General requirements for LED drives

Drive LED is facing many challenges, such as the forward voltage varies with temperature, current, and LED positive voltage of different individuals, different batches and different suppliers will also have differences; in addition, LED's "color point" will be with the current and the change of temperature drift.

In addition, the application will usually use more than LED, which involves the arrangement of multiple LED problem. In a variety of ways, the preferred drive in a series of single string LED, because this way regardless of how the forward voltage changes, the output voltage how to "drift", provide excellent current matching performance. Of course, users can also use parallel, series parallel connection and cross connection and other permutations for the need to "match" LED forward voltage applications, and other advantages. Such as in the cross connection, if one of the LED open circuit failure, only 1 LED circuit drive current will be doubled, so as to minimize the impact on the entire circuit.

General requirements for LED drives

Common LED arrangement

The arrangement of LED and the specification of LED light source determine the basic drive requirements. The main function of the LED driver is to limit the current flowing through the LED under certain operating conditions, regardless of the input and output voltages. The working circuit of LED drive the basic diagram as shown in Figure 2, the so-called "isolation" means no physical electrical connection between the AC line voltage and LED, the most common is the use of transformer to electrical isolation and non isolation "are not applied to electrical isolation transformer.

It is worth mentioning that, in the LED lighting design, AC-DC power conversion and constant current drive these two parts of the circuit can be used in different configurations:

1, the overall configuration, that is, the two together, are located in the lighting fixture, the advantages of this configuration, including the optimization of energy efficiency and simplify the installation, etc.;

2) distributed configuration, that is, both exist alone, this configuration simplifies security considerations, and increase flexibility.

The LED driver according to different application requirements, you can use a constant voltage output, the output current range for a certain voltage clamp; can also use a constant current output, the output is designed to strictly limit current; may also adopt constant current and constant voltage output, which provides constant output power, so the positive voltage as the load LED to determine the current.