JFETs as a current source and a question.

[Harald Kapp]

Up to 100 mA design. But the LEDs I used are rated at 30 mA so I wouldn't expect them to last long at 100 mA.

An expectation that will be fulfilled in short time.

 

[Herschel Peeler]

An expectation that will be fulfilled in short time.

Just for grins and giggles I ran three of the LEDs at full power for a while. Measured current was less than expected. As current increased voltage across the LED did also until I maxed the 12 Volt limit, then current started dropping. Instead of the expected 100 mA I got about 75 mA. Still more than twice rated current. They ran fine for about 15 minutes then I shut it down. My breadboard is battery powered and it was just wasting battery power. About 70 mA is what the LEDs run in my flashlight. Batteries (3 x AA) and no resistor or any kind of current limiting. I figure I get about 30 hours a year out of the LEDs before they die.
The LEDs I used for this exercise are the same ones I put in my flashlight. 18,000 mcd, 30 mA, 5,000 K.