This paper presents new models that account for the non-ideal properties of semiconductor BJT switches responsible for the switching action in PWM converters. These models can be used for both the DC and small-signal AC analyses of PWM switching regulators. Terminal voltages and currents of the switching elements of the converter are related using switching functions which account for the non-ideal characteristics of the semiconductor switches, such as delay, rise, storage, fall and reverse recovery times. Models have been derived and used in DC and AC small-signal analysis of the three basic topologies: buck, boost, and buck-boost converters operating in the continuous conduction mode. The switching times of the semiconductor switches result in a change of the duty cycle which affects both the DC and small-signal performance of the converters. The change in the DC conversion ratio due to the switching times is shown for the three converters. It is also shown that a resistance is introduced into the AC model. This resistance can be positive, which increases the damping in the system, or can be negative, leading to instability.