Adaptive current-threshold detector for an adaptive on-time Buck converter at light load

The adaptive on-time control technique has been tremendously utilized in DC---DC converters for its fast transient response, easier design and high efficiency at light load. In some applications the output voltage ripple of DC---DC converters has to be maintained within an acceptable level to achieve superior performance, which depends largely on the load current for adaptive on-time buck converters when operating in discontinuous conduction mode. This paper proposes an adaptive current-threshold detection method for reducing the output voltage ripple. An actual detector circuit is presented to implement the method. This circuit monitors the relationship between the peak inductor current and the load current at light load. Then it outputs a logic signal which controls the turn-on time of the main power MOSFET and hence the peak inductor current. Therefore, the magnitude of the output voltage ripple is controlled. The current-threshold detection method has been verified in an adaptive on-time buck converter by simulation and experimental results. The proposed method can also be used in other constant on-time converters.