Buck Puck LED Driver?

Discussion in 'General Electronics Chat' started by spinnaker, Jan 27, 2010.

  1. spinnaker

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    I have a LED spot light from a old garden solar light. The light was powered by a 12V battery connected to a LED driver. The driver / charge controller os fried.

    The light has 36 large white LEDs. 12 rows of 3 LEDs in series.

    The Sarge has already me a lot of help on this in another thread and we have determined that the driver had a PT4115. According to the datasheet and sensing resistor, it was putting out 606 ma,

    I have tried contacting the totally worthless Silicon Solar (even their email does not work properly) and they tell me they know nothing about the type of LED in this light.


    I would like to make use of the light in an upcoming project.

    I do not know if I have enough confidence to build a buck regulator from scratch and was thinking of using a Buck Puck.

    The one I have in mind has an adjustable current through an internal trim resistor. A really nice feature of this device is it solves a second problem supplying regulated 5VDC for a PIC that I intend to include in the project.

    Has anyone had experience with these devices? What are the chances it will work with these unknown LEDs? Is it a matter of working ot not working or are there long term effects that may occur? The only thing I can think of is if I did not calculate the current correctly and but stress on those LEDs shortening their life.
     
  2. retched

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    Shortening the life of the led's with over-current will be the likely scenario. You should be able to find out the info on these leds.

    Can you pull out 1 led for testing?

    But you want to make sure the power to the PIC is regulated so if something weird does happen with the led circuit, you don't send too much current into your PIC. Also, if you loose a few of the LEDs, you will loose their voltage drop causing too many volts to the PIC.
     
    Last edited: Jan 27, 2010
  3. spinnaker

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    Sure I could probably pull one. Looks pretty easy to do. What did you have in mind?



    Yep it is regulated. In fact the datasheet says that the 5VDC is there for a MCU. :) There is an input for an external dimmer pot but the datasheet says it can also use PWM from a MCU.
     
  4. SgtWookie

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    One of the strong points of the PT4115 is the low "headroom" required. None was even stated in the datasheet.

    BuckPucks require at least a couple of volts of "headroom". I'm afraid that you won't be able to drive your 12v array from a 12v battery using a BuckPuck.

    I think you're going to have to build one.
    This one looks interesting - check out the circuits in the datasheet; not very complex:
    http://www.futureelectronics.com/en...-linear-mode/Pages/1293489-ZXLD1360ET5TA.aspx
     
  5. spinnaker

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    Yeah think you mention "headroom" in the previous thread. I guess that means the puck will actually drop a couple of volts?




    Hummm, that is that surface mount stuff. I bought a FET with the same packaging. I am not sure my soldering skills are good enough to work that small. Not to mention my hands shake a bit.

    I was short of hoping the buck puck would work for me. Any other alternatives? Maybe a different battery setup? But then I might have charging issues.
     
  6. spinnaker

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    The other thing I would need to worry about then would be building a regulator for my PIC.


    What would happen with the buck puck? Would the light not work at all? Or just dim?



    Could I modify the light? Maybe take out a row or two of LEDs?
     
    Last edited: Jan 27, 2010
  7. SgtWookie

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    You know, that PT4115 in the original board might still work - and it's a DIP, and you can salvage the inductor from the board. Just unsolder the thing. Price is right, too. ;)
     
  8. spinnaker

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    No it is TINY! About the same size and package as the one you posted. I can't imagine desoldering it as well as soldering it.

    I suppose I could remove the charge controller circuitry but without a schematic that might be difficult.


    What about the removal of LED idea?

    I really do not have a lot of faith in anything this company has turned out. excpcept maybe the light. It is hard to mess that up. :)
     
  9. SgtWookie

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    You'd have to short across an entire row (or column) worth of LEDs.
     
  10. retched

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    Does the original circuitry still work?
     
  11. SgtWookie

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    The charge portion of the original circuit failed; he gets practically no charge current.

