Soft-Switching : The Flyback Converter Case

Static conversion of electrical energy involves switching converters. Switching conversion has the advantage of higher efficiencies compared to a linear voltage regulator [D3075] .

The implementation of a switching converter includes the choice of a topology adapted to the intended application, the choice of switches and the switching frequency to achieve energy modulation. The topology may also include an isolating element, such as a transformer, for isolated conversion. If the topology is not isolated, such as a buck or boost topology, it requires external passive filtering elements such as an inductor and a capacitor.

These passive elements depend not only on the power to be transmitted, but also on the switching frequency. In fact, these elements are present to store energy in order to linearize or modulate power in the converter.

We can therefore immediately see that the lower the switching frequency, the greater the capacity of these passive elements to store energy.

With the aim of logically reducing the volume of these converters in on-board applications such as aeronautics, automobiles or spacecraft, it seems worthwhile to increase the switching frequency as much as possible, but without compromising energy efficiency. More energy loss leads to a problem of thermal accompaniment of the converter, which then loses the benefit of volume or mass.

However, there are major constraints to increasing this frequency: circuit interference amplifies ripples, electromagnetic compatibility (EMC) becomes complicated and standards difficult to comply with.

It is between these two antagonistic tendencies that soft switching finds its place. The power switch, which controls static conversion, switches thanks to a pulse generated by a control element, which forces it to change state. In switching, the switch's intrinsic characteristics generate losses that have a major impact on conversion efficiency. In the case of soft switching, a resonant circuit element charges or discharges the switch's intrinsic elements, in order to obtain switching without energy loss (voltage or current) before the control element imposes the change of state. This is known as zero-voltage or zero-current switching. Losses are then theoretically reduced to zero.

Among the multitude of converter types and applications, one particular application, which has received little industrial attention,...