changes and you have it. All of these reference designs are AC input with Power factor correction front ends.
Here is the Evaluation board – UCC28810-EVM002. This design is for higher power applications such as street lighting or High bay lighting applications. It has a universal input voltage range, meaning that it can be used anywhere in the world and produces up to 90Watts of power. It has power factor correction and is dimmable with external PWM dimming signals. The boost PFC provides an output voltage that then goes through a transition mode inverted buck that generates a constant current for a string of LEDs. As you can see from the picture, it would very neatly fit the form factor similar to today’s CCFL ballasts.
This is the efficiency plot of evaluation board at different line voltages. At high power the input voltage variation has very little influence on the efficiency, averaging about 90%. At the lower power levels, you can see that the efficiency is its lowest but still above 85%. This design would meet any existing energy star compliance levels.
Here shows the Power Factor Test results as a function of output power regulated with PWM dimming. Note that under all power levels and line voltage, the power factor remained above 0.9, again, meeting world wide regulatory agency requirements.
This chart shows the dimming accuracy at three different power levels over the whole input voltage range from 85 to 265 volts. Note how there is very little change in both load and line variations.
Here shows the LED current regulation over line voltage, again, very little change so very good regulation.
The design is called the Multi transformer LED driver for driving multiple LED strings. What it really is, is a “series connected input, to a parallel equivalent output”. Today, driving multiple strings with high efficiency and good current matching requires the use of a DC/DC switching regulator for each string. The DC/DC converter approach is usually a buck converter and has for components, an inductor, 1 or 2 MOSFETs, a handful of passives Rs and Cs and of course a controller. Comparing the total system cost of this arrangement to the Multi transformer, you will see that most of the components are eliminated in the multi transformer. The Transformer may be marginally more expensive than the switching DC/DC inductor but besides this cost difference, most of the other parts are eliminated. This is the real value of the Multi transformer regulator. Also note how the multi transformer does not require feedback from the secondary side which eliminates an opto-coupler. The multi transformer is very flexible and scalable allowing different numbers of transformers in series and also allowing flixibility on the number of LED in each string. The multi transformer can also be used in lower voltage DC input applications, just eliminate the PFC section and scale components as needed..
The diagram here shows a simplified implementation for demonstration purposes. The input is AC line voltage rectified through a bridge then fed into a PFC boost stage. The output of the BOOST is then fed into a transition mode inverted Buck regulator circuit which produces a well regulated constant current that feeds a half bridge controller circuit. The half bridge then circulates the regulated current back and forth through the series connected primaries of the multiple transformer architecture. If this constant current on the primary is well regulated, you can have very tight current regulation on the secondary side. On this particular design, the secondary side has rectifiers that direct both the negative and positive current swings to the strings of the LEDs. You can expect very little differences in LED string current matching because any differences would be from 2nd or 3rd order effects. We have measured better than 1% difference in our reference designs. The Multi transformer can also be dimmed with PWM dimming signals for intelligent lighting applications such as street lights that dim naturally to ambient light changes
This is another configuration of the multi transformer. It is the actually preferred method as it allows 2 strings to be regulated per transformer even further reducing system cost. A DC Blocking capacitor is added in the lower leg of the secondary side of the transformer. This capacitor balances the circuit for the minor differences in the string forward voltage characteristics or if an LED shorts as it balances each string and prevents the transformer from saturating. You will notice how filter capacitors are also added to output to provide clean low ripple DC current to the strings.
The chart shows the efficiency of the multi-transformer under various line and load conditions. Each color represents different line voltages. Notice the lower efficiency levels are at the low power levels but still exceeds 85%. This easily exceeds energy star efficiency standards.
This graph shows the line regulation. The line voltage is varied over the whole universal input range and there was very little deviation on the current regulation of the LED strings. The output current in this case was set for 440mA.
Here shows the efficiency vs. PWM dimming percent and each line represents different input voltages.
