Control circuit of a switched-mode power converter and method thereof

摘要

A method for controlling voltage crossing a power switch of a switched-mode power converter includes the steps of: controlling a switch frequency of the power switch of the switched-mode power converter to a first frequency as activating the switched-mode power converter; and then changing the switch frequency of the power switch to a second frequency after the switched-mode power converter is activated for a predetermined time; wherein the first frequency is lower than the second frequency.

主权项

1. A control circuit of a switched-mode power converter, the control circuit comprising:
a multiplexer for providing an output signal with a low voltage level when activated in start-up, and providing the output signal with a high voltage level after being activated for a period of time; a clock generator for providing a clock signal according to the output signal of the multiplexer; a pulse width modulation controller for providing a pulse width modulation signal according to the clock signal; a jitter unit for providing a jitter signal to the clock generator, wherein the jitter unit comprises:
a first capacitor, wherein a voltage level thereof is the jitter signal;a first current source for charging the first capacitor when the jitter signal is less than the reference signal;a first switch coupled to a second current source, wherein the second current source charges the first capacitor when the first switch is turned on;a second switch coupled to a third current source, wherein the third current source discharges the first capacitor when the second switch is turned on; anda first hysteresis comparator having an input terminal coupled to the first capacitor, a first reference voltage, and a second reference voltage, wherein the first hysteresis comparator is used for alternatingly turning on the first switch and the second switch when the jitter signal is greater than the reference signal; and a comparator for comparing the jitter signal with a reference signal to control the multiplexer; wherein the output signal with the low voltage level is according to the jitter signal.