AN2644 datasheet(5/64 Pages) STMICROELECTRONICS

5 / 64 page

AN2644

Classification of resonant converters

5/64

Classification of resonant converters

Resonant conversion is a topic that is at least thirty years old and where much effort has

been spent in research in universities and industry because of its attractive features: smooth

waveforms, high efficiency and high power density. Yet the use of this technique in off-line

powered equipment has been confined for a long time to niche applications: high-voltage

power supplies or audio systems, to name a few. Quite recently, emerging applications such

as flat panel TVs on one hand, and the introduction of new regulations, both voluntary and

mandatory, concerning an efficient use of energy on the other hand, are pushing power

designers to find more and more efficient AC-DC conversion systems. This has revamped

and broadened the interest in resonant conversion. Generally speaking, resonant

converters are switching converters that include a tank circuit actively participating in

determining input-to-output power flow. The family of resonant converters is extremely vast

and it is not an easy task to provide a comprehensive picture. To help find one's way, it is

possible to refer to a property shared by most, if not all, of the members of the family. They

are based on a "resonant inverter", i.e. a system that converts a DC voltage into a sinusoidal

voltage (more generally, into a low harmonic content ac voltage), and provides ac power to a

load. To do so, a switch network typically produces a square-wave voltage that is applied to

a resonant tank tuned to the fundamental component of the square wave. In this way, the

tank will respond primarily to this component and negligibly to the higher order harmonics,

so that its voltage and/or current, as well as those of the load, will be essentially sinusoidal

or piecewise sinusoidal. As shown in Figure 2, a resonant DC-DC converter able to provide

DC power to a load can be obtained by rectifying and filtering the ac output of a resonant

inverter.

Figure 2.

General block diagram of a resonant inverter, the core of resonant

converters

Different types of DC-AC inverters can be built, depending on the type of switch network and

on the characteristics of the resonant tank, i.e. the number of its reactive elements and their

configuration [1].

As to switch networks, we will limit our attention to those that drive the resonant tank

symmetrically in both voltage and time, and act as a voltage source, namely the half-bridge

and the full-bridge switch networks. Borrowing the terminology from power amplifiers,

Resonant

tank circuit

Switch

network

Vin

Vout

Resonant Inverter

Resonant

tank circuit

Switch

network

Vin

Vout

Rectifier

Low-pass

filter

Resonant Converter

Resonant Inverter

Resonant

tank circuit

Switch

network

Vin

Vout

Resonant Inverter

Resonant

tank circuit

Switch

network

Vin

Vout

Resonant

tank circuit

Switch

network

Vin

Vout

Resonant Inverter

Resonant

tank circuit

Switch

network

Vin

Vout

Rectifier

Low-pass

filter

Resonant Converter

Resonant Inverter

Resonant

tank circuit

Switch

network

Vin

Vout

Rectifier

Low-pass

filter

Resonant

tank circuit

Switch

network

Vin

Vout

Rectifier

Low-pass

filter

Resonant Converter

Resonant Inverter

AN2644 Datasheet(PDF) 5 Page - STMicroelectronics

AN2644 Datasheet(HTML) 5 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

Datasheet Download

Link URL