This slide is probably the most revealing of the multi-transform architecture . It shows the LED string current in the output of the three transformers over the entire universal input range, note how they are on top of each other. Also note that the scale on the left side if from 90 to 100% just to demonstrate the tightness of the current matching. This slide is a real demonstration of the value of the multi transformer topology. We essentially eliminated 90% of the components that would be required by a switching regulator for each string. The greater the number of LED string that need driving, the more cost effective it becomes.
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LED General Illumination Solutions Power Supply Control
LED General Illumination Solutions Power Supply Control <ul><li>Source: T EXAS I NSTRUMENTS </li></ul>
Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module introduces the LED general illumination applications, the benefits of the UCC28810/11 lighting power controllers, and 2 reference designs. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>LED general illumination applications and market drivers </li></ul></ul><ul><ul><li>UCC28810/11 power controllers overview </li></ul></ul><ul><ul><li>Reference design 1 – UCC28810-EVM002 </li></ul></ul><ul><ul><li>Reference design 2 – UCC28810-EVM003 </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>21 pages </li></ul></ul>
LED General Illumination Applications Characteristics Cost Efficiency Reliability PFC (10W) Safety Dimming soft white color changing Characteristics Efficiency Low maintenance Reliability PFC PLC Safety EMC Cool whites Color washing Dimming Incandescent, Halogen, CFL replacements, Task, Desk, Wall Accent lighting, down lights display, retail, emergency, safety, medical, garden patio, pathway, handrail lighting Characteristics Efficiency Low maintenance Reliability PFC PLC Safety EMC cool whites Color washing Dimming Area, Parking, Street, Roadway, Ornamental, Pathway, Signage, Contour, Architectural, Letter, Medical, Monitors, Displays High Bay, Stadium, Airport, Street, Roadway, Large Display, Sports Field, Construction, Search Lights, Temporary LED Lighting Residential and Commercial < 25W or 3,000 lm Outdoor and Industrial 20W – 75W or 2000 lm - 10000 lm Large Infrastructure 65W – 500W 8000 lm - 60,000 lm
LED Lighting Market Drivers <ul><li>The movement of the Green economy: </li></ul><ul><ul><li>Estimates are that 19% to 25% or world energy usage is for lighting </li></ul></ul><ul><ul><li>Diminishing primary energy consumption to cut down on greenhouse gasses </li></ul></ul><ul><li>High cost of energy </li></ul><ul><ul><li>Energy prices will continue to increase </li></ul></ul><ul><ul><li>Reducing operating expenditures for enterprise operations </li></ul></ul><ul><li>Legislation is essentially banning incandescent lighting sources. </li></ul><ul><ul><li>Australia, Canada, Taiwan, Ireland and California will ban incandescent light bulbs as early as 2010 </li></ul></ul>
LED Lighting Market Drivers (cont’d) <ul><li>Maintenance & reliability value proposition of LED lighting systems </li></ul><ul><ul><li>Replacing lights such as in tunnels, roadways and warehouses to name a few. </li></ul></ul><ul><ul><li>The 60Khours lifetime of LED will make these events significantly less frequent. </li></ul></ul><ul><li>Total cost of ownership </li></ul><ul><ul><li>The cost of HB LEDs is going down – LED lighting is becoming more affordable and soon will be in range of FL </li></ul></ul><ul><li>Performance Advancements of LED lighting systems </li></ul><ul><ul><li>LED based lighting lends itself to being controlled so dimming or color mixing differentiates LED lighting from other lighting technologies. </li></ul></ul><ul><ul><li>Low temperature operation, instant off and on </li></ul></ul>
