STATEMENT OF CORRESPONDING APPLICATIONS

This application is based on the Provisional specification filed in relation to New Zealand Patent Application Number 584057, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a load balance circuit. In particular it relates to a load balance circuit for use with a halogen ballast circuit.

BACKGROUND ART

The 12 volt halogen bulb has been a staple installation due to the improvements in efficiency they provide over standard incandescent light bulbs. Newer technologies such as compact florescent and LED bulbs provide even greater efficiency advantages. By way of comparison, a compact florescent (CFL) typically produces 65 lumens per Watt of input power compared to a typical 18 lumens per Watt of input power for a halogen bulb.

As the world becomes more conscious of energy usage, particularly in uses such as lighting, demand exists for migration of the current halogen lighting technologies towards more efficient technologies. This demand resulted in the progression from incandescent light bulbs to more efficient halogen bulbs and now halogen bulbs to compact florescent and LED solutions.

The adoption of halogen technology required installation of a ballast circuit to convert the relatively high mains voltage to a low voltage useable by a Halogen bulb. Over the lifetime of halogen installations, technological advancements have created a scenario whereby a great deal of differing technologies exists for providing the voltage conversion necessary for low voltage halogen bulbs. Replacement of existing fittings is costly and therefore resistance exists in migration from halogen light sources to CFL or LED bulbs. Therefore it would be advantageous that a solution exist which would allow a compact florescent or LED bulb to be located halogen light fitting regardless of the technology that the light fitting employs for voltage conversion.

The difficulty in achieving this goal is primarily due to variation in ballast circuit technology that has been developed over the lifetime of halogen installations.

Circuits for voltage conversion in halogen installations fall into two classifications, magnetic and electronic. Magnetic ballast circuits include a laminated electrical transformer which reduces the mains utility voltage to 12v RMS and provides a mains frequency alternating current to the halogen bulb. This will be typically in the range of substantially 50 or 60Hz. Electronic ballast circuits incorporate a switch mode power supply circuit which provides 12v RMS and provides a high frequency alternating current to the halogen bulb. Electronic halogen transformers can include any number of switch mode converter topologies. Some are self oscillatory, while others are driven circuits. They operate from 10 kHz to 200 kHz depending on the manufacturer, make and model. Some of them operate at variable frequency and are modulated by the mains utility waveform.

Electronic ballast circuit circuits are designed to operate over a fairly tight range of output loading conditions. This is because a halogen bulb is a highly consistent and predictable load; typically halogens are either 20 W or 50 W and therefore an electronic ballast circuit can be designed to exactly meet the load requirements. This is advantageous in that the expense associated with designing and manufacturing a stable power output for a wide range of output loads is unnecessary. Achieving power supply stability can be particularly difficult under very light loads. Magnetic ballast circuits do not experience instability at low loads; they do however experience overheating problems if overloaded.

It will be appreciated that the development of a single high efficiency light bulb that can be readily used in any existing halogen light fitting, regardless of the type of ballast circuit incorporated in that fitting, is no simple task. The problems that must all be overcome in order to achieve this goal are many and varied and include:

■ achieving functionality at mains frequency 12 VAC; ^■ achieving functionality at high frequency 12 VAC;

■ providing additional filtering to electronic ballast circuits to ensure stable operation at below rated power output;

^■ preventing conducted electromagnetic emissions generated from the

downstream switch mode power supplies connected at the output of the halogen transformer to be transferred to the mains utility wiring; and

^■ achieving the above in a compact, reliable and cost effective solution.

It will be appreciated by a person skilled in the art that achieving any one of the goals listed would require only moderate skill. However, in order to achieve all of the features simultaneously, as is required by the present invention, poses a significantly more difficult challenge and one that has yet to be solved.

As one skilled in the art would know, the mathematics involved in calculating component values that simultaneously provide all of the goals listed above would challenge even the most skilled practitioner. In particular the simultaneous calculation to:

^■ provide a load impedance at high frequencies which both meets or exceeds a minimum power requirement;

^■ provide a load impedance at high frequencies which is less than a

maximum power requirement; and ■ provide stable operation when used with high frequency AC ballast circuits, wherein the energy content is in the range of 10 kHz to 200 kHz, would prove extremely difficult.

