JPH063379B2 - Fluorescent display tube dimmer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a light control device for a fluorescent display tube used in an automobile or the like.

[Conventional technology]

Conventionally, there is a fluorescent display tube (hereinafter referred to as FLT) used to display meters such as a speedometer and a tachometer. In recent years, in order to improve visibility, in addition to blue green, yellow, Multicolor color display is performed by emitting light from amber, red and the like. Normally, in an FLT in which a blue-green display section and other colors are mixed, the driving voltage of the other color display section is higher than the driving voltage of the blue-green display section, so a driving IC that generates the same voltage is used. It cannot be used directly. (Blue-green drive voltage: 20V, other color drive voltage: 3
Therefore, conventionally, as shown in FIG. 5, a driving circuit including transistors Tr ₃ and Tr ₄ is added to another color display section.

[Problems to be solved by the invention]

As described above, when the FLT light emitting element is used in the instrument panel portion, it is necessary to increase the display brightness because the surroundings are bright in the daytime and reduce the brightness at night to reduce the nighttime. However, since the daytime brightness of the FLT is quite high, it is necessary to reduce the brightness at a large rate at night. Therefore, at night, the blinking ratio of the FLT is reduced by a pulse signal for a dimming signal having a constant frequency. Lighting pulse time at this time is 1
Since it is around 0 μs, the extinction ratio (T ₁ / T, T ₂ / T) of the blue-green display part and other color display parts is different due to the delay of the transistors Tr ₃ and Tr ₄ , and it is different from the blue-green display part. However, there is a problem that the color display section of is bright.

Therefore, an object of the present invention is a dimming device for a fluorescent display tube having a first light emitting portion driven by a first voltage and a second light emitting portion driven by a second driving voltage different from the first voltage. And a dimming device for a fluorescent display tube capable of dimming both the first light emitting part and the second light emitting part by preventing different dimming rates at the time of dimming at night. To do.

[Means for solving problems]

The present invention provides at least two means for solving the above problems.
A dimming device for a fluorescent display tube having first and second light emitting parts that are respectively driven by a first voltage and a second voltage so as to emit a color, the dimming means generating a dimming signal by an external operation. And supplying a transmission pulse signal to each of the first and second light emitting units, and changing the duty ratio of the transmission pulse signal to a predetermined value when the dimming signal is input,
And a dimming driving unit for dimming the second light emitting unit, and a voltage switching unit for switching the first driving voltage of the first light emitting unit to a predetermined low voltage when the dimming signal is input. Characterize.

〔Example〕

 A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a circuit diagram showing the first embodiment, and FIG. 2 is a waveform diagram showing waveforms of respective parts of the circuit diagram shown in FIG. Reference numeral 1 is a lighting switch, which is turned on at night to turn on a night illumination light (not shown) and generate a dimming signal. Reference numeral 2 is an oscillation circuit that generates an oscillation pulse signal with a predetermined duty ratio at a predetermined frequency (20 to 50 KHz) when the lighting switch 1 is turned on. Incidentally, a not-shown rheostat is connected to the oscillation circuit 2, and the oscillation circuit 2 is connected from the rheostat. Pulse signal (variable duty ratio at about 200 Hz) and the predetermined frequency (20 to 50 KHz) are superposed. This oscillation pulse signal is called a dimming signal, and the duty ratio is lighting time (T ₁ ) / cycle (T). 3 is a microcomputer, which calculates a control signal based on inputs from a vehicle speed sensor, an engine cooling water temperature sensor, a fuel sensor, etc., and drives a fluorescent display tube (FLT) drive IC.
Output to.

The FLT driving IC 4 is a driving circuit that causes the blue-green segment 5a serving as the second light emitting portion of the fluorescent display tube 5 to emit light. A dimming signal from the oscillation circuit 2 is input to the FLT driving IC 4, and when the dimming signal is at a high (H) level, the FLT driving IC 4 outputs a low (L) level,
When the dimming signal is at the L level, the H level of the output V ₁ is output. 6 is a voltage switching circuit, which is a transistor Tr ₁
˜Tr ₄ and Zener diode Z _D , and switches the driving voltage of the color segment 5b to V ₂ or V ₃ . The transistor Tr ₂ is connected to the voltage V ₂ (> V ₁ ), and the transistor Tr ₁ is connected to the lighting switch 1. When the Zener diode Z _D is lighting switch 1 is ON, to create a color segment 5b luminance adjustment voltage V ₃ of the first light emitting portion to regulate the voltage V ₃ (<V _2).

The operation will be described based on the above configuration.

Now, during daytime operation, when the lighting switch 1 is off, the dimming signal is not generated because the switch 1 is not turned on. Further, since the oscillation circuit 2 is not supplied with power for oscillation, its output is at L level. Therefore, the driving voltage from the FLT driving IC 4 to the blue green segment 5a of the FLT 5 is not modulated at all, so that the blue green segment 5a lights up with the highest brightness. Further, since the dimming signal is not input to the voltage switching circuit 6, the transistor Tr
₁ is turned off, and the voltage V ₂ is applied as it is to the emitter of the transistor Tr ₂ . Therefore, the color segment 5b of the FLT 5 is driven by the voltage V ₂ and lights up with the highest brightness.

