JPH05234694A - Fluorescent tube lighting device - Google Patents

Abstract

PURPOSE:To achieve a predetermined dimming by adding an starting control circuit to a dimmer circuit for a fluorescent tube lighting circuit which allows a fluorescent tube to light upon starting without dimming or maximum dimming and starts dimming after a certain period, that is, after the fluorescent tube fully lights. CONSTITUTION:The voltage of a DC power supply 4 is supplied to a fluorescent dimmer circuit 10 via a power supply switch 5. Once the switch 5 is activated, a transistor 12 stays on because electric currents flow through the transistor 21 of a fluorescent lighting start period dimmer control circuit 20 and the voltage of the DC power supply 4 is supplied to a fluorescent tube 1 through an inverter circuit 2 as it is. When the electric potential of a condencer C1 becomes about 0.6V after a given period of time, the transistor 21 is turned off and the transistor 12 is turned on or off by the output of a pulse generation circuit 13 to enter a normal dimming state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent tube lighting device, and more particularly, to a fluorescent tube suitable for use in a fluorescent tube device, such as a fluorescent tube used as a backlight in a liquid crystal display device or the like. Regarding lighting device.

[0002]

2. Description of the Related Art A fluorescent tube is used for a backlight of a liquid crystal display device or the like. However, since the fluorescent tube is turned on by a high voltage AC voltage, a DC / AC conversion circuit called an inverter circuit is used. Is converted into alternating current and applied. Furthermore, in order to make the brightness of the fluorescent tube variable (dimming), the applied voltage to the fluorescent tube is made variable and the current flowing through the fluorescent tube is controlled. If the voltage applied to the tube is lowered and it is attempted to illuminate, the characteristics at the time of illuminating may be deteriorated, which may cause adverse effects such as not illuminating or not illuminating at regular brightness.

As described above, a fluorescent tube is used as a backlight of a liquid crystal display device, but an inverter circuit as shown in FIG. 3 is used as a lighting circuit of the fluorescent tube. In FIG. 3, 1 is a fluorescent tube, 2 is an inverter circuit,
As is well known, this circuit applies a DC voltage of the DC power supply 4 to the inverter circuit 2 by the switch 3 and converts the DC voltage into an AC voltage by the inverter circuit 2. A high voltage AC voltage is applied to the fluorescent tube 1 to turn on the fluorescent tube 1. At this time, the fluorescent tube 1
Is proportional to the current flowing through the fluorescent tube 1. Therefore, in order to make the brightness of the fluorescent tube 1 variable, the current flowing in the fluorescent tube 1 may be made variable, and the voltage applied to the fluorescent tube 1 may be changed. As an example of the method of changing the voltage applied to the fluorescent tube 1, the switch 3 is periodically turned on / off to change the width of the on-time, that is, the total period of the lighting period and the extinguishing period is used as a basic period, A method in which the effective value of the voltage applied to the fluorescent tube 1 is changed by controlling the voltage applied to the inverter circuit according to the combination of the lighting period and the extinguishing period within the basic period, and the current flowing through the fluorescent tube 1 is changed to change the brightness. There is.

FIG. 4 is a block diagram for explaining an example of a conventional fluorescent tube lighting device with a light control device. In the figure, 5 is a power switch and 10 is a light control circuit. Three
The ON / OFF of the transistor 12 is controlled by the pulse from the pulse generating circuit 13 to control the voltage applied to the primary side of the inverter circuit 2 to control the voltage applied to the primary side of the inverter circuit 2. Two
It controls the current applied to the secondary side.
That is, by adjusting the position of the volume of the voltage variable resistor 11, the base voltage of the transistor 12 is controlled, the on / off of the transistor 12 is controlled, and the "high" period of the pulse voltage from the transistor 12 is controlled. The ratio of the "low" period is controlled to control the current applied to the secondary side of the inverter circuit 2.

FIG. 5 shows a transistor 1 when dimming is small.
2 shows the output voltage waveform of Fig. 2 (Fig. (A)) and the output voltage waveform of the transistor 12 when dimming is large (Fig. (B)), and as is well known, "high" period (lighting period) T ₁ and " The larger the ratio T ₁ / T ₂ to the low period (light-off period) T ₂ , the larger the dimming.

FIG. 6 is a detailed circuit diagram of the dimming circuit 10 shown in FIG. 4. In this case, when the power switch 5 is turned on,
As indicated by T in FIG. 7, since the dimming is started at the same time as the lighting of the fluorescent tube 1 is started, for example, if the dimming is set to the minimum by the volume 11, the lighting of the fluorescent tube 1 is performed. The dimming is started at the same time as the start, and a minimum current flows at the time of start, and it is difficult to turn on the light especially at low temperatures.

