# COB LEDs

Forget about using an LM317 as current limiting resistor.

Bad way of driving power LEDs. The LM317 itself needs 2volts to work, and that's also converted to heat. Leo..

Paul__B: But how would you use a current limiter to control an 11.5 V LED from a 12 V supply?

When I tested the '12V' supply it was actually about 10.5-11V.

Wawa: Forget about using an LM317 as current limiting resistor.

Bad way of driving power LEDs. The LM317 itself needs 2volts to work, and that's also converted to heat. Leo..

What's a better way to do it? (aside from just buying a driver) I'm keen to learn!

Using a linear voltage regulator seems quite a common method?

http://www.designingwithleds.com/constant-current-led-driver-circuits/

That's the article I was reading. The link I posted above is the second link in that article.

LM317. Dropout voltage at 500mA and 50C = 1.75volt (datasheet). Plus the 1.25volt across the sense resistor. The circuit will drop 1.75 + 1.25 = 3volt.

Do you have 3volt more than Vf of the cob LED? Leo..