Electrodeless discharge lamp including impedance matching and filter network

• US 5,541,482 A
• Filed: 05/19/1993
• Issued: 07/30/1996
• Est. Priority Date: 05/20/1992
• Status: Expired due to Fees

• Current Assignee: Diablo Research Corporation
• Original Assignee: Diablo Research Corporation
• Inventors: Siao, Roger
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): Ratliff, Reginald N.
• Application Number:
  US08/064,779
• Time in Patent Office: 1,168 Days
• Field of Search: 315/248, 315/267, 315/276, 315/278, 315/39, 330/188, 330/195, 330/207
• US Class Current: 315/248
• CPC Class Codes: H05B 41/24 in which the lamp is fed by high frequency ac, or with separate oscillator frequencyH05B41/26 takes precedence

Abstract

An impedance matching and filter network is disclosed. The network performs two preselected impedance transformations and provides a filtering function to attenuate harmonics of an electrical signal delivered at an input of the network. The network may advantageously be structured in the form of balanced dual filters which are referenced to a virtual ground between them, the virtual ground being connected to a shield which surrounds the electric components. The network is particularly suitable for use with electrodeless discharge lamps to provide an impedance matching function for the induction coil and to limit RFI.

Claims

1. An electrodeless discharge lamp comprising:

a radio frequency generator;

an amplifier connected to an output of said radio frequency generator;

a coil network comprising an induction coil; and

an impedance matching network connected between said amplifier and said coil network, said impedance matching and filter network for providing two preselected impedance transformations for said coil network at different operating conditions of said lamp.

2. The electrodeless discharge lamp of claim 1 wherein one of said operating conditions occurs approximately when said lamp turns on and the other of said operating conditions is the steady-state operation of said lamp.

3. The electrodeless discharge lamp of claim 1 wherein said impedance matching network comprises a means of filtering harmonics of the radio frequency signals generated by said generator to inhibit the passage of said harmonics to said induction coil.

21. The electrodeless discharge lamp of claim 1 wherein

said impedance matching network is for providing two preselected impedance transformations at impedances which differ by a factor of at least ten.

35. The electrodeless discharge lamp of claim 2 wherein the Q of said impedance matching network is less than approximately two during the steady-state operation of said lamp.

36. The electrodeless discharge lamp of claim 2 wherein said impedance matching network comprises a first and second capacitors having respective first terminals connected to a first output terminal of said network, a second terminal of said first capacitor being connected to a second output terminal of said network, a first inductor connected between said second terminal of said first capacitor and a second terminal of said second capacitor, and a second inductor having a first terminal connected to said second terminal of said second capacitor.

37. The electrodeless discharge lamp of claim 36 wherein the reactance of said first capacitor is high at an output frequency of said radio frequency generator but low at frequencies of harmonics of said output frequency.

38. The electrodeless discharge lamp of claim 36 wherein said first inductor has a self-resonant frequency which is significantly higher than an output frequency of said radio frequency generator.

39. The electrodeless discharge lamp of claim 36 wherein a parallel resonant frequency of said first inductor and said second capacitor is equal to an output frequency of said radio frequency generator.

40. The electrodeless discharge lamp of claim 36 wherein said second capacitor resonates with said first inductor when said lamp turns on.

41. The electrodeless discharge lamp of claim 36 wherein said second inductor has a self-resonant frequency located near the frequency of the 10th harmonic of an output frequency of said radio frequency generator.

42. The electrodeless discharge lamp of claim 36 wherein said impedance matching network further comprises a third capacitance having a first terminal connected to said first output terminal of said network and a second terminal connected to a second terminal of said second inductor, and a third inductor connected to said second terminal of said third capacitor.

43. The electrodeless discharge lamp of claim 42 wherein the electrical characteristics of said second and third inductors are similar.

44. The electrodeless discharge lamp of claim 42 wherein the self-resonant frequency of said third inductor is set about one harmonic order lower than the self-harmonic frequency of said second inductor.

45. The electrodeless discharge lamp of claim 42 wherein the respective reactances of said second and third capacitors are very small at frequencies above the frequency of the 10th harmonic of an output frequency of said radio frequency generator.

46. The electrodeless discharge lamp of claim 44 wherein the respective reactances of said second and third capacitances are small compared to the respective reactances of said second and third inductors at frequencies of the harmonics below the 10th harmonic of an output frequency of said radio frequency generator.

47. The electrodeless discharge lamp of claim 42 wherein the respective Q'"'"'s of said first, second and third inductors and said first, second and third capacitors are greater than 100.

48. The electrodeless discharge lamp of claim 36 wherein the respective Q'"'"'s of said first and second inductors and said first and second capacitors are greater than 100.

4. An electrodeless discharge lamp comprising:

an oscillator;

an amplifier connected to an output of said oscillator; and

an induction coil network, said induction coil network comprising an induction coil and a vessel containing a selected gas, said induction coil being operative to create a plasma of charged particles in said gas after said lamp has been turned on;

wherein said induction coil network has a first inherent impedance measured at a pair of input terminals of said network when said lamp is initially turned on and a second inherent impedance at said input terminals when said lamp is in a steady-state on condition; and

said lamp comprising in addition an impedance matching network connected to said induction coil network, said impedance matching network having a pair of input terminals, said impedance matching network operative to transform said first inherent impedance to a first desired impedance measured at its input terminals when said lamp is initially turned on, and to transform said second inherent impedance to a second desired impedance measured at its input terminals when said lamp is in a steady-state on condition.

