LED drive general performance requirements

LED faces many challenges, such as forward voltage changes with the change of temperature, current, and different individuals, different batch, different suppliers LED forward voltage difference also; In addition, the LED 'color' will be as the change of current and temperature and drift.

in addition, applications typically use multiple leds, it involves more than LED arrangement problem. Various kinds of arrangement, the preferred drive series single series of LED, because this way no matter how change forward voltage, output voltage ( Vout) How to 'drift', all provide excellent current matching performance. Of course, the user can also use parallel, serial - Parallel combination and cross connection and other arrangement, need for 'mutual matching' LED the application of the forward voltage, and other advantages. As in cross connection, if one of the LED by fault, open circuit in only one LED drive current can double, so as to minimize the impact on the entire circuit.

figure 1: common LED arrangement

the arrangement of LED and LED light source, the requirement specification determines the basic drives. The main functions of the LED drive device is under the scope of certain working conditions limit, the current through the LED and no matter how to change the input and output voltage. LED drive basic working circuit diagram as shown in figure 2, where the so-called 'isolation' means ac line voltage and the LED ( The input and output) No physical electrical connections between, the most commonly used is to use transformer to electrical isolation, while 'isolation' no use high-frequency transformer to electrical isolation. Figure 2:

LED drive basic working circuit diagram.

it is worth mentioning that in LED lighting design, AC - DC power converter with constant current drive circuit can use different configurations: the two parts (1) One-piece ( integral) Configuration, that is, both fuses in together, in which both are located in lighting lamps and lanterns, the advantages of this configuration including optimizing efficiency and easy installation, etc. ; 2) Distributed ( 分布式) Configuration, that is, both exist alone, this configuration to simplify security concerns, and increased flexibility.

LED driver according to different application requirements, can be used in a constant voltage ( CV) Under the output work, that is, the output of a range of current clamping voltage; Also can use constant current ( CC) Output work, the design of the output to strictly limit current; Also may use constant current constant voltage ( CCCV) Output work that provides a constant power output, so for LED forward voltage to determine the current load.

in general, the LED lighting design needs to consider the following factors:

output power: involves the scope of LED forward voltage, electric current and the LED arrangement etc.

power supply: AC - DC power supply, DC - DC power supply, directly driven by AC power supply

performance requirements: that move light, dimmer mode ( Analog, digital or multistage) , lighting control

other requirements: energy efficiency, power factor, size, cost, troubleshooting, Protective properties) , to conform to the standard and reliability etc.

more consideration: mechanical connection, installation, maintenance/replacement, life cycle, logistics, etc