Class-E Rectifiers and Power Converters: The Operation of the Class-E Topology as a Power Amplifier and a Rectifier with Very High Conversion Efficiencies

In the late 1970s, interest in reducing the value and size of reactive components motivated power supply specialists to operate dc-to-dc converters at hundreds of kilohertz or even megahertz frequencies. Passive energy storage (mainly magnetics) is the dominant factor in the size of power electronics and also limits its cost, reliability, and dynamic response. With the goals of miniaturization and improved control bandwidth, researchers had to face the frequency-dependent turn-on and turn-off losses associated with the use of rectangular waveforms in the hard-switched topologies of that time. Similar to approaches for RF/microwave power amplifiers (PAs), the introduction of resonant circuits allowed shaping either a sinusoidal voltage or current, with parasitic reactive elements absorbed by the topology in the neighborhood of the switching frequency. The resulting resonant power converters, obtained by cascading a dc-to-ac resonant inverter with a high-frequency rectifier, first transform the dc input power into controlled ac power and then convert it back into the desired dc output [1].