Resistors and power supply needed for 8 IR LEDs?

Should they be set up in parallel or series? If possible, draw up a schematic.

PedroDaGr86 years ago
Need more information. Are they high power LEDs or standard 5mm type? What is the forward voltage of the LEDs. What is the voltage that will be supplied?


If they are high power LEDs you want to run them in series and constant current regulate them. Otherwise, you can have an issue where one LED starts conducting more than another and end up in thermal run away (where the LED conducting more causes it to get hotter, which lowers its resistance, which causes it to conduct more until finally it is taking more current than it can handle and it burns out).

If they are the other type. Then a convenient website is the Series parallel array calculator
http://led.linear1.org/led.wiz

You input the supplied voltage, the forward voltage of the LEDs, the current you want to run the LEDs at and the number of LEDs. It does the rest outputing an array with the required resistors and their sizes.
PKTraceur (author)  PedroDaGr86 years ago
Forward V=1.28 at 100mA, http://www.radioshack.com/product/index.jsp?productId=2062565
Since you didn't give me your supply voltage here are two options.
For a 12V power supply:
+----|>|----|>|----|>|----|>|---/\/\/----+ R = 56 ohms
+----|>|----|>|----|>|----|>|---/\/\/----+ R = 56 ohms


each 56 ohm resistor dissipates 560 mW
the wizard thinks 1W resistors are needed for your application
together, all resistors dissipate 1120 mW
together, the diodes dissipate 1440 mW
total power dissipated by the array is 2560 mW
the array draws current of 200 mA from the source.

If you are using a 9V supply instead, things are much nicer:

+----|>|----|>|----|>|----|>|---/\/\/----+ R = 18 ohms
+----|>|----|>|----|>|----|>|---/\/\/----+ R = 18 ohms

each 18 ohm resistor dissipates 180 mW
the wizard thinks ½W resistors are needed for your application
together, all resistors dissipate 360 mW
together, the diodes dissipate 1440 mW
total power dissipated by the array is 1800 mW
the array draws current of 200 mA from the source.
PKTraceur (author)  PedroDaGr86 years ago
Thanks!