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3 watt Luxeon driver circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bryan1, Sep 24, 2005.

  1. bryan1

    bryan1 Well-Known Member

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    Hiya Audioguru,
    The 3 watt LED I'm using isn't a Lumined, I got from www.oatleye.com on their LED page. Well the LED is small when I say small it's a perfect fit in the colimating lense which is just under an inch in diameter. I'll have no problem with heat as the box I'm using is alumimuim and the LED it'self is mounted on 1/4" thick Alumimuim. When I buy my next one's I'll get a 15 degree colimating lense aswell as the 25 degree one. I reckon setup on a turrent they will make excellent spot lights for shooting. Anyway I might try the idea of using a 555 to switch the light off afeter a certain time as I have about a dozen 555's sitting around.

    Cheers Bryan :D
     
  2. williB

    williB New Member

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  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hi Bryan,
    Do you know who made your LED to get some specs and ratings for it?
    Are you shooting Wallabees?
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I just noticed that the real Luxeon 5W LED has a 6.84 voltage so must have two LEDs inside.
    It is strange that its lifetime is rated for only "over 500 hours".
     
  6. Oznog

    Oznog Active Member

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    bryan, I think you're missing the purpose of a ballast. It must be higher or you can toast the LED!
    The LED's voltage for a given current is not very predictable. It varies by lot and goes down with increasing temp, which normally increases current. Since the I/V slope of any diode, LEDs included, is quite sharp as its voltage goes down the current can increase exponentially, blowing the device even though you met the design voltage. The reg is not high accuracy either.

    At 0.01 ohm your 7805 will probably go into current or thermal limit. If you want to drive this at 3.7v @ 700mA then get rid of the diode- that diode is bad! You need 1.85 ohms to drop the 1.3v of difference between 5v and 3.7v at 700mA.

    That LED will die in an instant- way faster than you can unhook it- if you drive it wrong. So you need to figure out how these work and have a plan before sticking things together.
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Again, "LEDs should be driven at a constant current".
     
  8. bryan1

    bryan1 Well-Known Member

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    Hiya Guy's,
    Eh Oznog thank you for all the advice you've given me so far, I haven't done anything since I took the photo last night so I'll wait and buy the $9.10 kit WilliB gave the link to ( Thanks WilliB ). I'm going to order a few more LED's from oatley's so for the price I'll use their kit to be on the safe side. When the supertex chips turn up I'll get my head into researching the datasheets and have a go at making my own. Oh and Audioguru the purpose of the spotlight is for shooting our national emblem the kangaroo. I've got about 12 of them residing on my farm and I'm kinda partial to kangaroo tail soup :lol:. When I get a chance I'll take a photo or two as 2 of them I saw today R huge. :shock:

    Cheers Bryan :D
     
  9. williB

    williB New Member

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    :wink:
    you are getting a wind genny?? cool...
    who makes it..?or is it a home brew??
    details plz..?? lol
     
  10. bryan1

    bryan1 Well-Known Member

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    Yea Willi,
    It's an old mainframe tape drive motor rated at 50 volts nominal I've had for years and I've nearly finished the tilt up mast for it but I've got to remake the frame for the genny with a furling tail as we get some violent wind gusts here.

    Cheers Bryan :D
     
  11. williB

    williB New Member

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    cool..
    what current does it draw..?
     
  12. Oznog

    Oznog Active Member

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    Do be aware of the efficiency issue. At 12v source, with or without the 5v reg, your efficiency is 30%. This is of course a significant amount of heat as well. Any linear solution will have this problem. The HV9910 is around 95% efficient provided you choose a decent inductor.

    If you're buying devices for area light rather than a flashlight, I would urge you to look up Lamina ceramics devices. Their BL2000 have a far, far more efficient heat strategy. It's a paper-thin wafer you attach with thermal epoxy to a flat surface of any thick chunk of aluminum. They're around $13 for colors, $18 for white. Laminas are much more powerful than Luxeons. Their light comes from a number of emitter chips on the wafer and is thus more difficult to focus, so it generally does not make a great flashlight.
    http://www.laminaceramics.com/docs/BL_2_White_43.pdf

    Bitchin cool- it hardly stands out from the heatsink at all, but makes LOTS of light. Luxeon emitters can't really be mounted straight on heatsinks because they didn't electrically isolate the thermal backing. The Luxeon Star doesn't solve that problem either.

