BACKGROUND

Technical Field

[0001] The subject matter of the present disclosure relates to lighting devices and, more particularly, to devices and circuitry that pre-heat components of lighting devices (e.g., gas discharge lamps).

Description of Related Art

[0002] Several types of ballasts are known to operate lighting devices. The type of ballast often depends on the environment in which the lighting device/ballast will be used. For example, to turn a lighting device on with minimal delay, instant start ballasts can ignite or strike the lighting device by applying a high voltage lamp signal across the lighting device. This lamp signal causes an arc to form between the filaments. On the other hand, some circumstances necessitate the lighting device minimize the striking potential/voltage of the lamp signal. To satisfy this requirement, rapid start ballasts provide a pre-heat signal to the filaments prior to ignition. The pre-heat signal has sufficient voltage to warm the filaments, thereby reducing the magnitude of voltage of the lamp signal necessary to ignite or strike the lighting device. The rapid start ballast generates the pre-heat signal and the lower- voltage lamp signal concurrently.

[0003] Unfortunately, both the instant start ballasts and the rapid start ballasts cause deterioration of the filaments and, in particular, of the emissive coatings on the filaments. Deterioration reduces lamp life. Failing to pre-heat the filaments (e.g., as in the instant start ballasts) and applying the lamp signal across the lamp during preheating of the filaments (e.g., as in the rapid start ballasts) are known to cause premature deterioration of the filaments. However, although rapid start ballasts are often in favor because the extent of pre-mature deterioration is less with this type of ballast, rapid start ballasts are less efficient. [0004] Programmed start ballasts address the short-comings in the instant start ballast and the rapid start ballast. This type of ballast provides a pre -heat signal to increase the temperature of the filaments. After the filaments reach the temperature desired, the ballast eliminates the pre-heat signal and then provides a lamp signal to ignite or strike the lighting device. Switching between the pre-heat signal and the lamp signal often involves manipulation of the power signal that drives the lamp. Examples of programmed start ballasts often include an inverter that operates at one frequency to pre-heat the filaments and then "sweeps" to another frequency to ignite and operate the lighting device. Nevertheless, circuitry including the inverter necessary to implement the operation of the ballast can be complex and costly.

BRIEF DESCRIPTION OF THE INVENTION

[0005] The present disclosure describes embodiments of a pre-heating device to supplement operation of ballasts such as the instant start and rapid start ballasts above. The pre-heating device generates a pre-heating signal in the form of a current having a sine (or cosine) waveform. This pre-heating signal reduces electromagnetic interference compared to circuitry that deliver voltage-based pulse signals for preheating the filaments.

[0006] Other features and advantages of the disclosure will become apparent by reference to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Reference is now made briefly to the accompanying drawings, in which:

[0008] FIG. 1 depicts a block diagram of an example of an exemplary lighting device configured to pre-heat filaments of a lamp;

[0009] FIG. 2 depicts a schematic diagram of a topology for an exemplary preheat device for use in the lighting device of FIG. 1; and [0010] FIG. 3 depicts plots of waveforms for signals that occur during operation of an exemplary pre-heat device such as the pre-heat device of FIG. 2.

[0011] Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 illustrates a schematic diagram of an example of a lighting device 100 (e.g., a gas discharge lamp) that includes a pre-heat device 102 of the present disclosure. The pre-heat device 102 generates a pre-heating signal, e.g., current that pre-heats filaments in one or more lamps 104 for a period of time before ignition of the lamp 104 occurs. The pre-heat device 102 can couple with an electronic ballast 106 (also a "ballast 106"). During operation of the lighting device 100, a lamp signal from the electronic ballast 106 ignites the filaments.

