I am planning on making a Luxeon floor lamp and had a few questions maybe you all could answer. I was wondering if you knew why the white leds are rated in 4500k as opposed to the nm of the others. Is it that much brighter or is that simply the color? I am thinkning of buying 5 Star III's, as they offer the Lambertian light pattern and a 140 degree viewing angle. I am planning on using Linear's LM317T circuit for driving them, as it supports up to 8 I believe. Anyway, let me know what you all think. TIA Derek
Since it it white light which is a combination of all the others, you don't get a single wavelength that you can measure. K is the color temperature lower is a more red/yellow while higher is a more blue color, all still "white" light though.
oh! while we are on the luxeon topic... isn't it possible to make a regulator circuit that doesn't make as much heat? I made that circuit, only with a 7805... I guess it puts out a little more heat, but i would like it to be even less.. (sorry for the thread hijacking...)
The 7805 regulator gets rid of the extra power via heat so in essence it is a little heater. You could build a switching power supply and that would put out less heat then a linear supply. The only way to get less heat out of a linear power supply, I know of, is to make it more effecient by getting as close to the minimum voltage requirement as possible. I think for 7805 it is 8v minimum. You can use a low drop-out regulator and get even closer and that would reduce the amount of heat being produced.
yeah... i know i might have to build a switching powersupply... Is there any good ready IC's that you know of? when i use the 7805 it's the resistor that gets hot, not the regaulator itself (not wery much atleast)
A common trick to powering Luxeons off a 5v switching PSU is to wire it in series with a 4.7 ohm, 1w resistor. Another trick is to connect it in series with a fan (or several fans in parallel) and power the whole device off 12v (use a bench PSU and some fans to experiment).
use diodes in series, much like http://www.cpemma.co.uk/sdiodes.html It still makes the same amount of heat but its spread over all the diodes instead of one chip
With a 317T there'd be more heat from the regulator, less from the resistor. The total heat waste is the same. For 320mA constant current, the 7805's resistor wastes 5 x .32 = 1.6W, the 317T's resistor wastes 1.25 x .32 = 0.4W. 317T is more efficient if you're running a few lights in series, an extra 3.75V available from the supply. You can put 8 in series with a 35V supply, as that's close to the top limit of the 317T. Putting any in parallel on a lower voltage input is more tricky, with the price of the Stars I'd use a 317T on each string.
How is the circuits they use in those luxeon flashlights? Do they use the battery's internal resistance, or something? I had plans of using a few luxeons in the lanterns (?) on a boat... (you know, the red and green lights)... the whole point is to save power,but it wont save much with the regulator circuits wasting all that power...
The only real advantage of the constant-current source system is where the source voltage varies a lot (like a car alternator/battery or running off a charged capacitor) and you want to run near the LED's max limit, or where you might be switching in different numbers of LEDs. If the supply voltage is anything like stable and you can make the supply slightly more than the LEDs need, a resistor is more efficient. I think you can make a transistor CCS with less than the 3V loss of the 317T.
to address the switching power supply Q, there is a TI IC, I'll post it as soon as I find it again. But you need a few more things like a flyback transformer, big coil and a fairly large output cap, at least one high current diode, and a power transistor or MOSFET in addtion to the control IC. Cannibalizing an old PC or laptop supply is probally the better option.
The only switching powersupply IC I am familiar with is the 723 coupled with a 556 IC. The build of the circuit is really easy and can perform step-up/step-down voltage conversions. I have a schematic for +12 to +5v step-down conversion for 1.5A and 3.0A as well as all necessary theory of operation and calculations step-by-step if you are interested.
so I should just scout a 35v DC supply? I know it will be kinda expensive, but I have never built a psu.....
It would be easier & cheaper (not to mention safer) to find a regulated 12V power block rated at 1200mA or more. Taking 3.42V for forward voltage, a 5.6 ohm resistor in series with 3 white luxeons should give about 310mA. Two strings like that and another with 2 x 8.2 ohm resistors in series with 2 luxeons (giving 315mA) will make up the 8. The resistors need to be 2W or more.
I know where to get said small supplies. If you can get your hands on old external enclosures, you may be able to find one with a PSU that can handle it. I have one I salvaded from an old IBM external SCSI enclosure that has a 5 volt line rated for 1600mA. Another option is to check wholesale electronics sites. If you are from the US, you can try MCM, or Jameco. I would also suggest allelectronics, and parts express. But ether the site has changed drastically, or I have the wrong site for allelectronics (why I didn't post the link) and parts express is promarially sound gear.
Perhaps of interest to you. There's his dude on e-Bay selling PWM driving circuits for Luxeons. His online shop is here.
hmm they want $24.95 plus $5 shipping...I'm thinking I can't get the parts for cheaper than that? Can anyone verify that this is an ok deal? http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3240&item=5910148306&rd=1&ssPageName=WDVW
Hmm i did not notice that price . And yes you can build this for WAY below $27, but i can't help you with schematics, not smart enough for that .
well if I can build the lamp for under $100 I will be happy. After all, its not like the leds will burn out like incandescents anytime soon
