TECHNICAL FIELD

The invention relates to a lamp. In particular it relates to a lamp including a fluorescent bulb and a ballast.

BACKGROUND ART

The present invention is of particular application to situations where high energy light lamps (bulbs) are employed which operate from a low voltage input.

The 12 volt halogen bulb is currently used in many types of lights.

However, using a low energy fluorescent bulb in place of a 12 volt halogen bulb is often not practical due to the fact that circuitry, containing the transformer to increase the 12 volt input voltage to the 1200 volts required to operate a fluorescent light source, can be prone to failure due to heat build up.

Attempts to try and overcome this problem often require the housing of the fluorescent bulb to include: sufficient airspace within, and a number of ventilation apertures; to try and minimise the build up of heat. Typically, as a result, such fluorescent bulbs are bulky and are unable to fit into a lighting apparatus so as to replace a 12 volt halogen bulb. The heat build up in such bulbs can also be compounded by increases in room temperature and the heat given off by the light source during operation.

It would be useful if there could be a fluorescent lamp which could overcome these difficulties and be used in place of a 12 volt halogen lamp in many situations. Such a lamp would allow a user to take advantage of the long operating lifetimes and low energy consumption of fluorescent lamps in comparison with incandescent and halogen lamps. Ballast components to address the foregoing problems are known. However these can be relatively expensive, costing around US 40-50 cents each, which represents a significant additional cost to a light bulb.

It would therefore also be useful if there could be provided a relatively low cost alternative to using a separate chip or controller as a ballast component.

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.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

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

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

According to one aspect of the present invention there is provided a lamp which includes:

a fluorescent light source; and

a housing in which the light source is retained;

wherein the housing encloses an electronic ballast including a transformer capable of raising an input voltage of between 9-14 volts to that required to operate the lamp;

characterised in that the transformer is coupled to a current regulation circuit which maintains a substantially constant and limited current during operation of the fluorescent light source and wherein the lamp includes a 12 volt electrical connector.

Preferably the input voltage may be substantially 12 volts.

Preferably, the housing may have a cross sectional diameter which is substantially 45mm or less. A housing of this size has the advantage that it may be used with some common lighting fixtures as used for halogen lamps, a standard MR16 halogen bulb having an outer diameter of approximately 50mm.

The housing may generally be substantially tubular in nature. Preferably, the housing includes a reflective internal surface which is proximate the fluorescent light source.

In preferred embodiments the current regulation circuit may be an electronic ballast which includes at least one passive impedance device. Alternatively, in other embodiments the current regulation circuit may be an electronic ballast which includes an intelligent chip, a self oscillating controller or a switch mode controller for example.

According to another aspect of the present invention there is provided a lamp including:

a fluorescent light source; and

an electronic ballast including a transformer having an output connection to provide power to the fluorescent light source;

characterised in that the electronic ballast includes at least one passive impedance device which provides feedback resisting a change of current in the transformer during operation of the fluorescent light source.

According to another aspect of the present invention there is provided electronic ballast for a lamp including a fluorescent light source, the ballast including;

a transformer having an output connection to provide current to the fluorescent light source;

characterised in that the ballast includes at least one passive impedance device which provides feedback resisting a change of the current in the transformer during operation of the fluorescent light source.

electronic In preferred embodiments the passive impedance device is a coupled inductor.

In preferred embodiments the integrated ballast includes a transformer capable of raising an input voltage of between 9-14 volts to that required to operate the lamp; In preferred embodiments the transformer is coupled to a current regulation circuit, which, in use, maintains a substantially constant current within the specified current ratings of the attached CFL.

The fluorescent light source may generally be in the form of a Tubular Fluorescent Lamp, Cold Cathode Fluorescent Lamp (CCFL), Compact Fluorescent Lamp (CFL), or the like.

In one preferred embodiment the light source is an integrated compact fluorescent lamp

Reference to a compact fluorescent lamp (CFL) should be understood to mean a fluorescent tube that has been formed in a compact shape, such as a spiral or U, or any other shape as is well known in the art.

