JPH09270298A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a discharge lamp without shortening the intrinsic effective life period by arranging a protection circuit which operates when the voltage at both ends of the discharge lamp during operation exceeds the reference voltage value fixed by the specified life judging curve. SOLUTION: A lamp voltage detecting device 12 sends the voltage value at both ends of a small fluorescent tube 20 to a lamp life judging circuit 14, and a lamp current detecting circuit 13 sends the lamp current value between the GND side of the fluorescent tube 20 and a ballast 11 for the small fluorescent tube to the lamp life judging circuit 14. When the fluorescent tube 20 comes close to the final period of the life and the voltage value corresponding to the current value exceeds the reference voltage value, the circuit 14 sends a signal to the ballast 11, and stops the supply of current. The reference voltage value is higher than the initial voltage value corresponding to any current value within the variable current range for moderating light of the fluorescent lamp 20, and is a voltage value corresponding to a current value obtained from the circuit 13 according to a current-voltage life judging curve showing a negative characteristic which decreases with increase in current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device, and more particularly to a small fluorescent lamp having an outer diameter of 10 mm or less, which is used for a backlight of a liquid crystal display device, a light source device for a scanner, a light source device for illumination, and the like. The present invention relates to a lighting device for a discharge lamp suitable for lighting a tube.

[0002]

2. Description of the Related Art In a discharge lamp, for example, a hot cathode type small fluorescent tube, the amount of the emitter coated or contained in the filament of the electrode gradually decreases with use, and when the end of its life is approached, most of the emitter is The disappearance of the cathode voltage causes the lamp voltage to rise, and at the same time, the temperature of the electrode part of the small fluorescent tube also rises. Continuing will cause an accident on peripheral equipment. In order to prevent such a situation,
In a lighting device for lighting a small fluorescent tube, the lamp voltage value at the end of the life of the small fluorescent tube is larger than the lamp voltage value at the beginning of use of the small fluorescent tube (hereinafter, also referred to as “initial voltage value”). Hereinafter, also referred to as "terminal voltage value".) A voltage value with a smaller constant height is used as a reference voltage value, and when the lamp voltage of the small fluorescent tube exceeds the reference voltage value, current is supplied to the small fluorescent tube. A protection circuit is provided for stopping.

On the other hand, as a lighting device used for a backlight of a liquid crystal display device for lighting a small fluorescent tube having an outer diameter of 10 mm or less, the brightness of the display is adjusted according to the brightness of the usage environment. In order to be able to do, a thing having a dimming function of dimming the small fluorescent tube by changing the magnitude of the lamp current supplied to the small fluorescent tube is used, and also in this small fluorescent tube lighting device, Conventionally,
The protection circuit was configured to activate when the lamp voltage exceeded a certain reference voltage value.

However, the small fluorescent tube lighting device having such a dimming function has the following problems. FIG. 5 is a diagram showing a current-voltage characteristic curve of the small fluorescent tube when the magnitude of the lamp current is changed in the variable current range of 10 to 25 mA. In this figure, (a) shows the small fluorescent tube. The current-voltage characteristic curve at the initial stage of use, (b) is the current-voltage characteristic curve at the end of the life of the small fluorescent tube. As shown in this figure, the current-voltage characteristic curve (a) at the beginning of use of the small fluorescent tube and the current-voltage characteristic curve (b) at the end of its life of the small fluorescent tube show that the lamp voltage increases as the lamp current value increases. It shows a negative characteristic that the value becomes small. Therefore, in order to reliably operate the protection circuit before the small fluorescent tube reaches the end of life state, the reference voltage value E0 is set to the minimum lamp voltage value at the end of life of the small fluorescent tube, that is, the maximum of the variable current range. It is necessary to set it to a value sufficiently smaller than the terminal voltage value a at the lamp current value of 25 mA. However, if the reference voltage value E0 is set to a value sufficiently smaller than the terminal voltage value a, the maximum voltage value in the initial use of the small fluorescent tube, that is, the minimum lamp current value 10 in the variable current range is set.
Since the difference from the initial voltage value b in mA is small, when the small fluorescent tube is used at a current of 10 mA, the lamp voltage value may exceed the reference voltage E0 due to, for example, a change in the lamp voltage that may normally occur. As a result, although the small fluorescent tube is still normal, the small fluorescent tube cannot be turned on because the protective circuit malfunctions so to speak.

