Method and apparatus to regulate an output voltage of a power converter at light/no load conditions

A controller for a primary side control power converter, the controller comprising:

• a feedback circuit coupled to compare a feedback signal representative of a bias winding voltage of the power converter with a voltage reference;
• a driver circuit coupled to output a switching signal having a switching period to control a switch to regulate an output of the power converter in response to the feedback signal and a current limit, wherein the driver circuit allows the switch to turn on and off during an enabled switching period and prevents the switch from turning on during a disabled switching period, and wherein the driver circuit enables the switching period in response to the feedback circuit indicating that the feedback signal is less than or equal to the voltage reference and disables the switching period in response to the feedback circuit indicating that the feedback signal is greater than the voltage reference;
• and
• a current limit adjust circuit coupled to adjust the current limit by a first amount in response to a first number of disabled switching periods indicating a first load current at the output of the power converter, and by a second amount in response to a second number of disabled switching periods indicating a second load current at the output of the power converter, wherein a difference between the first amount that the voltage reference is adjusted and the second amount that the voltage reference is adjusted is nonlinear with respect to a difference between the first load current and the second load current at the output of the power converter.