CFLs provide a number of advantages over other forms of lighting, including long operating lifetimes (around 6,000 to 15,000 hours compared with about 750 to 1000 hours for typical incandescent lamps). The energy required to operate a CFL may also be (for the same luminous flux) around 50% less than that required to operate a halogen lamp and around 80% less than that required to operate a 240V incandescent lamp. CFLs may also be safer to use than halogen lamps, which require UV filters over the halogen bulbs, and can be handled more easily than halogen lamps (the operating lifetime of which can be significantly shortened if the surface of the bulb becomes contaminated, for example by fingerprints).

For ease of reference only the fluorescent light source will from now on be referred to as a CFL.

In a preferred embodiment the lamp includes an electrical connector configured to connect with a 12V electrical connection. In a preferred embodiment the 12V connector is a two pin connector. In especially preferred embodiments the connector is an industry standard GX2.5 bi-pin connector, such as is standard on MR16 halogen bulbs.

Bi-pin connectors are the industry standard connector used for connecting MR16 halogen lamps to 12V supplies. An advantage of a light bulb according to the present invention including a bi-pin connector is that it may be plugged directly into a 12V fitting designed for an MR16 12V halogen lamp. Furthermore, having a cross sectional diameter substantially corresponding to 45mm (halogen lamp fittings are typically fabricated to fit the industry standard MR16 bulb format, that being 50mm in diameter), allows the lamp to be used in lighting appliances normally used with MR 16 Halogen lamps. Therefore, in many instances, such as for vertically mounted halogen lamp fittings, a halogen lamp can be replaced by a fluorescent lamp according to the present invention without the need to replace the fitting. In this way the advantages provided by CFLs over halogen lamps can be provided by replacing the halogen lamp with a CFL (configured as above) in the same fitting.

Although the current invention has been described in relation to the MR16 standard, as typically used in domestic halogen light fittings, the present invention is equally suited for use with any light fitting supplied by 12V AC or DC, therefore any reference to the MR16 standard should not be seen as being limiting.

In some preferred embodiments the CFL lamp may be connected to the ballast with a four-pin connector. Use of a four-pin connector assists with preheating the lamp filament prior to initiation of the gas discharge. Preheating may increase the operational lifetime of the CFL

In other embodiments the CFL lamp may be connected to the ballast with a two pin connector, not providing the facility for pre-heating of the lamp filaments. The low voltage input may be AC or DC. It is envisaged in addition the low voltage input can be sourced from any type of commonly known transformer used to supply substantially 12V AC or DC.

Reference to electronic ballast throughout this specification should be understood to refer to a device, consisting of a number of electronic components connected in a circuit, configured to limit the amount of current in an electric circuit.

A ballast (typically now electronic although magnetic ballasts may be used) is commonly used in circuits where the load is not static, instead presenting a negative, or negative differential, impedance whereby increasing current flow causes the resistance to drop, thereby creating a runaway effect of increasing current and decreasing resistance. Fluorescent light sources are one such device that exhibits a negative impedance, thus a non-current limited fluorescent light source would draw an ever increasing amount of current from the power supply until failure of the tube, or some component of the supply.

An electronic ballast according to the present invention includes a transformer capable of raising an input voltage of substantially 12V to that required to initiate a gas discharge in the CFL. Typically this may occur at around 1200V to 1500V.

In a preferred embodiment the electronic ballast includes a passive impedance device in the electronic ballast. In especially preferred embodiments this is a coupled inductor.

Reference to a 'coupled inductor' as used herein refers to one or more inductors sharing some substantial degree of mutual inductance therebetween. It would therefore be apparent to a person skilled in the art that any variation in the current flow in one inductor, will result in a corresponding alteration in the current flow in the other inductor. Preferably the coupled inductor includes two inductive elements; these are for clarity referred to as the primary inductor and secondary inductor. Reference to a passive impedance device throughout this specification should be understood to refer to an electronic element that is not capable of power gain. Examples of passive devices include resistors, capacitors, inductors, diodes and transformers.

