System and method providing over current protection based on duty cycle information for power converter

A system controller for protecting a power converter, the system controller comprising:

• a signal generator configured to generate a threshold signal;
• a comparator configured to receive the threshold signal and a current sensing signal and generate a comparison signal based on at least information associated with the threshold signal and the current sensing signal, the current sensing signal indicating a magnitude of a primary current flowing through a primary winding of a power converter;
• and
• a modulation and drive component coupled to the signal generator and configured to receive at least the comparison signal, generate a drive signal based on at least information associated with the comparison signal, and output the drive signal to a switch in order to affect the primary current, the drive signal being associated with one or more first switching periods and a second switching period following the one or more first switching periods, the one or more first switching periods corresponding to one or more first duty cycles, the second switching period including an on-time period and an off-time period;
• wherein the signal generator is further configured to, for the second switching period,
• determine a first threshold signal value based on at least information associated with the one or more first duty cycles;
• set a time to zero at a beginning of the on-time period;
• and
• if the time satisfies one or more first predetermined conditions, generate the threshold signal so that the threshold signal decreases, from the determined first threshold signal value, with the increasing time in magnitude.

A system controller for protecting a power converter, the system controller comprising:

• a signal generator configured to generate a threshold signal;
• a comparator configured to receive the threshold signal and a current sensing signal and generate a comparison signal based on at least information associated with the threshold signal and the current sensing signal, the current sensing signal indicating a magnitude of a primary current flowing through a primary winding of a power converter;
• and
• a modulation and drive component coupled to the signal generator and configured to receive at least the comparison signal, generate a drive signal based on at least information associated with the comparison signal, and output the drive signal to a switch in order to affect the primary current, the drive signal being associated with a plurality of switching periods, each of the plurality of switching periods including an on-time period and an off-time period;
• wherein the signal generator is further configured to, for each of the plurality of switching periods,
• set a time to zero at a beginning of the on-time period;
• if the time satisfies one or more first predetermined conditions, generate the threshold signal so that the threshold signal increases with the increasing time in magnitude;
• and
• if the time satisfies one or more second predetermined conditions, generate the threshold signal so that the threshold signal decreases with the increasing time in magnitude.

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

• generating a threshold signal;
• receiving the threshold signal and a current sensing signal, the current sensing signal indicating a magnitude of a primary current flowing through a primary winding of a power converter;
• generating a comparison signal based on at least information associated with the threshold signal and the current sensing signal;
• receiving at least the comparison signal;
• generating a drive signal based on at least information associated with the comparison signal, the drive signal being associated with one or more first switching periods and a second switching period following the one or more first switching periods, the one or more first switching periods corresponding to one or more duty cycles, the second switching period including an on-time period and an off-time period;
• and
• outputting the drive signal to a switch in order to affect the primary current;
• wherein the process for generating a threshold signal includes, for the second switching period,
• determining a threshold signal value based on at least information associated with the one or more duty cycles;
• setting a time to zero at a beginning of the on-time period;
• if the time satisfies one or more first predetermined conditions, generating the threshold signal equal to the determined threshold signal value so that the threshold signal is constant in magnitude as a function of the time;
• and
• if the time satisfies one or more second predetermined conditions, generating the threshold signal so that the threshold signal decreases with the increasing time in magnitude.

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

• generating a threshold signal;
• receiving the threshold signal and a current sensing signal, the current sensing signal indicating a magnitude of a primary current flowing through a primary winding of a power converter;
• generating a comparison signal based on at least information associated with the threshold signal and the current sensing signal;
• receiving at least the comparison signal;
• generating a drive signal based on at least information associated with the comparison signal, the drive signal being associated with one or more first switching periods and a second switching period following the one or more first switching periods, the one or more first switching periods corresponding to one or more duty cycles, the second switching period including an on-time period and an off-time period;
• and
• outputting the drive signal to a switch in order to affect the primary current;
• wherein the process for generating a threshold signal includes, for the second switching period,
• determining a threshold signal value based on at least information associated with the one or more duty cycles;
• setting a time to zero at a beginning of the on-time period;
• and
• if the time satisfies one or more predetermined conditions, generating the threshold signal so that the threshold signal decreases, from the determined threshold signal value, with the increasing time in magnitude.

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

• generating a threshold signal;
• receiving the threshold signal and a current sensing signal, the current sensing signal indicating a magnitude of a primary current flowing through a primary winding of a power converter;
• generating a comparison signal based on at least information associated with the threshold signal and the current sensing signal;
• receiving at least the comparison signal;
• generating a drive signal based on at least information associated with the comparison signal, the drive signal being associated with a plurality of switching periods, each of the plurality of switching periods including an on-time period and an off-time period;
• and
• outputting the drive signal to a switch in order to affect the primary current;
• wherein the process for generating a threshold signal includes, for each of the plurality of switching periods,
• setting a time to zero at a beginning of the on-time period;
• if the time satisfies one or more first predetermined conditions, generating the threshold signal so that the threshold signal increases with the increasing time in magnitude;
• and
• if the time satisfies one or more second predetermined conditions, generating the threshold signal so that the threshold signal decreases with the increasing time in magnitude.