I have a question for David. I'm am trying to develop a driver circuit for driving two Cree MC-E's at 350 mA. My power source is eight nimh AA batteries in series (8 - 11 volts operating range). There are several different ways to arrange the total of 8 leds and am wondering if any particular arrangement can be expected to give the best performance. Right now I am considering three different driver arrangements:
(a) one buck driver powering 4 parallel strings of two leds (driver current = 1400 mA)
(b) two buck drivers with each driver powering 2 parallel strings of two leds (driver current = 700 mA)
(c) one boost driver powering one string of 8 leds (driver current =350 mA)
Any suggestions on what configuration is best suited for this application?
Thank you for using CREE!
To keep your design simple and maximize Battery run time I would choose option C.
To reduce your system losses - do not use the Spring type battery holders - they have very high resistance.. use either blade holer or flying leads..
Good Luck and let me know how your design turns out
Thanks for the advice earlier on LED configuration and battery holders. I made some measurements on my battery holder and you are correct that there is a lot of resistance in the springs. Right now I don't know of any suitable off the shelf battery holders that don't use springs so at least for now I think I have to live with it.
After looking at LED configuration some more, I'm in the process of building a board with two MCEs configured as four parallel strings of two LEDs. This configuration has the advantage of also being compatible with two XM-L LEDs so I'll be testing it both ways. Thanks again for the help and I'll let you know how it goes.
Element14 has Cree LEDs mounted on boards, this may help you experiment and learn more..
I did a quick search on the store portion of Element 14 I did a battery holder search and found lots of good non spring holders
here is my search results:
here is a link on one of the holders from Keystone
hope this get you pointed in the right direction ..
you will be shocked at the performance of the XM-L - lower Vf and a fantastic LPW performance -
Good luck -
David , Element 14 make a demo kit sold by Farnell / Newark as XM-L Kit Farnell stock number 2059066
They say it comprises
CREE XM-L lighting class LED, XP driver, Aavid Thermalloy heatsink, Ledil spot and wide angle lenses
can you point me at a data sheet, I looked on the Cree site but cant find it.
I am new to element14 and don't see a way to post a question. Instead, the instruction said to post a reply.
Am I daft? I am writing to ask you if you have seen the RTG 904 portable lighting led driver?
Hi Mr. David,
I am from INDIA, you know the country which recently won the Cricket World Cup. HUH finally! it gives a great amount of satisfaction. Ok so actually i am an Electronics Engineer & I am palnning to set up a LED light manufacturing unit. I am motivated to do so because LED's are the BUZZ word today & secondly what better way to help my society, as millions of indians still living in the dark ages.
I am not much worried about the electronic driver design as i have some years of design experience also on the LED front i am getting great help from CREE india, i will be recieving sample LED's from CREE in a few days to speed up my design.
Now the thing worrying me the most is the manufacturing set up and how to bring it all together as i don't have prior experience of manufacturing, like the machinery required , then should there be a Surface Mount Tech Machine, How to design and manufacture Dichroic reflectors, than what about the front end software tools required for designing , simulation , thermal analysis etc
In short the only thing i have right now is the design of drivers and the LED's & the thing i need is a complete end product. I will be grateful if you can provide some inputs.
Congratulations on INDIA winning the Cricket World Cup!
Cree would love to help you succeed in your efforts to develop Solid State Lighting in INDIA.
We have posted a lot of our knowledge base on Cree's landing page on Element14 (see link below)
Check out the Application notes, Reference designs and Tools Section
From a system design stand point, check out Cree's online System design tool: Product Characterization Tool (PCT)
This tool allows you to enter you System Design requirements (System Lumens, Optical Efficiency, Electrical Efficiency)
then helps you evaluate the right LED drive current to optimize your design.
