Low profile LED Circut Design

Discussion in 'The Projects Forum' started by tc61, Feb 11, 2009.

  1. tc61

    Thread Starter New Member

    Feb 11, 2009
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    Hello, I am trying to work up a schematic for a project.

    The project involves running 2 30ma LEDS off of line voltage. The LEDs will be powered off line voltage until power is lost, then I need to power the LEDs of a small coin cell battery for about 2 hours, until the cycle starts again. The added kick to the project is that the circuit must be no more than 4mm in height; I can remotely move the battery to another location that I have some space 20mmx20mmx40mm.

    Question can someone help me design a circuit up to accomplish this in a timely manor. I would be willing to compensate you for your time. I am sure I need to supply more details and can do so if needed,

    Thanks in advance.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    I hope you are working on the problem. Be kinda awkward if nobody bites....
     
  3. tc61

    Thread Starter New Member

    Feb 11, 2009
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    Why would it be awkward?

    Just looking for some expertise.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    We work cheap. If efficiency is not a concern, use 3 resistors , 2 to 5 1N4004 diodes, batterys, and LEDs, might throw in a fuse 1/4A. Rechargable batteries??
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Lost thumbnail??
     
  6. tc61

    Thread Starter New Member

    Feb 11, 2009
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    yes it would be a coin cell rechargable battery

    when you say efficiency what do you mean? The life of the LED's or Battery?

    thanks for your help
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    Put a capacitor in front of the bridge, it will limit current without dissipating wattage.

    This will reduce actual power used on the AC line, and reduce heating dramatically.

    Check the AAC book article on LEDs, about ¼ of the way down.

    http://www.allaboutcircuits.com/vol_3/chpt_3/12.html
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    ' efficiency " referred to power disipation. As Bill said adding a cap would improve efficiency; my problem was finding a cap[ or several in parallel] under 4 mm. To properly assign values need to know voltage drop across LEDs @ 30 mA. How about moving every thing except LEDs in to " other space"? Battery voltage needs to be greater than LED & one Si, or Ge diode. I am still using a LED night light that I designed 3 yrs. ago, one bright white LED , a cap in each AC leg & a small resistor[ 1k +-] to protect against hv trancients.
     
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