Adaptive enabling and disabling is described for valley switching in a power factor correction boost converter. In one example, a boost converter control system includes an amplitude detector to receive an amplitude signal from a boost converter that is related to ringing of the boost converter output. The amplitude detector determines the ringing amplitude. A valley switching controller compares the ringing amplitude to a first high amplitude threshold when valley switching is enabled and generates a valley switching disable signal if the ringing amplitude is below the first high amplitude threshold. A cycle controller coupled to the boost converter generates a drive signal to control switching of the boost converter and coupled to the valley switching controller receives the valley switching disable signal to generate the drive signal without valley switching in response to the valley switching disable signal.