Switch-mode power converters with demagnetization detection and methods thereof

A controller for a power converter, the controller comprising:

• a first drive signal generator configured to generate a first drive signal to turn off a first transistor at a first time and turn on the first transistor at a second time, the first transistor being configured to receive an input voltage and related to a primary winding coupled to an auxiliary winding and a secondary winding, the secondary winding being related to an output voltage, the second time being later than the first time;
• a second drive signal generator configured to generate a second drive signal to turn on a second transistor at a third time, the second transistor being coupled to the first transistor and related to the primary winding, the third time being later than the first time and being earlier than the second time;
• and
• a demagnetization detector configured to generate a demagnetization signal based at least in part on a first voltage and a second voltage and output the demagnetization signal to the second drive signal generator, the first voltage being related to the auxiliary winding, the second voltage being related to the output voltage;
• wherein the demagnetization detector is further configured to:
• detect an end of a demagnetization process based at least in part on the first voltage and the second voltage;
• and
• in response to detecting the end of the demagnetization process, change the demagnetization signal from a first logic level to a second logic level;
• wherein the second drive signal generator is further configured to:
• in response to the demagnetization signal changing from the first logic level to the second logic level, change the second drive signal to turn off the second transistor at a fourth time, the fourth time being later than the third time and being earlier than the second time.