AN1300 Datasheet, PDF (1/9 Pages) STMicroelectronics – L6598 BASED 12V/3A RESONANT APPLICATION

AN1300
APPLICATION NOTE
L6598 BASED 12V/3A RESONANT APPLICATION
by Eric Danstrom
Off-line switching power supplies have two major problems: high switching losses, and an operating en-
vironment, which is very sensitive to the radiation of Electromagnetic Interference (EMI) and Radio Fre-
quency Interference (RFI). The switching losses are a largest creator of EMI (conducted) and RFI
(radiated), so their control and reduction is a major benefit to the power supply designer. Resonant tech-
niques offer a hope for greatly reducing the switching losses and hence the factors contributing to the
EMI and RFI. This paper will present and organized approach to the design of a 36-watt, full-resonant,
off-line converter that can be used for portable PC applications.
Operation of the Resonant Converters
Full-resonant converters are based upon the half-bridge and full-bridge PWM topologies. They are driven with
a symmetrical waveform whose frequency is changed to control the output voltage. There is a deadtime provid-
ed between the conduction of the upper and lower power switches to turn-on with zero voltage witching. Here
the drain voltage of the MOSFET turning off immediately swings to the opposite voltage and causes the oppos-
ing antiparallel diode to conduct The opposing MOSFET can then turn-on with a very low drain-to-source volt-
age.
There are two major types of resonant converters: the parallel- resonant converter shown in figure 1a, and the
series-resonant converter shown in figure 1b.
Figure 1. The Two Types of Resonant Converters
(a) Parallel
October 2000
(b) Series
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