A Versatile OCP Control Scheme for Discontinuous Conduction Mode Flyback AC/DC Converters

Abstract

This study presents a versatile over current protection (OCP) control scheme, which can be widely used in discontinuous conduction mode (DCM) flyback converters. The proposed scheme can not only reduce the variation of output current caused by different line voltages, but also improve the performance of DCM converters in start-up, dynamic response, and the overload protection (OLP) process. It consists of an OCP compensation circuit and a current-pump circuit. Instead of being a constant value, the peak voltage across the sense resistor in a converter that uses the proposed circuit will oscillate with time when the converter regulates a constant output current. To verify the feasibility and performance of the proposed circuit, an IC controller that uses the proposed OCP circuit has been designed and fabricated in 0.35-μm 5-V/40-V high-voltage CMOS technology. Experimental results show that the constant output current precision of the prototype is within ±1% when the input line voltage changes from 90 to 265 Vac. In other tests including start-up, dynamic response, and the OLP process, the performance of the proposed prototype shows an improvement of 9%–19% over conventional converters.