All references, including any patents or patent applications cited in this

specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided an electronic circuit for connection between a halogen ballast and a load circuit for stabilising the output of the ballast, wherein the electronic circuit comprises: ■ at least one inductor; and

^■ at least one capacitor; wherein the capacitor(s) and inductor(s) are configured to:

^■ alter the output characteristics of; or

■ provide a balanced minimum required load to; said ballast.

In preferred embodiments the ballast is a mains input halogen transformer.

Halogen transformers fall into two classifications, magnetic and electronic.

Magnetic transformers have a laminated electrical transformer inside which reduces a mains utility voltage input to substantially 12 VRMS at an output.

Electronic transformers incorporate a switch mode power supply circuit which reduces a mains utility voltage input to substantially 12 VRMS at an output.

It will be apparent to a person skilled in the art that both magnetic and electronic transformers could be constructed and designed using a large number of different techniques, using different components and switch mode converter topologies. For the purposes of the present invention a magnetic transformer can be considered to provide an alternating current output of substantially 50Hz or 60Hz. In contrast an electronic transformer provides a high frequency alternating current in the range of 10 kHz to 200 kHz. It will however be apparent to a person skilled in the art that a high frequency alternating current could be provided outside of the 10 kHz to 200 kHz range, therefore the present invention should not be limited to same.

Typically halogen fittings are designed for single bulbs; however multiple bulb configurations do exist. Therefore transformers will be configured in multiples of the minimum and maximum bulb values, for example:

In preferred embodiments the input load is a switch mode power supply driving a high efficiency light source.

In preferred embodiments the high efficiency light source is a compact florescent tube. In other preferred embodiments the high efficiency light source is an LED bulb.

It will be known to a person skilled in the art that an LED bulb comprises one or more light emitting diodes connected in a parallel and/or series arrangement.

In other embodiments the output light source may be any other form of high efficiency lighting, such as metal halide or sodium vapour gas discharge lamps, and therefore the exact nature of the light source should not be seen as being limiting.

It will be apparent to a person skilled in the art that if it were possible to directly replace a halogen bulb associated with an electronic transformer with a more efficient a compact florescent, LED or other lighting technology, the electronic transformer would be unstable as it would be operating below its stable minimum output power. With present technology, a compact florescent bulb will consume approximately one quarter the power of an equivalent halogen bulb for the same output luminosity. Therefore, if a compact florescent which draws sufficient power is used, for example 20 W, this would be equivalent to fitting an 80 W halogen, which in many circumstances is undesirable in terms of the intensity of the lighting.

In preferred embodiments, in use, the electronic circuit provides a further reactive impedance to the output of an electronic transformer. In preferred embodiments, in use and at high frequencies, the reactive impedance makes up the balance of the required minimum load when combined with the actual load impedance.

In especially preferred embodiments, the reactive impedance makes up the balance of the required minimum load when combined with the actual load impedance when used in the range of frequencies from 10 kHz to 200 kHz.

It will be appreciated by a person skilled in the art that the reactive impedance must meet or exceed the minimum load requirements of an attached electronic transformer, but must also remain below the maximum load specification for that attached electronic transformer. If the maximum load specification is exceeded the electronic transformer may exceed its maximum temperature limits and therefore fail prematurely.

In preferred embodiments, in use, the electronic circuit provides additional filtering to a halogen transformer to prevent conducted electromagnetic emissions from a connected downstream switch mode power supply from transferring upstream to the mains utility wiring.

In especially preferred embodiments the additional filtering provided by the electronic circuit stabilises the output of an electronic transformer at a lower power than the minimum output power rating for that electronic transformer.

In preferred embodiments the inductance value of the electronic circuit is substantially 2.2 μΗ to 22 μΗ.

In preferred embodiments the capacitance value of the electronic circuit is substantially 2.2 nF to 220 nF.

A further characteristic of electronic halogen transformer circuits is that they incorporate a vast array of different switch mode converter topologies. Different topologies generate different harmonic content in their output waveforms. Typically the output harmonics are in the range from 20 kHz to 400 kHz depending on the manufacturer, make and model. Some electronic transformer circuits include features such as spread spectrum switching, which results in the output frequency sweeping over a range of frequencies, the purpose of which is to reduce the level of electromagnetic interference.

In preferred embodiments the electronic circuit provides stable operation of an electronic transformer over a frequency range of between 10 kHz to 200 kHz.

