Circuit and Method of Output Power Detection for a Converter Circuit

An apparatus comprising:

• a flyback converter circuit operating in a transitional mode, the flyback converter circuit including a transformer with a primary side and a secondary side, wherein power from the secondary side comprises the output power, and wherein the primary side includes a first and a second winding;
• a controller circuit operatively coupled to the first and second windings of the primary side of the transformer, wherein the controller circuit controls the current in the first winding and is configured to provide a rectified voltage waveform from the voltage of the second winding, and wherein the current has a saw-tooth profile that remains approximately constant;
• a filter operatively coupled to the controller circuit to receive the rectified voltage waveform;
• a comparator circuit operatively coupled to the filter to receive an average voltage signal from the filter and operatively coupled to a pre-set voltage signal scaled according to a turns-ratio of the transformer, wherein the comparator circuit is configured to provide a signal when the average voltage signal exceeds the pre-set voltage signal.

A method of controlling output power from a converter circuit comprising:

• controlling a current profile of a winding of a primary side of a transformer of the converter circuit to be approximately constant;
• sensing a voltage waveform from a second winding of the primary side of the transformer of the converter circuit;
• producing a rectified voltage waveform from the voltage waveform;
• averaging the rectified voltage waveform to produce an average voltage;
• comparing the average voltage to a pre-set voltage corresponding to an output power limit;
• providing a signal according to a function of the comparing the average voltage to the pre-set voltage to control the output power of the converter circuit.