Charge control: modeling, analysis, and design

There are many ways to use the inductor current of a PWM converter as part of its feedback control mechanism. A simple and widely used method is peak current-mode control which uses the instantaneous inductor current as part of the control signals. Charge control is a special type of current-mode control. It uses the integration of the on-time inductor current as the feedback control signal. The characteristics of charge control are studied. A complete small-signal analysis is performed for the control scheme. Subharmonic oscillation similar to that of peak current-mode control is found, and the relationship between subharmonic oscillation and the line/load condition of charge control is defined. Based on the analysis, design guidelines which guarantee the stability of the control system under given line and load ranges are proposed. The small-signal model was confirmed experimentally