For all valid LED drive currents, the PCT quickly and easily does the following:
- Shows all critical LED design parameters, such as luminous flux and efficacy, for selected LED models
- Performs de-rating calculations based on junction temperature (Tj)
- Calculates LED valuations, such as lumens per dollar (lm/$)
- Estimates simple LED design parameters, such as the number of LEDs required and total power consumption
The PCT uses specifications and characteristics from LED data sheets to accurately compare LED parameters with changes in flux, price and junction temperature. The PCT can compare up to three LED models side-by-side to aid in making critical design choices.
To get to market fast you may want to look at Cree's more integrated Lighting modules and LED Array products like the LMR4, LMR2 (coming soon), MPL, CXA20
Cree also works with complimentary suppliers and system design experts to help you get to market faster..
Understanding what problem you are trying to solve is one of the most important starting places.. How much light is need in your application
Cree published a very good application note which documents the design process the system..
here is the link..
Hopefully this is a good starting point on your journey to changing the lighting world in INDIA!
- Shows all critical LED design parameters, such as luminous flux and efficacy, for selected LED models
Would you clarify deltaCCT?
Thank you for the great question!
Delta CCT = the Change in CCT over angle – (CCT = correlated color temperature)
when we talk about delta CCT we are usually talking about the how much the color of the white light changes over the viewing angle of the LED (smaller is better ). This is critical for some applications like linear lighting and a don’t care for outdoor lighting
what size LED die are usually used for low-, medium-, and high-power LEDs?
thank you for the question:
From the element14 webinar I gave on March 29th 2011 slide 18 titled LED Chips: Size Doesn't Matter
I show power die from Cree's ETC and EZ chip families that range from 0.35x0.47mm to 1.4x1.4MM in size
The link to the on-demand presentation is here: https://newark.webex.com/newark/lsr.php?AT=pb&SP=EC&rID=49322112&rKey=23487de9a1e644c9
from Cree's small chip family the chip size is 200x200μm
hope this answers your question
This portion of the presentation conveys the message to focus on the application and use the right LED @ the drive current needed to solve your lighting problem at the right price.
Cree invented the XM-L for the next generation of designs needing high lumen packages like high bay, street lights, low bay to reduce the inital Cost and Total Cost of ownership
we are focused on creating the right parts for each lighting application to enable the market to adopt Solid State lighting NOW.
What are the chances that CREE will start putting more information in their datasheets, or at least offer some guidance on what the datasheets don't say?
Take the X-Lamp XR-E for example. Any absolute maximum ratings? no just Characteristics, any recommended operating conditions? no just characteristics.
Characteristic maximum current 1A (> 5000K white), 0.7A (others). DC pulse characteristic 1.8A, 1kHz, 10% (all). What about other frequencies and duty cycles? What about pulse ratings for photo-flash type applications? What about current ripple ratings at 10s or 100s of kHz as typically produced by switchmode drivers? What about guidance on the consequences of over/under driving? You don't need 50,000 hours life from a photo-flash for example.
You make the things, you must know a lot about them but seem to leave your customers guessing.
Inverter vs Driver?
My electrical engineering senior design project is going to be a power generating bicycle with a number of different lighting systems along with some other features. I'm thinking about using electroluminescent wire for lighting the bike frame, so I know I'll need an inverter.
My question is, what is the difference between an inverter and a driver? When I look at different websites that sell EL wire, they all seem to use the terms inverter and driver interchangeably. Is a driver just an inverter with a built in power supply?
The generator on the bike will provide enough power to energize all the electronics, so I don't want something that is battery operated, but most of the products I've seen are. Will I just have to rig the inverter/driver to be able to incorporate it into our power system?
I apologize if I posted this in the wrong location. Let me know if I should have posted this elsewhere.
you are luck!
