Single-stage PFC converter with constant voltage and constant current

1. A power converter comprising:

a transformer;

a power device coupled to the transformer for switching the transformer to product an output of the power converter;

a switching controller receiving a feedback signal for generating a switching signal coupled to drive the power device, wherein an input circuit of the switching controller is coupled to the transformer to sample an input signal for generating the feedback signal, and the input signal is correlated to the output of the power converter; and

a capacitor coupled to the switching controller to provide frequency compensation for a feedback loop of the power converter;

wherein an input of the power converter is without a electrolytic capacitor, and a maximum output current of the power converter is a constant current;

wherein the input circuit further generates a voltage-feedback signal and a demagnetizing-time signal according to the input signal, and enabling of the demagnetizing-time signal indicates that the transformer is fully demagnetized; and

wherein the switching controller comprises:

an integrator generating a current-feedback signal according to the input signal and the demagnetizing-time signal;

a first error amplifier comparing the voltage-feedback signal with a first reference signal;

a second error amplifier comparing the current-feedback signal with a second reference signal, wherein outputs of the first and second error amplifiers are coupled to the capacitor to generate a compensated signal; and

a PWM circuit receiving the compensated signal and the demagnetizing-time signal and generating the switching signal according to the compensated signal and the demagnetizing-time signal.

2. The power converter as claimed in claim 1 , wherein an output voltage of the power converter is a constant voltage when an output current of the power converter is lower than a maximum value.

3. The power converter as claimed in claim 1 , wherein bandwidth of the feedback loop is lower than a line frequency.

4. The power converter as claimed in claim 1 , wherein the switching controller generates the switching signal operated in a boundary current mode (BMC).

5. The power converter as claimed in claim 1 , wherein the integrator is for a constant current control.

6. The power converter as claimed in claim 1 , wherein the first and second error amplifiers develop the feedback loop, and the first and second error amplifiers are multi-vector error amplifiers.

7. The power converter as claimed in claim 1 further comprising:

a bridge-rectifier coupled to a line input of the power converter; and

a high-speed diode coupled between the bridge-rectifier and the transformer.

8. The power converter as claimed in claim 1 , wherein, the switching controller is a primary-side controlled circuit.

9. A power supply circuit comprising:

a bridge rectifier coupled to input of the power supply circuit;

a transformer coupled to the bridge rectifier;

a power device coupled to the transformer for switching the transformer to product an output of the power supply circuit;

a switching controller receiving a feedback signal for generating a switching signal coupled to drive the power device, wherein an input circuit of the switching controller is coupled to the transformer to sample an input signal for generating the feedback signal, and the input signal is correlated to the output of the power supply circuit; and

a capacitor coupled to the switching controller to provide frequency compensation for a feedback loop of the power supply circuit;

wherein the bridge rectifier is developed by high speed diodes, output of the bridge rectifier is without an electrolytic capacitor, and a maximum output current of the power supply circuit is a constant current;

wherein the input circuit further generates a voltage-feedback signal and a demagnetizing-time signal according to the input signal, and enabling of the demagnetizing-time signal indicates that the transformer is fully demagnetized; and

wherein the switching controller comprises:

an integrator generating a current-feedback signal according to the input signal and the demagnetizing-time signal;

a first error amplifier comparing the voltage-feedback signal with a first reference signal;

a second error amplifier comparing the current-feedback signal with a second reference signal, wherein outputs of the first and second error amplifiers are coupled to the capacitor to generate a compensated signal; and

a PWM circuit receiving the compensated signal and the demagnetizing-time signal and generating the switching signal according to the compensated signal and the demagnetizing-time signal.

10. The power supply circuit as claimed in claim 9 , wherein an output voltage of the power supply circuit is a constant voltage when an output current of the power supply circuit is lower than a maximum value.

11. The power supply circuit as claimed in claim 9 , wherein bandwidth of the feedback loop is lower than a line frequency.

12. The power supply circuit as claimed in claim 9 , wherein the switching controller generates the switching signal operated in a boundary current mode (BMC).

13. The power supply circuit as claimed in claim 9 , wherein the integrator is for a constant current control.

14. The power supply circuit as claimed in claim 9 , wherein the first and second error amplifiers develop the feedback loop, and the first and second error amplifier are multi-vector error amplifiers.

15. The power supply circuit as claimed in claim 9 , wherein reverse recovery time of the high-speed diodes is lower than 500 nsec.