UCC28810/11 LED Lighting Power Controller <ul><li>AC Input General LED Lighting Applications </li></ul><ul><li>Industrial, Commercial and Residential Lighting Fixtures </li></ul><ul><li>LED Lighting Ballasts </li></ul><ul><li>Outdoor Lighting: Street, Roadway, and Parking Lot lighting </li></ul><ul><li>Interior and exterior Ornamental LED Lighting </li></ul><ul><li>Light bulb replacements </li></ul>Applications Benefits Features Eliminates the need for an external Driver 750 mA gate drive current Low power consumption, better efficiency and provides consistent performance in high volume lighting production Low Startup Current and Accurate Internal Vref Improves reliability and life time of lighting fixture UVLO, OVP and Open Feedback Cost Effectively improves performance of LED in secondary side LED control schemes Improved Transient Response Uniform Dimming of LED fixture achieved without changing wall dimmer Application circuit implements industry standard triac phase-angle dimming Achieves lighting standards requirements, reduces cost and size Implements Single Stage Power Factor Correction and LED current regulation Low Cost, High Efficiency and Low EMI Transformer Zero Energy Detection (Transition Mode Control)
Reference Designs UCC28810-002EVM 350 mA 90-264 V ac 75 W UCC28810 UCC28811 UCC28810- EVM003 : High Power, Multi-transformer LED Fixture Driver for High Bay, Roadway and Stadium lighting 900 mA 90-264 V ac 90 W UCC28810 UCC28811 UCC28810- EVM002 : High Efficiency AC input, Power Factor Corrected, Dimmable LED Street Light Driver Parts I out V in P out Reference Design
High Efficiency LED Street Light UCC28810-EVM002 Evaluation Board <ul><li>Key Benefits: </li></ul><ul><li>Active Power Factor </li></ul><ul><ul><li>Low THD </li></ul></ul><ul><li>High efficiency </li></ul><ul><ul><li>Boost Follower </li></ul></ul><ul><li>Extremely robust , </li></ul><ul><ul><li>the LEDs are well protected </li></ul></ul><ul><li>Extremely simple to use : </li></ul><ul><ul><li>TM Buck inherently stable </li></ul></ul><ul><ul><li>no compensation required </li></ul></ul><ul><li>Fast LED Current Response </li></ul><ul><ul><li>well suited for PWM Dimming </li></ul></ul><ul><li>Universal Range Input voltage </li></ul><ul><li>High Reliability, long life </li></ul>UCC28810-002
UCC28810-EVM002 LED Current Regulation Over Line
Multi Transformer LED Driver UCC28810-EVM003 Reference Design <ul><li>Benefits : </li></ul><ul><li>Inherent input voltage surge protection, extremely robust, </li></ul><ul><ul><li>Cycle By Cycle current control on TM buck, same peak current regardless of input voltage </li></ul></ul><ul><li>Inherent Over Current and Short Circuit Protection </li></ul><ul><ul><li>TM buck provides constant current source, variable voltage output </li></ul></ul><ul><li>Feedback from primary not necessary </li></ul><ul><ul><li>no optocoupler </li></ul></ul><ul><li>Extremely simple to use: </li></ul><ul><ul><li>inherently stable </li></ul></ul><ul><ul><li>no compensation required </li></ul></ul><ul><li>High efficiency </li></ul><ul><ul><li>Transition Mode Buck and DC Transformer Half Bridge operate in ZVS </li></ul></ul><ul><li>Very Good LED String Current Matching </li></ul><ul><ul><li>Primary Current of all Half Bridge transformers is the same. </li></ul></ul>
Multi Transformer LED Driver UCC28810-EVM003 Reference Design BRIDGE RECTIFIER AC EMI FILTER PFC Boost Follower Transition Mode Inverted Buck UCC28810/11 Half Bridge DC/DC Driver Transformer UCC 25600 ENABLE DIMMING Current Driver
UCC28810-EVM003 Four String Two Transformer Implementation <ul><li>Single, primary referenced current control & dimming (AM or PWM) for all LEDs. </li></ul><ul><li>Large number of LED connected in series yet the voltage on LEDs is safe (low) and isolated from the AC line </li></ul><ul><li>Readily scalable to very high power levels </li></ul><ul><li>Excellent LED current matching between strings </li></ul><ul><li>High Efficiency and Power Density </li></ul><ul><li>Simple and Robust Control, Immune to transients </li></ul>
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