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Lm317 led current?

Discussion in 'LEDs and Optoelectronics' started by dizwold, Feb 1, 2015.

  1. dizwold

    dizwold

    17
    1
    Nov 14, 2013
    Hi,

    I'm building a PCB drill with a set of LED's, to point on the item being drilled. Apart from the drill side-of-things, could someone advise me accordingly with regards to my proposed circuit below.
    I apologise in advance for R3 'i couldn't find the correct part in Eagle', but it is, a 1K Pot, using 1 input, and then the output from the slider. The LED's '8 of them', are 'i think', 2.8volts 20ma.
    What i'm trying to accomplish is a variable 'dimmer', for the LED's, but to also have a feedback to keep the required current.

    Any input is welcome.

    Regards.

    Dizwold.
     

    Attached Files:

  2. BobK

    BobK

    7,632
    1,657
    Jan 5, 2010
    KJ6EAD likes this.
  3. cjdelphi

    cjdelphi

    1,098
    104
    Oct 26, 2011
    would an el cheapo 1k pot handle the current? 0.020 x voltage (1.25v)
     
  4. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    Finish the calculation. How many Watts will the pot be required to dissipate; and the fixed resistor? What's the power rating of the pot?
     
  5. cjdelphi

    cjdelphi

    1,098
    104
    Oct 26, 2011
    I would not.. I'd build a regulator instead
     
  6. dizwold

    dizwold

    17
    1
    Nov 14, 2013
    The pot is rated @ 0.20W. It's from TE;

    http://www.te.com/catalog/bin/TE.Co...6368,23815&LG=1&PG=1&IDS=490932,490933,490934

    I've tried BobK's idea of using the device a Current Source, but this circuit doesn't allow much control with the pot, it's more like an on/off switch with a little bit of variable light control.

    The circuit @ the top of this thread seems to work well. I've had it operating for about 20 mins with no problems, and nothing seems to get to hot. It also gives me a lot more variable control of the LEDs?
     
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