A flyback AC-DC driver using a novel output voltage detection method

Abstract

In this paper, a flyback AC/DC converter without auxiliary windings, opto-couplers or output voltage feedback resistors is proposed. A novel method for detecting output voltage and output current was adopted. By detecting the voltage difference between the two ends of the primary winding, the secondary winding current and output voltage were detected. Peripheral devices have been saved, costs have been reduced, and the integration degree of the switching power supply system has been greatly improved. The chip was designed and produced under 0.18um UHVBCD technology. A 22W flyback converter with this chip as the core is developed. The test results show that the constant current characteristic is good, the line regulation is 1.4%, and the load regulation is 2.1%. The output over voltage protection function is good, with an accurate threshold: the line regulation is only 3.4% and the temperature coefficient is only 4.5%. The experimental results of prototype demonstrate the effectiveness of the proposed circuit.