An integrated circuit used for a switching converter has a power supply circuit for providing a power supply voltage, and a control circuit. The switching converter has a switching circuit converting a DC input voltage into an output signal. The power supply circuit has a protection circuit, an UVLO unit and a current source coupled to a power supply capacitor. The protection circuit detects whether the DC input voltage is at a brown-in state. The UVLO unit generates a lock out signal by comparing the power supply voltage with a upper threshold voltage and a lower threshold voltage. The lower threshold voltage is selectively limited to one of a first value or a second value based on the detection. The second value is less than the first value. The current source provides the power supply voltage under the control of the lock out signal.