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General Category => Analog discussion => Topic started by: rais6 on September 23, 2012, 17:41:58 PM

Title: Led Array Dimmer
Post by: rais6 on September 23, 2012, 17:41:58 PM
I want to make led array 8x12 = 96 leds which can be dimmed or brightened, i'm using 6 AA battery, so 9 V in total.
How is the configuration? I'm using 5 mm led which has Vf 3,1 V and maximum 20 mA
Title: Re: Led Array Dimmer
Post by: kam on September 25, 2012, 22:43:02 PM
6 batteries in series means 6x1.5=9 volts. Each LED needs at least 3 volts of forward voltage, so 3 leds in series will have low brightness. So you go for 3 leds per series. Each series needs 3.1x2 = 6.2 volts, so the resistor must drop 9-6.2=2.8V @ 20mA, R = 2.8/0.02 = 140 Ohms

So, you need 48 series of 2 leds each and one resistor of 140 Ohms (or 120 Ohms).... All of them connected in parallel.