SPICE modelling of a valley switching flyback power supply controller for improved efficiency in low cost devices

Abstract

The flyback switching mode power supply (SMPS) circuit is undoubtedly the most popular topology currently in low power applications, due to its low cost and simple structure. In the past, there have been many proposed optimizations to flyback designs utilising various techniques such as zero voltage switching (ZVS), active clamping, synchronous rectification, and more. However, most of these designs complicate the original snubbed structure of the flyback topology, and increases its cost. This paper presents the evaluation of a variable-frequency, soft-switching, snubbed, DC/DC flyback converter that utilizes valley switching for improving efficiency. The flyback controller is modelled using SPICE, and uses pulse skipping to maintain the equilibrium of the system based on the feedback from the output. Simulation models report up to 92.2% efficiency, which is almost comparable to ZVS and active clamping topologies. The main advantage of this design is the use of only a single switching transistor, with no additional inductors, correctional circuitry, or clamping action, thus guaranteeing a low cost design.