Integrated on-time extension for non-dissipative bleeding in a power supply

A controller for a switched mode power supply, the controller comprising:

• a zero-crossing detector coupled to generate a first signal prior to a zero-crossing of an input voltage of the power supply;
• a drive logic to be coupled to generate a drive logic output signal in response to a feedback signal representative of an output of the power supply, wherein the drive logic output signal is representative of an initial on-time;
• and
• an on-time extension block having a latch to generate a drive signal to control switching of the switch included in the power supply, wherein the latch is coupled to be set in response to the drive logic output signal and wherein the drive signal is to control switching of a switch to be coupled to the controller to remove charge from a filter capacitor of the power supply, wherein the drive signal is representative of a total on-time of the switch equal to a sum of the initial on-time and an extended on-time, wherein the extended on-time is responsive to the first signal.

A switched mode power supply, comprising:

• a switch;
• an energy transfer element coupled to the switch and coupled to generate an output in response to an input voltage;
• a filter capacitor coupled across the energy transfer element and the switch;
• and
• a controller coupled to regulate the output in response to the input voltage, wherein the controller includes:
• a zero-crossing detector coupled to generate a first signal prior to a zero-crossing of the input voltage;
• a drive logic to be coupled to generate a drive logic output signal in response to a feedback signal representative of an output of the power supply, wherein the drive logic output signal is representative of an initial on-time;
• and
• an on-time extension block coupled to the zero-crossing detector and the drive logic to generate a drive signal in response to the drive logic output signal, the drive signal to control switching of a switch to be coupled to the controller to remove charge from the filter capacitor to pull down a voltage on the filter capacitor such that the voltage on the filter capacitor substantially follows a magnitude of the input voltage, wherein the drive signal is representative of a total on-time of the switch equal to a sum of the initial on-time and an extended on-time, wherein the extended on-time is responsive to the first signal.