A Constant Current Rugulation for Discontinuous Conduction Mode Primary-Side Controlled Flyback Converter

This paper presents a constant current regulation for discontinuous conduction mode primary-side controlled flyback converter. It consists of a demagnetization time detector and a peak current threshold generator. Based on peak current control, the regulation is achieved by fixing the product of the peak current and the ratio of the demagnetization time to the switching period constant. Using a reference voltage and the demagnetization time provided by the demagnetization time detector, the peak current threshold generator generates the threshold signal, which is relative to the ratio of the demagnetization time to the switching period. The circuit is simulated in software of Spectre based on the nuvoton 0.35um BCD process and a control IC has been fabricated. Experimental results of a 7V/1.5A circuit prototype shows that the constant output current precision is within 5.4% when the input voltage changes from 100V to 320V and while the load changes from 1.6H to 4.5H, the output current changes by 4.1%.