A high power factor electronic ballast for a gas discharge lamp is disclosed which can provide bus voltage control in response to varying load conditions without the need for direct sensing of the load conditions. The electronic ballast includes an input stage; an output stage; a slow loop controller configured to regulate the bus voltage to a constant value during steady state operation; a hysteresis band over voltage protection (OVP) controller for maintaining the bus voltage in a predetermined hysteresis voltage band during open circuit and pre-ignition conditions; and an on-time limiting controller for guaranteeing a minimum on-time for the input stage. The electronic ballast further includes at least one DC bus capacitor for storing energy created from energy imbalances between the input and output stage. The novel construction makes it possible to regulate the bus voltage to a constant value under steady state conditions using the slow loop controller, and to prevent the bus voltage from increasing in an uncontrolled manner under open circuit and pre-ignition conditions using the over voltage protection controller. This is advantageously achieved without having to directly sense the load condition.