In contrast, an active device is an electronic element that is capable of providing gain. Active devices include transistors, integrated circuits and similar devices.

In preferred embodiments the coupled inductor includes primary and secondary windings which may be connected such that they are in an opposed relationship. In one preferred embodiment a coupled inductor comprises primary and secondary inductances which are formed by being counter wound in opposite directions on the same magnetic structure, such that a mutual inductance couples said two inductors. Other embodiments may include primary and secondary inductors wound in the same direction on the same structure, but connected in an opposed relationship.

The coupled inductor configured as above is connected to the ballast circuit in such a manner as to provide negative feedback to resist any rapid or out of specification change in the current flowing in the transformer when the lamp is operating.

Such a change in current can occur in ballasts of the prior art (which do not include a coupled inductor) as a result of overheating of the components of the ballast, and in particular of the switching elements.

Preferably the ratio of the primary to secondary inductances is substantially in the range from about 1 :5 to about 1 :8.

The ratio of the inductance values will vary depending on the power rating of the CFL. A significant advantage of using a coupled inductor as described above is that it may take up less physical space within the housing as well as being less expensive than alternative methods of providing a current limited and regulated supply, such as through the use of active circuitry. Both of these features are important in providing a lamp which is relatively compact in size and at a cost that makes it an attractive alternative to the use of a halogen lamp.

In some other embodiments the passive device may be a resistor. In others it may be an air gap in the transformer core used to adjust the inductance of the circuit.

In a preferred embodiment the electronic ballast includes switching elements in the form of bipolar transistors.

Bipolar transistors are preferred as switches as they may provide a low cost solution while meeting the requirements for switching speed and low storage time.

According to a further aspect of the present invention there is provided a housing for a fluorescent light source which is configured to retain the fluorescent light source, wherein the housing includes:

- a transformer which is capable or raising an input voltage of between 9-14 volts to that required to operate the lamp;

- a current regulation circuit; and

- a 12 volt electrical connector.

Thus, preferred embodiments of the present invention may have a number of advantages which can include:

• Providing a retrofittable fluorescent lighting option in many instances where a 12V halogen bulb is used. • Providing a fluorescent lamp which can be run from a 12V AC or DC input supply;

• Providing a fluorescent lamp which is relatively low cost;

BRIEF DESCRIPTION OF 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 1A shows an isometric view of a lamp according to one embodiment of the present invention;

Figure 1B shows a plan view of the lamp shown in Figure 1 A;

Figure 1C shows a left side cross sectional view of the lamp shown in Figure 1A;

Figure 1D shows a profile view of the lamp of Figure 1 A;

Figure 1E shows a right side cross sectional view of the lamp of Figure 1 A;

Figure 2 shows a schematic diagram of an electronic ballast according to one embodiment of the present invention;

Figure 3 shows a schematic diagram of an electronic ballast according to another embodiment of the present invention;

Figure 4 shows a schematic diagram of an electronic ballast according to one embodiment of the present invention;

Figure 5 shows a schematic diagram of an electronic ballast according to another embodiment of the present invention; Figure 6 shows a schematic diagram of an electronic ballast according to another embodiment of the present invention; and

Figure 7 shows a schematic diagram of an electronic ballast according to another embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

A lamp according to a preferred embodiment of the present invention is generally indicated by arrow (1) in Figures 1 A, 1B ₁ 1C, 1 D and 1E.

The lamp (1) includes a fluorescent light source, in the form of a compact fluorescent lamp (CFL) (2), shown in Figures 1C and 1E.

The CFL (2) is shown enclosed within a lamp housing (3) which also has a ballast housing (4), also shown is internal reflective surface (21) proximate the CFL (2), all as shown in Figures 1C and 1E.

The housing (3) also contains a transformer (not shown) located within the ballast housing (4) which is capable of raising an input voltage of between 9 to 14V to that required to operate the lamp (1, 2).

