Ballast stabilizer for discharge lamps and lighting circuit using the same

Abstract

 A ballast stabilizer for a fluorescent discharge lamp (1) is made of an electrically resistive material layer (32) disposed on a base plate (31). The base plate (31) may be of insulating material and form part of the appliance body (11), particularly the lamp holder. Such a ballast stabilizer has a comparatively large area with the result that heat dissipation during operation of the lamp is improved and temperature rise is held at a minimum. At the same time, the ballast stabilizer requires practically no extra space and can be produced at low cost.

Description

[0001] This invention relates to a ballast stabilizer for discharge lamps and to a lighting circuit using said ballast stabilizer.

[0002] To light a fluorescent lamp in a stabilized manner, it is necessary to install in the lamp power supply circuit a ballast stabilizer which limits the discharge current to its specified value or less.

[0003] Conventional ballast stabilizers of this type are mostly in the form of choke coils, which are bulky and heavy and which cause so high a rise in temperature owing to their heat generation during the lighting of the lamp that it is necessary to provide a sufficient space for heat dissipation between the choke coil and other parts, limiting the place available in the fluorescent lamp appliance for installing the ballast stabilizer, thus resulting in the disadvantage of imposing various restirictions on the engineering and aesthetic desing of the fluorescent lamp appliance.

[0004] Besides the aforesaid type of ballast stabilizers, use has heretofore been made of incandescent lamps or resistance wires; in each case, however, it is necessary to add thereto a discharge starting circuit comprising such electronic parts as expensive transistors, resulting in an increase in cost. Moreover, in the case of the former, the fluorescent lamp appliance must of necessity be used with an incandescent lamp, while in the case of the latter since ballast stabilizer is in the form of a mere resistance wire, it is difficult to handle and is inconvenient for the maker to build it into the appliance.

[0005] This invention has been accomplished to overcome the drawbacks described above and will now be described with reference to the drawings showing embodiments thereof. In the drawings,

Fig. 1 is a circuit diagram for a discharge lamp lighting circuit according to a first form of this invention;

Fig. 2 is a perspective view showing an example of a ballast stabilizer used in said lighting circuit;

Fig. 3 is a section taken along the line III-III in Fig. 2;

Fig. 4 is a perspective view of a fluorescent lamp appliance using the lighting circuit of Fig. 1;

Fig. 5 is a perspective view looking at said appliance from a different position;

Fig. 6 is an enlarged section taken along the line VI-VI in Fig. 5;

Fig. 7 is a sectional view of a fluorescent lamp appliance wherein an auxiliary electrode is fabricated to serve as a reflector hood; and

Fig. 8 is a circuit diagram for a discharge lamp lighting circuit according to a second form of the invention.

[0006] The numeral 1 denotes a fluorescent discharge lamp (hereinafter referred to briefly as the fluorescent lamp) having one electrode F₁ connected to one pole of an AC power source 4 through the secondary winding 2₁ of an autotransformer 2 connected in series with a ballast stabilizer 3, the other electrode F2being connected to the other pole of the AC power source 4. The terminal a of the secondary winding 2₂ of the autotransformer 2 is : connected to an auxiliary electrode 5 disposed in contact with or close to the outer wall surface of the fluorescent lamp 1. Further, the fluorescent lamp 1 has a glow lamp 6 connected in parallel therewith.

[0007] The aforesaid ballast stabilizer 3 is constructed as follows.

[0008] A base plate ₃₁ made of an insulating material, such as glass, epoxy resin or Bakelite, has an electrically resistive material, such as carbon type resistive paint, applied thereto as by printing, spraying or other means, said electrically resistive material being hardened by heating to form an electrically resistive material layer 32. In this case, the electrically resistive material is applied to the base plate 31 everywhere except its opposite end portions, to which an electrically conductive material, such as silver, is applied to form terminals 33, 33.

[0009] In the above case, the base plate 31 is made of a heat-resistant insulating material, but depending upon the type of the electrically resistive material, it may be applied without involving heat treatment, in which case it is not always ncessary to form the base plate 31 of an insulating material which withstands such heat treatment temperature. The base plate 31 is a flat plate, but it may be a curved plate, of course.

[0010] It goes without saying that the size of the ballast stabilizer 3 is such that it can be received in the fluorescent lamp appliance. Thus, the length and width of the base plate 31 are so determined that it can be housed in the appliance. The type and amount of the electrically resistive material to be applied to the base plate 31 are suitably selected to provide the specified value of electric resistance.

