Detecting transformer saturation in switched-mode power supplies

A controller for a flyback converter, the controller comprising:

• a voltage-dependent current source;
• a reference capacitor coupled to the voltage-dependent current source;
• a first comparator configured to compare a voltage across the reference capacitor to a saturation threshold voltage;
• a second comparator configured to compare a primary current to an overcurrent protection threshold, wherein the primary current is flowing through the primary winding of a transformer of the flyback converter;
• and
• logic circuitry configured to generate a trigger signal based on outputs of the first and second comparators;
• and
• wherein the controller is configured to:
• estimate a primary inductance of the transformer based on the voltage across the reference capacitor,
• detect a saturation condition based on the estimated primary inductance and the primary current, and
• implement a protection mechanism in response to the detected saturation condition.

A method for operating a flyback converter, the method comprising:

• monitoring a primary current of a transformer;
• estimating a primary inductance of the transformer based on a voltage across a reference capacitor;
• comparing the estimated primary inductance to a saturation threshold;
• comparing the primary current to an overcurrent protection threshold;
• detecting a saturation condition based on the comparisons of the estimated primary inductance and the primary current;
• and
• implementing a protection mechanism in response to the detected saturation condition.