Next, the case where the lighting switch 1 is turned on during night driving will be described. In this state, the oscillation circuit 2 receives the dimming signal and oscillates (20 to 50 KHz) to generate a dimming signal. The oscillator circuit 2 actually forms a dimming signal by superimposing pulse signals (about 200 Hz) from a rheostat (not shown), but FIG. 2 (a) shows a predetermined problem which is a problem in this embodiment. Frequency (20-50KH
The part of the extinction signal of z) is shown. The oscillation pulse signal causes the FLT driving IC 4 to modulate the voltage applied to the blue-green segment 5a of the FLT 5 to a constant dimming rate as shown in FIG. 2 (b), so that the lighting time of the blue-green segment 5a ( T ₁ ) is decreased and the dimmed light is turned on. At the same time that the lighting switch 1 is turned on, the dimming signal is input to the voltage switching circuit 6 and the transistor Tr ₁ is turned on. Therefore, the Zener diode Z _D regulates the drive voltage to V ₃ (<V ₂ ). Therefore, the voltage applied to the color sag 5b of the FLT 5 decreases from the voltage V ₂ applied to the normal color sag 5b to V ₃ when the lighting switch 1 is turned on, as shown in FIG. 2 (c). Here, the transistors Tr ₃ and Tr ₄ connected between the FLT driving IC 4 and the color segment 5b are
There is a delay with respect to the dimming signal whose frequency is high and the lighting time is around 10 μs. Therefore, color segment 5
When the voltage applied to b is constant at V ₂ , the extinction rate of the color segment 5b and the extinction rate of the blue green 5a differ, and the color segment 5b becomes too bright. However, at the time of dimming in the present embodiment, the voltage applied to the color segment 5b is reduced from V ₂ to V ₃ by the Zener diode Z _D of the voltage switching circuit 6, and the voltage is reduced by the delay of the transistors Tr ₃ and Tr _4. It is possible to correct the change in light rate.

The relationship between the voltages V ₂ and V ₃ at this time is that the transistor T
Delay of r ₃ and Tr ₄ and each segment 5a, 5 of FLT5
It is set by the relationship between the brightness of b and the drive voltage. That is, F
Since the brightness of LT5 is proportional to the 5/2 power of the driving voltage, if the extinction ratio of the blue-green segment 5a is ¼ of the daytime, the transistors Tr ₃ and Tr will be reduced as shown in FIG. _If the extinction rate of the color segment 5b due to the delay of ₄ becomes 1.5 / 4, the condition that the brightness of both is the same: 1/4 = 1.5 / 4 × (V ₃ / V ₂ ) ^5/2 V ₃ It should be set to = 0.85V ₂ . As described above, when the light is dimmed, the voltage applied to the color segment 5b is decreased from V ₂ to the predetermined voltage V ₃ , so that the transistor T
If the change in the extinction ratio due to the delay of r ₃ and Tr ₄ is corrected, the extinction ratio of the blue green segment 5a and the color segment 5b can be made the same.

Next, another embodiment will be described. Figure 3 is a voltage switching circuit 6 ', in which using the relay 7 in place of the Zener diode Z _D. Voltage switching circuit 6 ', when the transistor Tr ₁ is turned on, the relay 7 is switched from the voltage V ₂ to a predetermined voltage V _3, to lower the voltage applied to the color segment 5b. As described above, another configuration may be used as long as it is a voltage switching circuit that lowers the driving voltage of the color segment 5b to a predetermined voltage during dimming. FIG. 4 shows three color segments, for example, blue green segment 5a and yellow green (color) segment 5.
One of the display modes for displaying the engine rotation speed is shown by the display combining b and the red segment 5b '.
In particular, in such a display mode, when the dimming ratios of the blue green segment 5a and the yellow green segment 5b at the time of dimming are different, the dimming of both segments becomes unbalanced and the visibility of the display deteriorates. . Therefore, when the present invention is applied to the display form shown in FIG. 4, it is possible to display a good balance even when the light is dimmed.
In addition, as such a display form, there are a vehicle speedometer, a tachometer, a fuel gauge, a thermo gauge, and the like.

[Effect of device]

As described above, according to the present invention, the first
The light emitting section and the second light emitting section are appropriately dimmed, and it is possible to perform suitable light control in which the brightness balance between the two is achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram showing waveforms at various points in the circuit diagram shown in FIG. 3, FIG. 3 is a circuit diagram showing another embodiment, and FIG. 4 is a form diagram showing one display form of a fluorescent display tube. The figure shows the conventional circuit diagram, No. 6
The drawing is a waveform diagram showing waveforms at various portions of the circuit diagram shown in FIG. 1 ... lighting switch, 2 ... oscillation circuit, 4 ... fluorescent display tube drive IC, 5 ... fluorescent display tube, 5a ... blue green segment, 5b ... color segments, 6,6 '... voltage switching circuit, _{Z D} ... Zener diode, 7 ... Relay.

Claims (1)

[Claims] 1. A first device for emitting at least two colors,
A dimming device for a fluorescent display tube having first and second light emitting parts each driven by a second voltage, the dimming device generating a dimming signal by an external operation, and the first and second light emitting devices. The transmission pulse signal is supplied to each of the parts, and when the dimming signal is input, the duty ratio of the transmission pulse signal is changed to a predetermined value to change the duty ratio of the first and
And a dimming driving unit for dimming the second light emitting unit, and a voltage switching unit for switching the first driving voltage of the first light emitting unit to a predetermined low voltage when the dimming signal is input. A dimmer device for a fluorescent display tube.