WO2014085951A1

WO2014085951A1 - Ballast with programmable filament preheating

Info

Publication number: WO2014085951A1
Application number: PCT/CN2012/085720
Authority: WO
Inventors: Chenghua Zhu
Original assignee: General Electric Company
Priority date: 2012-12-03
Filing date: 2012-12-03
Publication date: 2014-06-12

Abstract

A system and method for powering discharge lamps including circuitry for controlling the filament preheating energy provided to one or more gas discharge lamps. The system, in some embodiments, provides a preheating circuit as a program-start mechanism to preheat the electrodes of a fluorescent lamp before the required voltage for striking an arc between the electrodes is applied. The preheating circuit is connected in series in the main resonant circuit and includes a preheat transformer, a switch, and DC capacitor. The preheating circuit provides preheating to filaments of the discharge lamps for a preset time before cutting of the preheating such that no further voltage is applied to the filaments thereby improving the efficiency of the system.

Description

BALLAST WITH PROGRAMMABLE FILAMENT PREHEATING

I. Field of the Invention

[0001] The present invention relates generally to electronic ballasts. More particularly, the present invention relates to electronic ballasts with filament preheating energy control.

II. Background of the Invention

[0002] Arc lamps, such as fluorescent lamps, produce light by an electric arc. The lamps include two electrodes, typically made of tungsten or carbon, which are separated by a gas. The arc refers to the discharge that occurs upon ionization of the gas. A high voltage is applied, i.e., pulsed, across the electrodes of the lamp to ignite or strike the arc. After striking the arc the discharge can be maintained at a lower voltage. An electrical circuit including an igniter and a ballast is required to strike the arc in the lamp. The ballast is typically wired in series with the lamp in order to provide two function including maintaining the arc and limiting the current needed to operate the lamp.

[0003] Typical programmed start ballasts provide a low-glow preheating current to the lamp filaments when the ballast is activated. Preheating can extend lamp life because it helps avoid damage to cathodes of the lamp that would accompany firing the lamp with a cold filament.

[0004] Conventional lamp preheating solutions offer a simple circuit for an inverter driving a load of two series connected lamps. Auxiliary windings are wound on the same core as an inductor to provide the preheat current to the lamp filaments. Capacitors are used to provide a lower impedance at the preheat frequency and a higher impedance at normal operating frequency to reduce filament loss after ignition of the lamp. This preheating method is disadvantageous due to the preheating energy not being fully cut off after ignition. Further, the power loss on the filaments continues to persist during operation, which significantly decreases efficiency.

III. Brief Description of the Invention

[0005] Given the aforementioned deficiencies, what is needed, therefore, is a lighting ballast including filament preheating that fully deactivates after ignition and minimizes power loss on the filament during operation.

[0006] Embodiments of the present invention provide a lighting system including a transformer, a power switch, a preheating controller, and a capacitor.

[0007] In the embodiments, the lighting system is configured to apply a heating voltage to the filaments of a lamp during the preheating stage of the lamp. The lighting system is configured to cut off the voltage applied to the filaments of the lamp during normal operation of the lamp. By cutting off the voltage applied during normal operation, loss at the filaments during normal operation is mitigated and efficiency of the lamp is improved.

[0008] In at least one aspect, the embodiments provide a lighting apparatus, including a transformer in communication with filaments of a lamp. A power switch is in communication with the transformer. A preheating controller is in communication with the power switch and the transformer. During operation, the transformer applies a current to the filaments during a preheating stage of the lamp. The preheating controller turns the power switch to an on position and an off position depending on the operating stage of the lamp.

[0009] In yet another aspect, the embodiments provide a lighting system, including a preheating cut-off circuit and a capacitor in communication with a preheating transformer of the preheating cut-off circuit. The preheating cut-off circuit includes a preheating transformer in communication with a lighting ballast of a fluorescent lamp. The preheating circuit also includes a power switch in communication with the preheating transformer, and a preheating controller in communication with the power switch and the preheating transformer.

[0010] During operation, the preheating transformer provides power to the fluorescent lamp during a preheating stage of the fluorescent lamp. The preheating controller turns the power switch to an on position during preheating of the fluorescent lamp and to an off position following preheating of the fluorescent lamp. The capacitor cuts off the power applied to the preheating transformer following preheating of the fluorescent lamp.

