JPH0434896A - Fluorescent lamp device - Google Patents

Abstract

PURPOSE:To achieve long life of a lamp without reducing the emission efficiency by properly controlling a cathode descending voltage of a pair of electrodes of a fluorescent lamp to an optimal value. CONSTITUTION:When a fluorescent lamp 2 is lighted, a lamp voltage is applied between a pair of electrodes 3a and 3b from a lighting circuit 3, and the lamp is preheated. An arc discharge is then formed, and since an ultraviolet ray is generated by exciting a quicksilver atom, a fluorescent film is excited, and a visual light is thus emitted. The cathode descending voltage of each of electrodes 3a, 3b is detected by each of cathode descending voltage detection circuits 9a, 9b through each of probes 6a, 6b, at every negative semi-cycle of the voltage to be applied at the time. The voltage is compared with a voltage set by a controller 10, and a control signal is sent to a circuit 3, and by controlling a preheating current given to the electrodes 3a, 3b, the long life of the fluorescent lamp 2 can be achieved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a fluorescent lamp device suitable for a backlight of a liquid crystal display panel, etc., and in particular, to improve the electrode life of a hot cathode fluorescent lamp. The present invention relates to a fluorescent lamp device that achieves the following.

(Prior art) At the Illuminating Society of Japan's National Conference Nα7 in 1989, hot cathode fluorescent lamps operating at a lamp current of 10 to 40 mA,
It has been reported that the cathode drop voltage has a negative correlation with the electrode life, and that if the cathode drop voltage is 14 V or less, a life of 2000 hours or more can be ensured.

The same report also examines how to select design parameters such as filler gas pressure and coil dimensions for hot cathode fluorescent lamps in order to lower the cathode drop voltage.

This shows that the higher the filler gas pressure is and the smaller the dimensions of the coil (wire diameter, surface area, heat capacity), the more stable arc discharge can be maintained even in a small current range.

For example, when a hot cathode fluorescent lamp is operated with a lamp current of 15 mA using a single coil with a surface area of 4.3 - made of 3.6 MG tungsten wire as an electrode and filled with argon gas at 20 Torr, the cathode drop voltage is 1
3V, and an electrode life of over 3000 hours is possible.

(Problem to be Solved by the Invention) However, as the pressure of the enclosed argon gas increases, the elastic collision loss within the positive column increases and the electron temperature decreases.
As a result of the decrease in the generation efficiency of 4 nm ultraviolet light, the luminous efficiency (j!m/W) of the lamp decreases.

Further, when the electrode coil becomes smaller, the emitter cannot be applied sufficiently, so there is a problem that it is difficult to significantly extend the life of the electrode coil.

Furthermore, the cathode drop voltage does not necessarily maintain a constant value during the life of the lamp, and when the lamp is lit for a long time, the surface condition of the emitter of the electrode deteriorates and the work function increases.

Furthermore, if the lamp blinks frequently,
Since the surface of the emitter is also subjected to severe ion bombardment due to sputtering, the surface condition deteriorates and the work function increases.

As a result, even if the cathode drop voltage is low in the initial state of the lamp, the cathode drop voltage increases during the lamp's life, resulting in an unexpectedly short life.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a fluorescent lamp device that can extend the life of the electrodes without lowering the cathode drop voltage and reducing the luminous efficiency of the lamp. There is a particular thing.

[Structure of the invention]

(Means for Solving the Problems) The present invention has been made focusing on the fact that the cathode drop voltage can be lowered by increasing the electrode temperature, and is configured as follows.

That is, the present invention provides a fluorescent lamp device including a fluorescent lamp incorporating a pair of electrodes coated with an emitter, and a lighting circuit that preheats the pair of electrodes to light the fluorescent lamp. A cathode drop voltage detection means for detecting the voltage, and a control means for increasing the preheating current applied to the pair of electrodes when the cathode drop voltage detected by the cathode drop voltage detection means is higher than a set voltage. It is characterized by

(Operation) When the pair of electrodes are preheated by the lighting circuit and the fluorescent lamp is lit, the cathode drop voltage of the pair of electrodes of the fluorescent lamp is detected by the cathode drop voltage detection means.

