Demonau

Hi Audioguru, Thanks for your help, it's very much appreciated. Demon

Hi audioguru, Thanks for the reply and the welcome. I really don't understand much about this as you can probably tell from my description of the problem. I think you're correct in assuming the 1.1V diode is to reduce the voltage thus protecting the LED's. (or I think that's the purpose) The LED's I buy are all sold that way, within a range, in this case 3.0V - 3.4V, which is why I'm confused as to which resistor to use. In your answer you suggested testing the LED's and sorting them into the various voltages. Firstly, I'm not sure how to go about that and secondly, there's quite a few thousand of these. In the near future I'll be getting these particular PCB's made, and for each set there'll be about 20,000 LED's so I'm fairly sure they won't test each individual LED. The LED's are supplied to me from a manufacturer and I've asked them to supply me with LED's all of the same voltage. For some reason they are unable to supply LED's of the same voltage except in small numbers. From your answer, I presume now it's because they have to test each individual LED. Audioguru, is there any other way around this problem? Thanks for your help. Demon

Hi Everyone, Would someone please give me some advice for the following problem? I'm not an electronics person so please forgive any incorrect descriptions. I want to calculate what value resistor to use when connecting LED's in series. In all cases the supply voltage is 12V. I need the LED's to burn as brightly as possible but I also need to reduce the risk of them burning out. The voltage (VF) of the LED's is listed as 3.0 - 3.4 20mA and I don't know which voltage to use in the calculation. The set up I have now uses 3V LED's and is configured as follows. The first case I have is a panel of 22 LED's connected in series 3x3x3x3x3x3x3x1 Each series of three LED's has a 100 ohm resistor. Each series of two LED's has a 270 ohm resistor. Each single LED has a 430 ohm resistor. There is one 1.1V diode connected to each panel of 22 leds. The other set ups are a panel of 16 LED's and a panel of 11 LED's connected as described above. I hope I've given you enough info and described this correctly. Thanks.