AC-DC CONVERTER AND CONTROL CIRCUIT THEREOF

• US 20120020119A1
• Filed: 01/31/2011
• Published: 01/26/2012
• Est. Priority Date: 07/20/2010
• Status: Active Grant

• Current Assignee: Delta Electronics Incorporated
• Original Assignee: Delta Electronics Incorporated
• Inventors: Tang, Pak-Chuen, Ching, Kwong-Ming, Poon, Chung-Hei
• Granted Patent: US 8,331,113 B2
• Time in Patent Office: Days
• US Class Current: 363/21.02
• CPC Class Codes: H02M 1/425 using a single converter stage both for correction of AC input power factor and generation of a high frequency AC output voltage
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention discloses a control circuit for an AC-DC converter. The control circuit includes a power control circuit for comparing an input current sensing signal generated by sensing an input current of the AC-DC converter and a power level control input and in response thereto generating a frequency modulation control signal, in which the frequency modulation control signal is used to control the output power of the AC-DC converter and suppress harmonics of the input current, and a square wave generator connected to the power control circuit for generating a driving signal used to drive the switch circuit of the AC-DC converter according to the frequency modulation control signal, in which the frequency of the driving signal is varied with the frequency modulation control signal, thereby suppressing harmonics of the input current and regulating the switching frequency the AC-DC converter, and regulating the output power of the AC-DC converter.

Claims

1. A controller for controlling a switch circuit of an AC-DC converter, comprising:

a power control circuit for comparing an input current sensing signal generated by sensing an input current of the AC-DC converter and a power level control input and in response thereto generating a frequency modulation control signal, wherein the frequency modulation control signal is used to control an output power of the AC-DC converter and suppress harmonics of the input current of the AC-DC converter; and

a square wave generator connected to the power control circuit for generating a driving signal used to drive the switch circuit of the AC-DC converter according to the frequency modulation control signal, wherein a frequency of the driving signal is varied with the frequency modulation control signal, thereby suppressing the harmonics of the input current of the AC-DC converter and regulating a switching frequency of the switch circuit, and regulating the output power of the AC-DC converter.

2. The controller according to claim 1 wherein the power control circuit includes a proportional subtractor circuit.

3. The controller according to claim 2 wherein the power control circuit further includes a reverse current isolation device connected between the proportional subtractor circuit and the square wave generator for preventing a reverse current from flowing from the square wave generator to the proportional subtractor circuit.

4. The controller according to claim 3 wherein the reverse current isolation device includes a diode.

5. An AC-DC converter, comprising:

a rectifier connected to an input side of the AC-DC converter for rectifying an input AC voltage into a rectified DC voltage;

a filter circuit connected to an output end of the rectifier for suppressing electromagnetic interference and high-frequency noises of the input AC voltage, thereby generating a DC voltage with a waveform being analogous to the input AC voltage after being half-wave rectified or after being full-wave rectified;

a transformer having a primary side connected to the filter circuit and a secondary side;

a switch circuit connected to the primary side of the transformer and the filter circuit for controlling an energy transfer between the primary side and the secondary side of the transformer;

a current sensor connected to the rectifier for sensing an input current of the AC-DC converter and generating an input current sensing signal accordingly; and

a control circuit connected to a control terminal of the switch circuit for generating a driving signal used to drive the switch circuit according to the input current sensing signal and a power level control input, thereby suppressing harmonics of the input current of the AC-DC converter and regulating an output power of the AC-DC converter;

wherein a frequency of the driving signal is varied with the input current sensing signal and the power level control input.

6. The AC-DC converter according to claim 5 further comprising a resonant circuit connected between the switch circuit and the primary side of the transformer for transferring energy of the input AC voltage to the primary side of the transformer by resonance.

7. The AC-DC converter according to claim 6 wherein the resonant circuit includes a resonant capacitor, a first resonant inductor, and a second resonant inductor, and wherein the first resonant inductor is a leakage inductance of the transformer and the second resonant inductor is a magnetizing inductance of the transformer.

8. The AC-DC converter according to claim 5 further comprising a quasi-resonance circuit connected to the switch circuit and the primary side of the transformer for accommodating a resonant frequency with resonance effect according to the switching operation of the switch circuit, thereby allowing the energy of the input AC voltage to be transferred to the primary side of the transformer and further allowing the energy of the input AC voltage to be transferred from the primary side of the transformer to the secondary side of the transformer.

9. The AC-DC converter according to claim 5 wherein the control circuit includes:

a power control circuit for comparing the input current sensing signal generated and the power level control input and in response thereto generating a frequency modulation control signal, wherein the frequency modulation control signal is used to control the output power of the AC-DC converter and suppress the harmonics of the input current of the AC-DC converter; and

a square wave generator connected to the power control circuit for generating the driving signal according to the frequency modulation control signal, wherein a frequency of the driving signal is varied with the frequency modulation control signal, thereby suppressing the harmonics of the input current of the AC-DC converter and regulating a switching frequency of the switch circuit, and regulating the output power of the AC-DC converter.

10. The AC-DC converter according to claim 9 wherein the power control circuit includes a proportional subtractor circuit.