A very simple analog control for QSW-ZVS source/sink buck converter with seamless mode transition

A simple, analog, control circuit is proposed for seamless transition between source and sink modes in a Quasi-Square-Wave Zero Voltage Switching (QSW-ZVS) source/sink buck converter. The inductor current is controlled by a variable-width hysteretic current mode control. The upper and lower bounds of the hysteretic band are clamped to ensure QSW-ZVS operation with a single current command from the control loop and independently from the power flow direction. This enables the control of any PWM converter able to operate in QSW-ZVS with a single control loop. If the proposed circuit is used, using a complex multi-mode or look-up-table based digital control is no longer required, simplifying the implementation and lowering the cost of the converter. A 50 W buck converter is built to demonstrate the proposed control circuit and experimental measurements are shown to verify its correct operation.