LED Parrallel help

Discussion in 'The Projects Forum' started by zach48191, Mar 21, 2013.

  1. zach48191

    Thread Starter New Member

    Mar 21, 2013
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    Ok so here is the background project that I am working on. It is an LED flashlight that will utilize the joule thief to maximize the efficiency of the flashlight. The problem I am having atm is choosing the correct power source as I will have the use conventional batteries (AA or AAA). I was just wondering if my calculations are correct for the LED portion of the circuit. I have attached a picture of the schematic and here is the numbers that I came up with.

    LEDs I am using a super white LEDs Vf = 3.2-3.4v @ 20mA-30mA suggest 16-18mA per manufacture datasheet. Pd = 105 mW

    Ok so I calculated that if I want to use 3 LEDs in series I will need about 12V and a current resistor for each leg at roughly 116 ohm or I bumped it to 120 ohms as shown.

    Power dissipated will be about 59.4 mW so 1/4 W resistors are fine.

    My question is will this work for the first part of my project as a simple LED circuit?
    [​IMG]
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,979
    3,686
    It looks fine. If you are expecting no more than 12v and 3.2v is the worst case for each LED then your resistor can be 100 ohm.

    12 - (3x3.2) = 2.4 volts.

    2.4 / .025 amps = 100 ohms.

    120 will be fine too.

    Don't expect overwhelming brightness from the 6 LEDs. These are just indicator lights.

    Also, can your joule thief put out 50 milliamps?
     
  3. zach48191

    Thread Starter New Member

    Mar 21, 2013
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    The LEDs are super bright LEDs, that is why such the high Vf. So using 6 LEDs should be very bright flashlight, but with the switch acting like a dimmer we will be able to adjust the level of brightness with resistance. The joule thief is the next part I will be working on, but honestly it is an idea I would like to incorporate into the circuit.

    Do you think that a joule thief is viable in the circuit above, or is that asking too much for the amount of current needed to power the circuit?
     
  4. zach48191

    Thread Starter New Member

    Mar 21, 2013
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    Please could anyone help me out so I can understand if this will work with the joule thief or not.
     
  5. steveomiami

    New Member

    Apr 20, 2013
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    The while point of a joule thief is to squeeze the last bit out of dead batteries
     
  6. steveomiami

    New Member

    Apr 20, 2013
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    Try posting on Candlepowerforums, they can answer your question there for sure. That forum is all about building flashlights
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,848
    767
    I haven't try the Joule thief, it seems use it on a low battery, but your battery is 12V, do you think is necessary to use that circuit, specially you want to using the flashing function, why you not to use NE555, it's easy to flashing the LED and easy adjust the light brighness.
     
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