Ballast circuit with lamp cathode protection and ballast protection

• US 6,653,800 B2
• Filed: 11/06/2001
• Issued: 11/25/2003
• Est. Priority Date: 11/06/2001
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Chen, Timothy
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, THUY V
• Application Number:
  US09/682,990
• Publication Number:
  US 20030085670A1
• Time in Patent Office: 749 Days
• Field of Search: 315/244, 315/260, 315/283, 315/287, 315/291, 315/307, 315/334, 315/DIG.2, 315/DIG.5, 315/DIG.7
• US Class Current: 315/244
• CPC Class Codes: H05B 41/2985 against abnormal lamp operating conditions
• CPC Class Codes: H05B 41/2988 for protecting the lamp against abnormal operating conditions

Abstract

A ballast circuit for driving a fluorescent lamp is provided. The ballast circuit comprises: a self-oscillating circuit; and a series resonant circuit. The series resonant circuit comprises: an inductor; a capacitor; and two diodes. The arrangement of the series resonant circuit: a) causes less power to be dissipated by first and second lamp cathodes when a lamp is coupled to the ballast circuit and increases lamp life, b) protects the ballast circuit from self-destruction when no lamp is coupled to the ballast circuit, and protects the ballast circuit from self-destruction when either the first, second, or both cathodes of a lamp coupled to the ballast circuit have failed.

Claims

1. A ballast circuit for driving a fluorescent lamp, comprising:

a self-oscillating circuit for producing a periodic a.c. signal having a first cycle and a second cycle; and

a series resonant circuit operationally coupled to the self-oscillating circuit and adapted for operationally coupling with a first and second cathode of the lamp, the resonant circuit further including;

a resonant inductor operationally coupled to the self-oscillating circuit,

a resonant capacitor,

a first diode with an anode lead and a cathode lead operationally coupled between the resonant inductor and resonant capacitor and adapted for operationally coupling across the first cathode of the lamp, and

a second diode with an anode lead and a cathode lead operationally coupled between the resonant capacitor and the self-oscillating circuit, wherein the leads of the second diode are in an opposite orientation from the leads of the first diode with respect to the series resonant circuit, and the second diode being adapted for operationally coupling across the second cathode of the lamp;

wherein at least one of the first and second diodes substantially blocks resonant circuit current from flowing during a predetermined first or second cycle of the self-oscillating circuit when the lamp is coupled to the ballast circuit and one or more of the first and second cathodes of the lamp has failed.

2. The ballast circuit of claim 1, wherein the first diode provides half wave rectification of the voltage across the first cathode of the lamp when the lamp is coupled to the ballast circuit.

3. The ballast circuit of claim 2, wherein the second diode provides half wave rectification of the voltage across the second cathode of the lamp when the lamp is coupled to the ballast circuit.

4. The ballast circuit of claim 3, wherein the half wave rectification of the voltage across the first and second cathodes of the lamp when the lamp is coupled to the ballast circuit reduces the power dissipated by each cathode and increases lamp life.

5. The ballast circuit of claim 1, wherein the first diode substantially blocks resonant circuit current from flowing during a predetermined first or second cycle of the self-oscillating circuit when the lamp is coupled to the ballast circuit and the first cathode of the lamp has failed.

6. The ballast circuit of claim 5, wherein the self-oscillating circuit is prevented from oscillating and the ballast circuit is protected from self-destruction when a lamp is coupled to the ballast circuit and the first cathode of the lamp has failed.

7. The ballast circuit of claim 1, wherein the second diode substantially blocks resonant circuit current from flowing during a predetermined first or second cycle of the self-oscillating circuit when the lamp is coupled to the ballast circuit and the second cathode of the lamp has failed.

8. The ballast circuit of claim 7, wherein the self-oscillating circuit is prevented from oscillating and the ballast circuit is protected from self-destruction when a lamp is coupled to the ballast circuit and the second cathode of the lamp has failed.

9. A ballast circuit for driving a fluorescent lamp, comprising:

a self-oscillating circuit for producing a periodic a.c. signal having a first cycle and a second cycle; and

a series resonant circuit operationally coupled to the self-oscillating circuit and adapted for operationally coupling with a first and second cathode of the lamp, the resonant circuit further including;

a resonant inductor operationally coupled to the self-oscillating circuit,

a resonant capacitor,

a first diode with an anode lead and a cathode lead operationally coupled between the resonant inductor and resonant capacitor and adapted for operationally coupling across the first cathode of the lamp, and

a second diode with an anode lead and a cathode lead operationally coupled between the resonant capacitor and the self-oscillating circuit, wherein the leads of the second diode are in an opposite orientation from the leads of the first diode with respect to the series resonant circuit, and the second diode being adapted for operationally coupling across the second cathode of the lamp;

wherein the first diode substantially blocks resonant circuit current from flowing during a predetermined first or second cycle of the self-oscillating circuit when no lamp is coupled to the ballast circuit.

10. The ballast circuit of claim 9, wherein the second diode substantially blocks resonant circuit current from flowing during the opposite cycle of the self-oscillating circuit from the cycle in which current is substantially blocked by the first diode when no lamp is coupled to the ballast circuit.

11. The ballast circuit of claim 10, wherein the self-oscillating circuit is prevented from oscillating and the ballast circuit is protected from self-destruction when no lamp is coupled to the ballast circuit.

12. A ballast circuit for driving a fluorescent lamp, comprising:

a self-oscillating circuit for producing an a.c. signal;

a resonant inductor with first and second leads, the first lead operationally coupled to the self-oscillating circuit;

a resonant capacitor with first and second leads;

a first diode with an anode lead operationally coupled to the first lead of the resonant capacitor and a cathode lead operationally coupled to the second lead of the resonant inductor; and

a second diode with an anode lead operationally coupled to the second lead of the resonant capacitor and a cathode lead operationally coupled to the self-oscillating circuit;

wherein the first diode is adapted for operationally coupling with a first cathode of the lamp and the second diode is adapted for operationally coupling with a second cathode of the lamp;

wherein the first and second diodes;

a) cause less power to be dissipated by the first and second lamp cathodes when the lamp is coupled to the ballast circuit and increase lamp life, b) protect the ballast circuit from self-destruction when no lamp is coupled to the ballast circuit, and protect the ballast circuit from self-destruction when either the first, second, or both cathodes of the lamp coupled to the ballast have failed.

13. A series resonant circuit for a ballast circuit, wherein the ballast circuit is adapted for driving a fluorescent lamp, the series resonant circuit comprising:

a resonant inductor adapted for operationally coupling with a self-oscillating circuit of the ballast circuit;

a resonant capacitor with first and second leads;

a first diode with an anode lead and a cathode lead operationally coupled between the resonant inductor and resonant capacitor and adapted for operationally coupling with a first cathode of the lamp; and

a second diode with an anode lead and a cathode lead operationally coupled between the resonant capacitor and the self-oscillating circuit and adapted for operationally coupling with a second cathode of the lamp;

wherein the first and second diodes protect the ballast circuit from self-destruction.

14. The series resonant circuit of claim 13, wherein the first and second diodes cause less power to be dissipated by the first and second lamp cathodes when the lamp is coupled to the ballast circuit and increase lamp life.

15. The series resonant circuit of claim 13, wherein the first and second diodes protect the ballast circuit from self-destruction when the lamp is coupled to the ballast circuit and either the first, second, or both cathodes of the lamp have failed.

16. The series resonant circuit of claim 13, wherein the first and second diodes protect the ballast circuit from self-destruction when no lamp is coupled to the ballast circuit.