Stability issues and modelling of ripple-based constant on-time control schemes operating in discontinuous conduction mode

Ripple-based constant on-time (RBCOT) control schemes have recently received much attention for the DC converters used in many applications, mainly because of the relatively high efficiency under light-load condition while preserving other features such as fast step-load response and small component count. Since the converter is usually operated under discontinuous conduction mode (DCM) under light-load condition, an effort to investigate the RBCOT schemes under DCM is practically important. Rigorous mathematical analyses are used to investigate the feedback stability issues of the buck converters using RBCOT control schemes operating in DCM. Two RBCOT control schemes are considered: the basic RBCOT scheme and the basic RBCOT with virtual-inductor-current signal (VICRBCOT). It is proved that it is always stable for the basic RBCOT converter operating in DCM, but that is not the case for the VICRBCOT converters. A proper design procedure to maintain stability for both the continuous conduction mode and the DCM operations in VICRBCOT converters is proposed and verified.