The discussion centers on the implementation of soft switching in synchronous buck converters, exploring its necessity, benefits, and the implications of using different switching methods. Participants examine the efficiency trade-offs, control complexity, and the role of components like flyback diodes and MOSFETs in the switching process.
Participants do not reach a consensus on the necessity of soft switching in synchronous buck converters, with multiple competing views regarding its implementation and classification of commutation types.
Discussions include various assumptions about the efficiency trade-offs and control mechanisms involved in synchronous buck converters. The definitions of soft and hard commutation are also subject to interpretation, which may affect the understanding of the switching processes discussed.
I've never heard of it as "soft commutation" just because of the diode. The anti-parallel diode is used in a lot converters with "soft commutation" though. That's largely because the schottky diode is often a better diode than the FET's body diode. Some type of diode is needed, body or anti-parallel, to implement deadtime which ensures both switches aren't on at the same time during commutation. The external diode is a way to reduce dead time losses.Baluncore said:I believe a simple flyback diode would be classed as “soft commutation”. If you parallel the flyback diode with a MOSFET you can improve efficiency by reducing the flyback diode voltage drop. The gate of the parallel MOSFET would need a control signal from somewhere, and could then be called “synchronous rectification” or even “hard commutation” because it is forced.
4.1 INTRODUCTION
In the Chapter 3, it has been shown that AC supply of inductive or capacitive loads can be achieved very satisfactorily (high efficiency, low distortion). It has also been shown that the performance of these resonant inverters was tightly linked to the commutation process in these switching devices all of which execute one controlled switching and one inherent switching.
We will define as a soft-commutated direct converter a converter only involving switches, each of these switches having at most one controlled switching and at least one inherent switching, the controlled and inherent switchings being if necessary different from one switch to another. So the soft commutation is not compatible with totally controlled switches. In soft-commutated converters the power transfer is controlled by means of switches or by a set of switches with thyristor or dual thyristor switching features.
The term 'soft commutation' is legitimate since those switches that have one controlled switching and one inherent switching can be fitted with lossless snubbers (a series inductor when turn on is controlled or a parallel capacitor when turn off is controlled) so that the switching losses are considerably reduced.