Power LED with 6 to 20 volts keeping LED at full brightness

[John1397]

I am trying to power a LED 20ma 3 volt keeping LED at same brightness at 20 volt and at 6 volt dc. I tried a 4.6 volt zener across from + to - and a resistor ahead of zener on the positive side the putting another resistor in positive line to drop 4.6 volts down as not to burn out LED. I never got that far as when you place the zener across from positive to negative it gets hot at 20 volts I either have a bad zener or there are limits to how much voltage one can apply. The zener is rated 1/2 watt I do not know if this would be enough for driving a LED. I tried just a 900 ohm resistor to power the LED at 20 volts works good but as voltage drops to 6 you loose brightness. Voltage regulators usually have fixed input and variable output, but I want fixed output and variable input?

 

[KeepItSimpleStupid]

Use an LT3092 https://www.google.com/url?sa=t&rct...soF7flwEufoUdYA&bvm=bv.73612305,d.cWc&cad=rja or LM334 https://www.google.com/url?sa=t&rct...922LIPb81jMVoaZUQ7KuCVQ&bvm=bv.73612305,d.cWc

Set the current to 20 mA.

 

[k7elp60]

Or you could use a LM317L with a 62 ohm resistor between the output pin and the adjust pin. Input to pin 3, resistor from pin 1 to pin 2 and the output connected from pin 1 to ground.

 

[ronsimpson]

The current regulators look good. LM317, T3092, ect.
20V X 20mA = 400mWatts. Some of the power is in the LED but most of the power will be in the regulator. With the small packages the heat will be near maximum.

 

[Externet]

Keep it simple !
----> https://www.digikey.com/product-detail/en/NSIC2020BT3G/NSIC2020BT3GOSCT-ND/3694474