Electronic – Benefits of class E resonant rectifier


I have recently been reading about VHF switch mode power supplies and one thing that I haven't been able to figure out is what really is the point of resonant rectification. I could understand the point from the load matching point of view i.e. the rectifier needs to look like a certain load in order for the resonant inverter to stay in the intended resonance. I also understand the benefit that is got from ZVS if the rectifier is implemented using transistors i.e. synchronous rectification. However, what puzzles me is that I see lots of mentions about ZVS of schottky diodes and that makes absolutely no sense to me.

For example this paper Low Power Very High Frequency Switch-Mode
Power Supply With 50 V Input and 5 V Output
has the following sentence: "Just as the MOSFET has an output
capacitance, the diode has a junction capacitance. In order not
to dissipate this energy in the diode, it is important that the
transition is made smoothly, so the capacitance is discharged
before the diode turns on." What is the other option? Turn the diode on before it's junction capacitance has been discharged? How could you possibly do that? This point has been made in lots of other sources too i.e. this slide lists "The diode turn off at zero voltage" as a property of resonant rectifier. Because of this I am a bit unsure if I understand the whole concept at all or not.

To sum up I am interested if I have got the benefits of resonant rectification right and also I would like to know what is meant by ZVS in the context of schottky diodes or any diode for that matter.

Best Answer

After lots of searching I think I found a proper explanation. This paper introduced a new type class E resonant rectifier and provides the following explanation about the benefits relating to the switching of the diode: "The diode-junction capacitance is included in the parallel capacitance and threrefore does not adversely affect circuit operation at high operating frequencies. The diode turns on and off at low du/dt, yielding low switching losses and low switching noise. Moreover, the absolute value of di/dt at turn-off is limited by an external circuit, significantly reducing the reverse-recovery effect."