[0013] Examples of the pre-heat device 102 offer a number of advantages over other modalities to pre-heat the filaments. One advantage is that the pre-heat device 102 is not necessarily incorporated into, nor dependent upon, the design of the lighting device 100. This feature affords pre-heat functionality in a single design that is compatible with various configurations of the lighting devices 100. For example, the pre-heat device 102 is compatible with lighting devices that have a single lamp or a plurality of lamps. The pre-heat device 102 is also compatible with different Rh/Rc values, which defines the ratio of the hot cathode resistance (Rh) to the cold cathode resistance (Rc) in the lighting device. The pre-heat device 102 is further compatible with different types of ballasts 106. For example, the pre-heat device 102 may couple with an instant start ballast and/or a rapid start ballast to form a programmed start ballast. This combination of the pre-heat device 102 and the ballast provides a preheat signal to first increase the temperature of the filaments and then provide a lamp signal to ignite or strike the lamp and generate light.

[0014] Another advantage is that the pre-heat device 102 minimizes the number of components necessary to generate the pre-heat signal. This features reduces costs as well as permits smaller and more compact configurations of the circuitry that operates the lighting device 100. Yet another advantage is that the pre-heat energy in the pre-heat signal is sufficient to permit the pre-heat device 102 to operate remote from the ballast 106. Thus, although not shown in FIG. 1, the pre-heat device 102 can operate multiple filaments and/or multiple lighting devices, as desired, but does not have to be in the immediate vicinity and/or adjacent the filaments 104.

[0015] Referring back to FIG. 1, the ballast 106 receives a drive signal from a power supply 108. The drive signal is typically an alternating current (AC) voltage signal (also an "AC voltage signal) found in a home or office premise. The drive signal can have a voltage, e.g., 120 V, 270 V, etc. In one example, the ballast 106 includes a filter component 110, a power factor correction (PFC) component 112, and an inverter component 114. The filter component 110 removes electromagnetic interference (EMI) from the AC voltage signal, which if not removed can disrupt operation of the ballast 106. The PFC component 112 converts the filtered AC voltage signal, e.g., from an AC voltage signal to a DC voltage signal. The inverter component 110 converts the DC voltage signal to the lamp signal to ignite and drive the filament 104 and produce light.

[0016] In one embodiment, the pre-heat device 102 can couple a power signal (e.g., the DC voltage signal) from the PFC component 112. The power signal energizes the pre-heat device 102 to generate the pre-heat signal. As discussed more below, the pre-heat signal comprises, in one example, current having a sine or cosine waveform. These waveforms generate less electromagnetic interference than other signals (e.g., pulse signals) typical of conventional circuits that are used for preheating.

[0017] FIG. 2 depicts a topology for an exemplary pre-heat device 200 that can be used as the pre-heat device 102 of FIG. 1. The pre-heat device 200 couples with a lamp 204 to pre-heat filaments found therein. This topology includes various components (e.g., resistors, capacitors, switches, diodes, etc.) that are useful for the present design. This disclosure also contemplates other configurations of components that would form topologies other than that shown the figures. [0018] Moving from left to right in the diagram, the pre-heat device 200 includes an inductor winding 214 that can couple a power signal from a PFC inductor (e.g., PFC inductor 112 of FIG. 1) or from a separate power supply. Diodes (e.g., a diode 216 and a diode 218), capacitors (e.g., a capacitor 217 and a capacitor 219), and the inductor winding 214 form a rectifier bridge, which transfers AC voltage (from the inductor winding 214) to the DC voltage . The DC voltage can vary, although in one example the voltage is about 60 V.

[0019] The pre-heat device 200 also includes a drive circuit 220. Artisans skilled in the relevant electrical and lighting arts will recognize the construction of the drive circuit 220 as shown in FIG. 2. In one example, the drive circuit 220 comprises a self- oscillating driver that oscillates in response to the power signal. A microcontroller can substitute for and/or supplement the drive circuit 220 in other examples of the pre-heat device 200. Examples of the drive circuit 220 can oscillate at about 120 KHz or more, with one particular example of the drive circuit 220 oscillating at from about several KHz to several MHz. The present disclosure contemplates other configurations of elements and components for use in and as the drive circuit 220, wherein the overall configuration of the drive circuit 220 operates in the manner described herein.

