October 2007

Rev 1

1/13

AN2530

Application note

Solution for 150 W half bridge resonant DC-DC converter

Introduction

This application note describes a 150 W Half bridge resonant DC-DC converter. This type of

SMPS is highly attractive due to its high achievable efficiency, very low noise and compact

size.

Resonant converters are among the least common SMPS topologies. There are several

reasons why they are not often used, but we will not discuss these reasons in this

application note. However, it is worth noting that the resonant topologies have undeniable

advantages over the "hard switching" topologies. The very high achievable efficiency of over

90% and up to 95% is very common, as well as their low generated noise due to ZVS (zero

voltage switching) and resonant energy transfer.

Other related advantages derived from these converters are their compact size due to their

need for smaller power switches (Power MOSFETs usually), smaller transformers, and less

generated heat (the lower losses are a part of this). Less heat means a smaller heat sink

and a longer life for power components.

If the necessary care is taken in the design phase, the results are very good and the typical

issues normally associated with these topologies are avoided.

ST's L6598 half bridge driver has been chosen for this design. Please refer to the L6598

datasheet for full specifications and capabilities, or to other documentation, application

notes and books where it is used, in order to have the best picture of this design. All

references are provided in Figure 7.

This application note concentrates only on the power aspects, because as already

mentioned, there are excellent guides for the driver (aside from the datasheet) as well as

application notes for SMPS in general, magnetics, topologies, etc.

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