JPH0632316B2 - Fluorescent lamp lighting control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device using a fluorescent lamp, and more particularly to a lighting control device suitable for an instrument panel of an automobile using a liquid crystal display device.

[Conventional technology]

In recent years, digital display devices have been widely used as instrument panels for automobiles, and therefore liquid crystal display devices have been widely used.

By the way, in such a liquid crystal display device for an automobile, since a color display system is generally adopted, a light source for illumination is often required. At this time, a fluorescent lamp has been mainly used as the light source.

However, if a general hot cathode type fluorescent lamp is used as this fluorescent lamp, its life is relatively short and it is not practical. Therefore, it has been conventionally used, for example, in JP-A-60-7.
As disclosed in Japanese Patent No. 0660, cold cathode fluorescent lamps have been mainly used.

On the other hand, also in the case of using a hot cathode type fluorescent lamp, as disclosed in, for example, Japanese Patent Laid-Open No. 60-72198, when the discharge current of the fluorescent lamp becomes 50% or less of the rated value, heat is generated. A method has been proposed in which the preheating current of the cathode is reduced to prolong the life.

[Problems to be solved by the invention]

Among the above-mentioned conventional examples, the method using a cold cathode fluorescent lamp has the following problems. That is, this cold cathode fluorescent lamp has a long life because there is no filament, but the luminous efficiency is lower than that of the hot cathode fluorescent lamp.
Moreover, at low temperature, it cannot be turned on unless it is heated with a heater.

In addition, the latter method of reducing the preheating current can obtain a long service life at the time of continuous lighting, but does not particularly consider the longevity at the time of frequently turning on and off the light. There is.

Further, in an automobile, when the ignition switch is operated and the engine is started, a large current flows to the starter. Therefore, as is well known, the voltage of the battery significantly decreases, and during this period, the fluorescent lamp for illuminating the liquid crystal display device Preheating of the hot cathode (filament) becomes insufficient.

However, at this time, if the fluorescent lamp is used in a high-luminance state in which a large discharge current flows to the hot cathode, deterioration of the cathode is remarkable and the life of the fluorescent lamp is shortened.

In particular, automobiles are sometimes used for delivery of various items such as milk and newspaper delivery. In such cases,
Engine start and stop are often repeated,
As a result, the conventional technique has a problem that it is difficult to keep the life of the fluorescent lamp for illuminating the liquid crystal display device long.

An object of the present invention is to provide a fluorescent lamp lighting control device for a liquid crystal display device for a vehicle, which can maintain a sufficiently long life even when it is used for lighting a liquid crystal display device for a vehicle in which engine start and stop are frequently repeated. To provide.

[Means for solving problems]

The above-mentioned problem is solved by suppressing the discharge current of the fluorescent lamp to be small for a predetermined time from the time when the ignition switch for starting the engine is turned on until the battery voltage is restored to the predetermined voltage.

[Work]

When the temperature of the cathode is insufficient, the discharge current is suppressed to suppress the occurrence of the spatter phenomenon at the cathode portion, and thus the life can be extended.

〔Example〕

Hereinafter, a fluorescent lamp lighting control device according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is an embodiment of the present invention and shows an example in which the present invention is applied to control lighting of a fluorescent lamp used for illuminating an instrument panel of an automobile using a liquid crystal display element.
Is a battery, 2 is an ignition switch, 3 is an inverter circuit for lighting and dimming the fluorescent lamp 4, and 5 is a control circuit for dimming the inverter circuit 3.

The control circuit 5 includes a microcomputer, and functions to output the duty signal a to the inverter circuit 3 by the input from the write switch 6 and the input from the variable resistor 7.

In addition, the inverter circuit 3, the transformer TR, the capacitor C
1-C4, transistors Q1-Q3, diodes D1-
D2 includes resistors R1 to R4, among which transistors Q1 and Q2, resistors R1R2R3, a capacitor C1, a transformer TR, and a blocking oscillator of a depletion type are configured. Then, when the ignition switch 2 is turned on, power is supplied and oscillation is started, whereby the AC voltage boosted by the transformer TR is supplied to the fluorescent lamp 4. At this time, current is also supplied to the filament of the fluorescent lamp 4 at the same time through the capacitors C2 and C3.

The discharge current of the fluorescent lamp 4 is controlled via the ballast capacitor C4, the diode D1 and the transistor Q3. When a discharge discharge flows in the opposite direction, it passes through the diode D2.

The transistor Q3 is ON / OFF controlled by the control circuit 5 via the resistor R4. And the transistor Q3
Discharge current flows only when is ON, and the O of signal a at this time
The discharge duty is controlled by the N duty, and the brightness can be adjusted by being proportional to the discharge current.

This dimming control is used for dimming control at night. That is, since the illumination of the instrument panel using the liquid crystal display element needs to be dimmed at night, the brightness of the illumination is reduced to 50% when the light switch 6 is turned on. Further, the variable resistor 7 is used so that the light can be freely adjusted between 50% and 10%. For this reason, the control circuit 5 determines the input signals from the switch 6 and the variable resistor 7, and outputs the duty signal a of ON duty corresponding to the control input.

