Power splitter circuit for electrodeless lamp

A lamp assembly adapted to operate as one of a total number of lamp assemblies that are connected together in series and connected to a ballast. The lamp assembly comprises an electrodeless, closed-loop, tubular lamp envelope enclosing mercury vapor and a buffer gas, and a transformer core disposed around a portion of the lamp envelope. An input winding is disposed on the transformer core so that it has a particular number of turns, Ninput. An auxiliary winding is disposed on the transformer core so that it has a particular number of turns, Nauxiliary. The auxiliary winding is adapted to connect to the ballast and to couple with the input winding. The ratio of the particular number of turns Ninput to the particular number of turns Nauxiliary is substantially proportional to the total number of lamp assemblies that are adapted to operate in series together.

TECHNICAL FIELD

The present invention generally relates to low pressure, electrodeless discharge lamps. More particularly, the invention is directed to a power splitter circuit to split radio frequency power supplied by a ballast among a plurality of low pressure, electrodeless discharge lamps connected to the ballast.

BACKGROUND

Very high output (VHO) fluorescent lamp systems provide efficient, high lumen output, and good color rendering. A VHO fluorescent lamp includes an electrode at each end of a fluorescent tube, however, the electrodes substantially limit the life of a typical VHO fluorescent lamp. Another type of lamp system is an electrodeless gas discharge lamp system which includes an inductively coupled fluorescent lamp and a high frequency ballast. Electrodeless gas discharge lamp systems use electromagnetic induction instead of an electrode at each end of a fluorescent tube. Since the electrodeless gas discharge lamps do not include electrodes, the electrodeless gas discharge lamps provide many of the same benefits as the VHO fluorescent lamp systems while additionally providing a longer lamp life.

Multiple electrodeless gas discharge lamps are commonly used to illuminate a single location. A single high frequency ballast is typically used to power each electrodeless gas discharge lamp.

SUMMARY

Conventional ballasts for operating a single electrodeless gas discharge lamp suffer from a variety of deficiencies. For example, in situations such as when a plurality of electrodeless gas discharge lamps are used to illuminate a large area, such as a tunnel, it would be desirable to operate the electrodeless gas discharge lamps at a reduced power level to avoid excessive light. Doing so with a number of conventional ballasts, each operating only a single electrodeless gas discharge lamp, is problematic at best. Additionally, it would be more economical to have a single ballast that could be adapted to power multiple electrodeless gas discharge lamps, instead of having a one-to-one lamp-to-ballast ratio.

Embodiments of the invention relate to a power splitter circuit to split power provided by a single ballast among a plurality of lamp assemblies that are connected together in series. As such, embodiments provide an electric lamp system in which the intensity of the light generated by the electric lamp system is distributed among a plurality of lamp assemblies. For example, the power splitter circuit may be used to allow a ballast that is designed to power a single lamp assembly at a first power level to power two lamp assemblies, each at a second power level that is reduced relative to the first power level. As such, in accordance with embodiments of the invention, the power splitter circuit allows a ballast to be converted so that it provides distributed light.

In an embodiment, there is provided a lamp assembly adapted to operate as one of a total number of lamp assemblies that are connected together in series and connected to a ballast. The lamp assembly includes: an electrodeless, closed-loop, tubular lamp envelope enclosing mercury vapor and a buffer gas; a transformer core disposed around a portion of the lamp envelope; an input winding disposed on the transformer core, the input winding having a particular number of turns, Ninput; and an auxiliary winding disposed on the transformer core and adapted to connect to the ballast and to couple with the input winding, the auxiliary winding having a particular number of turns, Nauxiliary. A ratio of the particular number of turns Ninputto the particular number of turns Nauxiliaryis substantially proportional to the total number of lamp assemblies that are adapted for operating in series together.

In a related embodiment, the transformer core may be a first transformer core and the input winding may be a first input winding, and the first transformer core, the first input winding, and the auxiliary winding may form a first driving inductor, and the lamp assembly may further include a second driving inductor having a second transformer core disposed around another portion of the lamp envelope and a second input winding disposed on the second transformer core and adapted to connect to the ballast.

