Leds classic secondary constant current power supply circuit analysis

In this paper, to the secondary constant current LED lighting power supply of some of the common methods are summarized. LED driver power supply will directly determine 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. First of all, let's talk about more popular TL431 constant current ways. A single TL431 constant current circuit as shown above, you are using a single TL431 constant flow diagram. The principle of this circuit is very simple, mainly using the 2, 431. 495 v benchmark for constant current, the LED and also limit 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 of constant current is quite high. Disadvantages: due to 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. But the fatal flaw of this circuit is not empty, is not suitable for the external type of LED power supply, so let's for some of the pitfalls of circuit is improved. A single TL431 constant-current modified circuit as shown above, is to use a single TL431 modified schematic principle of constant current: this circuit is also use the 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 restrict LED the pressure drop. 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 precision and 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, constant current point will change accordingly. 12 string of LED lights, such as one of the most common is the most 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%. Two TL431 constant current circuit, we can see from the picture, the left ZENER through Photo limit of constant pressure effect, but not protect Shutdown but always ZENER CARDS with the right. It will be very hard to fill 350 ma Currentsensor. This circuit has a biggest characteristic is: within a certain range can be precise constant pressure constant current. Three TL431 constant current circuit actually this circuit is based on the original circuit adds a constant voltage circuit. Transistor constant current scheme principle of this figure is by changing the triode IB current to control the LED current, there is also big shortcoming. LM358 constant current circuit, the circuit is a circuit is relatively simple, the advantages of high precision of constant current, is not affected by temperature, lower cost, is currently the most manufacturers use classic circuit, you take it as a reverse proportion and operational amplifier will understand the beauty. Actually LED change of secondary constant current power supply is more, for everyone here enumerate circuit may not be completely, just choose some of the more classic circuit for analysis.