Definition of single-ended vs. double-ended SMPS

Question

I have seen references to switched-mode power supplies as being either single-ended or double-ended.

How are these terms defined and contrasted with respect to SMPS design?

Answer 1

I would agree with the following definition: "Isolated power converter topologies can be classified as either single-ended or double-ended depending on the usage of the B-H curve. During the operation, if the flux swings in only one quadrant of the B-H curve, then the topology is classified as single-ended. If the flux swings in two quadrants of the B-H curve, then the topology is classified as double-ended. For a given set of requirements, a double-ended topology requires a smaller core than a single-ended topology and does not need an additional reset winding." Quoted from here: Article

In this regard, 2-switch forward or flyback circuits are still considered single-ended: in most of them the core flux never resets to the opposite quadrant. Also this book

illustrates such examples of 2-transistor single-ended converters (diagrams on top of page 1085 in case it did not display the link correctly). It is also theoretically possible to have the opposite case: a single-switch double-ended converter circuit, essentially a mix of forward and flyback circuits at its secondary side; however, it is seldom used due to impracticality. By these examples I'm trying to show that the number of switches in circuit has no direct relation to its property of "endness": it can be made 2-switch single-ended, or 1-switch double-ended, or other more usual combinations of 1-sw single-ended or 2-sw double-ended.

Answer 2

The term "double-ended" is used for only Flyback and Forward converters that using two series-connected active switches (BJT or MOSFET) instead of one. Each switch is placed on each end of primary winding of the power transformer and they are all connected in series. Traditional ones that contains only one switch are called "single-ended".

Actually, the term "double-ended" is not widely used, some academic articles used this term. These converters are commonly known as "two switch flyback converter" and "two switch forward converter", respectively.

PS: I'm writing this from my smartphone. I wish I could add a schematic for each, but you can Google "two switch flyback" or "two switch forward" to get a lot of useful info.