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

• US 20050258778A1
• Filed: 05/19/2004
• Published: 11/24/2005
• Est. Priority Date: 05/19/2004
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Chen, Wei
• Granted Patent: US 7,161,305 B2
• Time in Patent Office: Days
• US Class Current: 315/209.R
• 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 at least one switch for generating an AC signal from a DC signal, the AC signal being generated by a first portion of the network periodically opening and closing;

filtering means being coupled between the network of the said at least one switch and the load, the filtering means filtering the AC signal delivered to the load, wherein the filtering means includes a step-up transformer having at least one primary winding that receives the AC signal from the network of the said at least one switch and having a secondary winding that is coupled to the load; and

impedance means coupled to the said at least one transformer primary winding to form a resonant circuit for periodically opening and closing the switch, generally at a resonant frequency of the filtering means, so that alternating electrical power is supplied to the load under a range of voltages provided by the DC signal.

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

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

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

5. The apparatus of claim 1, wherein the filter is disposed between a secondary winding of the step-up transformer and the load.

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

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

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

9. The apparatus of claim 1, wherein the DC signal has a narrow voltage range.

10. The apparatus of claim 1, wherein the load current is regulated through the duty cycle of the switch.

11. The apparatus of claim 1, wherein the load current is regulated by changing the frequency.

12. The apparatus of claim 1, wherein the switch is a MOSFET.

13. The apparatus of claim 1, wherein the transformer has two primary windings.

14. The apparatus of claim 1, wherein a diode is in series with one primary winding of the transformer.

15. The apparatus of claim 1, wherein a semiconductor device, different from the switching component, is in series with one primary winding of the transformer.

16. 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 at least one semiconductor device for generating an AC signal from a DC input signal, the AC signal being generated by a first portion of the network periodically opening and closing;

filtering means being coupled between the network of the said at least one semiconductor device and the load, the filtering means filtering the AC signal delivered to the load, wherein the filtering means includes a step-up transformer having two primary windings that receive the AC signal from the network of the said at least one semiconductor device and having a secondary winding that is coupled to the load, and wherein the filtering means further includes a capacitor in parallel with the load; and

impedance means coupled to the said transformer primary windings to form a resonant circuit for periodically opening and closing the switch, generally at a resonant frequency of the filtering means, so that alternating electrical power is supplied to the load under a range of voltages provided by the DC input signal.

17. The apparatus of claim 16, wherein the discharge lamp is a Cold Cathode Fluorescent Lamp (CCFL).

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

19. The apparatus of claim 16, wherein the filter is disposed between a secondary winding of the step-up transformer and the load.

20. The apparatus of claim 16, wherein the filter is a second order filter that includes an inductance component and a capacitance component.

21. The apparatus of claim 16, wherein the filter is a second order filter that includes an inductance component and a capacitance component, the inductance being provided by the transformer.

22. The apparatus of claim 16, wherein the filter is a second order filter that includes an inductance component, a first capacitance component, and a second capacitance component, the second capacitance component being in series with the load.

23. The apparatus of claim 16, wherein the DC signal has a narrow voltage range.

24. The apparatus of claim 16, wherein the load current is regulated through the duty cycle of the switch.

25. The apparatus of claim 16, wherein the load current is regulated by changing the frequency.

26. The apparatus of claim 16, wherein the semiconductor device is a MOSFET.

27. The apparatus of claim 16, wherein a diode is in series with one primary winding of the transformer.

28. The apparatus of claim 16, wherein a MOSFET, different from the switching semiconductor device, is in series with one primary winding of the transformer.

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

receiving a DC signal;

opening and closing a switching device by a resonant circuit using the DC signal;

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

generating an alternating signal in the primary windings of a transformer by chopping the DC signal;

stepping up the alternating signal of the transformer'"'"'s primary winding into its secondary winding;

filtering the stepped-up alternating signal; and

supplying the filtered signal to the discharge lamp.

30. The method of claim 29, wherein the DC signal is received by a single-ended circuit.

31. The method of claim 29, wherein switching is done by a MOSFET.

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

33. The method of claim 29, wherein filtering is done by a second order filter that includes an inductance component and a capacitance component.

34. The method of claim 29, wherein filtering is done by a second order filter that includes an inductance component and a capacitance component, and a second capacitance component, the inductance being provided by the step-up transformer.