Systems and methods for constant voltage mode and constant current mode in flyback power converters with primary-side sensing and regulation

A method for regulating a power converter, the method comprising:

• receiving a first sensed signal, the first sensed signal being associated with a first winding coupled to a secondary winding for a power converter, the secondary winding being related to at least an output current for the power converter;
• generating an output signal based on at least information associated with the first sensed signal, the output signal being related to demagnetization;
• receiving the output signal;
• generating a ramping signal based on at least information associated with the output signal;
• receiving the ramping signal and a first threshold signal;
• processing information associated with the ramping signal and the first threshold signal;
• generating a first comparison signal based on at least information associated with the ramping signal and the first threshold signal;
• receiving a second sensed signal and a second threshold signal, the second sensed signal being associated with a first current flowing through a primary winding coupled to the secondary winding for the power converter;
• processing information associated with the second sensed signal and the second threshold signal;
• generating a second comparison signal based on at least information associated with the second sensed signal and the second threshold signal;
• receiving the first comparison signal and the second comparison signal;
• processing information associated with the first comparison signal and the second comparison signal;
• generating a modulation signal based on at least information associated with the first comparison signal and the second comparison signal;
• receiving the modulation signal;
• outputting to a switch a drive signal based on at least information associated with the modulation signal to affect the first current flowing through the primary winding;
• wherein:
• the output signal is associated with a demagnetization duration;
• the drive signal is associated with a switching period;
• and
• a ratio of the demagnetization duration to the switching period is kept constant.

A system for regulating a power converter, the system comprising:

• a first signal generator configured to receive at least an input signal and generate at least an output signal associated with demagnetization, the input signal being related to at least an output current for a power converter;
• a first controller configured to receive at least the output signal and generate at least a first control signal based on at least information associated with the output signal;
• a second controller configured to receive a first sensed signal and a first threshold signal and generate a second control signal, the first sensed signal being associated with a first current flowing through a primary winding for the power converter;
• an oscillator configured to receive at least the first control signal and generate at least a clock signal based on at least information associated with the first control signal;
• a second signal generator configured to receive at least the clock signal and the second control signal and generate at least a modulation signal;
• a gate driver configured to receive at least the modulation signal and output at least a drive signal to a switch, the switch being configured to affect the first current flowing through the primary winding;
• wherein:
• the output signal is associated with a demagnetization duration;
• and
• the drive signal is associated with a switching period;
• wherein the system is further configured to:
• keep a ratio of the demagnetization duration to the switching period constant;
• and
• keep a peak of the first sensed signal constant in magnitude.