[0011] In addition, the way the electrically resistive material layer 32 is formed on the base plate 31 is not limited to the methods mentioned above; for example, vapor deposition and other means may be used.

[0012] The autotransformer 2 should have a satisfactory operating characteristic in the high frequency band; usually, it has a size of about 2 cm^3. For example, Model SF-2A manufactured by Nippon Electric Company, Ltd., which has said size, is used.

[0013] In operation when the AC power source 4 is turned on, the glow lamp 6 is energized by one pole of the AC power source 4 through the primary winding 2₁ of the autotransformer 2, and one electrode F₁ of the fluorescent lamp 1 on one hand and by the other pole of the AC power source through the other electrode F₂ of the fluorescent lamp 1 on the other hand, so that the glow discharge in the glow lamp 6 is started. As a result, the electrodes F₁ and F₂ of the fluorescent lamp 1 are preheated, and the subsequent ceasing of the glow discharge causes a transient current to flow through the primary winding 2₁ of the autotransformer 2, so that a stepped-up high voltage is produced in the secondary winding 2₂. Since this high voltage is applied between one pole F₁ of the fluorescent lamp 1 and the auxiliary electrode 5, the discharge is started between the two electrodes F₁ and F₂, producing a discharge current flowing through the ballast stabilizer 3.

[0014] An experiment on lighting will now be described. In this case, the ballast stabilizer 3 was constructed by applying a carbon type resistive paint to a 3-cm wide and 58-cm long base plate 31 of epoxy resin everywhere except the opposite end portions each of which measures 2 cm, applying a silver paint to the opposite end portions to provide terminals 33, 33, and heating these paints at 150°C for 4 hours to harden them, the resulting resistance being about 180Ω. A 20-watt fluorescent lamp 1 ana a 100-V AC power source were used. When the power source was turned on, a discharge current of about 330 mA flowed through said ballast stabilizer 3. The ballast stabilizer 3 never became heated so much as to exceed 60°C. The stability of the discharge current during lighting was as good as when the conventional ballast stabilizer was used.

[0015] In the fluorescent lamp lighting circuit described above, the glow lamp 6 may be replaced by a negative- resistance element (e.g., one manufactured by Mitsubishi Electric Corporation) while retaining the same result as described above.

[0016] Figs. 4-6 show an example of a fluorescent lamp appliance using the aforesaid lighting circuit, wherein the appliance body 11 is formed of a plate with its end edges bent upward. Although the ballast stabilizer 3 has been described as being formed by providing the electrically resistive material layer 32 on the base plate 31 which is separate from the appliance body 11, it is possible to use the appliance body 11 itself as a base plate and form the electrically resisting material layer 32 thereon. If the appliance body 11 is an electrically conductive plate, this invention may be embodied by forming an insulating layer of enamel or the like on the upper surface of the plate and superposing an electrically resistive material layer 32 on said insulating layer. The auxiliary electrode 5 is in the form of an aluminum plate disposed between the appliance body 11 and the fluorescent lamp 1. If said auxiliary electrode 5 is widened, it may serve as a reflector hood, as shown in Fig. 7. In addition, 12, 12 denote the sockets of the discharge lamp 1; 13 denotes the socket of the glow lamp; 14, 14 denote set screws for attaching the auxiliary electrode 5 to the appliance body 11; and 15, 15 denote coil springs interposed between the appliance body 11 and the auxiliary electrode 5.

[0017] Fig. 8 shows a lighting circuit using said ballast stabilizer 3 according to another embodiment of the invention, wherein one electrode F₁ of a fluorescent lamp 1 is connected to one pole of an AC power source 4, while the other electrode F₂ is connected to the other pole of said _AC power source 4 through a triac 25, which is a switching element, and the ballast stabilizer 3 connected in serires with the latter. The numeral 22 denotes a step-up autotransformer with its primary winding 22₁ connected to the AC power source 4 through the ballast stabilizer 3 and its secondary winding 22₂ having its output terminal b connected to the electrode F₂ of the fluorescent lamp 1 through a series combination of resistors R1 and F₂. The numeral 26 denotes a diac connected between the junction between the resistors R₁ abd R₂ and the gate of the triac 25. The numeral 27 denotes a preheating transformer with its primary winding 27₁ connected to the AC power source 4 through said ballast stabilizer 23 and its secondary windings 27₂, 27₂ connected to the electrodes F₁ and F₂ of the fluorescent lamp 1,respectively.

