Volt-ampere characteristics of LED

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Choosing a high-quality LED driver design requires a solid understanding of the electrical properties of the LED itself. LEDs are highly sensitive to voltage fluctuations, and even small variations can significantly impact their performance and lifespan.

As shown in the figure below, the volt-ampere characteristic curve of an LED with a rated current of 20 mA and a forward voltage of 3.3 V illustrates how the current through the LED changes dramatically with even minor voltage differences. This non-linear behavior means that controlling the current is crucial for maintaining consistent brightness and ensuring long-term reliability.

Therefore, it's essential to use a driver chip that provides constant current regulation. The forward voltage of the LED will adjust based on the current, but the luminance output is directly proportional to the current flowing through it. A stable current ensures a stable light output, which is vital for applications like backlighting in LCD displays.

For example, let’s take the 029967 constant current control chip from 02MICRO, a leading company in CCFL inverter and LED driver technologies. This chip is widely used in various lighting solutions due to its precision and efficiency. Using this chip, we can design an LED driver solution for a 32-inch LCD TV backlight.

In this application, the 32-inch LED backlight LCD TV uses a 6-channel driver IC capable of handling 120 mA per channel. It drives a total of 150 white LEDs arranged in 25 series strings. Each string consists of 6 LEDs, and the entire system is designed to provide uniform and efficient illumination across the screen.