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
    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
    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


    Apr 5, 2008

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

  4. knowtankyou

    Thread Starter Member

    Feb 29, 2016
  5. knowtankyou

    Thread Starter Member

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

    Well-Known Member

    Sep 13, 2015
    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
    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
    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
    ps. In my family it is spelled tang yew, as in Tang yew berry mulch.