Unified Three-Terminal Switch Model for Current Mode Controls

Current mode controls have been widely used in many power converters with various topologies. Small signal equivalent circuit model is an effective tool for controller design. However, no unified equivalent circuit model applicable to various converters is available. This paper proposes a unified three-terminal switch model for current mode controls with constant frequency and variable frequency modulations operating in continuous conduction mode, providing an accurate and simple equivalent circuit for various converters using current mode control schemes. By identifying the invariant three-terminal structure in current mode control pulsewidth modulation (PWM) converters, which consists of active switch, passive switch, inductor, and closed current loop, the terminal current and voltage relationships are studied and represented by a small signal equivalent circuit. A small signal model for a current mode control PWM converter can be obtained by point-by-point substitution of the PWM switch with its equivalent circuit. The proposed model is verified by simulation and experimental results of various converters, and compared with other models to demonstrate its accuracy. The proposed model is accurate up to half of switching frequency.