I happen to have lots of experience with power -
Inverter takes DC and makes AC - so for CFL and EL products you need to have AC signal - many people call the products that convert the power from DC to AC drivers or inverters ..
if you want to use the most efficient light source you will need to use LED technology - which will require a different kind of driver - dc/dc constant current driver-
Element 14 has many suppliers that you can help wih your power requirements
Good luck on your project
You are in Luck - Cree Agrees with you - We are trying to make it easier to adopt Solid State Lighting..
if you look at the latest Cree Data sheet for the
Cree® XLamp® XM-L EasyWhite™ LEDs
Cree choose to bin this part close to the target application operating conditions (MR16 20W LED replacement)
•Binned at 85°C with single EasyWhite bin per CCT
customers no longer have to guess or do math to figure out what LED CCT and Flux at 85C Tj
we even added a chart labeled "RELATIVE CHROMATICITY VERSUS CURRENT AND TEMPERATURE (CRI 80)"
to help customers understrand how their design will function in Pulsed Over-Current above the max rating:
Pulsed Over-Current Driving of XLamp LEDs: Information and Cautions
Please give us feedback on what you need to help you solve your lighting problems
Thanks David. The over-current diving document is exactly the kind of thing I was looking for last year (before it existed).
Still a bit vague but thankfully doesn't contain anything at odds with what we had been guessing.
i wish it showed lumens at pulse current instead of LPW on that main chart but Cree is a very conservative when it comes to specifications and wants our custoemrs to have Zero failures under any condidtions.. I can appreciate the challange of trying to change the world but not have any setbacks due to percieved quality issues..
Good luck changing the world with us!
I am thinking about using an LED matrix like this part for my senior design project:
This would be one segment of a taillight of my power generating bicycle that I mentioned in an earlier post. I am going to wire up the different pins in different ways to show both a brake light and turn signals. It says that the forward voltage is 1.8V. Does this mean that if I wire all the lights together in series, that I'm going to need to supply 115.2V?
After some thought into how I would actually wire this thing up, I realized that I wouldn't be able to connect them in series anyway, because of how each LED is connected in the matrix circuit. It looks like the only way to do it would be to connect them all in parallel. So I think this means that I would just need to apply 1.8 V total. Correct me if I'm wrong.
you are close on the 1.8V - Remember LEDs shoudl be driven with constant current source to have better brightness control.
From your link the Forward Voltage range is : 1.8/2.4V Red - 2.2/2.8V Green (Typical/Maximum)
The Forward current range is (If): 25mA / 30 mA (Red/Green)..
Good luck with your project
At the last Cree training I attended one of the Cree reps mentioned that Cree had entered the LED array (with the CXA2011) market partially due to customer demand for array products. The rep also mentioned that in many cases, discrete LED solutions would provide superior performance vs. a LED array. I am familiar with the advantages an array product offers over a cluster of discrete LEDs so can you please discuss the advantages using multiple discrete LEDs vs an array product of equivalent briteness. For an example lets say your target is 4000 lumens, in cool white.
I am a university student . I am doing a project where i have to design the power drivers for high power led that is capable of delivering the pulse current of 200A at 40V with 1 Mhz repitition. To build the circuitry that support the above parameters i will use MOSFET or IGBTs. What you suggests me which is the best transistor to use or you have another idea about these driver circuits.
I had this question from a member who watched the webinar. he's having difficulty posting
There was a reference in the presentation to what the human eye can distinguish between as far as color temperature is and it gets easier (less k change needed) as the light gets warmer.
Does anyone know where this reference comes from?
Color Temperature Discrimination (Source: Wyszecki and Stiles, Color Science)
•People’s ability to discern differences in color vary by CCT
•Specify your LEDs and design your systems tightly for indoor/warm colors; more loosely for outdoor/cooler
–3000K +/- 50K
–4000K +/- 90K
–5000K +/- 140K
–6500K +/- 240K
hi David, i want to replace my light pendent over my marine fishtank with led, at the moment i use 3x150watt metal halide, can you tell me how many led is equivalent to 1x150watt halide, the colour temp of them are 14000k, is this possible as it will drastically reduce my electric bill
Hope you can help me, as I have searched the net, Only came up with how to make what I am after, I am after an MR16 type 6 V bright LED lamp.