    Whether the LED driver portion works or not has not been determined, I don't think.
     
  12. retched

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    [ed]
    The charge circuit is dead, so what about charging the battery externally than replacing it into the device to get our numbers?
    What type of battery was in the original device?
    [/ed]

    It would be nice to get the power circuit operational to see what the power was. Well, that is, the power this designer put to the leds.

    Are there any resistors in line with any of the leds? Or the resistors for the adj of the power regulator? That would help to tell what kind of power they were looking for.

    How about an overall voltage drop reading then devide by 32(# of leds) That may get us into the ballpark for requirements. A powersupply with variable voltage and current, slowly stepping up until you had nice light. That would get you a number to work with.

    What type of test or bench equiptment do you have access to?
     
    Last edited: Jan 28, 2010
  13. spinnaker

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    No it's fried. Not sure what happened but it was all working and the next thing I know it was fried.

    I wish it was still working then I could either incorporate it into my project or at least get voltage measurements and such, so if I needed to redesign something I'd have a starting point.
     
  14. spinnaker

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    It does not appear like there is anything in series with the light except for the coil off of the PT4115. It looks like that buck regulator feeds the light direct.

    I was thinking the same thing on a variable supply. I actually just built a 2 - 35VDC variable supply. I might as well put it to good use.

    Would I need to use a current limiting resistor? If so what would be a good starting value?
     
  15. spinnaker

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    An update on the original board.

    I just went over the board again with the same results as last time. Thought I would post them in hopes someone could give me a hint of how to fix it.

    Here is what I found before and just found again now.

    The fuse was blown. I jumped in a similar .5 amp fuse. The fuse did not blow but the light did not work either. I did notice that there was one small transistor that gets very hot. It is an S9013 and it's collector is connected to the gate of a F9540N power Mosfet. I believe this is the MOSFet that switches the solar panel off after the battery is charged. The solar panel is connected via a resistor to the source of the mosfet.


    And if this circuit is malfunctioning, it might make sense that the light does not light because the board senses the voltage on the panel. It turns the the light on when the voltage is zero (or whatever low output they picked) from the panel.

    Could that S9013 be shorted?
     
  16. retched

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    The s9013 could very well be shorted. The unwise method of powering could have fried your components.

    You would think that with about a 2v drop across each led, you would need quite almost 65v to light the set. Can you tell if they are wired in series or parallel?

    Can you easily pull one led? That way you can have the numbers you need and get on with the build.

    Also, draw out the wiring diagram for the leds. That will show how they are wired and in turn how they should be powered.
     
  17. spinnaker

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    What should I have done?




    There are a total of 36 LEDs. There are sets of 3 LEDs in series. Each of these sets of LEDs are in parallel with one other. So if you think of the 3 in series as one big LED, there are 12 LED sets in parallel with one another.


    I will try and pull one to see if I can see any numbers.
     
    Last edited: Jan 28, 2010
  18. spinnaker

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    Before I pull one of the LEDs. They are pretty small. Would they even have a number on the back?
     
  19. retched

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    No, they wouldn't have a number on the back. But with one LED, you can hook up a 9v battery and a 330ohm 1/4watt resistor to get the voltage drop. For clear leds it will probably be around 3.4v. Once you know that for sure, you can design the power supply. I say it should be around 3.4v, but you may test it and find its 2.2v So you want to get that number, then we can chart it to see what the average current is with that type of LED.

    Once we have current and voltage, we can build the supply. (Im sounding like a broken record.)
     
  20. spinnaker

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    Thanks for all the help!! :)

    I have a 330 ohm resistor on hand.

    As mentioned, I also have a variable 0-32V 1A bench supply that I have built.


    I think I will pull the LED tomorrow. And do some testing.

    I sure hope we can get this working with something off the shelf or at least easy to solder up. As I said the nice thing about the buck puck is it provides me 5 VDC regulated.
     
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