Capacitive Coupled Step-Down DC-DC Converter With Touch Current Limitation

This article proposes a high-efficiency step-down dc-dc converter with limited touch current and voltage gain equivalent to the conventional buck converter. By including a capacitive coupling cell, it is possible to reduce touch currents, presenting a higher safety degree against electric shocks. The main operating stages and equations describing the proposed converter are presented. The capacitive coupling cell operates through the resonant switched-capacitor principle and the impact of the parasitic elements is evaluated. Even though it has a resonant stage, the converter operates with a fixed switching frequency, simplifying the control scheme. A design guideline based on the converter specifications and safety criteria is presented. Simulation results are included to compare the touch current generated by the proposed converter and that of the conventional buck converter, demonstrating the effectiveness of the proposal. Experimental results for a 3 kW prototype operating at 180 kHz switching frequency are presented, including waveforms of main components, closed-loop control performance and efficiency curve, with a peak around 97.8%. An experimental evaluation comparing the proposed converter and the LLC half-bridge converter is also performed. Finally, the touch current tests demonstrated that the risk is automatically eliminated by the proposed converter in approximately 60 ms.