I am experimenting with multiple LEDs in a parallel circuit. I bought some 2-pack Radio Shack high brightness white leds which are rated 3.3v+ forward voltage and 25 mA current on the package. Using an on-line led parallel calculator I deterimined that 5 of these LED's in parallel should require no resistor if supply voltage is in the 3.5v ballpark. In testing, I determined that they did indeed light properly at 3.5v on up to 3.8v. I did not want to burn them out by applying higher voltage. My supply voltage came from a 10.5v (1.5 amp) power supply hooked up to a 5k ohm pot.


Here are my three questions:

- 4 of the 5 LED's are bright and the 5th is noticeably dimmer. is this variation normal for products of this type?

- No-load voltage is definitely showing 3.5v to 3.8v. But hooked up to the LED's the supply voltage reads 2.56, no matter where the supply voltage was set (3.5 to 3.8). Is there a reasonably simple explaination for where the missing 1.2 supply volts went? Should I recalculate a higher supply voltage and stick a resister in for stability?

- Am I missing something in my intrepretation of `forward voltage'?


Thanks for any help you can give

Al (new member)