FIG. 2 shows the characteristics of the inverter circuit 3,
As the brightness of the fluorescent lamp 4 decreases, the preheating current flowing through the filament of the fluorescent body 4 automatically increases.

Therefore, according to this embodiment, even when the discharge current is reduced by controlling the dimming to a brightness as low as 10%,
It is possible to stably maintain lighting and discharge.

As described above, the control circuit includes the microcomputer, takes in the ON-OFF state of the ignition switch 2, and performs the control operation according to the time chart of FIG.

First, when at time t ₀ and is ignition Tsu Chillon Sui Tutsi 2 or ON, the time has elapsed the time t ₀ from a predetermined time T
Until t ₁ is reached, the ON duty signal a is output so that the discharge current corresponds to a luminance of 10% of the rated luminance. Then, at time t ₁ when the time T has elapsed, the ON duty of the signal a is set to the value given by the variable resistor 7, or 10
The value should be 0%.

As a result, according to the above-described embodiment, immediately after the ignition switch 2 is turned on, the discharge current of the fluorescent lamp 4 has the rated value regardless of the states of the light switch 6 and the variable resistor 7.
It is suppressed to 10%, and after that, when the predetermined time T has passed and the preheating of the cathode will be sufficiently obtained, the
100% or light switch 6 and variable resistor 7
The control for shifting to the discharge current value given by is performed. At this time, the preheating current of the filament is increased during this time T, but this is
It is automatically given by the characteristics of the inverter circuit 3 described in the figure.

Fig. 4 shows the fluorescent lamp being started (lighted from the unlit state)
It shows the relationship between the value of the discharge current (luminance) given at the beginning and the number of flashing lifespans. From this characteristic, as the luminance immediately after startup increases, the number of flashes until the lifespan expires decreases. I understand. This is because when a high voltage is applied at the time of startup, a large amount of electrons collide with the filament of the fluorescent lamp at high speed to cause a spatter phenomenon, and the activator applied to the filament evaporates.
That is, it can be seen that the life becomes shorter when the blinking is repeated in the state where the amount of electrons is large and the brightness is high. And
From this, even if the flashing is repeated under 100% of brightness, if the brightness is lowered to 10% immediately after startup and then raised to 100%, In other words, if it is carried out as in the above embodiment, it can be seen that the number of times of blinking can be made equal to that at the time of blinking under the condition that the luminance is about 10% and a remarkable improvement can be obtained.

FIG. 5 is a flow chart showing the processing contents of the control circuit 5, including the nighttime dimming processing by the light switch 6, which starts when the ignition switch 2 is turned on.

When the process of FIG. 5 is started, first, at S1, the signal a
The N duty is set to 10%, and it is checked in S2 whether the processing time T has elapsed. If the result is NO, the process returns to S1.
Therefore, the control explained in FIG. 3 is obtained by the processing of S1 and S2.

The results of the in S2 is YES, i.e. shifts to the processing of the third Tara summer time t ₁ later in Figure S3 to S5, the check the ON-OFF state of Raitosuitsuchi 6, decrease in daytime and nighttime Enter light control. That is, any one of S4 and S5 is repeated by the process S3.

In the above embodiment, the inverter circuit 3 is used, and an increase in the filament preheating current at the time T in FIG. 3 and an increase in dimming etc. are automatically obtained by the characteristics shown in FIG. As a result, the preheating current is automatically increased by limiting the discharge current of the fluorescent lamp, which has the effect of simplifying the configuration.

Further, in the above embodiments, since the control circuit 5 including the micro computer is used, the necessary control can be obtained only by adding the software-like configuration, which can greatly contribute to the cost reduction. Of course, the present invention is not limited to this, and it goes without saying that an embodiment having a hardware configuration may be used.

Example of Invention

As described above, according to the present invention, the hot cathode fluorescent lamp is used, and since it is possible to maintain a sufficiently long life even if the blinking is repeated at a high frequency, the problems of the related art are eliminated and various Like a car used for the delivery of goods,
Even in an automobile in which the start and stop of the engine is frequently repeated, the deterioration of the cathode can be surely suppressed, and the life of the fluorescent lamp for illuminating the liquid crystal display device can be kept sufficiently long.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a fluorescent lamp lighting control device according to the present invention, FIG. 2 is a characteristic curve diagram showing characteristics of an inverter circuit, and FIG. 3 is a diagram showing an operation of the embodiment of the present invention. FIG. 4 is a characteristic curve diagram showing an example of the characteristic of the fluorescent lamp, and FIG. 5 is a flow chart showing the operation of the embodiment of the present invention. 1 ... Battery, 2 ... Ignition switch, 3 ...
… Inverter circuit, 4 …… Fluorescent lamp, 5 …… Control circuit, 6
...... Light switch, 7 ... Variable resistor.

Claims (1)

[Claims] 1. A fluorescent lamp lighting circuit of a liquid crystal display device for an automobile, which performs dimming control in a cathode preheating state, is provided with a control means for reducing the brightness of the fluorescent lamp to 10% of a rated value, for starting an engine. A fluorescent lamp lighting control device for an automobile liquid crystal display device, characterized in that the control means is operated only for a predetermined time after the ignition switch is turned on.