LED constant current power supply circuit analysis

As the LED lighting is now more and more hot, as a pillar - LED life - LED drive power supply is also more and more get the attention of people.

we all know that the LED power supply in fact nothing special, its characteristic is the need to constant flow pressure limiting, and long term work under full load condition, so the requirement of efficiency is higher; Some power supply due to restrictions on the size of structure, with high requirements.

I will try to just below the middle and small power LED lighting power supply, talk about some common methods of secondary constant current to a conclusion; Not very comprehensive, is not very deep, but for some at the engineers will be managed to help.

statement: not all of the circuit are original, it is for the convenience of discussion, if involves the infringement problem, please let me know in time, in order to delete.

can literally, LED driver power supply will directly decide the reliability of the leds and life; As a power engineer, we need know the characteristics of the LED constant current drive, to ensure its brightness even, long-term reliable glow.

let's talk about more popular TL431 constant current ways.

1, a single TL431 constant current circuit

as shown above, is to use a single TL431 constant flow diagram of the

principle: the circuit is very simple, use the 2, 431. 495 v benchmark for constant current, limits the same LED the pressure drop, but also clear advantages and shortcomings. Advantages:

circuit is simple, less components, low cost, high precision because of the reference voltage TL431, R12, T13 as long as the mining height are broken precision resistor, precision constant current high

disadvantages:

the TL431 is 2. 5 v benchmark, therefore, the constant current sampling circuit loss is great, is not suitable for the power of the output current is too large.

the fatal flaw of this circuit is not empty, is not suitable for the external type of LED power supply.

you can discuss first, how to improve the defects, tomorrow I continue to post the modified circuit. 2, a single TL431 modified circuit with constant current

as shown above, is to use a single TL431 modified diagram

principle of constant current: this circuit is to use the same TL431 2. 495 v benchmark for constant current, keep up with the difference lies in reducing the current sampling circuit of voltage, as long as the total design R12, R13, the value of the R14 can limit pressure drop LED the above advantages:

circuit is simple, less components, low cost, compared with the above circuit, significantly reduce power dissipation in the sampling resistor, constant current high accuracy, overcome the fatal flaw of the above circuit can't idle, when individual leds breakdown, can automatically adjust the output voltage

disadvantages:

when the output light, the output voltage will be rise, rise from the current sampling circuit resistance and R12, the ratio of R13 decided to

3, two TL431 constant current circuit