In preferred embodiments the electronic circuit also functions as a filter for preventing high frequency electromagnetic radiation from being conducted from the load back through the ballast circuit.

Whilst the use of inductors and capacitors are well known in the art of electronics for the purposes of providing energy storage and filtering high frequency components, the present invention employs the novel approach of using an LC circuit to both provide the balance of a load applied to the output of an electronic halogen transformer circuit that has been designed to operate stably, and therefore efficiently, within a specific range of output loads and to provide additional filter components to the output of both electronic and magnetic transformers to prevent electromagnetic emissions from a connected downstream switch mode power supply from transferring upstream to the mains utility wiring.

According to a further aspect of the present invention there is provided a method of stabilising the output from a ballast circuit to an output load which is below an inbuilt stabilisation threshold of the ballast circuit, the method characterised by the steps of: a) placing an electronic circuit between the ballast circuit and the output load; b) configuring the electronic circuit to: ■ contribute a reactive load component to a ballast circuit which

provides a high frequency AC output; and

^■ provide additional filtering characteristics to stabilise the output of an electronic ballast circuit.

Preferably the reactive impedance includes at least one capacitor and at least one inductor.

In the context of the present invention a ballast circuit is a halogen transformer, electronic or magnetic, which reduces the mains supply voltage of typically 115 VAC or 230 VAC to substantially 12 VRMS. It will be appreciated that the output from a magnetic transformer will be an alternating current at substantially 50 Hz or 60 Hz, and the output from an electronic transformer will be an alternating current of between typically 10 kHz and 200 kHz.

It will be understood by a person skilled in the art that an electronic transformer, will be designed to operate stably for a specific range of output loads. Instability may manifest itself in any number of ways, each however contributes towards degradation in the functional lifetime of, typically, both the electronic transformer and the attached load. The minimum load draw that results in a stable (regular and uniform) output from the electronic transformer defines the inbuilt stabilisation threshold of that electronic transformer.

In preferred embodiments the output load comprises:

^■ a switch mode power supply; and ■ one or more high efficiency bulb(s).

In especially preferred embodiments the bulb is a compact florescent bulb.

In other preferred embodiments the bulb may be an LED bulb.

The power drawn from an alternating current transformer (electronic or magnetic) can be considered as comprising both real and reactive components. Only the real component of the power drawn from the electronic transformer performs any real work, the reactive component simply cycles back and forth between the electronic transformer and the reactive components.

In preferred embodiments the ballast circuit is a magnetic halogen transformer.

In other embodiments the ballast circuit is an electronic halogen transformer. In preferred embodiments, when connected to an electronic halogen transformer, the reactive components of the electronic circuit form a reactive impedance along with the load impedance.

In preferred embodiments the reactive impedance combined with the loading impedance is substantially equal to or lower than the minimum load requirement of the electronic halogen transformer. In especially preferred embodiments the reactive impedance combined with the load impedance is substantially equal to or lower than the minimum load requirement of the electronic transformer at substantially 10 kHz to 200 kHz.

In preferred embodiments, when connected to an electronic transformer, the electronic circuit provides an additional filtering stage to what is incorporated in the electronic transformer.

In especially preferred embodiments the additional filter stage allows the electronic transformer to function stably at a lower output power level than its rated minimum.

The determination of the correct component values is based upon the minimum power rating of the electronic transformer, measured in Volt-Amps (VA), and the minimum consumption of the rectifier circuit, switch mode power supply and attached high efficiency light source combination, measured as a vector comprising a real power consumption in Watts and a reactive power consumption in Volt Amps (reactive) VAR. The difference between the minimum VA rating of the electronic transformer and the vector sum of the real and reactive components of the rectifier circuit, switch mode power supply and attached high efficiency light source provides the minimum VAR that must be drawn by the reactive impedance circuit.

In preferred embodiments the electronic circuit provides stable operation of an electronic transformer over a frequency range of between 10 kHz to 200 kHz.

