Boost LED driver with boundary controller

Abstract

A method of the boost LED driver is studied. There are two methods to control the brightness of white LEDs. The first method is to change the LED current and the second method is to apply PWM dimming signal. First approach means that LEDs current can be changed to control the brightness of LEDs. However, changing LEDs current can cause shift in correlated color temperature in white LEDs. For the second approach is to control the LEDs current from zero to a high level (e.g.50mA) of the LEDs without changing the LEDs current when LEDs are turned on. Therefore, the advantage of this method is to maintain the color and intensity of LEDs remain unchanged. But, a fast transient response control have to implement in the PWM dimming control. For instance, we need to apply 200Hz dimming signal with 1% duty cycle, the width of on-time is 50us. If the response time of the driver is not fast enough , the LEDs current may not reach the high level within 50us on-time cycle. Therefore, fast response LED driver is required. This report will detail the background theory of LED dimming, boundary control will be used to design fast LED drivers. Hardware results on implementing LED dimming will be shown.