ULN2003 or single transistors

Discussion in 'General Electronics Chat' started by stoopkid, May 27, 2012.

  1. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
    1
    I'm gonna be using some shift registers to PWM some sets of RGB LEDs using an arduino shiftPWM library. There will be five different sets of LEDs, three colors for each and three series of three LEDs that I wish to power from 12v. So that will be 15 channels of 12v, 60mA each. Should I use a bunch of 3904 and 3906 transistors, or should I use some ULN2003 chips? Can the ULN2003 operate at arduino PWM frequency? Would it get too hot at 420mA per chip?

    If I used regular transistors, I can just sink the cathode of the LEDs with a 3904, pulled high, right? Would that be a better idea than trying to use the chip?

    What would you do here?

    Thanks
     
    Last edited: May 27, 2012
  2. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    2003's are good and save space. I use them to drive 7 seg displays up to 600mA (total, per chip), and have no problems.

    Dan.
     
  3. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    If you're using shift registers anyway, you might want to look at serial-to-parallel sinking or sourcing driver ICs or serial-to-parallel constant current sinking driver ICs (no LED current limiting resistors required).

    The Micrel MIC5891 serial-to-parallel sourcing driver IC has separate VCC and VBB inputs which help reduce circuit complexity for driving segments with multiple LEDs in series at a higher voltage. For example, the following circuit uses my MacMux method to drive sixteen 12-volt channels using only three I/O pins.

    Good luck on your project.

    Cheerful regards, Mike

    [​IMG]
     
    Last edited: May 27, 2012
    Sparky49 likes this.
  4. Sparky49

    Active Member

    Jul 16, 2011
    834
    417
    I agree with MMcLaren - try using display drivers.

    Transistors would work, but for ease of construction I would use drivers.
     
  5. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
    1
    I need to drive the cathodes. Another forum suggested the use of a TPIC6B59 which is the 595 and MOSFETs built in for up to 500mA per chip I think. Is that a similar idea? I need whatever I use to be compatible with the 74HC595 because the library I am depending on uses it.
     
  6. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    Just curious... Why wouldn't you have the choice of driving anodes or cathodes? Among the features listed on the ShiftPWM web page is;

     
    Last edited: May 28, 2012
  7. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
    1
    Because I already have the LEDs and they are common anode
     
  8. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    Ok. Sorry! I suspect that if you had described them as "five common anode RGB LEDs" in your first post you could have saved us both some time.
     
  9. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    Look at the TLC5916 constant-current driver.
    /mike
     
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