Electronic Thesis and Dissertation Repository


Master of Engineering Science


Electrical and Computer Engineering


Moschopoulos, Gerry


The DC-DC flyback power converter is widely used in low power commercial and industrial applications ( > 150 W) such as in computers, telecom, consumer electronics because it is one of the simplest and least expensive converter topologies with transformer isolation. Its main power circuit consists of just a semiconductor device like a MOSFET operating as a switch, a transformer, an output diode and an output filter capacitor. The converter switch, however, is susceptible to high voltage spikes due to the interaction between its output capacitance and the leakage inductance of the transformer. These spikes can exceed the ratings of the switch, thus destroying the device, and thus flyback converters are always implemented with some sort of snubber circuit that can clamp any voltage spikes that may appear across their switch.

There are two types of snubbers: passive snubbers that consist of passive electrical components such as capacitors, inductors and diodes and active snubbers, that consist of passive components and an active semiconductor switch. It is generally believed that passive snubbers are less expensive but also less efficient than active snubbers, but this belief has been placed in doubt with recent advances in passive snubber technology. Flyback converter with regenerative passive snubbers that dissipate little energy have been recently proposed and have greater efficiency than traditional passive snubbers. Although the efficiency of passive snubbers has improved, no comparison has been made between these new passive snubbers and active snubbers as it is still assumed that active snubbers are always more efficient.

The main focus of this thesis is to compare the performance of an example passive snubber and an example active snubber. These example snubber circuits have been selected as being among the best of their type. In this thesis, the steady-state operation of each snubber circuit is explained in detail and analyzed, the results of the analysis is used to create a procedure for the design of key components, and the procedure is demonstrated with a design example. The results of the design examples were used to build prototypes of flyback converters with each example snubber and the prototypes were used to obtain experimental results. Based on these experimental results, conclusions about the efficiency of flyback converters with passive regenerative and active snubbers operating under various input line and output load conditions are made in this thesis