A single-stage AC-to-DC converter includes a bus capacitor, a power factor correcting module, a resonant converting module and a control module. The power factor correcting module generates, based on an AC (alternating current) input voltage, a first control signal and a second control signal, a DC (direct current) bus voltage across the bus capacitor and an intermediate voltage switching between the bus voltage and zero. The resonant converting module generates a DC output voltage based on the intermediate voltage. The control module generates, based on the bus voltage, the first and second control signals, each of which switches between an active state and an inactive state and has a duty cycle associated with the bus voltage.