# The best combination

Discussion in 'General Electronics Chat' started by Vasanthkini, Aug 12, 2010.

1. ### Vasanthkini Thread Starter Member

Jun 9, 2010
40
2
Greetings Friends !

I have to design a led tube light and i have 12 LEDs with me.Each LED needs 85mA of current and 4V to be on.Now,i can go for different combinations and they are:

Number of strings Number of LEDs per string Total Voltage Total Current
4 3 12 340mA
3 4 16 255mA

i.e 4 strings of 3 LEDs each takes a total voltage of 12 (3LEDS * 4V ) and a total current of 340mA (85mA * 4 strings)

Etc..

Which combination would be the best for design?And how can we conclude on this?

Thank You

2. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
Due to individual current variations of the comonents and wanting to waste a minimal amount through dropping resistors, the more LEDs in a series string is often the most preferrable approach.

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3. ### russ_hensel Distinguished Member

Jan 11, 2009
820
47
Much depends upon how you plan on driving the led's and the voltage available. You have to have a circuit that maintains a somewhat constant current. If this circuit is cheap, easy and efficient then use parallel combinations at fairly low voltage. If the circuit is expensive, somewhat harder, and efficient then use series at fairly high voltage. If you amplify the question a better answer might be available.