A wide variable current range, for example, 5 to 25 m
When dimming the small fluorescent tube in the range of A, as shown in FIG. 6, the maximum voltage value at the initial stage of use of the small fluorescent tube, that is, the initial voltage value c at the minimum lamp current value 5 mA in the variable current range is , The value may be larger than the terminal voltage value a at 25 mA, in which case the reference voltage value for activating the protection circuit cannot be set practically, and accordingly, the variable current for dimming cannot be set. It is necessary to limit the range to a narrow range.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made based on the above circumstances, and its object is to provide:
In a discharge lamp lighting device provided with a protection circuit that operates when the lamp voltage exceeds a reference voltage value, the protection circuit can be reliably operated before the discharge lamp reaches the end of life state, and further, It is an object of the present invention to provide a lighting device for a discharge lamp which can be used without shortening the originally effective life of the discharge lamp.

[0007]

The discharge lamp lighting device of the present invention supplies a current of a set magnitude within a variable current range for dimming, so that the current-voltage characteristic has a negative characteristic. A discharge lamp lighting device for lighting a discharge lamp, wherein the voltage across the discharge lamp during operation exceeds a reference voltage value determined by a current-voltage life determination curve set in advance in the variable current range. The current-voltage life determination curve has a voltage value corresponding to the set current value in the discharge lamp at any current value in the variable current range. The negative characteristic curve is higher than the lamp voltage value in the initial stage of use and decreases as the current value increases.

In the discharge lamp lighting device of the present invention, when the variable current range is set in a range including at least 10 to 20 mA, the current-voltage life determination curve is
The voltage value at 10 mA is 30 to 70 V higher than the initial voltage value at 10 mA of the discharge lamp, and 20
The voltage value at mA is preferably 20 to 50 V higher than the voltage value at 20 mA of the discharge lamp.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail for the case of forming a small fluorescent tube lighting device. FIG. 1 is a block diagram showing a schematic configuration of an example of a small fluorescent tube lighting device according to the present invention. In this small fluorescent tube lighting device, a small fluorescent tube ballast 11 is connected to an appropriate DC power source 10 to form a so-called constant current supply type lighting power supply circuit.
1, a small fluorescent tube 2 through a lamp voltage detection circuit 12
The high voltage side terminal of 0 is connected, and the GND side terminal of the small fluorescent tube 20 is connected via the lamp current detector 13. Reference numeral 14 denotes a lamp end-of-life judgment circuit. This lamp end-of-life judgment circuit 14 operates the protection circuit according to a current-voltage life judgment curve described later according to the lamp current value sent from the lamp current detector 13. When the lamp voltage value sent from the lamp voltage detection circuit 12 exceeds the reference voltage value, it has a function of sending a protection circuit operation signal to the fluorescent tube ballast 11,
The fluorescent tube ballast 11 is provided with a protection circuit that shuts off the current to the small fluorescent tube 20 when receiving a protection circuit operation signal.

FIG. 2 shows an example of a typical inverter circuit of the compact fluorescent lamp ballast 11. In this figure, L1 is a choke coil, C1 is an electrolytic capacitor, C2 is a film capacitor, C3 is a ceramic capacitor, and Q1.
And Q2 is a transistor and T1 is a transformer.

A current-voltage life judgment curve is preset in the lamp life end judgment circuit 14. An example of this current-voltage life judgment curve is shown in FIG. In this figure,
(A) is a current-voltage characteristic curve (hereinafter, also referred to as “initial characteristic curve”) in the initial use of the small fluorescent tube 20, (b).
Is a current-voltage characteristic curve at the end of life of the small fluorescent tube 20 (hereinafter, also referred to as “terminal characteristic curve”).
Is a current-voltage life determination curve (hereinafter, also referred to as “determination curve”). In this example, the variable current range for dimming the small fluorescent tube 20 is 5 to 25 mA, and the determination curve (C) is set in this variable current range.

As shown in FIG. 3, the determination curve (c) has a voltage value higher than the initial voltage value corresponding to the current value in the small fluorescent tube 20 at any current value in the variable current range. It is a negative characteristic curve in which the voltage value decreases as the current value increases.

