Frequency stabilization and synchronization of free-running current-mode-controlled converters

Abstract

Power converters with free-running current-mode control (hysteretic, constant-“off”- time, or constant-“on”-time) can be frequency-stabilized or can be synchronized to a reference frequency. Those can by accomplished by feedforward, feedback, or phase-locking techniques. With hysteretic control, the frequency is controlled by varying the current hysteresis. With constant-“off”-time or constant-“on”-time control, the frequency is controlled by varying the “off” time or the “on” time, respectively. We consider all possible methods of frequency stabilization and synchronization for the three types of free-running current-mode control, used with the three basic types of power converters (buck, boost, and buck-boost). We give analyses and practical design information for the most-important combinations, and experimental data for a buck converter with constant-“off”-time control and feed-forward frequency stabilization.