CONTROL CIRCUIT AND METHOD OF A POWER CONVERTER

摘要

A feedback signal stabilized by a capacitor and related to an output voltage of a power converter is used to acquire the output power information of the power converter, and a control circuit uses a second clock not related to the switching frequency of the power converter to count a duration time of the feedback signal being higher than a threshold. When the duration time is higher than a preset time, an abnormal output power of the power converter is distinguished and the power converter will be turned off. The feedback signal will not vary severely even if the output terminal of the power converter is interfered, and the counted duration time will not be influenced when the switching frequency is changing caused by a load changing.

主权项

1. A control circuit of a power converter using a first capacitor to generate a feedback signal according to a signal related to an output voltage of the power converter; the control circuit comprising:
a switch circuit generating a driving signal to switch a power switch, for modulating the output voltage, wherein the switch circuit includes a first oscillator providing a first clock to determine a frequency of the driving signal; a first comparator connected to the switch circuit, for comparing the feedback signal with a first threshold and asserting a first off-signal to the switch circuit so as to turn off the power converter when the feedback signal being higher than the first threshold; and an overpower protecting circuit including:
a second comparator comparing the feedback signal with a second threshold; anda timer connected to the second comparator, for counting a duration time of the feedback signal being higher than the second threshold and asserting a second off-signal to the switch circuit so as to turn off the power converter when the duration time being higher than a preset time.