Techniques and corresponding circuitry and drivers are disclosed for improving power factor (PF) and total harmonic distortion (THD) of a flyback power factor correction (PFC) topology operating in transition-mode. In one or more embodiments, the PF and THD are improved by correcting the on-time of the switching element of the flyback PFC topology to actively shape the wave of the PFC input current. In some embodiments, the on-time is corrected using a phase-lock-loop module that synchronizes with the rectified input line voltage signal and a output regulator module that corrects the switch on-time. The control may be implemented using a digital or an analog controller.
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