Driver circuit for 8 LED in series

Discussion in 'The Projects Forum' started by medic mad, Nov 26, 2015.

  1. medic mad

    Thread Starter New Member

    Oct 10, 2015
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    I am looking for a driver circuit or any simple circuit to glow 8 green LED in series/parallel using 9 Volt battery ..

    i have attached the LED datasheet

    its forward Current 20 mA.
    forward Voltage 3.1V
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The simplest circuit would be 4 parallel strings, each string comprising 2 LEDs in series with a 150 Ohm 1/4 W resistor.
    LED current would reduce as the battery voltage dropped. A more complex circuit would use a respective constant-current 20mA source for each string.
    Either way, the total current would be ~80mA, so a little 9V battery wouldn't last long.
     
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  3. medic mad

    Thread Starter New Member

    Oct 10, 2015
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    thanks for the prompt reply is there any circuit to improve battery life for the above mention design 4 parallell strings and 2 LED in series
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    No unless you are willing to sacrifice brightness..
    If so just change the resistor value to change the string current.
    Drive them at 5mA instead of 20
     
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  5. spinnaker

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    Oct 29, 2009
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    Take a look at a buckpuck. I use one from this company but with a larger array than you have,. They work very well. You might be able to find a smaller device. It would be the easiest way to go.
     
  6. medic mad

    Thread Starter New Member

    Oct 10, 2015
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    thanks to every one.

    kindly find the attachment and tell me if i need to improve the circuit.


    20151126_224037_1024x438.jpg
     
  7. Dodgydave

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    Jun 22, 2012
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    Looks good. 7.5 V with approx 19mA led current, but the Lm317 needs 3V minimum drop input to output.

    I would have made the 240R resistor 120R, and used 610R instead of 1K2, but it still gives same result.
     
    Last edited: Nov 26, 2015
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  8. Alec_t

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    To get maximum efficiency a DC-DC boost converter could be used to raise the 9V to > 25V, so that the 8 LEDs could be connected in series and draw about 20mA total.
     
  9. medic mad

    Thread Starter New Member

    Oct 10, 2015
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    thank a million sir,one more help how to include 8 photo darlington in same circuit op560a.pdf

    is it possible to use all 8 PD in same circuit or if using 9v battery is not suitable i will go for 12v adapter
     
  10. Dodgydave

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    Jun 22, 2012
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    Your lm317 needs a minimum of 3V drop to make it work, if you want to input 9V, your maximum output is 6V for it to keep up.
     
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  11. Alec_t

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    Sep 17, 2013
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    The circuit would depend on what you want to do with them.
     
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  12. medic mad

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    Oct 10, 2015
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    is it possible to make this circuit? by merging 9v to 7805 and adding 8 photodarlington in parallel with 10k resistor


    20151127_010538_1024x469.jpg
     
  13. spinnaker

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    Oct 29, 2009
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    You do not want to use a 7805 if you want efficiency. You want a buck regulator. The 7805 is a linear regulator. And you really want to regulate current and not voltage.
     
  14. Colin55

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    Aug 27, 2015
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    Here's an answer 10LEDsOn9v.gif
     
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  15. spinnaker

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    Nice. Do you have that in a traditional schematic? Might be easier to follow. How many wraps on the bolt? Or what value coil can be used in it's place?
     
  16. Alec_t

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    Sep 17, 2013
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    No, because that circuit doesn't show any photodarlingtons ;). Where did you want to connect them and what would they be driving?
     
  17. Dodgydave

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    Jun 22, 2012
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    that circuit is better with the 7805, are you trying to make a torch?
     
  18. medic mad

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    Oct 10, 2015
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    sorry forget to add schematics

    please consider the npn darlington as photo darlington op560a

    is it possible to to add both circuit? and can it be driven by 9volt battery? View attachment 92802
     
  19. medic mad

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    Oct 10, 2015
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    [that circuit is better with the 7805, are you trying to make a torch?]


    no this have to connect with opticfiber oneside led and the other side photodarlington
     
  20. Dodgydave

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    Jun 22, 2012
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    I wouldn't use a Lm317, better to use the 7805, it will power all the circuit both leds and receivers,
     
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