RGB driver connecting ground side of outputs question

Discussion in 'The Projects Forum' started by russpatterson, Oct 9, 2013.

  1. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    Hello,

    I'm making some RGB LED lights, using these buck puck drivers,

    http://www.luxdrive.com/content/3021-BuckPuck.pdf

    My question is, for the output leads that go to the LED strings, can I tie the ground sides together (and run less wire)? They are diodes after all but I don't want to screw up the current sensing in the drivers by adding something else to their ground output pins. I've always kept them separate in the past.

    Here's a rough schematic
    http://screencast.com/t/x1mZJZ1u
    [​IMG]

    Thanks!
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,659
    632
    No wonder you can't tell from the datasheet -its a real "black box". I would not try connecting the LED- connections in parallel unless the manufacturer said it was ok. If you the ask the manufacturer this question, they might add it to the datasheet so others won't have this question.
     
  3. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    I was looking at the datasheet and noticed that they have the LED- pin and the ground of the microcontroller connected tied together in their uC sample schematic. [​IMG]

    They also say:
    "Note that the input needs to source a minimum of 4.75VDC into a 1.5Kohm
    input impedance. Also, as is the case with a dc control signal, the logic input ground should to be common to the
    LED- output terminal."

    So if the uC ground and LED- are tied, then that implies that all the LED-'s are tied to the uC ground and all LED-'s are tied together. Can anyone confirm?

    Also, I'm trying to determine if it's ok to connect two driver control pins to the same uC output pin. It says 5V into a 1.5kohm input impedance. Will my PIC output pin be able to drive to drivers with it's 5V 20mA rating? Are you supposed to derive current givent the "5V into 1.5kohm" numbers?


    Thanks!
     
    Last edited: Oct 16, 2013
  4. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    It turned out that when the uC ground pin was tied to the LED output ground of the driver, the uC would reset once the input voltage got to about 22V and above. Connecting the uC ground to the ground of the input voltage worked fine. The schematic sample in the BuckPuck data sheet shows how to connect it wrong. (at least for the buckpuck)
     
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