Design and Implementation of LED Driver with Variable Inductor-Controlled Quasi-Resonant Converter

The resonant tank circuit of quasi-resonant converters, which operate based on the resonant switch concept, provides soft switching by shaping the voltage or current of the switch and conducts energy transfer from input to output. Thus, variable frequency switching emerges as a natural control technique. The disadvantage of this technique is that the operating frequency needs to be changed over a wide range to regulate the output power against changing input voltage and output load. As a result, the design of input and output filters becomes difficult, EMI noise increases, and drivers and switches capable of operating at very high frequencies are required. To reduce or eliminate the disadvantages, variable inductor control is proposed for power control of zero voltage switching quasi-resonant buck converter used as an LED driver. The 40W LED driver, with an input voltage ranging from 18V to 25V, is designed to operate at the switching frequency of 150kHz, and its prototype is built. The operating parameters of the variable inductor are determined through finite element analysis. The variable inductor-controlled driver is tested for dynamically changing input voltage and LED module. The test results show that the power switch of the closed-loop controlled driver is turned on under zero voltage conditions against a wide range of varying input voltage, and the LED module current follows the reference current. Test results confirming the validity of the theoretical analysis and the feasibility of the variable inductor-controlled LED driver are presented.