Synchronous buck converters benefit significantly from implementing soft switching to enhance efficiency and reduce ringing during operation. While soft switching is not mandatory, its application can simplify control by allowing it to be implemented on just one switch, thus retaining most efficiency benefits. The discussion highlights the importance of using anti-parallel diodes or MOSFETs for improved performance, as well as the distinction between soft and hard commutation based on control signals. Relevant literature, including open access papers, provides further insights into soft switching techniques in DC-DC converters.
PREREQUISITESElectrical engineers, power electronics specialists, and anyone involved in the design and optimization of DC-DC converters will find this discussion beneficial.
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.