daft question on LED indicators and high VDC

[irving2008]

Cropwell has a good point and running the LED at a lower current reduces the heat generated - assuming sufficient brightness.

You can't change the laws of physics - any linear analog solution needs to dissipate 0.88w @ 20mA LED current and using more esoteric devices doesn't change that. The NUD chip is a great solution for driving strings of LEDs and/or where input voltage varies. It's simply overkill for this requirement and adds unnecessary complexity. Incidentally the NUD chip would need 2sq in of copper (the same 40 x 30mm board) to stay within ratings and from the data sheet would run a junction temperature of 113degC and a lead temperature of 46degC due to marginally better thermal characteristics than the diode, but for 10degC difference its not worth the hassle.

@binary. Your assertion that a string of LEDs would generate no heat is wrong. LEDs are around 50% efficient and do generate heat in the junction. They don't emit IR like incandescent bulbs so don't feel hot through radiated heat. But a standard 5mm 2.2v red LED run at 20mA would consume 0.02 x 2.2 = .044W of which 50% is light and 50% is heat. A string of 20 would indeed drop 44v but would still generate 4.4W of heat, the other 4.4W being light energy. But bulky overkill !!!