The Variable-Bandwidth Hysteresis-Modulation Sliding-Mode Control for the PWM-PFM Converters

This paper proposes the sliding-mode (SM) control method for the pulsewidth modulation -pulse frequency modulation (PWM-PFM) converters, in which both the duty cycle and the switching frequency are utilized as control parameters. Being different from the conventional PWM-PFM modulator, the proposed method utilizes a direct hysteresis modulation (HM) SM controller to perform the PWM, and, meanwhile, employs a quasi-indirect SM controller to control the bandwidth of the HM, so as to realize the PFM. With the proposed method, the control circuit is of low cost and is simple but the transient and steady responses are still satisfactory. The design, simplification, and implementation of the proposed SM control method are illustrated by using a typical single-switch-double-buck converter in this paper. The experimental results agree well with the analysis and show the validity of the proposed method.