The purpose of this study is to model a synchronous switching step-down regulator using simulink and to characterize individual sub-blocks like buck converter, OTA, Comparator, gate drive circuitry and digital logic to facilitate easy and less expensive IC implementation. Small signal model of buck converter is developed considering components parasitics and various transfer functions are evaluated. A simple graphical method is deduced from traditional graphical method to arrive at loop transfer function for voltage control, current control and state of the art V2 control scheme easily. The loop transfer function is examined for its stability and compensation techniques are presented for stable closed loop operation. The complete simulink block diagram is built from parameterized sub-blocks for voltage and V2 control scheme. All the three control schemes are compared for different figures of merit. The system is simulated and transient response for load and line variations for voltage and V2 schemes are compared. Inferences are drawn for current mode control and it is concluded that V2 has fastest transient response with easy compensation and less stringent bandwidth requirement of OTA. The simulink model verified the figure of merits of V2 control scheme for which negligible literature exists on its small signal model and compensation. The modeling method and graphical analysis can be easily applied to any converter topology and control schemes.School of Electrical & Computer Engineerin