[0011] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. IV. Brief Description of the Drawings

[0012] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.

[0013] FIG. 1 is a circuit diagram of a lamp preheating circuit in accordance with an embodiment of the present invention.

[0014] FIG. 2 is a circuit diagram of an alternative embodiment of the lamp preheating circuit in accordance with the present invention.

[0015] FIG. 3 is a circuit diagram of an embodiment of a preheating control circuit in accordance with FIG. 1.

[0016] FIG. 4 is a flowchart of a method for controlling the preheating energy applied to a lamp in accordance with an embodiment of the present invention.

[0017] The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the art.

V. Detailed Description of the Drawings

[0018] The following detailed description is merely exemplary in nature and is not intended to limit the applications and uses disclosed herein. Further, the invention is not bound by any theory presented in the preceding background or summary, or the following detailed description. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility.

[0019] The system of the present invention, in some embodiments, provides a preheating circuit as a program-start mechanism to preheat the electrodes of a fluorescent lamp before the required voltage for striking an arc between the electrodes is applied. While embodiments of the present invention are described herein primarily in connection with fluorescent lamps, the concepts are also applicable to other types of gas discharge lamps. Other gas discharge lamps may include, for example, compact fluorescent lamps (CFLs), self-ballasted compact fluorescent lamps (CFLi-s), and the like.

[0020] FIG. 1 is a schematic diagram of a lamp preheating circuit in accordance with an embodiment of the present invention. In FIG. 1, lamp preheating cut-off circuit 100 provides a programmable preheating solution that deactivates the pre-heating energy to an electronic lighting ballast (not shown in detail), e.g., a series resonant inverter 150, following ignition of a fluorescent lamp. The lamp preheating cut-off circuit 100 includes a preheat transformer 110, a power switch 120, a preheating controller 130, and a capacitor 140. The power switch 120 includes a gate (Qp gate) and a source (Qp source) connected to the preheating controller 130. The power switch 120 may be, for example, an N-channel MOSFET used for preheating control. The preheating controller 130 turns power switch 120 ON and OFF depending on its operating stage, as discussed in further detail below.

[0021] The series resonant inverter 150 may include, for example, an inverter driver circuit 155 that receives a direct current (DC) from a power source 170, e.g., DC bus Vdc, to power the filaments of a fluorescent lamp. The inverter driver circuit 155 may be an integrated circuit (IC) controller such as, for example, a model UBA2015T produced by NXP Semiconductors of Eindhoven, The Netherlands. Direct current is supplied from positive (+) and negative (-) posts of DC bus 170 to the inverter driver circuit 155 via gates Ql, Q2.

[0022] In FIG. 1, MOSFETs Ql and Q2 form a half bridge. During operation, Ql and Q2 are controlled by inverter driver circuit 155 to be ON and OFF alternately such that they generate a square wave voltage on the middle point of the half bridge. Resonant inductor Lr and resonant capacitor Cr form a resonant tank that transforms the square wave voltage to sine wave voltage.

[0023] Auxiliary windings LI, L2, and L3 of the series resonant inverter 150 are wound on the same core as preheat transformer Lp of the lamp preheating cut-off circuit 100. Connecting the auxiliary windings LI, L2, and L3 on the same core as the preheating transformer Lp allows a preheating current to be applied to the lamp 160A, 160B. Current limiting capacitors CI, C2, and C3 are connected in series with the auxiliary windings LI, L2, and L3 to prevent the auxiliary windings LI, L2, L3 from short circuiting due to, for example, faulty wiring of outputs, and the like. Capacitor C4 is a DC blocking capacitor. Capacitor C6 is a current limiting capacitor.

[0024] During the preheating stage, the power switch 120 of the lamp preheating cut-off circuit 100 is controlled to be OFF. The preheat transformer 110 is connected in series with resonant inductor Lr and provides preheating energy to the lamp filaments through the secondary windings LI, L2, and L3. [0025] During a normal operating stage (steady state) of the lamp 160A, 160B, i.e., following the glow mode of the lamp, the power switch 120 is controlled to be ON and the preheat transformer 110 is shorted by capacitor 140, e.g., a luF capacitor. Shorting the preheat transformer 110 by the capacitor 140 fully cuts back the preheating energy. Therefore, the lamp experiences no power loss on the filaments during normal operation.

