LED 555 PWM 1%-99% suggestions

Discussion in 'The Projects Forum' started by knowtankyou, Mar 6, 2016.

  1. knowtankyou

    Thread Starter Member

    Feb 29, 2016
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    Thank you to this forum for the help on my previous thread. Taking to heart the suggestions made there I have started a new circuit simulation.
    please find attached the result of how I interpreted what was suggested.

    This 555 circuit uses the discharge and not the output, which I found interesting.
    the frequency was in the 200-200 hz range, is that a good operating point for the 555?
    I would be open to suggestions on the NPN transistor for SMD solutions, also the FET is just what I grabbed. I assume a lower on resistance is ideal for this application.
    have a great day
     
  2. knowtankyou

    Thread Starter Member

    Feb 29, 2016
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    0
    PS, I am still open to suggestions on White LEDs in the 1-3watt range.
    directional distribution is preferred to flood, but that is a minor point right now.
    I think the LTspice library was showing discontinued LEDs, but I think they are OK for simulation.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    Could you post a schematic?
    This could be a screendump of the LTspice screen.

    Bertus
     
  4. knowtankyou

    Thread Starter Member

    Feb 29, 2016
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    0
  5. knowtankyou

    Thread Starter Member

    Feb 29, 2016
    32
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    is 0.1 ohms a good internal battery resistance for a deep cycle marine battery?
     
  6. dannyf

    Well-Known Member

    Sep 13, 2015
    1,767
    357
    Your previous circuit can be made to work.

    For the one you are working on, look for 555-based smps circuits and you can easily repurpose them as a constant current led driver. It is much more efficient than that you have here.
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
    1,232
    I kind of like it. :D
    If you put 3 three watt watt LEDs in series the efficiency would not be to bad at a nominal battery voltage and at charge voltages you probably don't care.
    Just change the emitter resistor to .75 or 1 ohm to limit the current.
    The internal resistance of the battery is probably in the milliohms.
     
  8. knowtankyou

    Thread Starter Member

    Feb 29, 2016
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    0
    Thank you Ronv, I will actually have (3) 12V batteries and I hope to make my LED string operate at around 36V.
    I agree with your opinion, the losses of one FET vs 10-11 LEDs will be minimal. I just need to get through about 6 hours of night fishing.
    33w of LED and lets say 3w loss of this circuit, is doing about 90% efficiency.
    and I figure using 6AH to run this for a fishing run.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    ps. In my family it is spelled tang yew, as in Tang yew berry mulch.

    ak
     
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