AC/DC cascaded power converters having high DC conversion ratio and improved AC line harmonics

• US 20040079953A1
• Filed: 10/28/2002
• Published: 04/29/2004
• Est. Priority Date: 08/17/2002
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Supertex Incorporated (Microchip Technology Incorporated)
• Inventors: Gu, Wei, Mednik, Alexander, Schie, David Chalmers
• Granted Patent: US 6,781,351 B2
• Time in Patent Office: Days
• US Class Current: 257/82
• CPC Class Codes: H02M 1/4208 Arrangements for improving power factor of AC input
• 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

AC/DC cascaded power converters having high DC conversion ratio and improved AC line harmonics provide low input harmonic currents, high power factor and efficient operation for low voltage DC outputs when coupled directly to a source of unfiltered rectified AC voltage. The power converter incorporates an intermediate storage element that provides most or all of the energy storage capacitance within the power converter and a blocking device that enables continuous energy transfer from AC line to output to achieve unity power factor and regulated output while maintaining low AC input current ripple.

Claims

1. A power supply circuit comprising:

a rectifier stage for receiving an AC voltage input and for producing a first DC voltage;

a direct-coupled first converter stage providing power factor correction and coupled to an output of said rectifier stage for converting said first substantially DC voltage to an intermediate DC voltage lower than a peak value of said first substantially DC voltage, said first converter stage comprising a first inductor coupled in functional series with a first diode, said series coupled circuit connected to said output of said rectifier stage, whereby said first converter stage is prevented from conducting energy into said rectifier when said first DC voltage falls substantially below a threshold; and

a second converter stage directly coupled to said first converter stage for converting said intermediate DC voltage to an output DC voltage.

2. The power supply circuit of claim 1, wherein said first inductor has a first terminal connected to a first terminal of said first diode, and wherein a second terminal of said first diode is connected to said rectifier.

3. The power supply circuit of claim 2, wherein said first converter stage further comprises:

a first capacitor having a first terminal connected to a second terminal of said inductor and a second terminal connected to an input of said second converter stage; and

a switch having a first terminal connected to said first terminal of said first capacitor and a second terminal connected to a common node of said power supply circuit.

4. The power supply circuit of claim 3, wherein said first capacitor is a non-electrolytic capacitor.

5. The power supply circuit of claim 3, wherein said first converter stage further comprises a flyback diode having a first terminal connected to said second terminal of said first capacitor and a second terminal connected to a second terminal of said first diode.

6. The power supply circuit of claim 3, wherein said second converter stage is a passive converter stage controlled by said switch.

7. The power supply circuit of claim 6, wherein said second converter stage is a buck converter stage.

8. The power supply circuit of claim 6, wherein said second converter stage is a buck-boost converter stage.

9. The power supply circuit of claim 6, wherein said second converter stage is a transformer isolated forward converter stage.

10. The power supply circuit of claim 6, wherein said second converter stage is a transformer isolated flyback converter stage.

11. The power supply circuit of claim 6, wherein said second converter stage is a buck converter stage adapted to regulate an output current of said second converter stage.

12. The power supply circuit of claim 6, wherein said second converter stage is a buck-boost converter stage adapted to regulate an output current of said second converter stage.

13. The power supply circuit of claim 1, wherein said rectifier includes one or more capacitors connected between said output of said rectifier stage and a common node of said power supply circuit, wherein all of said one or more capacitors are non-electrolytic capacitors, and wherein all of said one or more capacitors comprise all of the external capacitance connected between said output of said rectifier stage and said common node of said power supply.

14. The power supply circuit of claim 1, wherein said first inductor includes a secondary winding coupled to an output of said second converter stage.

15. The power supply circuit of claim 14, wherein said secondary winding is connected to an output of said second converter stage through a second diode, whereby said secondary winding provides and alternative path for delivery of energy stored in said first inductor to said output of said second converter stage, whereby a voltage stress on a first capacitor within said second converter stage is reduced.

16. The power supply circuit of claim 1, further comprising a semiconductor light source connected to an output of said second converter stage, and wherein said first converter stage and said second converter stage are adapted to supply controlled output current through said semiconductor light source.

17. The power supply circuit of claim 16, wherein said AC voltage input has a phase-controlled characteristic for controlling a brightness of said semiconductor light source.

18. A power supply circuit comprising:

a rectifier stage for receiving an AC voltage input and for producing a first DC voltage;

a direct-coupled first converter stage coupled to an output of said rectifier stage for converting said first DC voltage to an intermediate DC voltage lower than a peak value of said first DC voltage, said first converter stage comprising means for preventing reverse flow of current from said first converter stage to said rectifier stage; and

a second converter stage directly-coupled to said first converter stage for converting said intermediate DC voltage to an output DC voltage.

19. The power supply circuit of claim 18, wherein said first converter stage further comprises primary storage means for storing energy received from said AC voltage input.

20. A method for converting an AC power signal to a DC power output comprising the steps of:

rectifying said AC power signal to produce an unfiltered rectified power signal;

switching said unfiltered rectified power signal via a direct-coupled input stage into an intermediate energy storage element to produce an intermediate DC voltage lower than a peak value of said unfiltered rectified power signal;

blocking said intermediate storage element from reverse conducting to said unfiltered rectified power signal when said unfiltered rectified power signal drops below a threshold voltage; and

switching said intermediate DC voltage directly into an input of a second converter stage for producing a low voltage DC output.