12v LED Strip Dimming using KC24W Constant Current Driver

Discussion in 'The Projects Forum' started by rumpole, Jul 14, 2015.

  1. rumpole

    Thread Starter New Member

    Jul 7, 2015
    2
    0
    Hi all,
    I'm currently super frustrated trying to get a simple LED circuit working (I've spent a lot of hours trying!). Hoping someone here can help a beginner out a little :)

    Here's what I'm trying to do:
    I bought a small amount of 12v LED strip (about 30cm worth), and I wish to be able to dim the strip using a potentiometer. I purchased the KC24W LED Constant Current driver to help me achieve this (data sheet link is below), particularly because I noticed it featured an analogue dimming control. This took my fancy since I'm trying to keep things simple and don't feel any where near confident enough to get involved with PWM.

    I'm struggling trying to figure out how to do the dimming part of the circuit. On the data sheet, it clearly states that dimming can be done using either PWM or analoge (my preferred option) using the 2nd pin. The data sheet also sais to use '0-10v', where 0v will be "full on"(maximum brightness?), and 4.5v will be "full off" (lowest brightness?).
    I've got my circuit diagram shown below, and the bit highlighted in red is what I can't figure out how to do. Could someone please help me understand this, and if possible provide an extension to my circuit diagram showing what it should look like and how I can control this '0-10v' or '0-4.5v' using a potentiometer (I bought a 100k pot but suspect I may have picked the wrong one - I guessed at the time of purchase) ?
    Also does the '0-10v' source share the same GND the KC24w (pin 4) ? As one of my tests I tried simply providing 1.5v using a AA battery and expected a result however nothing happened.


    * The LED strip is rated at 12V, and when I run it in series with my multimeter it draws 165mA @ 12v.
    * KC24W data sheet link: http://www.jaycar.com.au/medias/AA0...JlNzI4ODdhYWM4ZGI5OWMyYmRjMGNhZDliNzBkODljN2I



    LED Circuit.png

    Thanks a lot,
    Rumpole
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    On page 2 of the datasheet is says the programming current into/out of (who knows?) the analog programming pin is 0.2 mA, or 200 uA. If this were connected directly to the +12 through a resistor, a resistance of 60 K would deliver 200 uA (assuming the nominal analog input impedance is zero, a worst case condition). So the source impedance for the analog input needs to be less than 60 K. (In lieu of actual design data, we're winging it here.)

    Exchange your 100 K pot for one somewhere between 1 K and 10 K. If the pot is not marked with pin numbers, rotate the pot fully counter-clockwise and measure the resistance from the center pin to each outside pin. The zero ohm pin is #1, the high resistance pin is #2, and the wiper is #2. Delete the 6.8K resistor. Connect pin 3 to the +12, pin 2 to the analog input, and pin 1 to GND. Start with the pot fully counter clockwise and the LEDs should be on. *Slowly* increase it until the LEDs are off. This should happen at less than 50% rotation (see chart on p. 3). If the off-to-full adjustment range is crowded down to one end of the pot, put the 6.8K back in series with the wiper connection to the analog input and see if that expands the range a bit.

    ak
     
  3. JWHassler

    Member

    Sep 25, 2013
    201
    33
    The two resistors serve to reduce the "0-10V" input-range to a "0-6.9V" range: large enough to span the the entire dimming range without wasting much potentiometer-travel.
    Connect a pot like this:
    upload_2015-7-14_7-56-41.png
    The value of the pot is not easy to nail down ( takes someone with data-sheet skillz) but, judging from the resistor-values in the example, 10K should work.

    It just doesn't feel right to have the positive-input at the bottom of the sheet.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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  6. rumpole

    Thread Starter New Member

    Jul 7, 2015
    2
    0
    Thanks everyone for your replies. I didn't have any success unfortunately. No matter what I tried I couldn't get the LED's to dim. They were either full brightness or off. I also tried a 1k,10k, and 50k Pot, in place of the 100k pot I was using.

    I've seen the cheap dimmers available online but where's the fun in that :) I'm treating this as a 'project' and want to at least attempt to do as much of it myself as I can.

    I'm doing a little research on PWM circuits so I think I'll scrap the KC24W LED driver I bought & put in a PWM circuit like everyone else seems to be doing these days. Also I'll be powering it off a bunch of AA's so to reduce bulk I'm also considering either purchasing a step-up voltage regulator to 12v or if I can find a circuit diagram, making one :)

    I'll post back here once I have any update.

    Cheers
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    If you simply put a 1.5V battery across ground pin and dimming input pin and nothing happened then either you have a wiring error or the driver is junk..
    That simple test will dim the LEDs..
    Now it could be that you simply can't see the difference.. So use a 9V battery.
     
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