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

Abstract

In the late 70's, the interest in reducing the value and size of reactive components moved power supply specialists to operate dc-to-dc converters at hundreds of kHz or even MHz frequencies. Passive energy storage (mainly magnetics) dominates the size of power electronics, limiting also its cost, reliability and dynamic response. Motivated by miniaturization and improved control bandwidth, they had to face the frequencydependent 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 acto-dc rectifier, first transform the dc input power into controlled ac power, and then convert it back into the desired dc output [1]. This paper provides some historic notes on the operation of the class-E topology, introduced worldwide to the RF/microwave community by Nathan O. Sokal [2], as a power inverter and as a rectifier, with very high conversion efficiencies up to microwave frequencies. Recent research advances and implementations of class-E rectifiers and dc-to-dc converters at UHF and beyond are included. Offering competitive performance in terms of efficiency for RF power recovery, together with a wide bandwidth for low-loss power conversion, their potential for some modern applications is highlighted.

A New Design Method for Class-E Power Amplifiers Using Artificial Intelligence Modeling for Wireless Power Transfer Applications

“…There are several topologies for class-E PAs, such as shunt capacitance [15], sub-nominal conditions [16] and inverse class-E [17]. Class-E PAs are widely used in several applications, such as biomedical [18], DC-DC power converter [19], rectifiers [20], RF heating [21], and wireless power transfer (WPT) [22,23] applications. The amplifiers can be realized in the forms of discrete [8][9][10][11][12] and integrated circuits (ICs) [24,25].…”

A Zero-Transient Dual-Frequency Control for Class-E Resonant DC–DC Converters

“…to allow operations at high switching frequencies with many advantages in terms of power density [1]- [3], EMI [3]- [5] and dynamic performances [6], [7]. They usually take advantage of techniques commonly used in Radio-Frequency power amplifiers [8]- [11] to reduce switching losses and overcome the drawback of hard-switching converters [12], [13], where losses increase with the operating frequency. As such, resonant converters are capable of operating in the frequency range from a few MHz to hundreds of MHz.…”

Synchronous Push–Pull Class E Rectifiers With Load-Independent Operation for Megahertz Wireless Power Transfer

“…Thus, the synchronous rectifiers can operate as time-reversed inverters. Synchronous class E rectifiers can be found in many DC-DC converters with the operation frequency from kHz to GHz [23]- [27]. However, so far, there are few articles discussed the synchronous class E rectifiers for MHz-WPT systems, of which the resonant tank is different from that of conventional DC-DC converters [8]- [13].…”