> Antonio L. Benci wrote:
>> The attached diagram is a cct that I have used for many 
>> "Constant LED
>> Current" applications with Vin from 5V to 24V. Your 
>> mileage may vary.

> Seems rather inefficient to use a SHUNT regulator.
> Wouldn't it be simpler to use a FET in constant current 
> mode?
> 1 R, 1 FET, 1 LED.

Simpler, perhaps a little.
Cheaper, probably not.
Efficiency is not liable to usually matter much in this 
application.
But the FET solution will be less accurate and less 
repeatable and less flexible.

The TL431 is fully programmable for voltage across its 
specified range, with various accuracy versions available 
(typically 0.5%, 1%, 2% AFAIR). It is cheap and very 
available.


        Russell 

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