White LED driver requirements

The basic characteristic of white LED is the linear relationship between the current amount of white LED and the luminous quantity. Therefore, it is very important to strictly control the forward current of white LED to obtain the required luminous quantity. Compared with the conventional rectifier diodes, the only difference between the white LED and the conventional rectifier is that the range of the forward voltage varies from 3 to 4V. Because the relationship between the current and voltage of white LED is related to the environmental temperature and the production process, so the white light LED work in the voltage mode is easy to lead to white LED current out of control. Therefore, the best way to drive white LED is to make it work in the current mode.

Widely used color mobile phone to promote the production of white LED, white LED is regarded as the best solution for the mobile phone display screen backlight. First developed using a lithium ion battery powered white LED driver, which allows the supply voltage range is generally 2. 7 to 5. 5V. For the same reason, the number of white LED connected to a drive depends directly on the size of the LCD. Usually the use of white light LED 3 ~ 5, but for large display, you can use up to 10 white LED. Another limiting factor is the design of the drive circuit of the shape of the volume, the design should be selected in the smallest and thinnest structure of the driver circuit. Since the circuit is powered by a battery, the efficiency becomes a key factor in the selection of the driver. Another type of application of white LED is the camera flash, and the main difference between the backlight circuit is the output power. White light LED can be used to take pictures of mobile phones need 100mA ~ 1. 2A current, while ordinary backlight applications require only 20mA of current. If the backlight applications need the power of not more than 500mW, the backlight for the display of white LED drive circuit has a large selection of space. The application of the camera flash applications generally require 500mW ~ 5W power.

The driver can be seen as a special power supply to the white LED, which can drive multiple forward voltage drop in series, parallel or series parallel to 3. 0 to 4. 3V white LED, and meet the requirements of the drive current. The main requirements for white LED drivers are as follows.

In order to meet the low voltage power supply of portable electronic equipment requirements, should drive up and down, to meet the 1 ~ 3 rechargeable batteries or 1 lithium ion battery power requirements, and requirements to work voltage to the battery discharge voltage until termination.

The driver should have high power conversion efficiency to improve the service life of the battery or prolong the time interval between the two charges. At present, the high power conversion efficiency can reach 80% ~ 90%, which can reach to 60% ~ 80%.

When the white LED is used in parallel, it is necessary to match the current of each white LED to make the brightness uniformity.

Low power consumption, low quiescent current, and closed control. The general current should be less than 1mA.

ILED should be set to the maximum current of white LED, and the driver can be used in the process of adjusting the brightness of white LED (brightness adjustment).

With the perfect protection circuit, such as low-voltage latch, overvoltage protection, overtemperature protection, open circuit or short circuit protection.

The small package size, and the peripheral group Wu small and small area of printed circuit board to make up the.

The interference to the other circuit of small.

- easy to use, low price.

(from the world of Electronic Engineering: http://www.eeworld.com.cn/dygl/2012/0527/article_12455.html)