System and method providing reliable over current protection for power converter

摘要

System controller and method for protecting a power converter. The system controller includes a first controller terminal configured to output a drive signal to a switch to affect a first current flowing through a primary winding of a power converter. The power converter further includes a secondary winding coupled to the primary winding, and the drive signal is associated with one or more switching periods. Additionally, the system controller includes a second controller terminal configured to receive a sensing voltage from a sensing resistor. The sensing voltage represents a magnitude of the first current flowing through the primary winding of the power converter. The system controller is configured to process information associated with the sensing voltage and a reference voltage, and determine whether an average output current of the power converter is larger than a current threshold.

主权项

1. A system controller for protecting a power converter, the system controller comprising:
a first controller terminal configured to output a drive signal to a switch to affect a first current flowing through a primary winding of a power converter, the power converter further including a secondary winding coupled to the primary winding, the drive signal being associated with one or more switching periods; and a second controller terminal configured to receive a sensing voltage from a sensing resistor, the sensing voltage representing a magnitude of the first current flowing through the primary winding of the power converter; wherein the system controller is configured to:
process information associated with the sensing voltage and a reference voltage;determine whether an average output current of the power converter is larger than a current threshold, the average output current of the power converter being related to a second current flowing through the secondary winding; andin response to the average output current being larger than the threshold current, generate the drive signal to cause the switch open and remain open to protect the power converter; wherein the current threshold is equal to a first ratio multiplied by a second ratio, the first ratio being equal to a first number of turns of the primary winding divided by a second number of turns of the secondary winding, the second ratio being equal to the reference voltage divided by a resistance of the sensing resistor.