A power converter includes a zero-current detector having an adjustable offset voltage. The power converter includes a power converting unit and a switch driving circuit. The power converting unit generates a DC output voltage based on a pull-up driving signal, a pull-down driving signal and a DC input voltage. The switch driving circuit generates a first detection voltage signal based on the DC output voltage. The switch driving circuit includes a zero-current detector configured to adjust an offset voltage based on the first detection voltage signal and generate a zero-current detecting signal based on the offset voltage. The offset voltage and the zero-current detecting signal are associated with a current in the power converting unit. The switch driving circuit also includes a pulse-frequency modulating circuit configured to perform a pulse-frequency modulation (PFM) to generate the pull-up driving signal and the pull-down driving signal based on the zero-current detecting signal.