[0026] After a predetermined preheating time, a high alternating current (AC) voltage is applied to ignite the lamp 160 A, 160B. The preheating time may be set, for example, by the inverter control circuit 155. During this time, the preheating controller 130 controls the power switch 120 to be ON. The preheat transformer 110 is then shorted through capacitor 140, thereby cutting off the preheating.

[0027] During the normal operating stage, the power switch is controlled to always be ON and the preheat transformer 110 is always shorted (cut off) by capacitor 140. Therefore, the power loss on the filaments during this time will be near zero. The lamp preheating cut-off circuit 100 thereby ensures optimal efficiency by preventing loss on the filaments during normal operation of the series resonant inverter 150.

[0028] FIG. 2 is a circuit diagram of an alternative embodiment of the lamp preheating circuit in accordance with the present invention. A lamp preheating cut-off circuit 200 is substantially similar to lamp preheating cut-off circuit 100, discussed above with respect to FIG. 1. The lamp preheating cut-off circuit 200 provides a programmable preheating solution that cuts off the pre-heating energy to an electronic ballast, e.g., a series resonant inverter 250, following ignition of a fluorescent lamp. [0029] Similar to preheating cutoff circuit 100, the lamp preheating cut-off circuit 200 includes a preheat transformer 210, a power switch 220, a preheating controller 230, and a capacitor 240. The power switch 220 may be, for example, an N-channel MOSFET used for preheating control. The preheating controller 230 turns power switch 220 ON and OFF.

[0030] In addition to these components noted above, lamp preheating cut-off circuit 200 also includes a diode 240 connected to the DC power source 270, e.g., DC bus Vdc. The diode 240 provides low (preferably zero) resistance to current flow in one direction, and high (preferably infinite) resistance to current flow in the other direction. The diode 240 will clamp the preheating voltage from the power switch 220. Clamping the preheating voltage from the power switch 220 functions to further ensure very low (substantially zero) power loss on the filaments of the lamp 260 A, 260B. The diode 240 thereby helps to improve the efficiency of the lamp preheating cut-off circuit 200.

[0031] FIG. 3 is a schematic diagram of the embodiment of the preheating control circuit 130 shown in FIG. 1. A preheating control circuit 300 includes a resonant inductor 302, a rectifier 304, capacitor 306, resistor 308, zener diode 310, zener diode 312, capacitor 314, and resistor 316. The resonant inductor 302 is coupled to resonant inductor Lr and provides a control voltage signal to the gate of power switch Qp. Capacitor 306 and resistor 308 form a filter. Zener diode 310 sets a threshold voltage. When the voltage of capacitor 306 is higher than the threshold voltage, the capacitor 314 begins to charge and activate power switch Qp. The zener diode 312 clamps the gate voltage of power switch Qp. [0032] During the preheating stage of the lamp, an inverter (not shown) is operated at a high frequency and the voltage on resonant Lr is low. When voltage on capacitor 306 is lower than the threshold voltage, the capacitor 314 voltage will be low, and power switch Qp is controlled to be OFF. Preheat transformer Lp 110 and capacitor 140 form a resonant tank (LC circuit) that provides preheating energy to the filaments of lamp 160A, 160B.

[0033] Referring again to FIGs. 1 and 2, after a predetermined preheating time, the operating frequency of series resonant inverter, e.g., 150 and 250, is controlled by the inverter driver circuit (now shown) to become lower. High voltage is generated on the resonant inductor Lr and capacitor Cr causing the lamps 160A, 160B and 260A, 260B to ignite. The voltage of capacitor 306 rises to break down zener diode 310. Capacitor 314 is quickly charged to turn on power switch Qp and preheating is cut off.

[0034] During the normal operating stage of the lamp, the voltage of capacitor 314 remains high to keep the power switch Qp ON. Power switch Qp can be controlled to be ON or OFF in order to provide preheating energy or to cut off preheating energy, as desired. The lamp preheating cut-off circuit of the embodiments may therefore be used in dimming ballasts in order to improve the efficiency of the system by cutting of the preheating energy following the preheating stage of the lamp. The lamp preheating cutoff circuit thereby improves the efficiency of the lamp.

