Historical and Scientific Perspective

The flyback converter, which even today drives the raster scan of tube TV’s, was probably the first true switching converter. Until its development, self oscillating converters like the Royer Oscillator provided power conversion on a small scale. These circuits were finicky at startup, and relied on mag-amps, which were poorly understood, for operation.

After the Buckboost (the common name for the unisolated version of the Flyback,) came the Buck, in a number of forms, then the Boost.

These two were commonly referred to as the “Up” and “Down” converters. The Up Converter proved to be nearly impossible to isolate, and was noisy, and difficult to control. The Buck, conversely, was easy to control, with its minimum phase response; and ease of isolation and extension to multiple outputs; and benign behaviour in “Light” or discontinuous mode.

About the time the Boostbuck, or Cuk, family of converters was invented, a number of other new topologies were developed by Dean Venable, Dr. Landsman of MIT, and several others, including myself! But, as we shall see, all failed to offer the kind of performance required of a switched-mode power converter. Each has a weakness not shared by the OTC.

It was at PESC in 1977 that the term “Optimum Topology Converter” first appeared in print, in reference to the Cuk Converter. Since then, an enormous controversy has surrounded the issue, with many claims and counter-claims. It was in response to this great uncertainty that I undertook to find the absolute truth of the matter, stripped bare of personal, political, and financial considerations.

In the end, it turned out to be the case that the optimality of this family of converters is rooted deep in the very foundations of Electronics itself. By this I mean the asymmetry of Maxwell’s Equations, which govern the behavior of all switched-mode topologies. In the end, it is the existence of the electron itself that skews the voltage/current–capacitor/inductor–Norton/Thevenin duality of circuit theory, and dictates that, just as there is no capacitive transformer, all switchers are NOT created equal. In fact, they fall naturally into groups of four, mirroring the four terms in Maxwell’s equations that pertain to switched-mode topologies. And, just as the electron current J is the odd man out in those four equations, it is the Boostbuck topologies that stand above the Buck, Boost, and Buckboost.

The rule in Power Conversion, then, is not equality of duals, but is a one-out-of-four rule. For this reason alone, there is indeed an Optimum Topology Converter, regardless of details of implementation, application, technical ability, or finance.