In another related embodiment, the second input winding may have a particular number of turns, Ninput, equal to the particular number of turns of the first input winding. In yet another related embodiment, the lamp assembly may further include a load balancing capacitor connected to the transformer core and adapted to connect to the ballast. In still another related embodiment, the input winding may have a center tap that is connected to a ground conductor.

In another embodiment, there is provided an electric lamp system. The electric lamp system includes: a ballast adapted to power a total number of one or more lamp assemblies connected to the ballast, wherein the ballast supplies to the one or more lamp assemblies a predetermined radio frequency power that is independent of the total number of the one or more lamp assemblies that are connected to the ballast; and a plurality of lamp assemblies adapted to connect together in series and to connect to the ballast, wherein each of the plurality of lamp assemblies includes an electrodeless gas discharge lamp, and each of the plurality of lamp assemblies includes a driving inductor configured to split the radio frequency power among each of the plurality of electrodeless gas discharge lamps to produce a discharge in the lamp envelope from the split radio frequency power.

In a related embodiment, the driving inductor of each of the plurality of lamp assemblies may include: a transformer core disposed around a portion of the lamp envelope; an input winding disposed on the transformer core, the input winding having a particular number of turns, Ninput; and an auxiliary winding disposed on the transformer core and adapted to connect to the ballast and to couple with the input winding, the auxiliary winding having a particular number of turns, Nauxiliary; and the particular number of turns, Ninput, of the input winding and the particular number of turns, Nauxiliary, of the auxiliary winding may be selected so that the driving inductor splits the radio frequency power among each of the plurality of electrodeless gas discharge lamps. In a further related embodiment, the input winding may have a center tap that is connected to a ground conductor.

In another related embodiment, the driving inductor may include a first driving inductor having a transformer core disposed around a first portion of the lamp envelope, and the driving inductor may include a second driving inductor having a transformer core disposed around a second portion of the lamp envelope.

In yet another related embodiment, the electric lamp system may further include a plurality of load balancing capacitors, wherein each load balancing capacitor of the plurality of load balancing capacitors may correspond to one of the electrodeless gas discharge lamps, and each load balancing capacitor may be connected between the electrodeless gas discharge lamp and the ballast. In still another related embodiment, the electric lamp system may further include a load balancing capacitor connected between the ballast and the plurality of lamp assemblies.

In another embodiment, there is provided an interconnect circuit adapted to connect between a ballast and a lamp set. The interconnect circuit includes: an input terminal adapted to connect to the ballast and to receive an input current from the ballast, and a current transformer configured to generate an output current to a lamp set that has a particular total number of series-connected lamp assemblies by stepping down the input current received from the ballast as a function of the particular total number of the series-connected lamp assemblies. The current transformer includes: a current transformer core; a first current transformer primary winding and a second current transformer primary winding, wherein the first and second current transformer primary windings are bifilar-wound around the current transformer core; and a current transformer secondary winding single wound around the current transformer core, wherein the current transformer secondary winding has a particular number of windings Nsecondaryselected as a function of the particular number of the series-connected lamp assemblies in the lamp set. The interconnect circuit also includes an output terminal adapted to connect to the lamp set and to provide the output current generated by the current transformer to the lamp set.

In a related embodiment, the interconnect circuit may further include a load balancing capacitor connected at the input terminal and to the current transformer. In another related embodiment, the interconnect circuit may further include a load balancing capacitor connected at the output terminal and to the current transformer. In still another related embodiment, the ballast may be a radio frequency converter and each of the series-connected lamp assemblies may include an electrodeless gas discharge lamp.

