constant current LED

constant current LED It is normal nowadays to use a LED as a panel indicator whenever possible. However, in keeping with all electronic devices, they do have limitations and their operating parameters can make life diffi- cult at times. For instance, if the supply voltage varies by any great degree the brightness of the LED will follow suit. Should the voltage level become too 41high it will result in the LED s giving a permanently off indication! The ingeniou circuit here can get around these problems quite effectively. LED is nor The maximum current capability of a 5...24V - malty about 50 mA but brightness will not signifi cantly increase above 20 mA. This figure is about the optimum economic current level and the purpose of this circuit is to maintain this value irrespective of fluctuations in supply voltage levels. The two transistors, T1 and T2, form a constant current source and will maintain the current level to within the acceptable limits of 15 and 27 mA with variation...