    That brings up a good point. Do you have the star's board completely isolated from power supply's ground? If not you have a major problem.
     
  13. bryan1

    bryan1 Well-Known Member

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    Hiya Oznog,
    Those Lamina led's look awesum and I did notice there isn't a dealer in Australia which means I'll have to get them from the US. So postage could be the big killer but i'll e-mail mouser first as I don't want to get stung with $110 US in postage again ( that happened with digikey for 10-16 pin chips :shock: ). As most of my friends live off the grid I'm sure they would love a few for themselves so when I can afford it I'll get a few over and set them up. Oh and the LED is totally isolated from the box, I made sure it was before I glued it on the heatsink.
    Thanks for the link too mate

    Cheers Bryan :D

    P.S. Eh WilliB, I Lathe tested the genny I worked out around 250 watts output but in real life it will be different.
     
  14. williB

    williB New Member

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    around 5 A ehh , thats a respectable current.. :wink:
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hee, hee. :lol: I think Bryan is going to use the motor as a windmill's generator, not as a wind-making machine. :lol:
    Can you imagine trying to make a wind in the opposite direction to try and cancel the real wind?
    President Bush should get NASA to try and cancel those darn hurricanes.
    I hope they don't begin using nukes to get rid of hurricanes. Then bye, bye Cuba and Jamaica (and maybe also Florida?)
     
  16. Optikon

    Optikon New Member

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    where can I get a Mickey Mouse diode? Is their Vf lower than a schottky?
     
  17. williB

    williB New Member

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    :lol: i realize that , and i also realize a DC motors current draw is a good indication of the motors output when driven by wind , a lathe , or whatever.. :lol:
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Disneyland. :lol:
    Mickey Mouse diodes at the output of a voltage regulator ruin its superb regulation.
    Mickey Mouse diodes are also used with a pullup or pull-down resistor as OR gates for Cmos inverters.
    [​IMG]
    How do I insert this image?
     

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  19. bryan1

    bryan1 Well-Known Member

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    Hiya Guy's,
    Well I got my sample HV9910 chips from supertex today and they ended up coming from a local supplier :D Anyway below is a schematic for a high brightness LED, the output is 4.5 volts @ 900mA. Now I've just spent a couple of hours studying the datasheet and trying to workout how to get the output down to 3.6 volts @850mA. I'm going to use a 12 volt 7 amp/hour battery for the power supply. But I'm a bit stumped on how to work it out. If anyone can help me out on this I'll apprecieate it.

    Here is a link to the datasheet http://www.supertex.com/pdf/datasheets/HV9910.pdf

    Cheers Bryan :D
     

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  20. Oznog

    Oznog Active Member

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    What part confuses you?
    You need a 0.277 ohm resistor for the feedback. A huge variety of SMD low ohm resistors are available and are easy to solder onto the backside of prototyping board. Leaded ones have far less selection available.
    You can use a lower ohm resistor (higher is not possible) if you go with the external voltage reference solution.
    SOIC-8 transistors are a really good idea for this. Little heat and they have very low rds for efficient switching.

    Diode should be Schottky type. Rating it for at least the 900mA output current is good. There are very common 3 amp ones and I'd recommend those.

    That schematic you showed is an example which rarely works smoothly in the real world. You need a RC filter between CS and R10 with an RC time constant of 300nS. The surge (which can be large) of current turning on the gate also travels down the source and makes a momentarily higher voltage on R10, which may result in resetting the output latch. The problem becomes more likely when you use larger inductances which make a nice, clean, low ripple output. Low ripple means that the inductor may only be at 875mA when it switches the transistor on- gate takes 100mA from the HV9910, R10 reads like it's 975mA, way over the theshold, and shuts off the drive immediately.

    BTW- since I've already been through this- these are great inductors for this job (and cheap!):
    http://www.electro-tech-online.com/custompdfs/2005/10/sdr1806.pdf
    101K is probably the best choice for 900mA. Maybe 151K.
     
  21. bryan1

    bryan1 Well-Known Member

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    Hiya Oznog,
    Eh mate as you know thats a schematic I pulled off the datasheet. When you say use an R/C time constrant to 300uS could you possibbly show me how it's done. I'm not really sure how to implement that and even the general schematic shown on the data sheet doesn't show it either. I'm a mechanical bloke and electronic's are a great learning experience for me with real life things I can do. So any help I can get is both a help and a learning experince too.

    Cheers Bryan :D
     

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