LED Driver recommendation

Discussion in 'General Electronics Chat' started by Scott216, Nov 3, 2013.

  1. Scott216

    Thread Starter New Member

    Jun 16, 2011
    18
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    I'd like to drive 4 RGB LEDs from an Arduino Pro-Mini (5V version) using the PWM output pins. The LEDs would all be wired together, I don't need to control them individually. The LEDs are common anode drawing 20mA/color, like this one: http://www.sparkfun.com/products/10821/. I'm looking for suggestions on how to do this. I guess I could get a little MOSFET for each color and use that with a resistor to drive the LEDs, but I know there are a whole bunch of LED driver chips available. When when I searched on Digikey I was overwhelmed with the choices and didn't know where to start. LED Driver can be through-hole or SMD as long as the SMD can be hand soldered. I'd appreciate any suggestions.
     
  2. Danm1

    Member

    Jul 19, 2010
    55
    7
    Take a look at this......

    R1: approximately 100k-ohm resistor (such as: Yageo CFR-25JB series)
    R3: current set resistor - see below
    Q1: small NPN transistor (such as: Fairchild 2N5088BU)
    Q2: large N-channel FET (such as: Fairchild FQP50N06L)
    LED: power LED (such as: Luxeon 1-watt white star LXHL-MWEC)

    [​IMG]
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Do you mean you want all 12 component LEDs to be on at the same time? Don't you wish to vary the overall colour? Won't you require separate control of the R,G,B?
     
  4. Scott216

    Thread Starter New Member

    Jun 16, 2011
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    I do want to change the colors. For example if I want blue, all 4 LEDs would be blue. I don't need one LED to be blue and another to be red. So I'll control all 4 LEDs with 3 PWM pins.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Something like this then? You would need to choose resistor values according to the relative luminous efficiencies of the R,G,B component LEDs so that equal drive signals would give apparent equal brightness.
     
  6. Scott216

    Thread Starter New Member

    Jun 16, 2011
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    That looks like it would work. Could I combine the resistors for each color. For example, get rid of R1, R7, R10, R13 and instead just have one resistor by Q1; either right on the emitter or collector?
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    Common wisdom is that you shouldn't drive LEDs directly in parallel, because there will be slight variations in them that will cause the currents to be different. In fact (depending on how important this project is!) you can very likely get away with it, if the parts you use are all identical and kept at the same temperature. Try it on a breadboard and see if you like the result.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you wire LEDs directly in parallel you will probably find that one is annoyingly brighter than the other.
     
  9. Scott216

    Thread Starter New Member

    Jun 16, 2011
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    I didn't know that, thanks.
     
  10. Scott216

    Thread Starter New Member

    Jun 16, 2011
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    Instead of the three 2N3904 transistors, could I use one of these:
    MMPQ2222A.
    It has 4 NPN transistors in an 16-SOIC package. I'm trying to use more SMT components in my projects. Plus in this project space is kind of tight.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That IC looks fine for the job.
     
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