Control data determination from primary-side sensing of a secondary-side voltage in a switching power converter

An apparatus comprising:

• a controller wherein the controller includes an input to receive a primary-side sense signal, wherein the primary-side sense signal is from a portion of a switching power converter that includes a primary-side of a transformer and the sense signal represents a secondary-side voltage across a secondary-side of the transformer, and during operation the controller is configured to:
• determine one or more times between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage, wherein each resonant period occurs after the secondary-side voltage decreases to zero and before a current in the primary-side of the transformer increases from approximately zero;
• determine one or more resonant period factors using the one or more times between approximately zero crossings of the secondary-side voltage;
• and
• determine a time value that indicates when an approximate minimum value of the secondary-side voltage occurs during at least one of the resonant periods using (i) the one or more resonant period factors and (ii) an occurrence of an approximate zero voltage crossing of the secondary-side voltage during a resonant period of the secondary-side voltage;
• and
• generate a switch control signal pulse in accordance with the determined time value, which indicates occurrence of the minimum value of the secondary-side voltage, to control conductivity of a switch that controls current in the primary-side of the transformer of the switching power converter.

An apparatus comprising:

• a switching power converter, wherein the switching power converter includes a transformer having a primary-side and a secondary-side;
• a controller wherein the controller includes an input to receive a primary-side sense signal, wherein the primary-side sense signal is from a portion of a switching power converter that includes a primary-side of a transformer and the sense signal represents a secondary-side voltage across a secondary-side of the transformer, and during operation the controller is configured to:
• determine one or more times between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage, wherein each resonant period occurs after the secondary-side voltage decreases to zero and before a current in the primary-side of the transformer increases from approximately zero;
• determine one or more resonant period factors using the one or more times between approximately zero crossings of the secondary-side voltage;
• and
• determine a time value that indicates when an approximate minimum value of the secondary-side voltage occurs during at least one of the resonant periods using (i) the one or more resonant period factors and (ii) an occurrence of an approximate zero voltage crossing of the secondary-side voltage during a resonant period of the secondary-side voltage;
• generate a switch control signal pulse in accordance with the determined time value, which indicates occurrence of the minimum value of the secondary-side voltage, to control conductivity of a switch that controls current in the primary-side of the transformer of the switching power converter;
• and
• a load coupled to the secondary-side of the transformer of the switching power converter.