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

摘要

An example controller for a primary side control power converter includes a feedback circuit, a driver circuit, and an adjustable voltage reference circuit. The feedback circuit compares a feedback signal representative of a bias winding voltage of the power converter with a voltage reference. The driver circuit outputs 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 enables or disables a switching period based on the output of the feedback circuit. The adjustable voltage reference circuit adjusts the voltage reference by a first amount in response to a first number of disabled switching periods indicating a first load condition 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 condition at the output of the power converter.

主权项

1. 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, 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 an adjustable voltage reference circuit coupled to adjust the voltage reference 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.