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Thread: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

  1. #31
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jeffosborne View Post
    You need to include the super-simple LM336-2.5. It is a 3-pin device that looks like a small signal transistor. It connects to ground, and to the supply voltage through a 5K ohm resistor, and provides a very stable 2.5 volt output.
    If you need a 2.4 volt Zener Diode and you don't have anything else, you can use a Red 3mm or 5mm LED !

    They can also be used as a voltage-generating light detector !

  2. #32

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Man, the craftmanship of that light is extraordinary!

    Where did you get your red LED's? I am looking for some to make a night vision light of sorts. Thanks!

  3. #33
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    That is such a great idea, beautifully made! The design is fantastic - it looks so completely professional. I bet you could sell plenty of these to professional studio photographers.
    Resistance is futile...

  4. #34
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jeffosborne View Post
    Hey jason, it is good to hear you are trying out the circuit! My partial schematic's 2.5 volt reference is the output of a LM336-2.5 precision reference diode, that I include in most every design that requires a comparator.

    As the supply voltage varies, whether that is a battery's declining voltage, or some ripple or noise in a AC-to-DC power supply, the voltage divider that your potentiometer is a part of is delivering that variance to the comparator, causing the drift and error you are seeing.

    You need to include the super-simple LM336-2.5. It is a 3-pin device that looks like a small signal transistor. It connects to ground, and to the supply voltage through a 5K ohm resistor, and provides a very stable 2.5 volt output. Your potentiometer and resistor then provides a stable reference voltage to the comparator. The part is 31 cents each at Future Electronics.

    The thermal portion of the circuit was asked about also. Really, I must get the whole schematic drawn out and share it. It is on my to-do list!

    Cheers,
    Jeff
    ok I now have the LM336 and hooked it up so that it is supplying the 2.5 volts to the 220K ohm resistor, instead of the lm239 I used a lm339 dual comparator. I am still getting a dimming/brightening when I touch the POT or the heatsink on the led, or any of the other parts of the circuit? Am I doomed to not be able to use this cool circuit for myself? LOL

  5. #35
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jason 77 View Post
    I am still getting a dimming/brightening when I touch the POT or the heatsink on the led, or any of the other parts of the circuit?
    If you're getting dimming/brightening then yoru circuit is oscillating and your body capacitance is causing it to change.

    Try connecting a 0.001uF (1000pF) between the output of the 339 and the - input.

    Try shortening wiring and keeping the opamp input wires away from those carrying high current.

    You need a single-earthpoint to stop oscillations.

  6. #36
    Flashaholic* Walterk's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Very nice!

  7. #37
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by MikeAusC View Post
    If you're getting dimming/brightening then yoru circuit is oscillating and your body capacitance is causing it to change.

    Try connecting a 0.001uF (1000pF) between the output of the 339 and the - input.

    Try shortening wiring and keeping the opamp input wires away from those carrying high current.

    You need a single-earthpoint to stop oscillations.
    ok I re-did the circuit the best I could to use shorter wires and also to seperate the high power mosfet part from the comparator as well as use a .001uF cap like Mike suggested. I also messed up my previous post as I am using a LM393N dual comparator and not a LM339...

    Still having oscillation issues I guess as it still dimms and brightens when I touch or get near the circuit. Also the max amperage the led gets is like 1.3 amps and not the 900mA that I had calculated for this circuit....

  8. #38
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Comparators have very high gain, so you really need the capacitor across input and output, as well as a 10uF from +ve battery to earth (-ve).

    Especially if you have open wiring, rather than a Circuit Board.

  9. #39
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Sorry to leave the schematic yet undone, so many things to do it seems.

    Anyway thanks MikeAusC for your insightful observations. I did go over the spec sheet for the LM393 part, and saw that it does have an open-collector output, which is required here. It also operates well with low voltage inputs, which is also needed. So the part should be fine for this regulator. Jason, I wonder about the second comparator on this IC. If it is not being used, you should tie it's inputs to ground, so they are not open to making an oscillator. The output of the unused comparator can remain unconnected. Also, what is the value of the sense resistor you are using? And, do you have the 100K pull-up resistor on the output of the comparator?

    Thanks again for all the encouraging words regarding my light! It is a handy tool. It was used to shoot some baby photos lately, Noah is 6 months old:

    Jeff O.

