Design and implementation of a DCM flyback converter with self-biased and over-current protection circuit

Abstract

This paper presents a low-cost design of flyback converter in high-voltage and low-power application. The flyback converter is designed with the E–I Ferrite core MTC transformers with high permeability and high saturation point. The control circuit is designed around the integrated chip of UC3844 fixed frequency current mode controller incorporated with error amplifier, current sensing comparator, and a high totem pole output driver. External biasing is not required for the control circuit as it is directly biased from the high-voltage line and high-frequency transformer. Isolation is provided by transformer and optocoupler for input–output and power control circuit, respectively. Voltage and current are sensed through the resister divider circuit and shunt resistor, respectively. Control characteristics and performance of the flyback converter are simulated using PSIM software, and 20 W flyback converter hardwire circuit is built to validate the analytical results under variable load current and variable source voltage. Performance of the converter with variable input voltage (25–55 V) and variable load (50–200 Ω) is reported.