Mixed-Signal-Controlled Flyback-Transformer-Based Buck Converter With Improved Dynamic Performance and Transient Energy Recycling

This paper introduces a practical modification of the buck converter and a complementary controller that are well suited for point of load applications with highly dynamic loads. The presented flyback-transformer-based buck (FTBB) converter has faster transient response than the conventional buck, allowing for a reduction in the output capacitance without penalty in the size of the magnetic core. During heavy-to-light load transients, the FTBB converter also recycles excess energy stored in the magnetic component, providing a useful energy savings mechanism. In this modification, the conventional buck inductor is replaced with the primary winding of the flyback transformer, an extra switch, and a set of small auxiliary switches on the secondary side. During heavy-to-light load transients, the inductor current is steered away from the output capacitor to the input port, achieving both energy recycling and savings due to reduced voltage overshoots. The light-to-heavy transient response is improved by reducing the equivalent inductance of the primary transformer winding to its leakage value. A mixed-signal current-programmed mode controller regulates operation of the converter. The controller provides minimum output voltage deviation and ensures seamless transitions between different operating modes. The performance of the FTBB converter is verified with a 6-to-1-V, 3-W, 390-kHz experimental prototype. In comparison with an equivalent buck converter, the experimental system has about three times smaller maximum output voltage deviation, allowing for the same output capacitor reduction and, for frequently changing loads, about 7% decrease in power losses.