Method and apparatus for improving efficiency in a switching regulator at light loads

A method for regulating a power supply, comprising:

• switching with a drive signal a power switch coupled to an energy transfer element of the power supply to control power delivered to an output of the power supply;
• generating a feedback signal in response to the output of the power supply;
• maintaining a frequency of the drive signal at a fixed frequency for a first range feedback signal values;
• and
• varying the frequency of the drive signal without skipping cycles in response to the feedback signal for a second range of feedback signal values.

A switching regulator, comprising:

• a power switch coupled between first and second terminals;
• a control circuit coupled to a third terminal and coupled to the power switch, the control circuit coupled to receive an output sense signal responsive to an output of a power supply, the control circuit coupled to generate a drive signal to switch the power switch in response to the output sense signal to control the output of the power supply;
• and
• a timer circuit included in the control circuit, the timer circuit coupled to time an on-time of the drive signal, the timer coupled to the control circuit to vary a switching frequency of the drive signal without skipping cycles if the on-time of the drive signal is less than a first on-time value, the drive signal to have a fixed switching frequency if the on-time of the drive signal is greater than the first on time value.