Constant On/Off-Time Digital Current Control and Design Methods in Three-Level Flying-Capacitor Boost Converters for Fast Transient and Voltage Balancing

Constant
on/off
-time current-mode control (CMC) techniques are useful for wide-duty-ratio operations in multilevel flying-capacitor converters. In this article, event-based constant
on/off
-time digital CMC architectures are proposed in a three-level flying-capacitor (3L-FC) boost converter, which offers inherent current loop stability, fast transient performance, and active flying-capacitor voltage balancing with stable periodic behavior using one voltage sample per switching cycle. Furthermore, a unified discrete-time (DT) framework is proposed, which is used to derive accurate DT large- and small-signal models. The model accuracy is verified using SIMPLIS switch simulation, and fast-scale stability boundaries are obtained using the root locus plot of the closed-loop poles. A hybrid design approach is presented using continuous-time and DT small-signal models for a balanced tradeoff between simplicity and accuracy. An adaptive
on/off
-time approach is adopted to regulate the switching frequency and also to retain high load efficiency. A 100-W 12/48-V 3L-FC boost converter prototype is developed in the laboratory. Experimental results are presented to demonstrate superior transient performance with enhanced fast-scale stability boundaries using the proposed architectures.