The detected cathode drop voltage is compared with a set voltage by the control means, and when the cathode drop voltage is higher, the preheating current to the fluorescent lamp is increased.

For this reason, the pair of electrodes is further heated and raised in temperature by the increased preheating current, so that the cathode drop voltage thereof decreases. Since the cathode drop voltage of the electrode is reduced, the life of the electrode, that is, the fluorescent lamp can be extended.

In other words, according to the present invention, it is possible to extend the life of the fluorescent lamp.

(Example) Examples of the present invention will be described below based on FIGS. 1 to 5.

FIG. 1 is an overall configuration diagram showing the overall configuration of an embodiment of the present invention. In the figure, a fluorescent lamp device 1 includes a hot cathode fluorescent lamp 2 and a lighting circuit 3 that preheats the hot cathode fluorescent lamp 2 and lights it with alternating current. .

The fluorescent lamp 2 has a pair of hot cathode type electrodes 3a.

3b is built in the bulb 2a, and a fluorescent film (not shown) is coated on almost the entire inner peripheral surface of the bulb 2a, and a rare gas such as mercury and argon gas is sealed in the bulb 2a.

As shown in FIG. 2, these pair of electrodes 3a, 3b are a pair of left and right wells 5a that are erected on a button stem 4 made of glass, for example, with a required spacing.

It is installed between the upper ends of 5b.

Each electrode 3a, 3b is formed in a hot cathode type, for example, by coating a coil made of tungsten with an emitter made of (Ba, Ca, 5r)0, etc.

Further, probes 6a and 6b are erected on each button stem 4 at positions separated from each electrode 3a and 3b by, for example, about 3 to 50 meters.

Each probe 6a, 6b is an electrode terminal for detecting the cathode drop voltage of each electrode 3a, 3b. degree) covered with a glass sleeve 8 while protruding inward.

The multiple pairs of wells 5a and 5b are each connected to the lighting circuit 3, while, for example, 5a is connected to a preheating circuit (not shown).
The other end, for example, 5b is connected to a power supply circuit (not shown), and the lighting circuit 3 constantly supplies a preheating current to each electrode 3a, 3b to preheat it, and applies an AC lamp voltage to light the fluorescent lamp. It has become.

Each electrode 3a, 3b has multiple pairs of wells 5a, 5b.
The pair of left and right cathode drop voltages 9a, 9b in the figure
are electrically connected to each other.

These pair of cathode drop voltage detection circuits 9a, 9b are electrically connected to the pair of probes 6a, 6b, respectively, and each negative half cycle of the AC voltage applied to the pair of electrodes 3a, 3b is applied to each electrode 3a, 3b. It is designed to detect the cathode drop voltage.

The cathode drop voltages detected by these cathode drop voltage detection circuits 9a and 9b are given to the controller 10, where they are compared with a set voltage of, for example, 10V, and if the cathode drop voltage is higher than the set voltage, the height A control signal is given to the lighting circuit 3 to increase the preheating current according to the preheating current, thereby increasing the preheating current given from the lighting circuit 3 to the pair of electrodes 3a and 3b.

In addition, in FIG. 2, the reference numeral 11 is an exhaust pipe.

Next, the operation of this embodiment will be explained.

When lighting the fluorescent lamp 2, a lamp voltage is applied from the lighting circuit 3 between the pair of electrodes 3a, 3b of the fluorescent lamp 2, and these electrodes 3a, 3b are preheated.

As a result, when the pair of electrodes 3a, 3b is preheated to a predetermined temperature, dielectric breakdown occurs between these electrodes 3a, 3b, forming an arc discharge. Then, the mercury atoms in the fluorescent lamp 2 are excited to generate ultraviolet light, which excites the fluorescent film to emit visible light, and the fluorescent lamp 2 is turned on.

When this fluorescent lamp 2 is turned on, a pair of electrodes 3a.

Each cathode drop voltage detection circuit 9a, via each probe 6a, 6b every negative half cycle of the applied voltage applied to 3b,
9b detects the cathode drop voltage of each electrode 3a, 3b.