As described above, when the variable current range for dimming the small fluorescent tube 20 is in the range of 10 to 20 mA, the determination curve (c) shows that the voltage value E1 at 10 mA is small fluorescent light. It is preferable that the initial voltage value E2 at 10 mA of the tube 20 is higher by 30 to 70 V, and the voltage E3 at 20 mA is higher by 20 to 50 V than the initial voltage E4 at 20 mA of the small fluorescent tube 20. When the voltage value E1 and the voltage value E3 are less than the lower limit value of the above range, the protection circuit may be activated due to a change in the lamp voltage that may occur normally, so that the life of the small fluorescent tube 20 is reduced. It may result in shortening. On the other hand, when the voltage value E1 and the voltage value E3 exceed the upper limit value of the above range, the reference voltage value for operating the protection circuit is not sufficiently smaller than the terminal voltage value of the small fluorescent tube 20, It may be difficult to operate the protection circuit reliably before the small fluorescent tube 20 reaches the end of its life.

FIG. 4 is an explanatory sectional view showing an example of a small fluorescent tube 20 which is turned on by the lighting device of the present invention. In this small fluorescent tube, sealing parts 22 are formed at both ends of a straight tube type sealing body 21 made of lead glass, borosilicate glass or the like and having an inner diameter of 10 mm or less. Each of which is airtightly penetrated to extend in the axial direction of the sealing body 21, a lead wire 23 is provided, and each inner end portion of the lead wire 23 has a sleeve-like shape so as to face each other in the axial direction of the sealing body 21. An electrode 24 is provided. The inner peripheral surface of the sealing body 21 has, for example, a thickness of 10 to 30 μm.
m phosphor layers 27 are formed.

The electrode 24 in this example includes a metal sleeve 25 made of, for example, stainless steel, nickel, etc., and a coiled filament 26 made of tungsten, on the surface of which an emitter made of (Ba, Sr, Ca) O is applied. The metal sleeve 25 is arranged along the axial direction of the sealing body 21 so that the openings thereof face each other, and the filament 26 is arranged to be housed inside the metal sleeve 25.

More specifically, the metal sleeve 25 is held by the lead wire 23 with its openings facing each other, for example, by holding the tip end portion of the lead wire 23 by the base end portion which is flatly crushed. ing. Further, the filament 26 has its base end clamped and fixed by the base end portion of the crushed metal sleeve 25, and its tip end is positioned inward without exceeding the tip end of the metal sleeve 25.
It is arranged in the cylindrical hole of the metal sleeve 25.

Mercury and rare gas are enclosed in the envelope 21. This noble gas preferably contains argon and krypton as main components, and as an example, argon-krypton gas containing 10 mol% of krypton is sealed at a pressure of 50 Torr, and mercury is 4 m.
g enclosed.

The small fluorescent tube lighting device having the above structure operates as follows. A direct current is supplied from the DC power supply 10 to the small fluorescent tube ballast 11, and this small fluorescent tube ballast 1
1, the direct current is converted into a high frequency alternating current of 40 KHz, for example, and the converted high frequency alternating current is supplied to the high voltage side of the small fluorescent tube 20 via the lamp voltage detection circuit 12 as a current of a set magnitude. As a result, the small fluorescent tube 20 is turned on.

The lamp voltage detector 12 detects a lamp voltage value which is a potential difference between the high voltage side and the GND side in the small fluorescent tube 20 and sends the lamp voltage value to the lamp life judging circuit 14. On the other hand, the lamp current detection circuit 13
In (1), the lamp current value between the GND side of the small fluorescent tube 20 and the small fluorescent tube ballast 11 is detected, and this lamp current value is sent to the lamp life determination circuit 14. Then, in the lamp life determination circuit 14, the lamp current detection circuit 13
A reference voltage value for operating the protection circuit is determined by a preset determination curve (C) according to the lamp current value sent from the. Specifically, the voltage value corresponding to the lamp current value detected by the lamp current detection circuit 13 in the determination curve (C) becomes the reference voltage value.

As the life of the small fluorescent tube 20 approaches the end of its life after the usage time of the small fluorescent tube 20, the lamp voltage rises due to the decrease in the number of emitters.
When the lamp voltage value exceeds the reference voltage value, the lamp life determination circuit 14 sends a protection circuit operation signal to the small fluorescent tube ballast 11, which causes the small fluorescent tube ballast 1 to operate.
The protection circuit 1 operates and the supply of current to the small fluorescent tube 20 is stopped. Since the voltage value of the determination curve (c) is lower than the voltage value of the end characteristic curve (b) at any current value, after all, the small fluorescent tube 20 is finally brought to the end of life state. The supply of current to 20 is stopped.