[0007]

As described above, when dimming is performed when the fluorescent tube is lit, the voltage applied to the fluorescent tube is changed to control the current flowing through the fluorescent tube. When trying to light the fluorescent tube with the minimum, there may be a problem that the fluorescent tube does not light or does not light with correct brightness. Especially, when the ambient temperature is low, such a problem is likely to occur.

[0008]

In order to solve the above problems, the present invention provides an inverter circuit for converting a DC voltage into an AC voltage, and an ON / OFF control for the DC voltage applied to the inverter circuit. Then, in a fluorescent tube lighting device having a dimming circuit for controlling the output current of the inverter circuit, at the start of lighting, the ON period of the dimming circuit is made sufficiently long, and the ratio of the ON period and the OFF period after a lapse of a predetermined time. Is provided so that the ratio of the lighting period at the time of starting the fluorescent tube is made sufficiently larger than that at the steady state.

[0009]

[Operation] A control circuit at the time of start is added to the dimming circuit,
When the fluorescent tube is started, the lamp is turned on with maximum dimming or without dimming, and after a certain period of time, the lamp is completely turned on and then dimming is started to set a predetermined dimming.

[0010]

FIG. 1 is an electric circuit diagram for explaining an embodiment of a fluorescent tube lighting device according to the present invention, in which parts having the same functions as those of the prior art described in FIGS. 3 and 5 are shown. Are given the same reference numerals as in FIG. As described above, according to the present invention, in order to solve the problem of lighting when the dimming is started at the minimum, the dimming is not started or the dimming is started at the maximum, and the predetermined dimming is performed after the starting. The circuit 20 is a fluorescent tube lighting start dimming control circuit, that is, a circuit that does not perform dimming for a certain period when the fluorescent tube is started,
That is, in FIG. 1, a circuit 20 is a circuit added according to the present invention, and this circuit 20 is a circuit that does not perform dimming for a certain time when the fluorescent tube 1 is started. Now, the power switch 5 is turned on. Then, immediately after the power switch 5 is turned on, the base potential of the transistor 21 of the circuit 20 is the GND potential, so a current flows through the transistor 21 and the resistor R ₁ to the capacitor C _1, and as a result, the transistor 21 is turned on. Therefore, the transistor 12 is turned on (see t _{0 in} FIG. 2), and the maximum dimming (or no dimming) occurs. In this state, when electric charge is stored in the capacitor C ₁ and the voltage between the base and emitter of the transistor 21 exceeds about 0.6v, the transistor 21 is turned off and the output of the pulse generation circuit 13 starts to move (t in FIG. 2). ₁ ), dimming is effective. That is, according to the present invention, when the fluorescent tube 1 is turned on, the dimming is maximized during the period T ₀ shown in FIG.

[0011]

As is apparent from the above description, according to the present invention, even when the dimming of the fluorescent tube is set to the minimum, the fluorescent lamp is always turned on correctly. In particular, even when the dimming is minimum and the ambient temperature is low, the engine is started under the best conditions, so that it is possible to solve problems such as no lighting or no lighting at regular brightness.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining an embodiment of a fluorescent tube lighting device according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the circuit shown in FIG.

FIG. 3 is a diagram for explaining the operation principle of the fluorescent tube lighting device.

FIG. 4 is a diagram for explaining an example of a conventional fluorescent tube lighting device.

5 is a main part waveform diagram for explaining the operation of the circuit shown in FIG. 4;

FIG. 6 is a detailed electric circuit diagram for explaining an example of a conventional fluorescent tube lighting device.

FIG. 7 is a waveform diagram for explaining the operation of the circuit in FIG.

[Explanation of symbols]

1 ... Fluorescent tube, 2 ... Inverter, 4 ... DC power source, 5 ... Power switch, 10 ... Fluorescent tube lighting circuit, 20 ... Fluorescent tube lighting start dimming control circuit.

Claims (1)

[Claims] 1. A fluorescent tube having an inverter circuit for converting a DC voltage into an AC voltage, and a dimming circuit for controlling an output current of the inverter circuit by controlling ON / OFF of the DC voltage applied to the inverter circuit. The lighting device has a means for making the ON period of the dimming circuit sufficiently long at the start of lighting and setting a ratio of the ON period and the OFF period to a desired ratio after a lapse of a predetermined time.