A novel primary-side LED power regulation without auxiliary winding

This paper presents a primary-side control structure for operating high-brightness LED (HB-LED) strings under the constant power drive technique. To this end, an inner-outer-loop control structure is presented by utilizing an ac-dc flyback converter connected to an LED string. The proposed control structure regulates the LED power along with input current control. The input voltage and the duty cycle of flyback switch are utilized to estimate the LED power without any need to measurements from the flyback secondary or auxiliary sides. In the power control loop, the amplitude of the input current is calculated through which the LED power can be regulated. This amplitude is utilized as the amplitude of the desired input current for input current control loop, resulting in a high power factor. Experimental results are presented for delivering 20W to Cree CR22-32L LED string using the proposed power estimation and control techniques.