In another embodiment, there is provided an electric lamp system. The electric lamp system includes: a ballast adapted to power one or more lamp assemblies, wherein the ballast supplies radio frequency power independent of a quantity of the one or more lamp assemblies that are powered from the ballast; a lamp set of lamp assemblies that are adapted to connect together in series, wherein each lamp assembly in the lamp set includes an electrodeless gas discharge lamp having a closed-loop, tubular lamp envelope enclosing mercury vapor and a buffer gas, and each lamp assembly in the lamp set includes a first driving inductor and a second driving inductor, wherein the lamp set has a total number of the electrodeless gas discharge lamps; and a transformer connected between the ballast and the lamp set, wherein the transformer is configured to split the radio frequency power supplied by the ballast among each of the electrodeless gas lamps in the lamp set. The first and second driving inductors of each of the lamp assemblies of the lamp set are configured to receive the split radio frequency power from the transformer and to produce a discharge in the lamp envelope.

In a related embodiment, the transformer may be configured to step down current provided by ballast as a function of total number of electrodeless gas discharge lamps in the lamp set. In another related embodiment, the transformer may be a bifilar-wound transformer. In still another embodiment, the electric lamp system may further include a load balancing capacitor connected between the transformer and the ballast. In yet another related embodiment, the electric lamp system may further include a plurality of load balancing capacitors, wherein each load balancing capacitor of the plurality of load balancing capacitors may correspond to one of the electrodeless gas discharge lamps of the lamp set, and each load balancing capacitor may be connected between the transformer and electrodeless gas discharge lamp.

DETAILED DESCRIPTION

The present invention relates to an electric lamp system in which power supplied by a single ballast is split among a plurality of lamp assemblies that are connected together in series and to the ballast. Embodiments light produced from the power supplied by the ballast to be distributed via each of a plurality of series-connected lamp assemblies. In some embodiments, the ballast, such as a radio frequency (RF) power converter, has an output (e.g., one or more output terminals) adapted to directly connect to a single lamp assembly and supply RF power (e.g., RF current, RF voltage) thereto. The RF power supplied by the ballast at the output is predefined, independent of the total number of lamp assemblies that may be connected together in series at the ballast output. Each lamp assembly includes an electrodeless discharge lamp and a driving inductor to couple RF power supplied by the ballast to the electrodeless discharge lamp so that light is emitted therefrom. A power splitter circuit is connected between the electrodeless discharge lamp and the ballast in order to split the power between each of the electrodeless discharge lamps of the electric lamp system.

FIG. 1andFIG. 2illustrate a lamp system100. A lamp assembly110is adapted to connect to a ballast130(shown inFIG. 2) and to receive RF power from the ballast130. For example, the lamp assembly110may be an ICETRON® lamp and the ballast may be a QUICKTRONIC® electronic ballast, both available from OSRAM SYLVANIA Inc. As shown inFIG. 1, the lamp assembly110includes an electrodeless discharge lamp112and a driving inductor114. Referring generally toFIG. 2, the electrodeless discharge lamp112has a tubular closed-loop lamp envelope116that forms a discharge region118. The discharge region118encloses a buffer gas and a mercury vapor. The buffer gas may be a noble gas such as but not limited to krypton or argon. The lamp envelope116has an inside surface and an outside surface. The inside surface of the lamp envelope116has a phosphor coating120formed thereon, and is in contact with the discharge region118. A driving inductor114, shown inFIG. 1, includes a transformer core122disposed around a portion of the lamp envelope116and an input winding124disposed on the transformer core122. As further discussed below, in operation, the driving inductor114inductively couples the electrodeless discharge lamp112to the ballast130to power the electrodeless discharge lamp112.

The illustrated lamp assembly110includes a first driving inductor114A and a second driving inductor114B, both shown inFIG. 1. However, it should be noted that embodiments of the invention may include any number of one or more driving inductors114. The first driving inductor114A has a first transformer core122A disposed around a first portion of the outside surface of the lamp envelope116. The second driving inductor114B has a second transformer core122B disposed around a second portion of the outside surface of the lamp envelope116. In some embodiments, the first and second transformer cores122A and122B each form a closed loop around the outside surface of the lamp envelope116and have a torodial configuration. The first and second transformer cores122A and122B may be fabricated of a high permeability, low loss ferrite material, such as but not limited to manganese zinc ferrite.

