LED power secondary constant current plan summary

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. Often hear a lot of people say that: the LED power supply is a special power supply, with the average power is very different, so do the LED power supply are looking for professional LED power engineer. This statement to the LED power supply covered with a layer of mysterious veil, but as the power of professionals, we all know that the LED power supply in fact nothing special, its characteristic is the need to constant flow pressure limiting, and work under the condition of full load for a long time, so the requirement of efficiency is higher; Some power supply due to restrictions on the size of structure, with high requirements. Let me try on the medium 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.

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.

advantage: the 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: because 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.

the constant current circuit point calculation believe everybody knows: ID = 2. 495 / ( R12 / / R13)

sampling resistor R12, R13 power for PR = 2. 495 * 2. 495 / R13) , for small power supply, the power loss of considerable, so the circuit is not recommended to do current is larger than 200 ma products

2, a single TL431 modified circuit with constant current

as shown above, is to use a single TL431 modified schematic diagram of constant current

principle: this circuit is to use the same 2 TL431. 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 the LED above the pressure drop of the

advantage: the circuit is simple, less components, low cost, compared with the above circuit, significantly reduce the power consumption of 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

weakness: when the output light, the output voltage will be rise, rise from the current sampling circuit resistance and R12, the ratio of R13 decision.

this circuit is the real weakness: when a single LED the pressure drop of the consistency is not high, the constant current point will change accordingly.

12 string of LED lights, such as the most common form of the low pressure drop of 35. Around 5 v, the highest return to 37. 4 v ( Personal experience, the situation will be different, of course, different manufacturers) , the precision of constant current will differ to 5% 8%

3, two TL431 constant current circuit

this circuit as well as the biggest characteristic is: within a certain range can be precise constant pressure constant current.

4, 3 TL431 constant current circuit

but this circuit is based on the circuit of figure 3 adds a constant voltage circuit.