An apparatus including: a switching converter having a main switch configured to provide power to a transformer, an auxiliary switch configured to provide a release path for leakage inductance energy of the transformer, and a clamp capacitor coupled in series with the auxiliary switch; and a control circuit configured to control the main switch to be off and the auxiliary switch to operate to discharge the clamp capacitor when in an over-voltage protection mode. A method of controlling the switching converter can include: controlling the main switch to be off; and controlling the auxiliary switch to operate to discharge the clamp capacitor when in an over-voltage protection mode.