Oscillator applied to a control circuit of a power converter and control method thereof

摘要

An oscillator applied to a control circuit of a power converter includes a compensation module and an oscillation module. The compensation module outputs or sinks an adjustment current according to a compensation voltage corresponding to a load, a direct current voltage of a primary side of the power converter, and a reference voltage. The oscillation module outputs a clock signal according to the compensation voltage, a control voltage, and the adjustment current. The control circuit generates a gate control signal to a power switch of the primary side according to the clock signal. When the compensation voltage is less than a first predetermined voltage, a frequency of the gate control signal is a first fixed value, and when the compensation voltage is between the first predetermined voltage and a second predetermined voltage and greater than the second predetermined voltage, the frequency is varied with the compensation voltage.

主权项

1. An oscillator applied to a control circuit of a power converter, the oscillator comprising:
a compensation module for outputting or sinking an adjustment current according to a compensation voltage corresponding to a load of a secondary side of the power converter, a direct current (DC) voltage of a primary side of the power converter, and a reference voltage, wherein the compensation module comprises:
a voltage-to-current converting unit for generating a compensation current according to the compensation voltage; andan adjustment current generation unit coupled to the voltage-to-current converting unit for outputting or sinking the adjustment current according to the compensation current, the DC voltage, and the reference voltage, wherein when the DC voltage is less than the reference voltage, the adjustment current generation unit outputs the adjustment current, and when the DC voltage is greater than the reference voltage, the adjustment current generation unit sinks the adjustment current; and an oscillation module for outputting a clock signal according to the compensation voltage, a control voltage within the control circuit, and the adjustment current, wherein the control circuit generates a gate control signal to a power switch of the primary side of the power converter according to the clock signal; wherein when the compensation voltage is less than a first predetermined voltage, a frequency of the gate control signal is a first fixed value, and when the compensation voltage is between the first predetermined voltage and a second predetermined voltage and greater than the second predetermined voltage, the frequency is varied with the compensation voltage.