Design of Approximate 2DOF Digital Control for Widely Dimming LCL-T Resonant LED Driver

In this paper, the robust digital control method, Approximate 2 Degree Of Freedom (A2DOF) digital control method, is used for Light Emitting Diode (LED) current control. Since the dynamic range of light emitting diode current as a dimming function from 100% to 2% dimming are analog control, but it is not possible to make it very low current or is called "extremely dark". The reason is that the voltage and current characteristics of light emitting diodes are high non-linear, and the internal resistance changes greatly as the current decreases. The resonant circuit use LCL-T network circuit. Therefore, the digital control is appropriate. A robust digital controller derived from this control method is mounted on microcontroller, and experiments show that the lower limit of light emitting diode current can be expanded or less than 1%. The experimental results shown that the method has lower limit of light emitting diode current or extremely dark.