Soft-switching preconditioner with integrated DCDC-converter

Many applications in the field of consumer and office electronics require a power supply that provides one or several isolated low voltage outputs and at the same time a controlled high voltage at a buffer capacitor, typically 400 V, for larger consumers with a sufficient hold-up time. Usually this is realized with a boost-type up-converter that allows worldwide mains conditions. An extra converter for the isolated output is still needed, introducing extra cost and volume. Many proposals of integrated ACDC/DCDC converters have been made in the past on which [Qiao (2001)] gives a detailed overview. Normally these require extra power diodes, extra windings or cannot realize zero-voltage-transition switching under universal mains conditions. In addition, there is no independent control of the buffer voltage, leading to problems with the voltage rating of components or hold-up time [Redl (1995)]. This paper describes a topology, which integrates the functions of a preconditioner with a resonant DCDC-converter that allows independent control of the voltage of the electrolytic buffer capacitor and the isolated output. Because of the ability to realize soft switching over the full mains voltage range, a very high efficiency is achieved. The integration of the two functions, preconditioning and DCDC-conversion, in combination with the high switching frequency leads to a reduced count of miniaturized components.