Power controllers and power converters with configurable feedback loop for different nominal output voltages

A power controller for a power converter converting an input voltage into an output voltage, wherein the power converter is configured to, based on a selection signal, switch the output voltage from a first nominal output voltage to a second nominal output voltage less than the first nominal output voltage, the power converter includes a primary winding, a secondary winding and an auxiliary winding, the power controller comprising:

• a switch driver for providing a driving signal to a power switch to control an inductor current through the primary winding;
• and
• an ON-time controller for controlling an ON time of the driving signal according to a compensation signal;
• and
• a frequency controller for, based on the compensation signal and a feedback signal, controlling a switching frequency of the driving signal, wherein when the compensation signal becomes lower than a fold voltage the frequency controller reduces the switching frequency according to a frequency-reduction slope, when the output voltage is regulated at the first nominal output voltage the frequency-reduction slope has a first drop-off rate, and when the output voltage is regulated at the second nominal output voltage the frequency-reduction slope has a second drop-off rate less than the first drop-off rate;
• wherein the compensation signal is generated by comparing the output voltage with a reference voltage determined by the selection signal;
• and
• the feedback signal is at a feedback node coupled to the auxiliary winding.