Constant Current regulator

Discussion in 'General Electronics Chat' started by bedfordwheelnuts, Jul 14, 2011.

  1. bedfordwheelnuts

    Thread Starter New Member

    Apr 19, 2011
    7
    1
    Hi All,
    I am looking at the NSI45020AT1G constant current LED driver device from On Semi.
    I wondered if anyone else has used the device because on paper the device seems everything I need. I have bulit a prototype circuit, and I am dissapointed with the measured performance against the data sheet spec. I appreciate that the device regulates 20mA at +/- 10% but I am getting much worse regulation than that.
    Anyone had similar experience with this device?
    Kind regards
    Jeff
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Link to datasheet: http://www.onsemi.com/pub_link/Collateral/NSI45020A-D.PDF

    What is the total Vf of the LEDs that you have in series, and what is the source voltage across the entire series string including the regulator?
    Did you plan for the 1.8v minimum "overhead" that the regulator requires?
    Did you plan on variances in LED Vf in your strings?
    Do you have adequate heat sinking for the regulator? (this is a biggie, the datasheet has lots of information on this)
    What is the current that you are seeing through the LED or LED string?
    Does the current remain constant from first power-up through when it is unsatisfactory?
     
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