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

摘要

System and method for protecting a power converter. An example system controller for protecting a power converter includes a signal generator, a comparator, and a modulation and drive component. The signal generator is configured to generate a threshold signal. The comparator is 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. The modulation and drive component is coupled to the signal generator.

主权项

1. A signal generator for protecting a power converter, the signal generator comprising:
a modulation and drive component configured to generate a modulation signal to output a drive signal to a third switch in order to affect a primary current flowing through a primary winding of the power converter; a ramping-signal generator configured to receive the modulation signal and generate a ramping signal based on at least information associated with the modulation signal; a sampling-signal generator configured to receive the modulation signal and generate a sampling signal including a pulse in response to a falling edge of the modulation signal; a sample-and-hold component configured to receive the sampling signal and the ramping signal and output a sampled-and-held signal associated with a magnitude of the ramping signal corresponding to the pulse of the sampling signal; a comparator configured to receive a threshold signal associated with the sampled-and-held signal and a current sensing signal associated with the primary current and output a comparison signal to the modulation and drive component based on at least information associated with the sampled-and-held signal and the current sensing signal; a low pass filter configured to receive the sampled-and-held signal and generate a filter signal based on at least information associated with the sampled-and-held signal; a duty-cycle detection and counter component configured to receive the modulation signal, detect duty cycles of the modulation signal and generate a sample-enable signal based on at least information associated with the modulation signal, the modulation signal being associated with one or more switching periods, the one or more switching periods corresponding to one or more duty cycles; a compensation component configured to receive the modulation signal and generate a compensation signal based on at least information associated with the modulation signal; a first switch coupled to the compensation component; and a second switch coupled to the low pass filter; wherein the duty-cycle detection and counter component is further configured to:
if a first duty cycle of the modulation signal corresponding to a first switching period is larger than a duty-cycle threshold, generate the sample-enable signal at a first logic level; andif second duty cycles of the modulation signal corresponding to second switching periods are smaller than the duty-cycle threshold, generate the sample-enable signal at a second logic level, the second switching periods being a number of consecutive switching periods; wherein:
the first switch is configured, in response to the sample-enable signal being at the first logic level, to be closed to output the compensation signal as the threshold signal; andthe second switch is configured, in response to the sample-enable signal being at the second logic level, to be closed to output the filter signal as the threshold signal.