Power conversion circuit and operating method thereof

1. A power conversion circuit used for generating an output voltage, comprising:

an error amplifying circuit, having a first operation mode and a second operation mode and configured to provide an output signal;

a first comparison circuit, coupled to the error amplifying circuit and configured to receive the output signal and a ramp signal to generate a first comparison signal;

a second comparison circuit, configured to receive the output voltage and a first reference voltage and provide a second comparison signal; and

a control circuit, coupled to the error amplifying circuit, the first comparison circuit and the second comparison circuit and configured to provide a control signal to the error amplifying circuit according to the first comparison signal, the second comparison signal and an enabling signal to control an operation mode of the error amplifying circuit,

wherein when the error amplifying circuit operates in the first operation mode, the output signal is an error amplifying signal; when the error amplifying circuit operates in the second operation mode, the output signal is a second reference voltage.

2. The power conversion circuit of claim 1 , further comprising:

a logic circuit, coupled to the first comparison circuit and the second comparison circuit and configured to receive the first comparison signal and the second comparison signal to generate a pulse width modulation (PWM) signal.

3. The power conversion circuit of claim 1 , wherein when the output voltage is higher than the first reference voltage and the output signal in the first operation mode is lower than the ramp signal, the error amplifying circuit is controlled by the control signal and operates in the second operation mode.

4. The power conversion circuit of claim 1 , wherein when the enabling signal is in a first state, the power conversion circuit is switched to a discontinuous conduction mode (DCM); when the enabling signal is in a second state, the power conversion circuit is switched to a continuous conduction mode (CCM) and the error amplifying circuit operates in the first operation mode.

5. The power conversion circuit of claim 1 , wherein the control circuit comprises:

a determination circuit, configured to receive the output signal and determine whether a voltage value of the output signal is within a default voltage range.

6. A method of operating a power conversion circuit, the power conversion circuit generating an output voltage and comprising an error amplifying circuit to provide an output signal, the method comprising steps of:

(a) providing a first comparison signal according to the output signal and a ramp signal;

(b) providing a second comparison signal according to the output signal and a first reference voltage;

(c) providing a control signal according to the first comparison signal, the second comparison signal and an enabling signal to control the error amplifying circuit to operate in a first operation mode or a second operation mode;

(d) when the error amplifying circuit operates in the first operation mode, the error amplifying circuit generating the output signal according to the output voltage and a third reference voltage; and

(e) when the error amplifying circuit operates in the second operation mode, the output signal being a second reference voltage.

7. The method of claim 6 , wherein when the output voltage is higher than the first reference voltage and the output signal in the first operation mode is lower than the ramp signal, the error amplifying circuit operates in the second operation mode.

8. The method of claim 6 , wherein the step (c) further comprises:

determining whether a voltage value of the output signal is within a default voltage range.