The detected cathode drop voltage is compared with a set voltage in the controller 10, and if the detected cathode drop voltage is higher, the controller 10 sends a constant heating control signal to the lighting circuit 3 in accordance with the height. given to.

For this purpose, a pair of electrodes 3a are provided from the lighting circuit 3.

Since the preheating current given to electrode 3b increases, the temperature of the pair of electrodes 3a, 3b increases, so the temperature of the pair of electrodes 3a, 3b increases.
The cathode drop voltage of b is stepped down. As a result, the life of the fluorescent lamp 2 can be extended.

The correlation between the cold cathode drop voltage vK and the electrode temperature Tf is as shown in FIG. 3, for example, when the preheating current 11 of the pair of electrodes 3a and 3b is 100 mA and the cathode drop voltage is 16V. Sometimes, the preheating current is 150mA.
When the electrode temperature Tf of the pair of electrodes 3a and 3b is increased to
This shows that the temperature has increased to, for example, about 900° C., and that the cathode drop voltage has dropped from 16V to 8V.

According to the experimental results to obtain the graph shown in Figure 3, when fluorescent lamp 2 was simply turned on with a lamp current of 15 mA, the cathode drop voltage was as high as 16 V, and the lamp life was about 1,000 hours. On the other hand, when controlling the cathode drop voltage as in this example, the electrode life is about 5000
It was recognized that the lamp life was significantly extended.

In the above embodiment, a case was explained in which a pair of probes 6a and 6b were provided to detect the cathode drop voltage of a pair of electrodes 3a and 3b, but the present invention is not limited to this. For example, the probes 6a and 6b of
They may be replaced with a pair of conductor foils 2Qa and 20b shown in the figure, respectively.

The pair of conductor foils 20a, 20b are constructed by winding strip-shaped copper foils of a required width in an annular manner around the outer periphery of the bulb 2a at positions corresponding to the pair of electrodes 3a, 3b of the fluorescent lamp 2.

A pair of electrodes 3a are also formed by the conductor foils 20a and 20b.
, 3b can be detected, so
Although the same effects as in the above embodiment are achieved, the frequency of the lamp voltage is, for example, a commercial frequency (50Hz or 60Hz).
If the voltage is low, as shown in FIG. 5, integrating circuits 21a and 21b consisting of a capacitor C and a resistor R may be interposed between the cathode effect voltage detection circuits 9a and 9b.

〔Effect of the invention〕

As explained above, the present invention increases the preheating current given to the pair of electrodes when it is detected that the cathode effect voltage of the pair of electrodes of the fluorescent lamp has become higher than the set voltage. The cathode effect voltage can be lowered to a predetermined voltage by raising the temperature.

Therefore, according to the present invention, by appropriately controlling the cathode drop voltage of the pair of electrodes to an optimum value, it is possible to extend the lamp life without reducing the luminous efficiency.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of a fluorescent lamp device according to the present invention, FIG. 2 is an enlarged perspective view of the main parts around the electrodes shown in FIG. 1, and FIG. 3 is a diagram of the embodiment shown in FIG. Graph showing the correlation between cathode effect voltage, preheating current, and electrode temperature, 4th
This figure is an overall configuration diagram of another embodiment of the present invention, and FIG. 5 is a partially enlarged view of FIG. 4. 1... Fluorescent lamp device, 2... Fluorescent lamp, 3a. 3 b--Electrode, 6a, 6b--Probe, 9a,
9b... Cathode effect voltage detection circuit, 10... Controller,
20a. 20b...Conductor foil. Applicant's agent Hisa Hatano 0a *4tI! 1 No. 7r11 *Figure 5 C entrance

Claims (1)

[Claims] In a fluorescent lamp device comprising a fluorescent lamp incorporating a pair of electrodes coated with an emitter and a lighting circuit that preheats the pair of electrodes and lights the fluorescent lamp, the cathode detects the cathode drop voltage of the pair of electrodes. The method is characterized by comprising a drop voltage detection means and a control means for increasing the preheating current applied to the pair of electrodes when the cathode drop voltage detected by the cathode drop voltage detection means is higher than a set voltage. Fluorescent lamp equipment.