Frequency Control Method for the Wide Load Range Operation of Primary-Side Regulation Fly-Buck Converter

The primary-side regulation (PSR) fly-buck converter is limited because the output regulation deteriorates as the load increases due to the voltage drop caused by the leakage inductance. Therefore, existing applications of the fly-buck converter were limited to low-power applications of several watts. To overcome this limitation and enable the PSR fly-buck converter to be used in higher-power applications, this paper proposes a control method for compensating the output voltage drop using both duty ratio and switching frequency. Specifically, in the proposed method, pulse-width modulation (PWM) is performed below a certain load condition, and pulse-frequency modulation (PFM) is applied above a certain load condition through the estimated output current-based feedforward control. The validity of the proposed control method was verified through the experiments using a 100-W (20 V/5 A) PSR fly-buck converter prototype.