[0020] The drive circuit 220 couples with a switch 222. Switches for use as the switch 222 include various transistors such as field effect transistors (e.g., FETS, MOSFETS, etc.) and bipolar junction transistors (BJT). The switch 222 couples with resistors (e.g., resistor 224 and resistor 226) and a choke inductor 228. In one example, the switch 222, the resistor 224, the resistor 226, and the choke inductor 228 form a pre-heat inverter 230, which can also be classified as an example of a class E inverter. The DC voltage from the rectifier bridge energizes the pre-heat inverter 230.

[0021] As shown in FIG. 2, the pre-heat inverter 230 drives a resonant tank circuit 232 to provide pre-heating current having the sine or cosine waveforms, which minimize electromagnetic emissions that can disrupt ignition of the lighting device. The resonant tank circuit 232 includes, in one example, components such as a resonant inductor 234 and a resonant capacitor 236. Selection of these components can tune the resonant frequency of the resonant tank circuit 232 as necessary to store energy and to determine the quality (Q) factor of the resonant tank circuit 232. In one example, selection of components for the resonant tank circuit 232 have a Q factor that produces the sine or cosine waveform of the pre-heat signal. The resonant tank can be equipped with different configurations (one or more inductors and capacitors and/or a single capacitor or a single inductor). The configuration of these components can be selected in conjunction with the pre-heating requirements and/or other preheating factors (e.g., design factors of the lighting device).

[0022] A pre-heat transformer 238 couples with the resonant tank circuit 232. The pre-heat transformer 238 comprises a primary winding 240 and a secondary winding 242. The secondary winding 242 can couple with a filament 244 of the lamp 204 after the lamp 204 has been connected (or mounted) in the lighting device. If one lamp is used, the primary winding 240 and the secondary winding 242 may include two winding elements, one for each of the lamps filaments. On the other hand, if more than one lamp is used, specifically in a parallel configuration, then the primary winding 240 and the secondary winding 242 may have more than two elements. In one example, an absorbing capacitor 246 couples across the primary winding 240 and a transit capacitor 248 couples in series with the filament 244 to control current of the pre-heat signal at the filament 244.

[0023] During operation, energizing the pre-heat device 200 causes the drive circuit 220 to oscillate and, in effect, open and close the switch 222. The action of the switch 222 selectively couples (e.g., when the switch 222 is closed) the power signal to the primary winding 240. The power signal induces a voltage across the primary winding 240 and the secondary winding 242 of the pre-heat transformer 238. This voltage generates the pre-heat signal that pre-heats the filament 244. In one example, the drive circuit 220 operates the switch 222 at high operating frequency that drives the load network oscillating with the high Q factor, which, in turn, generates the preheat signal with a sine or cosine waveform.

[0024] FIG. 3 illustrates exemplary waveforms for the various signals that are present during operation of embodiments of pre-heat devices (e.g., the pre-heat device 200 of FIG. 2). The waveforms include a power signal waveform 302, a driver circuit signal waveform 304, a switching waveform 306, a pre-heat transformer waveform 308, and a filament waveform 310. The waveforms in FIG. 3 occur when the pre-heat device 200 is energized, e.g., in response to the power signal. For example, during one operation, a 60 V power signal (e.g., the power signal waveform 302) is applied to the pre-heat circuit 200. The driver circuit 220 oscillates, which causes the switch 222 (in this case a MOSFET) to open and closes as indicated by the changes in the gate voltage shown by the switching waveform 306. These changes generate the preheat signal current with a waveform shown by the filament waveform 310. In one example, the sine (or cosine) waveform results from operation of embodiments of the pre-heat devices (e.g., pre-heat device 200 of FIG. 2) as discussed above and contemplated herein.

[0025] As used herein, an element or function recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to "one embodiment" of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0026] This written description uses examples to disclose embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.