Extended Off-Time Control for CRM Boost Converter Based on Piecewise Equivalent Capacitance Model

Valley-switching (VS) and zero-voltage switching (ZVS) improves overall efficiency in critical conduction mode (CRM) boost converters. To achieve VS/ZVS, off-time of the main switch is often extended to match the resonance period by circuit inductor and parasitic capacitors of switching components. In this article, a piecewise equivalent model for parasitic capacitors is proposed to derive analytical solutions of the resonant process, by which the numerical solutions of VS/ZVS time is calculated. To precisely achieve VS/ZVS in a boost converter, corresponding extended off-time based on the numerical solutions is implemented with an extended off-time (EOT) controller. The EOT controller makes the inductor volt-second unbalance in continuous conduction mode (CCM) operation during one switching cycle, leading to the convergence to CRM operation. The analytical and experimental results correct the results derived by conventional equivalent model for parasitic capacitors, which leads to deviated VS/ZVS boundary and wrongly calculated off-time. The proposed model and controller are verified in a non-synchronous CRM boost converter based on GaN high electron mobility transistor (HEMT) and SiC diode. With the derived extended off-time, a peak efficiency of 99.15% is achieved at output power level of 200W.