Modeling and Design of a Linear-Assisted Zeta Conveter

Linear-assisted switching (PWM) converters have advantages over single switching topologies, mainly because of the reduction or elimination of bulky output capacitors and ultra-fast dynamical response. In this paper, a linear-assisted zeta converter is presented. The linear regulator circuit is composed by three bipolar transistors and an operational amplifier, which drives the transistor based on the error between the output voltage and its reference. The modeling of the whole circuit is presented, as well as a design example. The modeling of the zeta converter is similar to the conventional topology modeling, except the fact that the linear regulator current is considered as an extra state that substitutes the state regarding the output capacitor voltage. The zeta converter can be designed independently of the linear regulator circuit and simulations are used to validate the static operation of the overall topology. Experimental results confirm in practice the ripple compensation of the main zeta converter, where extra current is provided by the main converter, in order to drive the linear regulator that is responsible for the ripple compensation.