The first driving inductor114A has a first input winding124A wound around the first transformer core122A such that it has a particular number of turns, NinputA. Similarly, the second driving inductor114B has a second input winding124B wound around the second transformer core122B such that it has a particular number of turns, NinputB. In some embodiments, the particular number of turns NinputAof the first input winding124A and the particular number of turns NinputBof the second input winding124B are equal. One or more conductors (e.g., lead wires, conductive strip) electrically connect the first and second input windings124A and124B together. In the illustrated lamp assembly110, the first input winding124A and the second input winding124B are connected in parallel. The one or more conductors (e.g., lead wires, conductive strip), generally indicated at128, are adapted for electrically connecting the first and second input windings124A and124B to the ballast130, and may also serve as starting aids to initiate discharge in the electrodeless discharge lamp112.

In operation, the first and second driving inductors114A and114B receive RF energy from the ballast130, and in response thereto, produce a discharge (e.g., plasma) within the lamp envelope116. Thus, RF energy is inductively coupled to the discharge within the lamp envelope116by the first and second driving inductors114A and114B. In particular, the first and second input windings124A and124B receive RF current from the ballast130. In some embodiments, the first and second input windings124A and124B are driven in phase. The RF current through each of the first and second input windings124A and124B creates a time-varying magnetic flux that induces a voltage along the lamp envelope116. The first and second driving inductors114A and114B are positioned on the lamp envelope116such that the voltages induced therefrom add together. The total induced voltage (i.e., discharge voltage) in the lamp envelope116maintains a discharge within the lamp envelope116. As such, the first and second input windings124A and124B act as primary circuits for the respective first and second transformer cores122A and122B. The discharge acts a secondary circuit (e.g., one-turn secondary winding) for both the first and the second transformer cores122A and122B. Each driving inductor114A,114B is thus configured to step down primary voltage and to step up primary current.

The discharge produced in the lamp envelope116emits ultraviolet radiation. In accordance with the illustrated electrodeless discharge lamp112, the phosphor coating120on the inside surface of the lamp envelope116converts the ultraviolet radiation to visible light. In such embodiments, the lamp envelope116is fabricated of a material, such as but not limited to glass, that transmits visible light. In alternate embodiments, the electrodeless discharge lamp112may be used as a source of ultraviolet radiation. In such embodiments, the phosphor coating120is omitted from the lamp envelope116and the lamp envelope116is fabricated of an ultraviolet-transmissive material, such as but not limited to quartz.

Referring generally toFIG. 3, in some embodiments, the lamp assembly210is adapted to operate, in an electric lamp system200, as one of a predefined total number of lamp assemblies powered by a single ballast230to provide distributed light. In addition to the features discussed above in connection withFIGS. 1 and 2, each lamp assembly210in the electric lamp system200includes a power splitter circuit configured to split the RF power supplied from the ballast230by the predefined total number of lamp assemblies. As such, the RF power supplied from the ballast230is split between lamps212-1,212-2, etc. in the electric lamp system200. In some embodiments, current received by the electrodeless gas discharge lamps remains substantially constant independent of the load (e.g., number of electrodeless gas discharge lamps), and the electrodeless gas discharge lamps act as non-linear loads so that the discharge voltage produced by each of the electrodeless gas discharge lamps remains substantially constant independent of the received current.

FIG. 3is a simplified partial block, partial circuit diagram of an exemplary lamp system200adapted to provide distributed light via two lamp assemblies,210-1and210-2. The electric lamp system200includes two lamp assemblies,210-1and210-2, connected together in series and to the ballast230. Each of the lamp assemblies210-1and210-2includes a power splitter circuit (generally indicated at240-1and240-2) configured to split the RF power supplied from the ballast230in half so that the RF power supplied from the ballast230is divided substantially evenly among the two lamp assemblies210-1and210-2in the electric lamp system200.

