LED Driver Solution(2)

PWM dimming

Many LED application need dimming function, such as LED backlighting or building lighting dimmer. By adjusting LED brightness and contrast ratio can realize the function of dimming. Simple reducing device current might be able to adjust LED lighting. But if the LED works in lower than the rated current will cause many negative consequences, such as color difference problem.

The simple method to instead of adjusting current is to integrate PWM controller in the LED driver. The PWM signal is not directly used to control LED but to control a switch, for example a MOSFET, provides needed current for LED. PWM controller usually works in a fixed frequency and adjusts pulse width to match the required duty ratio. The current most LED chips are using PWM to control LED. To ensure that people won’t feel the flicker, PWM pulse frequency must be more than 100 Hz.

The main advantage of the PWM control is that through PWM dimming, the current is more accurate, thus to a great extent reduced the LED color difference.

Other characteristics of the LED driver

Because it can emit more light than traditional lighting source, high brightness LED occupied a place in many lighting applications. But these LEDs will produce more heat than traditional LED. Therefore, the LED driver needs overheating protection function to avoid heat of the damage in working.

Using a thermal resistor can realize overheating protection circuit, which can be used to cut off the LED power supply when the temperature reaches the preset value. In addition to overheating protection, there are other security issues to consider, for example, short circuit protection and open circuit protection.

In conclusion, choosing appropriate LED driver should consider LED performance, as well as the end product usage, and take dimming and heat dissipation problems into account. With high power LED application becomes ever more diverse, producers will provide more different LED driver solutions.