Methods and power controllers for primary side control

A power supply controller for performing primary-side control, comprising:

• a comparator for comparing a feedback voltage and an over-shot reference voltage, wherein the feedback voltage represents a secondary-side voltage of a secondary winding through an inductance-coupling effect;
• and
• an ON-triggering controller coupled to the comparator, wherein when the feedback voltage is lower than the over-shot reference voltage, the ON-triggering controller causes a power switch to operate at approximately a first switching frequency, and when the feedback voltage is higher than the over-shot reference voltage, the ON-triggering controller causes the power switch to operate at approximately a second switching frequency;
• wherein the second switching frequency is lower than the first switching frequency.

A power management system comprising:

• a transformer having a primary winding, an auxiliary winding, and a secondary winding;
• a power switch coupled to the primary winding for controlling an inductance current flowing through the primary winding;
• and
• a power supply controller for controlling the power switch, comprising:
• a feedback node coupled to the auxiliary winding;
• a comparator for comparing a feedback voltage and an over-shot reference voltage, wherein the feedback voltage represents a secondary-side voltage of the secondary winding through the feedback node and the auxiliary winding;
• and
• an ON-triggering controller coupled to the comparator, wherein the ON-triggering controller causes the power switch to operate approximately at a first switching frequency when the feedback voltage is lower than the over-shot reference voltage, and the ON-triggering controller causes the power switch to operate approximately at a second switching frequency when the feedback voltage is higher than the over-shot reference voltage;
• wherein the second switching frequency is lower than the first switching frequency.