5. The electrodeless discharge lamp of claim 4 wherein said second inherent impedance is at least ten times said first inherent impedance.

6. The electrodeless discharge lamp of claim 4 wherein said impedance matching network comprises a means of filtering harmonics of a radio frequency signal generated by said amplifier to inhibit the passage of said harmonics to said induction coil.

7. An electrodeless discharge lamp comprising:

a radio frequency amplifier having two output terminals;

an induction coil network having two input terminals; and

a first filter and a second filter, said first filter being connected between a first output terminal of said amplifier and a first input of said induction coil network, said second filter being connected between a second output terminal of said amplifier and a second input of said induction coil network, said first and second filters being joined together at a common node.

8. The electrodeless discharge lamp of claim 7 comprising a conductive shield for said amplifier, said common node being coupled to said conductive shield.

9. The electrodeless discharge lamp of claim 8 wherein said first and second filters and said amplifier are enclosed by said shield and said induction coil network comprises an induction coil, said induction coil being positioned outside said shield.

10. The electrodeless discharge lamp of claim 7 wherein said first and second filters are approximately symmetrical with respect to said common node.

11. The electrodeless discharge lamp of claim 7 wherein said induction coil network comprises a first capacitor connected between said first filter and an induction coil and a second capacitor connected between said second filter and said induction coil.

12. The electrodeless discharge lamp of claim 11 wherein said first and second capacitors are substantially similar.

13. The electrodeless discharge lamp of claim 7 wherein said first filter comprises a first inductance and a second inductance and said second filter comprises a third inductance and a fourth inductance, said first and third inductances being wrapped on a first common torroidal core.

14. The electrodeless discharge lamp of claim 13 wherein the magnetic coupling between the first and third inductances is less than 0.4.

15. The electrodeless discharge lamp of claim 13 wherein said first filter comprises first and second capacitors and said second filter comprises third and fourth capacitors, each of said capacitors being joined to said common node.

16. The electrodeless discharge lamp of claim 8 wherein during operation of said lamp said shield and a centerpoint of said coil are maintained at a chassis ground.

17. The electrodeless discharge lamp of claim 16 containing a pair of matched capacitors, one of said capacitors being connected to one input of said coil and the other of said capacitors being connected to the other input of said coil.

18. The electrodeless discharge lamp of claim 8 wherein said first and second filters are substantially symmetrical.

25. The electrodeless discharge lamp of claim 13 wherein said second and fourth inductances are wrapped on a second common torroidal core.

19. An electrodeless discharge lamp comprising:

a power supply;

a radio frequency oscillator;

an amplifier;

an induction coil for transmitting a radio frequency signal delivered by said amplifier so as to create a plasma of charged particles in a gas;

a first filter connected between said amplifier and said induction coil so as to inhibit the passage of radio frequency interference (RFI) to said induction coil; and

a second filter connected between said power supply and a power main contact of said lamp so as to inhibit the passage of a noise signal to said power main contact.

20. An electrodeless discharge lamp comprising:

a metal chassis, said metal chassis enclosing a source of a radio frequency signal and an amplifier for amplifying said signal; and

an induction coil positioned outside of said metal chassis, said metal chassis and the center of said coil being maintained at a virtual ground.

26. The electrodeless discharge lamp of claim 20 wherein said chassis further encloses a power supply.

27. The electrodeless discharge lamp of claim 20 wherein said metal chassis includes a plurality of compartments, each of said compartments being enclosed by metal shielding, a first compartment containing said source of a radio frequency signal and said amplifier.

28. The electrodeless discharge lamp of claim 27 wherein a second compartment contains a pair of filters, a node between said filters being connected to said metal chassis.

29. The electrodeless discharge lamp of claim 28 wherein a third compartment contains a line filter.

30. The electrodeless discharge lamp of claim 29 wherein a fourth compartment contains a power supply.

22. A discharge lamp containing a power supply, an oscillator and an amplifier, said amplifier being for generating an electrical signal having a frequency of at least 20 KHz, said discharge lamp further containing a line filter connected between said power supply and a power main contact of said lamp so as to inhibit the passage of a noise signal to said power main contact.

23. The discharge lamp of claim 22 wherein said discharge lamp is an electrodeless discharge lamp.

24. An electrodeless discharge lamp comprising:

a radio frequency generator;

an amplifier connected to an output of said radio frequency generator;

an induction coil having only two terminals; and

a filter network connected between said amplifier and said induction coil, said filter network being configured such that the voltages at the two terminals of the induction coil are of equal magnitude and opposite phase when said lamp is operative.

31. An electrodeless discharge lamp comprising an oscillator, an amplifier connected to an output of said oscillator, an induction coil network comprising an induction coil and a vessel containing a selected gas, and a pair of balanced filters connected between said amplifier and said induction coil network, wherein said amplifier and said oscillator are enclosed within and insulated from a metal chassis and wherein a common node between said pair of balanced filters is connected to said metal chassis.

32. The electrodeless discharge lamp of claim 31 further comprising a line filter enclosed in said metal chassis.

33. The electrodeless discharge lamp of claim 31 further comprising a power supply enclosed in said metal chassis.

34. The electrodeless discharge lamp of claim 31 wherein said filter is enclosed in said metal chassis.