# Driver circuit for 8 LED in series

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

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

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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.

Oct 10, 2015
15
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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

5. ### spinnaker AAC Fanatic!

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.

Oct 10, 2015
15
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thanks to every one.

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

7. ### Dodgydave AAC Fanatic!

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
8. ### Alec_t AAC Fanatic!

Sep 17, 2013
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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.

Oct 10, 2015
15
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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

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10. ### Dodgydave AAC Fanatic!

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.

11. ### Alec_t AAC Fanatic!

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

Oct 10, 2015
15
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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

13. ### spinnaker AAC Fanatic!

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 Member

Aug 27, 2015
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absf likes this.
15. ### spinnaker AAC Fanatic!

Oct 29, 2009
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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 AAC Fanatic!

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 AAC Fanatic!

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

Oct 10, 2015
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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

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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 AAC Fanatic!

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,