In particular, each lamp assembly210includes an auxiliary winding242wound around the first transformer core222A such that it has a particular number of turns, Naux. The auxiliary winding242is adapted to connect to the ballast230and to couple with a first input winding224A. Together, the first transformer core222A, the first input winding224A, and the auxiliary winding242form a power splitter circuit240that steps down RF current supplied by the ballast230. According to ideal transformer principles, the RF current is stepped down by a factor equal to the ratio (i.e., Ninput:Naux, Ninput/Naux) of the particular number of turns Ninputto the particular number of turns Naux. As such, in order to divide the RF current substantially evenly among each lamp assembly210in the electric lamp system200, the ratio Ninput/Nauxshould be equal to the number of electric lamp assemblies210in the lamp system. For example, applying the ideal transformer principles to the electric lamp system200shown inFIG. 3, the ratio Ninput/Nauxwould be equal to two. However, as generally known to be the case with transformers, the ideal transformer principles provide approximate values that may be adjusted based on non-ideal factors such as magnetizing inductance and magnetic flux leak that occur during operation. In order to account for such factors in embodiments of the invention, the ratio Ninput/Nauxis characterized as being substantially proportional (e.g., substantially directly proportional, substantially equal) to the total number of lamps that are adapted to operate in series together.

As illustrated in the electric lamp system200, in some embodiments a load balancing capacitor C1is connected between the lamp assemblies210and the ballast230. For example, the load balancing capacitor C1may be integrally formed as part of the ballast230. Alternatively, the electric lamp system200may include an interface circuit (not illustrated inFIG. 3) formed separately from the ballast230and the lamp assemblies210so that the interface circuit, the ballast230, and the lamp assemblies210are all separate components. According to this configuration, the interface circuit includes the load balancing capacitor C1to connect between the ballast230and the lamp assemblies210.

In operation, the first transformer core222A and the second transformer core22B are non-ideal transformers, and as such, exhibit finite magnetizing inductance. The magnetizing inductance acts as an inductive component electrically connected in parallel with the load (e.g., the lamp assembly210-1containing active electrodeless gas discharge lamp212-1). When a plurality of series connected lamp assemblies210-1,210-2, each including an electrodeless gas discharge lamp212-1,212-2, are connected to the ballast230to operate at a lower power, the inductive component is decreased proportional to the plurality of series connected lamps assemblies210-1,210-2, each including an electrodeless gas discharge lamp212-1,212-2. The load balancing capacitor C1compensates for the decrease in the inductance. Thus, the load balancing capacitor C1serves to compensate for the distribution of the load that results from splitting the RF power from the ballast230among each of the lamp assemblies210-1,210-2. For example, in the illustrated electric lamp system200, the load balancing capacitor C1causes the total impedance of the electric lamp system200having two lamp assemblies210-1and210-2to match (i.e., approximately match) that of an electric lamp system having a single lamp assembly.

In some embodiments, such as an electric lamp system300ofFIG. 4, a first input winding324A in each lamp assembly310has a center tap350that is connected to a ground conductor. The center tapped input winding324A minimizes electromagnetic interference (EMI) that may be present in the lamp assembly310. In other embodiments, such as an electric lamp system400ofFIG. 5, rather than having a single load balancing capacitor connected between the plurality of lamp assemblies and the ballast (as inFIGS. 3-4), each lamp assembly410includes a load balancing capacitor Clampconnected between an auxiliary winding442and a ballast430. This configuration reduces any residual difference in discharge current between electrodeless gas discharge lamps410-1,410-2, which may occur due to variation of magnetizing inductance of transformer cores440in each of the lamp assemblies410.