According to such a small fluorescent tube lighting device,
In the lamp life determination circuit 14, the reference voltage value for operating the protection circuit of the small fluorescent tube ballast 11 is determined by the determination curve (C) preset in the variable current range.
Since it is determined according to the lamp current value actually flowing through the small fluorescent tube 20, even when the small fluorescent tube 20 is turned on by any current value in the variable current range, it is possible to ensure that the small fluorescent tube 20 reaches the end of its life. The protection circuit can be activated. Moreover, since the judgment curve (c) can be set to have a voltage value that is sufficiently higher than the initial voltage of the small fluorescent tube 20 at any current value, the protection circuit can be protected by, for example, a change in the lamp voltage that normally occurs. It does not operate, so that the compact fluorescent tube 20 can be used without shortening its originally useful life period.

Further, since the reference voltage value for operating the protection circuit is determined according to the lamp current value, a variable current range for dimming the small fluorescent tube 20 is set in order to effectively operate the protection circuit. The limitation can be avoided and the variable current range can be set in a wide range.

Although the embodiment of the discharge lamp lighting device of the present invention has been described above, the present invention is not limited to this, and various modifications can be made. For example, the variable current range for dimming can be freely set according to the performance of the discharge lamp to be lit. Further, the lighting device of the present invention can be configured as a lighting device for lighting various discharge lamps other than the small fluorescent tube as long as the current-voltage characteristic is negative.

[0024]

According to the discharge lamp lighting device of the present invention, the reference voltage value for operating the protection circuit is determined according to the lamp current value by the preset current-voltage life determination curve in the variable current range. Since it is determined, the protection circuit can be surely operated before the end of the life of the discharge lamp, even when the discharge lamp is turned on by any current value in the variable current range. Moreover, the current-voltage life determination curve is set to have a voltage value that is sufficiently higher than the lamp voltage value at the initial stage of use of the discharge lamp at any current value. Does not operate, so that the discharge lamp can be used without shortening its original useful life.

Further, since the reference voltage value for operating the protection circuit is determined according to the lamp current value, the variable current range for dimming the discharge lamp is limited in order to effectively operate the protection circuit. This can be avoided, and the variable current range can be set in a wide range.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an example of a small fluorescent tube lighting device according to the present invention.

FIG. 2 is a circuit diagram showing an example of a typical inverter circuit of a small fluorescent tube ballast.

FIG. 3 is a diagram showing an example of a current-voltage determination life curve.

FIG. 4 is an explanatory cross-sectional view showing the configuration of an example of a small fluorescent tube that is turned on by the lighting device of the present invention.

FIG. 5 is a diagram showing a current-voltage characteristic curve of a small fluorescent tube in a lamp current range of 10 to 25 mA.

FIG. 6 is a diagram showing a current-voltage characteristic curve of a small fluorescent tube in the range of a lamp current of 5 to 25 mA.

[Explanation of symbols]

 10 DC power supply 11 Small fluorescent tube ballast 12 Lamp voltage detection circuit 13 Lamp current detector 14 Lamp life end judgment circuit 20 Small fluorescent tube 21 Encapsulation 22 Sealing part 23 Lead wire 24 Electrode 25 Metal sleeve 26 Filament 27 Phosphor layer C1 Electrolytic capacitor C2 Film capacitor C3 Ceramic capacitor L1 Choke coil T1 Transformer Q1, Q2 Transistor

Claims (2)

[Claims] 1. A lighting device for a discharge lamp for lighting a discharge lamp having a negative current-voltage characteristic by supplying a current of a set magnitude within a variable current range for dimming. , A discharge circuit is provided with a protection circuit that is activated when the voltage across the discharge lamp exceeds a reference voltage value determined by a current-voltage life determination curve set in advance in the variable current range. -The voltage life determination curve has a voltage value higher than the initial lamp voltage value corresponding to the set current value in the discharge lamp at any current value in the variable current range, and the current value is large. A discharge lamp lighting device having a negative characteristic curve in which the voltage value becomes smaller as it goes. 2. A variable current range is set in a range including at least 10 to 20 mA, and a current-voltage life determination curve is
The voltage value at 10 mA is 30 to 70 V higher than the initial voltage value at 10 mA of the discharge lamp, and 20
The discharge lamp lighting device according to claim 1, wherein the voltage value at mA is 20 to 50 V higher than the voltage value at 20 mA of the discharge lamp.