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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jeffosborne View Post
    Sorry to leave the schematic yet undone, so many things to do it seems.

    Anyway thanks MikeAusC for your insightful observations. I did go over the spec sheet for the LM393 part, and saw that it does have an open-collector output, which is required here. It also operates well with low voltage inputs, which is also needed. So the part should be fine for this regulator. Jason, I wonder about the second comparator on this IC. If it is not being used, you should tie it's inputs to ground, so they are not open to making an oscillator. The output of the unused comparator can remain unconnected. Also, what is the value of the sense resistor you are using? And, do you have the 100K pull-up resistor on the output of the comparator?
    Thanks for the advice Jeff and Mike, I rebuilt the circuit again and grounded the two inputs on the second comparator that isn't being used, as well as putting the .001uF cap across the output and - input of the comparator and the 10uF cap across the + and - of the power. Unfortunately the dimming/brightening problem persists, although much less so when touching the led heat sink than before... the pot still has the same amount of it though.

    Below is a drawing I did of how I have the circuit hooked up.. Any thoughts?

  11. #41

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Aside from its functional considerations the unusually high quality of your work has created a device that is very aesthetically pleasing, even beautiful.

    Brightnorm

  12. #42

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jason 77 View Post
    Thanks for the advice Jeff and Mike, I rebuilt the circuit again and grounded the two inputs on the second comparator that isn't being used, as well as putting the .001uF cap across the output and - input of the comparator and the 10uF cap across the + and - of the power. Unfortunately the dimming/brightening problem persists, although much less so when touching the led heat sink than before... the pot still has the same amount of it though.

    Below is a drawing I did of how I have the circuit hooked up.. Any thoughts?
    It would be better to tie one input to ground and one to something else besides ground, that way it stays in the same state. If you have them both the ground, then as the ground potential changes during switching etc... it can cause the unused comparitor to change states, and add noise to the power line, etc. All it takes is a tiny change for one pin to be above the other.

  13. #43
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    I would add another 10uF from the Comparator + input to ground.

    It's standard practice to Earth all unused inputs - provided you have a good ground point.

  14. #44
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Jason 77, your schematic looks fine EXCEPT - (1) I would get rid of the .001 capacitor at the sense resistor, and (2) check the voltage at the positive input of the comparator with the potentiometer set to max. .05 volts gives you 1.0 amp. I get .045 volts there at 850ma, for example. Also, I sent you a private message, not sure you check your forum messages... Jeff

  15. #45

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Jeff that is a great looking light you came up with! I'm wondering if you have any long term reports from using the light? How has it held up? Have you modified it any further? Have you made any newer versions? I'm working on a design myself and this light has been a huge help and inspiration. Thank you very much for detailing the build.

  16. #46
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    WOW awesome build but where are the night time shot's?

  17. #47
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    This is not a flashlight, this is an indoor studio light

    Jason 77, could it be that your issue lies in the use of a current sense resistor at 5% tolerance and an logarithmic pot as opposed to a linear taper?
    Last edited by Illum; 03-28-2011 at 10:05 PM.

  18. #48
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Howdy Illum, Potato42 and rokspyder!
    I can report that the high-CRI light has been getting a workout. At Christmas the family group photos were better than ever. Baby Noah comes every 3 months for new pics and I really enjoy that, and I did some product photography recently for my daughter's etsy site. My son used the light for a college graphics design class project, titled the Cinderblock. rokspyder, I hope this will suffice for that ever-popular night time shot:

    Here is the title page from the Cinderblock booklet he produced, also made using the high-CRI light:

    The high-CRI light remains unmodified. But I have made a new light that helps to fill-in with my photo lighting setup, Hydra-3. It is a non-high CRI neutral white Rebel-ES 1000-lumen flashlight and 2,000 lumen floodlight. It does have a light-stand fitting like the high-CRI light:

    I plan to post a complete write-up for the Hydra-3 soon.

    Jeff O.

  19. #49
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Very cool Jeff, I look forward to seeing the Hydra-3 write up!

  20. #50

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Thanks for the follow up Jeff! That Hydra-3 looks interesting as well. I see you used reflectors in that one. I am thinking of something along the lines of both your designs combined, although a bit larger. I found a company that extrudes heat sinks in a number of different sizes to use as the base. Where did you get the aluminum and what kind is it? It doesn't appear to be annodized, but perhaps you clear coated it? Since aluminum oxidizes so readily, I'm wondering if you've noticed any changes in the finish of your light. Also if you'll indulge one more question, why did you opt to build your "driver" rather than use an off the shelf component?

