Two types of control in the current mode resonant converter

The authors report the results of an in-depth study of the operation of a circuit controlled by pulsewidth modulation (PWM) through experiments and using a model. The experiment used an open-loop circuit to observe the relationship between the control current and output current. The circuit was analyzed by classifying the operation of the resonant circuit controlled by pulse frequency modulation (PFM) and/or PWM into four modes and comparing the results. The upper- and lower-frequency limits of PFM control were also considered. This analysis clarifies the mechanism which determines the gain phase characteristics of a series resonant converter under PFM and PWM control modes. The theoretical results agree closely with the experimental results. When the circuit is under PWM control, the lower limit for control frequency can be raised and the output current can be controlled from normal current to 0 A