[0035] FIG. 4 is a flowchart of a method for controlling the preheating energy applied to a fluorescent lamp in accordance with an embodiment of the present invention. The method 400 begins at step 402, during a preheating stage of a fluorescent lamp, by applying a current to the filaments of the fluorescent lamp via a transformer. At step 404, actuating, via a preheating controller, a power switch in communication with the transformer. The power switch is actuated between an ON position and an OFF position. Controlling the power switch to be ON or OFF selectively regulates the preheating energy applied to the fluorescent lamp. When the power switch is in the ON position, the preheating energy is applied to the fluorescent lamp. When the power switch is in the OFF position, the preheating energy is cut-off from the fluorescent lamp. At step 406, optionally clamping the preheating voltage from the power switch. Clamping the preheating voltage from the power switch enables substantially zero power loss on the filaments of the fluorescent lamp thereby improving the efficiency of the fluorescent lamp.

[0036] Alternative embodiments, examples, and modifications which would still be encompassed by the disclosure may be made by those skilled in the art, particularly in light of the foregoing teachings. Further, it should be understood that the terminology used to describe the disclosure is intended to be in the nature of words of description rather than of limitation.

[0037] Those skilled in the art will also appreciate that various adaptations and modifications of the preferred and alternative embodiments described above can be configured without departing from the scope and spirit of the disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the disclosure may be practiced other than as specifically described herein.

Claims

IN THE CLAIMS: We claim:

1. A lighting apparatus, comprising: a transformer in communication with filaments of a lamp, the transformer being configured to apply a current to the filaments during a preheating stage of the lamp; a power switch in communication with the transformer; and a preheating controller in communication with the power switch and the transformer, the preheating controller being configured to actuate the power switch between an on position and an off position.

2. The lighting system according to claim 1, wherein the power switch is connected in series with the transformer.

3. The lighting system according to claim 1, wherein the power switch is formed by a gate.

4. The lighting system according to claim 3, wherein the power switch includes an N-channel MOSFET.

5. The lighting system according to claim 1, wherein the preheating controller turns the power switch to an on position during a preheating stage of the lamp.

6. The lighting system according to claim 1, wherein the preheating controller turns the power switch to an off position during a normal operating stage of the lamp.

7. The lighting system according to claim 1, further comprising: a capacitor in communication with the transformer.

8. The lighting system according to claim 7, wherein the capacitor is connected in series with the transformer.

9. The lighting system according to claim 1, wherein the capacitor is configured to cut off voltage applied to the transformer during a normal operating stage of the lamp.

10. The lighting system according to claim 1 , further comprising a diode in communication with the power switch and a direct current bus, wherein the diode is configured to clamp a preheating voltage from the power switch.

11. A lighting system, comprising: a preheating cut-off circuit, including: a preheating transformer in communication with a lighting ballast of a fluorescent lamp, the preheating transformer being configured to power the fluorescent lamp during a preheating stage of the fluorescent lamp; a power switch in communication with the preheating transformer; and a preheating controller in communication with the power switch and the preheating transformer, the preheating controller being configured to turn the power switch to an on position during a preheating stage of the fluorescent lamp and an off position following the preheating stage of the fluorescent lamp; and a capacitor connected to the preheating transformer, the capacitor being configured to cut off the power applied to the preheating transformer following the preheating stage of the fluorescent lamp.

12. The lighting system according to claim 11, wherein the power switch is connected in series with the preheating transformer.

13. The lighting system according to claim 11, wherein the power switch is formed by a gate.

14. The lighting system according to claim 13, wherein the gate is an N-channel MOSFET.

15. The lighting system according to claim 11, further comprising: a capacitor in communication with the preheating transformer.

16. The lighting system according to claim 15, wherein the capacitor is connected in series with the preheating transformer.

17. A lighting method, comprising: applying, during a preheating stage, a current to the filaments of a fluorescent lamp via a transformer; and actuating, via a preheating controller, a power switch in communication with the transformer between an on position and an off position.

18. The lighting method according to claim 17, wherein actuating includes controlling the power switch to be on during the preheating stage of the fluorescent lamp.

19. The lighting method according to claim 17, wherein actuating includes controlling the power switch to be off following the preheating stage of the fluorescent lamp.

20. The lighting method according to claim 17, further comprising: clamping a preheating voltage from the power switch.