In a control circuit for powering up a switching power supply into a powered output bus, the control circuit is built such that before a turning-on of the switching power supply the controller reference is the slave that follows the bus voltage which is the master. At the moment when the converter is turned on, the master/slave relationship changes such that after the turning-on of the switching power supply the output voltage of the switching power supply is the slave that follows the controller reference. Hence, the status of the output level is memorized by the voltage loop prior to start-up of the converter such that the conflict between the soft-starting voltage loop of the converter and the pre-biased output is minimized.