Resonant converter

A resonant converter is a type of electric power converter, typically AC-to-DC or DC-to-DC, that is based around a circuit tuned to resonate at a specific frequency, called a resonant tank.^[1] As this circuit typically consists of two inductors and a capacitor, they are also referred to as LLC resonant converters. This resonant circuit is powered by the input, made to oscillate by a switching circuit, and one of the inductors is either part of or connected to a transformer, which magnetically couples to the output.

The use of a resonant circuit allows higher switching frequencies (in the hundreds of kHz^[1]) than a typical switched-mode power supply (typically under 100 kHz), which result in several advantages. The high frequency results in reduced switching losses and therefore an increase in conversion efficiency (nearing 98%^[2]), and a reduction in component size and in the amount of electrical noise generated.^[3] This means they can be smaller, lighter and more efficient than a comparable switching supply, and they find use in applications requiring large amounts of power.

Since the 2000s they have found applications in power demanding applications such as electric vehicle chargers^[3], power conversion for solar energy^[4], and hydrogen hydrolysis^[2], as well as power supplies for consumer electronics where there is a high power requirement or a space constraint.

There are multiple types of resonant converter, depending on the topology and the switching method:^[5]

• Series resonant converter
• Parallel resonant converter
• Class E resonant converter
• Class E resonant rectifier
• Zero-voltage switching resonant converter
• Zero-current switching resonant converter
• Two-quadrant ZVS resonant converter
• Resonant DC-link inverter