Trends in low power low voltage d.c./d.c. converters

Abstract

New integrated circuits are demanding very low supply voltages (1.5 V, 1.2 V, ...) with a very high quality. Low supply voltages allow for reducing the power consumption and increasing the integration density as well as the operation speed of the integrated circuits. Powering properly these new electronics loads is not a trivial question at all. New dynamic response specifications affect dramatically the design of the power supply. Topology selection does not depend only on size and efficiency considerations but also on its dynamic response.Size, efficiency and dynamic response are strongly related (Fig. 1). Critical issues in the design of low voltage power sup-plies are the topology selection, switching frequency, efficiency, dynamic response, packaging, input voltage, transformer design, etc. Design of these new power supplies is very complex, and all these aspects should be considered together Design of the transformer becomes very critical when auxiliary windings are needed to drive the Synchronous Rectifiers. Modern technologies are necessary to couple properly all the windings.Topologies used in the last years to supply low voltage circuits (forward with active clamp, half bridge with complementary control) are not the best option now, because their dynamic response is not good enough to supply properly the new loads.Topologies that drive symmetrically the transformer (classical half bridge, push pull) are a better option, but new techniques to implement self-driven synchronous rectification are necessary. Two possible solutions for powering the new IC are analyzed in this paper, and validated with experimental results.