Going to be supplying some leds with 5v....the led's require 3.2v - however i don t know what resistor i need to go for tech specs of led: Trying to do the working out... V = I x R : 5 = 0.03 x R So... R = 5 / 0.03 =166.66 So does that mean for that LED to function at 3.2v using a 5v line i will need a 166 ohm resistor?? btw i want to wire them up parallel! Help appriciated. thanks, c_d
I wouldnt run it at 30 mA, as thats the maxium and you risk burning LEDs out quickly, especially if you get one with a lower Vf then normal. And the V that you want to use is the difference between the LEDs voltage and the power supply, not just the power supply. so 5-3.0 = 2V R = 2V / .020A = 100 ohms For paralleling you would just give each LED its own resitor and hook it up the the 5v line. However... what I would do is put 3 in series, giving you 9v for the LED string, and power them off the the 12v line. so that would be: (12v-9v)/.02 A = 150 ohms Dont know what you're going to be using this in and if a series or parallel operation would work better for you. Either would work fine. Just dont be tempted to put 4 in series and put it across the 12v line with no resistors... you could get a few LEDs with a Vf of 2.8v. So the Vf of the string would be 11.2v then. Feeding that 12v would draw a lot more current then the LEDs are meant to handle , and it would end up frying.