Thus preferred embodiments of the present invention may have a number of advantages over the prior art which may include:

Providing an electronic circuit which allows a high efficiency bulb to be retro fitted into an existing halogen light fitting, regardless of the type of transformer associated with that fitting.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic representation of a first embodiment of a reactive impedance in accordance with the present invention; shows a schematic representation of a second embodiment of a reactive impedance in accordance with the present invention; shows a schematic representation of a third embodiment of a reactive impedance in accordance with the present invention; shows a schematic representation showing the placement of the embodiment of a reactive impedance as shown in Figure 1 within circuit according to the present invention;

BEST MODES FOR CARRYING OUT THE INVENTION

With respect to Figures 1 , 2, and 3 there are shown various schematic

representation of embodiments of reactive impedance circuits (1 ) in accordance with the present invention. The reactive impedance circuits (1 ) each include inductive (2) and capacitive (3) components. The reactive impedance circuit (1) also includes connection points A-A' and B-B'. The reactive impedance circuit (1 ) can be connected between a ballast circuit (4) (shown as a halogen transformer in Figure 4) and a load (5) (shown in Figure 4) in either a forward or reverse orientation, with either points A-B connecting to the outputs of the ballast circuit (4) and points A'-B' connecting to the inputs of the load (5) or vice versa. The embodiments shown in figures 1 , 2 and 3 each illustrate so called first order filter configurations. It will be appreciated by a person skilled in the art that a substantial number of both first order and higher order filters could be configured to provide the advantages conferred by the present invention. Therefore the exact configuration of the inductive (2) and capacitive (3) components should not be seen as being limiting.

With respect to Figure 4 there is shown the reactive impedance circuit (1 ) of Figure 1 attached between a ballast circuit in the form of a electronic halogen transformer (4) and a load (5) in the form of a rectification circuit (7) and an attached switch mode power supply (8). Not shown is the output load connected to the switch mode power supply (8), which would be in the form of a high efficiency light source (6) such as an LED bulb or compact florescent bulb. The combination of the rectifier circuit (7), switch mode power supply (8) and attached high efficiency light source (6) draws substantially less power than the minimum power rating of the electronic halogen transformer (4).

The output from the electronic halogen transformer (4) is high frequency AC, typically in the range of 10 kHz to 200 kHz. The reactive impedance circuit (1 ) functions to filter the harmonic content from the output of the electronic halogen transformer (4), and to also allow the electronic halogen transformer (4) to function stably below its rated minimum load. It will be apparent to a person skilled in the art that the downstream switch mode converter (8) is highly susceptible to high frequency harmonics and the interaction between those harmonics and the circuitry of the switch mode converter (8) could result in instability of the switch mode converter (8). Equally the switching harmonics generated by the switch mode converter (8) could cause instability in the electronic halogen transformer (4).

Therefore the reactive impedance circuit (1) also prevents harmonics from the switch mode converter (8) causing instability in the electronic halogen transformer (4).

The determination of the correct component values is based upon the minimum power rating of the electronic halogen transformer (4), measured in Volt-Amps (VA), and the minimum consumption of the rectifier circuit (7), switch mode power supply (8) and attached high efficiency light source (6) combination, measured as a vector comprising a real power consumption in Watts and a reactive power consumption in Volt Amps (reactive) VAR. The difference between the minimum VA rating of the electronic halogen transformer (4) and the vector sum of the real and reactive components of the rectifier circuit (7), switch mode power supply (8) and attached high efficiency light source (6) provides the minimum VAR that must be drawn by the reactive impedance circuit (1 ).

It will be apparent to a person skilled in the art that the exact component values required to obtain the calculated VAR rating will depend upon the configuration of the inductive (2) and capacitive (3) components that form the reactive impedance circuit (1 ). Again with reference to Figure 4 there is shown the reactive impedance circuit ( ) of Figure 1 attached between a ballast circuit, this time in the form of a magnetic halogen transformer (also designated 4), a load (5) in the form of a rectification circuit (7) and an attached switch mode power supply (8). Again, not shown is the output load connected to the switch mode power supply (8), which would be in the form of a high efficiency light source (6) such as an LED bulb or compact florescent bulb. In this case, the reactive impedance circuit (1 ) functions to allow the mains frequency AC supplied by the magnetic halogen transformer (4) to pass substantially unimpeded to the load, comprising rectifier circuit (7), switch mode power supply (8) and attached high efficiency light source (6). The reactive impedance circuit (1 ) also functions to prevent any high frequency conducted electromagnetic emissions, generated by the downstream switch mode power supply (8) connected at the output of the magnetic halogen transformer (4), from being transferred to the mains utility wiring (not shown).

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.