The switch-mode power supply(SMPS) using a pulse width modulation(PWM) control method shows a potential
unstable phenomenon that the output signal from the closed-loop compensation transfers the compared triangle signal several
times in a switching cycle. Therefore, the quasi-sliding-mode control(SMC) theory is used to analysis the large-signal
stability condition for the PWM controlled SMPS, such as the Buck and Boost converters. Finally, the simulation results
show the correction of the proposed theory.