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How to design the secondary constant current of LED power

With the LED lighting  becoming more and more hot,as the LED life support— LED  power drive is also gets more and more attention of people. In fact, LED power has nothing special, its characteristic is: Needs to constant flow pressure limiting. LED  power driver is directly determine the reliability and life of LED,the characteristics of the LED needs constant current drive,to ensure its brightness uniformity,light  can lighting long-term.
This is one of the TL431 constant current mode :003UTM~1

Principle:This circuit is very simple,using the  2.495 V benchmark of 431 as constant current,Limit the LED the pressure drop.
Advantage: the circuit is simple, less components, low cost, because of high precision the reference voltage of TL431, R12, T13 as long as adopts height precision resistor, precision of constant current is higher
Disadvantages: because the TL431 is the reference of 2.5 V, so the constant current sampling’s circuit  loss is great, it is not suitable for output power of current

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