  21. #51
    Flashaholic* griff's Avatar
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Killer Hydra-3........
    Sometimes, when I'm feeling down because nothing seems to be going right, I like to take a home pregnancy test. Then I can say, "Hey, at least I'm not pregnant

  22. #52
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    very nice! clean and pro!

  23. #53
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    very inspiring!
    22, 47.867, [Ar] 3d2 4s2, hcp, 21.9 W/(m·K), 420 nΩ·m(at 20 °C)

  24. #54

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Beautiful work, looks like an industrial piece of art. How many lumens is that putting out? Someone needs to build something like that with a bunch of reflectors or lenses and make a cannon of a search light with high cri (ha!).

  25. #55
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Nice project work. I am getting the urge to built up a photo light for personal use. - I hope you don't mind if I borrow some ideas from yours.
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  26. #56
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    HarryN, I would be flattered if my ideas are borrowed! Let me know if I can assist in any way. Here's a tidbit of info: my light could have supported 21 or 24 LED's and not just 18. The heatsink and fan operate rather leisurely, and could support more heat removal. More light is often good in the studio.

    Potato42, the aluminum is type 30-06, purchased at a local sheet metal shop. The finish on the light has not changed much over time, but I will consider an enamel clear coat for a future light. I built my own driver because I can (electronic design is my occupation), and because I wanted functions that off-the-shelf varieties do not offer. No PWM was one design objective, another being a linear regulator, and not switching regulator.

    Jeff

  27. #57
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    HarryN, I would be flattered if my ideas are borrowed! Let me know if I can assist in any way. Here's a tidbit of info: my light could have supported 21 or 24 LED's and not just 18. The heatsink and fan operate rather leisurely, and could support more heat removal. More light is often good in the studio.

    Potato42, the aluminum is type 30-06, purchased at a local sheet metal shop. The finish on the light has not changed much over time, but I will consider an enamel clear coat for a future light. I built my own driver because I can (electronic design is my occupation), and because I wanted functions that off-the-shelf varieties do not offer. No PWM was one design objective, another being a linear regulator, and not switching regulator.

    Jeff

  28. #58
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    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Once was a pile of parts...

    What fun it is to build!

    Jeff
    Last edited by jeffosborne; 04-12-2011 at 05:53 PM.

  29. #59

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jason 77 View Post
    ok I re-did the circuit the best I could to use shorter wires and also to seperate the high power mosfet part from the comparator as well as use a .001uF cap like Mike suggested. I also messed up my previous post as I am using a LM393N dual comparator and not a LM339...

    Still having oscillation issues I guess as it still dimms and brightens when I touch or get near the circuit. Also the max amperage the led gets is like 1.3 amps and not the 900mA that I had calculated for this circuit....
    Jason 77, if you haven't given up, allow me a silly question. You do realize that you have to supply ground and V+ to the comparator, right? These connections are not shown in the schematics reproduced in this thread.

  30. #60

    Default Re: Homemade 15 emitter high-CRI Rebel LED flood light with red and cyan boost

    Quote Originally Posted by jeffosborne View Post
    ... The pot controls a voltage level given to one input on the comparator: ...

    The brightness control is the 10K pot near the center.
    Jeff
    I'm more than a little confused by the schematic as given.

    1) At max pot setting, the + input is connected to a voltage divider of 6.667k / 226.667k, right (the parallel of 10k and 20k being 6.667k). The 2.5 volt reference, coming through this voltage divider is going to be (6667 / 226,667) * 2.5 = 0.0735 volts into the + input - right? The comparator is going to drive the MOSFET so as to make the - input approach the + input. So the voltage across the 0.05 ohm sense resistor is going to be 0.0735 volts - not 0.045 volts. That equates to a current through the sense resistor of 0.0735 / 0.05 = 1.47 amps - right? Not 0.9 amps, or 0.85 amps. So where am I going wrong?

    2) What is the purpose of the 20k fixed resistor? Wouldn't the voltage divider be just fine with a single fixed resistor in series with the pot? I am guessing maybe the fixed resistor is to lessen wiper noise on the signal.

    3) What is the purpose of the 100k resistor? Is the LM239 an open drain guy?

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