Referring toFIG. 6, in other embodiments the electric lamp system500includes an interconnect circuit560adapted to connect between a ballast530and a plurality of lamp assemblies (i.e., “lamp set”)510. For example, the interconnect circuit560may be formed separately from the ballast530and the lamp assemblies510such that the interconnect circuit560, the ballast530, and the lamp assemblies510are separate components. The interconnect circuit560is configured to split the RF power supplied from the ballast530between each lamp assembly510of the lamp set in order to provide distributed light. In the electric lamp system500, the interconnect circuit560is configured to split the RF power supplied from the ballast530between two lamp assemblies510-1and510-2. The two lamp assemblies510-1and510-2are electrically connected together in series.

The interconnect circuit560includes an input terminal562, a current transformer564, and an output terminal566. The input terminal562is adapted to electrically connect to the ballast530and to receive an input current therefrom. The current transformer564is configured to generate an output current by stepping down the current received from the ballast530as a function of the number of lamp assemblies in the lamp set. In some embodiments, the current transformer564is configured to operate in a lamp system having a predefined number of lamp assemblies. Thus, the current transformer564is configured to step down the current received from the ballast530by a factor equal to the predefined number of lamp assemblies. The output terminal566is adapted to connect to the lamp set. For example, the output terminal566may include a set of output terminals566-1,566-2to electrically connect each lamp assembly510-1,510-2in the lamp set to the current transformer564. As such, the output current generated by the current transformer564is provided to the lamp assemblies510in the lamp set.

In some embodiment, the current transformer564is a bifilar coil. Such a bifilar winding reduces electro-magnetic emission (EMI). In such cases, a bifilar coil serves to mitigate the common mode conducted interferences into the mains. The current transformer564has a core568(“current transformer core”). For example, the current transformer core568is formed from a ferrite material so that it has a magnetizing inductance greater than that of the lamp assemblies510. A first current transformer primary winding and a second current transformer primary winding are bifilar-wound around the current transformer core568such that the first and second primary windings have a particular number Nprimaryof turns. A current transformer secondary winding is single wound around the current transformer core568so that it has a particular number Nsecondaryof turns. A ratio, R, of the particular number of turns of the primary and secondary windings defines the step down factor of the current received from the ballast530as follows:

Accordingly, the number of turns of each of the windings, Nprimaryand Nsecondary, may be selected as a function of the number of lamp assemblies in the electric lamp system500so that the current is stepped down accordingly. In some embodiments, the number of turns of the primary winding Nprimaryis selected to minimize transformer loss, and the number of turns for the secondary winding Nsecondaryis then selected as a function of the number of turns of the primary winding Nprimaryand the number of lamp assemblies in the electric lamp system500.

The electric lamp system500includes a load balancing capacitor C1connected across the input terminal562and between the current transformer564and the ballast530. The load balancing capacitor C1may be included in the ballast530or, alternatively, included in the interconnect circuit560as shown inFIG. 6. As discussed above in connection withFIG. 3, the load balancing capacitor C1serves to compensate for the distribution of the load that results from splitting the RF power from the ballast530among each of the lamp assemblies510. For example, in the electric lamp system500, the load balancing capacitor C1causes the total impedance of the electric lamp system500having two lamp assemblies510-1,510-2to match (i.e., approximately match) that of an electric lamp system having a single lamp assembly.

Rather than having a single load balancing capacitor C1connected between the current transformer564and the ballast530as shown inFIG. 6, in an electric lamp system600ofFIG. 7, a load balancing capacitor Clampis connected between each output terminal set666-1,666-2, and the corresponding lamp assembly610-1,610-2. Thus, each lamp assembly610has a corresponding capacitor Clamp. The load balancing capacitors Clampmay be included in the ballast630or, alternatively, included in the interconnect circuit660as shown inFIG. 7. This configuration reduces any residual difference in discharge current between the electrodeless gas discharge lamps610-1,610-2that may occur due to variation of magnetizing inductance of the transformer cores640in each of the lamp assemblies610.

Throughout the entirety of the present disclosure, use of the articles “a”, “an”, and “the” to modify a noun may be understood to be used for convenience and to include one, or more than one, of the modified noun, unless otherwise specifically stated. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.