The lamp (1) includes a 12V electrical connector, shown as a bi-pin GX5.3 connector (5), shown in Figures 1A, 1B, 1C, 1D and 1E.

The electronic circuitry is housed within the ballast housing (4) is now described in relation to Figures 2 - 7. For ease of reference like elements have been designated with the same reference numerals in each of the embodiments depicted in Figures 2 - 7.

In Figure 2, there is shown a current regulation circuit in the form of an electronic ballast, generally indicated by arrow (6) for use with a lamp. The ballast (6) includes two interconnected circuits, a rectifying circuit (7) and a self oscillating inverter circuit (8). The rectifying circuit (7) and a self oscillating inverter circuit (8) being interconnected at a current regulated node (25), a non-current regulated node (13) and a return node (26).

The ballast (6) includes a transformer (9) providing an output to CFL terminals (10) to provide power to the CFL (2) (not shown in Figure 2). The connection (10) shown in Figure 2 is a 4 pin 12V connector.

Power is supplied to the ballast (6) through the 12V input (5, 11) which is in the form of a bi-pin GX5.3 connector.

The ballast (6) includes a passive device, in the form of a pair of coupled inductors (15). The coupled inductors (15) are configured such that both primary 23 and secondary 24inductors are connected in an opposing polarity. The ratio between the primary 23 and secondary 24 inductances is in the range of 1 :5 to 1:8 depending on the power rating of the CFL.

The schematic diagrams of a number of ballast circuits according to further embodiments of the present invention are shown in Figures 3 - 6, all are variants of well known ballasts of the prior art except for the novel inclusion of a coupled inductor (15) in place of a standard inductor (not shown). This change is significant as the coupled inductor of the present invention is configured to provide a current limited regulated supply. The coupled inductor (15) resists any change in the current flow when the lamp is operating normally. When the current drawn by the transformer (9) becomes excessive, the coupled inductor (15) acts to limit the flow of current due to the opposed nature of the inductive elements. The primary inductor (23) inducing an opposing emf in the mutually coupled second inductor (24), thereby reducing the voltage available at current regulated node (25) supplying the self oscillating inverter circuit (8).

A change in current through the coupled inductor 15 can arise when the operating temperature of the components (mainly the switching elements, typically transistors (16) as shown in Figures 2 -5, or MOSFETs (17) as shown in Figure 6) nears or exceeds their maximum operationing temperature specification.

This can occur as a result of power generated within the oscillating inverter circuit (8) combined with the heat generated by the fluorescent lamp during operation. Excessive heating causes the leakage current of the bipolar transistors (16) to increase, causing power to be dissipated (as heat) by the bipolar transistors (16) even when they are not being driven on. If the leakage becomes significant, the transistor is no longer able to dissipate the heat being generated in it, and a thermal runaway occurs whereby the transistor self heats to the point of destruction. Equally, a thermal runaway can occur in the MOSFET transistors (17), shown in Figures 6 and 7, as the temperature of a MOSFET (17) increases, its resistance increases correspondingly, causing the transistor to dissipate more energy (as heat) when it is switched on. If the resistance becomes too great the transistor will self heat to the point of destruction. As a consequence of either of these effects, the transformer (9) will draw more current from the rectifying circuit (7) to compensate for the extra power dissipated (as heat) in the switching elements (16, 17). Thus, what happens in prior art ballasts is that this can lead to a thermal runaway situation, destruction of the transistors (16, 17) and therefore failure of the lamp (1).

However, this situation is averted or significantly mitigated with use of the ballast (6) of the present invention as the current regulation provided by the coupled inductor (15) maintains the current within the desired operational range, thus limiting power dissipation in the inverter circuit (8). Together with the provision of suitable ventilation, as indicated by the apertures (22) in Figure 1A, 1B and 1D, the components may be kept within their specified operating temperature and the thermal runaway situation is therefore avoided. 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 of the appended claims.