[0018] In operation, when the AC power source 4 is turned on, the preheating transformer 27 provides preheating currents flowing through the electrodes F₁ and. F₂ of the fluorescent lamp 1, while the autotransformer 22 applies a stepped-up voltage, which is higher than the usual discharge voltage, to the fluorescent lamp through the resistors R₁ and R₂, so that the fluorescent lamp 1 is immediately lighted, with the discharge current flowing through the resistors R₁ and R₂. The resulting voltage drop due to the resistor R₂ yields a trigger signal applied to the triac 25 through the diac 26, thus firing the triac 25. As a result, the power supply circuit to the fluorescent lamp 1 is completed, supplying the specified discharge current through the ballast stablizer 3.

[0019] During the lighting of the fluorescent lamp 1, a current flows through the resistors R₁ and R₂ in a circuit separate from the aforesaid power supply circuit; however, since said resistors R₁ and R₂ are of tens of KΩ, the power loss due to the resistors R₁ and R₂ are very small.

[0020] In the lighting circuit described above, one or both of the resistors R₁ and R₂ may be replaced by a capacitor or capacitors of about 0.1 µF, and it is also possible to replace the triac 26 by a resistor.

[0021] Thus, the lighting circuit according to the second embodiment of the invention is designed to initiate the discharge by applying a voltage higher than the usual discharge voltage to the electrodes of the fluorescent lamp at the time of lighting. This means that a rapid- start type lighting circuit can be provided.

[0022] Since the ballast stabilizer of this invention is formed by forming the electrically resistive material layer 32 on the base plate 31, as described above, it is in the form of a plate, light in weight and less bulky.

[0023] Further, since the ballast stabilizer 3 has the electrically resistive material layer 32 whose surface area is much larger than that of a resistance wire, the characteristic of heat dissipation during heating is improved, so that its temperature rise during lighting can be reduced to a minimum.

[0024] Further, since the ballast stabilizer 3 is formed by providing the electrically resistive material layer 32 on the base plate 31, it can be produced with ease and at low cost.

[0025] Where said ballast stabilizer 3 or 23 is used in forming a lighting circuit, since the ballast stabilizer 3 or 23 itself is light in weight and less bulky and since that space between it and an adjacent part which is required for heat dissipation can be reduced, the discharge lamp appliance can be made light in weight and small in size and the engineering and esthetic design thereof can be diversified as well. Paticularly where it is used in a lighting circuit for a multi-lamp appliance, the latter can be easily designed to have a well-balanced external appearance.

[0026] The ballast stabilizers 3 and 23 can be offered at low prices, and since they are in plate form, they are easy to handle and to install in discharge lamp appliances, the number of installing steps being reduced. Since they allow the use of autotransformers which can be produced at low costs, it is possible to reduce the costs of the lighting circuit and the discharge lamp appliance.

[0027] Further, there is no humming sound during lighting, such as produced by a ballast stabilizer comprising a choke coil, and moreover the power factor is improved.

Claims

1. A ballast stabilizer for discharge lamps, comprising an electrically resistive material layer (32) formed on a base plate (31).

2. A ballast stabilizer for discharge lamps as set forth in claim 1, wherein said base plate (31) is made of insulating material.

3. A ballast stabilizer for discharge lamps as set forth in claim 1, wherein said base plate (31) is in the form of an electrically conductive plate having an insulating layer formed thereon, and said electrically resistive material layer (32) overlies said insulating layer.

4. A lighting circuit for discharge lamps, comprising a power supply circuit in the form of a series combination of a ballast stabilizer (3) as set forth in any of claims 1 to 3, the primary winding (2₁) of an autotransformer (2), and a discharge lamp (1), a circuit for applying the.output from the secondary winding (2₂) of said autotransformer (2) to an auxiliary electrode (5) disposed in contact with or close to the outer wall surface of said discharge lamp (1), and for cutting off preheating current to said discharge lamp (1).

5. A lighting circuit for discharge lamps as set forth in claim 4, wherein said electrically conductive plate is a component of the discharge lamp appliance.

6. A lighting circuit for discharge lamps as set forth in claim 4 or 5, wherein said auxiliary electrode (5) is in the form of a reflector hood for the discharge lamp appliance.

7. A lighting circuit for discharge lamps, comprising a power supply circuit having a series combination of a ballast stabilizer (3) as set forth in any of claims 1 to 3, a switching element, and a discharge lamp (1), a circuit for applying to said discharge lamp a voltage higher than the discharge voltage thereof, and a circuit for rendering said switching element conductive.

Drawing