I can only gind 12 V yet the lT BA30w tungstun I have is 6 V, I was hoping to convert my dive torch, as the life is only 40 or less , Do you have such a lamp , or can you make some. I am sure I can sell them On e bay for others like my self.
thank you Gary Bridger firstname.lastname@example.org
i have a question for David. I got a glimpse of something and i think thought it will be great to have a way to change its colour, so i thought of LED. i did my little wurvey and realised there is nothing like that in the market. My challenge is that i need to be developing the thing to be able to line the inside with LED or partner with a company that designs it. i want you to advise me because i'm scared to tell the idea out because it's a new concept and a very marketable one. tnx
I am looking for federal subsidy regualtions on commercial LED tube lighting.
I often meet with LED lights and manufacturer of test test bead not report parameters (because test instrument is not a manufacturer), have what good method? MY English isbad。
I am looking for low voltage, D size battery powered LEDs for outdoor use that are similar to a string of Christmas tree lights. Something like the decorative rope lights used on an outdoor deck but in shorter lengths, from 2' to 4' long. The LEDs need to be inside a clear type tubing that would be flexible. Please advise if you know of a good source.
Does anyone know if there have been any equivalents manufactured for the National LN1042N or LM1830N
Dear David, I am a student studying a product design course in London. I have to design and make a lighting feature which is suitable for mass production and i have chosen to make a light suitbale to be taken camping. I was wandering if you could advise me on any type of LED bulb that would be suitable for such products and if you could help me to find any camping light designers that i can get in contact with it would be appreciated. My light will have to be a small product to be suitable for camping and transportation so the bulb i need cannot use a large transformer.
Thanks for any help you can provide, Ruairi Daly
I work for Home Depot and we sell such a light. It runs off batteries so no converter is needed. You can find it on homedepot.com
I'm wanting to build a DIY "Kino Flo" type of studio light but using high brightness leds. I've seen this done using three row strips of leds, but have no idea of the source. The lighting units I'm wanting to build will be both in 2' and 4' lengths, up to 18" wide, similar to flurosecent tube fixtures. Could you give me an idea as to a source for these multi-row led strips? And what models numbers they may be. I will also need power source, dimmers, and dmx controllers.
What type of driver and configuration do you suggest when using a large number of LED's in an array?
I'm designing a led-backlight for a industrial vision control system using small smd IR-leds (SIR 91-21C/F7, max cont. current = 65mA, forward voltage 1.3 V - 2.6 V).
There're 312 led's on the PCB, arrange like 26 x 12 with a distance of 10 mm between them. I got 24 VDC availibly for power supply.
I was thinking to have 6 to 8 led's in series that will be connected in parallel to build the array. But what are the impact of the buck drivers current feed back
when adding many led's in parallel?
Or do I need to use several drivers to be able to power that number of led's?
diodes last 100,000 hours or more, but the converters used in ac led light bulbs and retro-fit fixtures only last 35,000 hours. Are there any improvements in converters on the horizon. I work for Home Depot, the leading retailer of led lighting, and I am very interested in the latest developments in led lighting. I sell hundreds of light fixtures using Cree diodes.
I am building a new hair salon and would like to use led lighting particularly in the hair color stations what would you recomend in either recessed or track mounted lighting ? I want to display the colors as they would appear in sun light, it is difficult to display in flouresent or incadesant lighting..
how can I use Arduino to make DTMF tone decoder What things do I need to use to build DTMF tone decoder?
Can you offer assistance to design LED driver for CXA 1507 ?
I bought a house but its and Old house (1929). It doesn't have any outdoor outlets and my wife love to put lights out doors when decorating for the holidays. Is there anyway to power standard lights with batteries? She has an a really good extior power station for her lights. I want to be able to plug in that to my battery power supply.
PLEASE SUGGEST SOURCES FROM PUNE OF LED LIGHT FIXTURE MANUFACTURER
I have a Cree dive tourch m And so do some of my fellow divers, Sadly after 3 months of use m the magnets in the swith rusted and the swith broke. How to get replacment switches, and not pay a fortune in postage to post to kotakinabalu Borneo ?
I want to create a LED light for hydroponics. I read that this is not difficult, and hope that an amateur can do it, since the commercial ones are expensive.
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