Method and apparatus for single-ended conversion of DC to AC power for driving discharge lamps

• US 7,336,038 B2
• Filed: 05/19/2006
• Issued: 02/26/2008
• Est. Priority Date: 05/19/2004
• Status: Expired due to Fees

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Chen, Wei
• Primary Examiner(s): Owens; Douglas W.
• Assistant Examiner(s): VU, JIMMY T
• Application Number:
  US11/419,354
• Publication Number:
  US 20060197465A1
• Time in Patent Office: 648 Days
• Field of Search: 315/225, 315/209.R, 315/291, 315/307, 315/224, 315/244, 315/276, 315/306, 315/362
• US Class Current: 315/209.00R
• CPC Class Codes: H05B 41/2821 by means of a single-switch converter or a parallel push-pull converter in the final stage H05B41/285 takes precedence

Abstract

The present disclosure introduces a simple method and apparatus for converting DC power to AC power, and, specifically, to single-ended inverter circuits for driving discharge lamps such as a Cold Cathode Fluorescent Lamp (CCFL) or an External Electrode Fluorescent Lamp (EEFL). Among other advantages, these circuits offer nearly symmetrical voltage waveform to drive discharge lamps when the duty cycle is close to 50%. They also eliminate the high current and high voltage resonant capacitor on the primary side, and reduce the voltage rating of a primary switch to twice the input voltage without the need for snubber circuits. The recommended inverters can be used to efficiently drive discharge lamps at low cost, particularly for applications with a narrow input voltage range. The lamp current can be regulated through the duty cycle modulation of the main switch.

Claims

1. An apparatus for converting a direct current (DC) signal into an alternating current (AC) signal, comprising:

a network of one switch for generating an AC signal from a DC signal, the AC signal being generated by the one switch of the network periodically opening and closing;

filtering means being coupled between said network of the one switch and a load, said filtering means filtering the AC signal delivered to said load, wherein said filtering means includes;

a transformer having at least one primary winding that receives the AC signal from said network of at least one switch and having a secondary winding that is coupled to said load;

a diode being connected to the at least one primary winding of said transformer;

at least one capacitor being in series with the at least one primary winding of said transformer, wherein the at least one capacitor is operable to store energy to be delivered to the secondary winding of said transformer; and

impedance means being in series with the second winding of said transformer, wherein the impedance is operable to resonate to the at least one primary winding of said transformer and said network of at least one switch.

2. The apparatus of claim 1, wherein said load is a discharge lamp.

3. The apparatus of claim 1, wherein said load is a Cold Cathode Fluorescent Lamp (CCFL).

4. The apparatus of claim 1, wherein said load is an External Electrode Fluorescent Lamp (EEFL).

5. The apparatus of claim 1, wherein said filter is a second order filter that includes an inductance component and a capacitance component.

6. The apparatus of claim 1, wherein said filter is a second order filter that includes an inductance component and a capacitance component, the inductance being provided by the transformer.

7. The apparatus of claim 1, wherein said filter is a second order filter that includes an inductance component, a first capacitance component, and a second capacitance component, said second capacitance component being in series with the load.

8. The apparatus of claim 1, wherein the power delivered to said load is regulated through the duty cycle of said switch.

9. The apparatus of claim 1, wherein the power delivered to said load is regulated by varying the frequency of said network.

10. The apparatus of claim 1, wherein said switch is a MOSFET.

11. The apparatus of claim 1, wherein said transformer has two primary windings.

12. The apparatus of claim 11, wherein said two primary windings are connected by a capacitor.

13. The apparatus of claim 1, wherein a semiconductor device, different from the switching component, is connected to one primary winding of the transformer.

14. An apparatus for converting a direct current (DC) signal into an alternating current (AC) signal for operating at least one electrical discharge lamp, comprising:

a single-ended network of one switch for generating an AC signal from a DC input signal, said AC signal being generated by the one switch of the network periodically opening and closing;

filtering means being coupled between said network of the one switch and a load, said filtering means filtering said AC signal delivered to said load, wherein said filtering means includes a transformer having two primary windings and a secondary winding that is coupled to said load;

a first capacitor being in parallel with said load; and

a second capacitor being in between said two primary windings of said transformer, wherein the second capacitor is operable to store energy to be delivered to the secondary winding of said transformer.

15. The apparatus of claim 14, wherein said discharge lamp is a Cold Cathode Fluorescent Lamp (CCFL).

16. The apparatus of claim 14, wherein said discharge lamp is an External Electrode Fluorescent Lamp (EEFL).

17. The apparatus of claim 14, wherein said filter is disposed between a secondary winding of the transformer and said load.

18. The apparatus of claim 14, wherein said filter is a second order filter that includes an inductance component and a capacitance component.

19. The apparatus of claim 14, wherein said filter is a second order filter that includes an inductance component and a capacitance component, the inductance being provided by the transformer.

20. The apparatus of claim 14, wherein the power delivered to said load is regulated through the duty cycle of said switch.

21. The apparatus of claim 14, wherein the power delivered to said load is regulated by varying the frequency of said single-ended network.

22. The apparatus of claim 14, wherein said switch is a MOSFET.

23. The apparatus of claim 14, further comprising a diode connected to one of the two primary windings of the said transformer.

24. The apparatus of claim 14, further comprising a third capacitor being in series with said load.

25. The apparatus of claim 14, further comprising a low RDSon MOSFET connected to the two primary windings of the said transformer.

26. A method of converting a direct converting a direct current (DC) signal into an alternating current (AC) signal for operating at least one electrical discharge lamp, comprising:

receiving a DC signal;

opening and closing a single switching device;

chopping said DC input signal by the opening and closing of said switching device;

generating an alternating signal in at least one primary windings of a transformer by chopping the DC signal, wherein a capacitor is coupled to at least one primary winding of the transformer;

stepping up said alternating signal of the at least one primary winding of the transformer into its secondary winding and deriving a stepped-up alternating signal;

filtering said stepped-up alternating signal and deriving a filtered signal through a filter; and

supplying said filtered signal to said electrical discharge lamp.

27. The method of claim 26, wherein said DC signal is received by a single-ended circuit.

28. The method of claim 26, wherein said switching device is a MOSFET.

29. The method of claim 26, wherein said step-up transformer has two primary windings.

30. The method of claim 29, wherein said two primary windings are coupled by a capacitor.

31. The method of claim 26, further comprising regulating the filtered signal by only varying the duty cycle of said alternating signal in the primary windings.

32. The method of claim 26, wherein said filter is a second order filter that includes an inductance component and a capacitance component.

33. The method of claim 26, wherein said filter is a second order filter that includes an inductance component, a capacitance component, and a second capacitance component, the inductance being provided by said transformer.