JPH063380B2 - Fluorescent display tube drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a drive device for a fluorescent display tube used in an automobile or the like, and in particular, a fluorescent device having two first and second light emitting parts of different emission colors. The present invention relates to a display tube that adjusts the brightness of both light emitting portions when dimming.

[Conventional technology]

Conventionally, there is a fluorescent display tube (hereinafter referred to as FLT) used in an instrument panel portion for displaying meters such as a speedometer and a tachometer. In recent years, in addition to blue green, yellow is used to improve its visibility. , Amber, red, etc. are developed to perform multicolor display.
Usually, in an FLT in which a blue-green light emitting portion and another color light emitting portion are mixed, a driving IC that generates the same drive voltage in order to adjust the brightness of both when normal light emission is performed.
Could not be used. Therefore, as shown in FIG. 4, switch means (transistors Tr ₁ and Tr ₂ ) for applying a drive voltage higher than the drive voltage of the blue-green light emitting portion to the drive voltage of the other color light emitting portions is provided.

[Problems to be solved by the invention]

When such a fluorescent display tube is used, it is necessary to increase the luminance of light emission in the daytime because the surroundings are bright and reduce the luminance to decrease the nighttime at night. However, since the daytime brightness of the FLT is considerably high, it is necessary to reduce the brightness at a large ratio at night, and the blinking ratio of the FLT is decreased at night by a dimming pulse signal of a predetermined frequency. Since the lighting pulse time at this time is around 10 μs, the transistor T
Due to the delay of r ₁ and Tr ₂ , the extinction ratios (T ₁ / T, T ₂ / T) of the blue-green light emitting part and other color light emitting parts are different,
There is a problem that other color light emitting parts are brighter than the blue green light emitting parts.

Therefore, an object of the present invention is to provide an F having the first and second light emitting portions.
A fluorescent display tube which is a driving device for an LT and is capable of dimming both of the first light emitting part and the second light emitting part while preventing the dimming ratios of the first light emitting part and the second light emitting part from being different at the time of dimming at night. It is to provide a drive device.

[Means for solving problems]

The present invention provides first and second means for solving the above problems.
A driving device of a fluorescent display tube having first and second light emitting portions which are respectively driven by different voltages, the first and second lines being respectively connected to the first and second light emitting portions. Driving means for sending a driving pulse signal of a voltage, a Hi level signal for normal lighting, and a dimming pulse signal of high frequency for dimming; and the second light emitting section provided in the middle of the second line. And a switch means for applying a second voltage to the first and second lines, and a pulse width of a dimming pulse signal at the time of dimming, which is provided on at least one of the first and second light emitting units, is made to match. And a correction means for causing the correction.

〔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 denotes a fluorescent display tube drive circuit, which drives a color segment 5a (for example, yellow) which is the second light emitting portion and a blue green segment which is the first light emitting portion. The drive circuit 1 inputs a dimming signal with a predetermined duty ratio at a predetermined frequency (20 to 50 KHz) to the BLK terminal, and the dimming signal is high (H).
When the level is low, the low (L) level is output to the output port, and when the dimming signal is low (L) level, the drive voltage V ₁
The high (H) level of is output to the output port. The duty ratio is the H level time T ₁ (T ₁ / T) with respect to the cycle T.
Say. This dimming signal is interlocked with a lighting switch (not shown) that is turned on at night, and is generated when this switch is turned on. Reference numeral 2 is a microcomputer, which calculates a control signal based on inputs of a vehicle speed sensor, an engine cooling water temperature sensor, a fuel sensor, etc., and outputs it to a drive circuit 1, and the drive circuit 1 responds to the signal from the microcomputer 2. Drive the segment to be illuminated.

The blue-green segment 5b of the fluorescent display tube 5 is directly driven by the output signal of the drive voltage V ₁ from the drive circuit 1. Further, the color segment 5a has a driving voltage V
Transistors Tr ₁ and Tr ₂ serving as switch means for applying ₂ (> V ₁ ), and a correction circuit 3 for delaying the rising of the pulse signal for turning on the transistor Tr ₁ for a predetermined time and correcting the pulse signal.
Are driven by the drive circuit 1.

The correction circuit 3 has an inverter I for the purpose of inverting the output.
It is composed of N, resistors R ₁ and R _2, and a transistor Tr ₃ for compensating for the damage of the transistors Tr ₁ and Tr ₂ . FIG. 2D shows the pulse output from the circuit 3, and by setting the resistance R ₂ to a predetermined resistance value, the delay time T ₃ when this pulse output waveform becomes H level and the transistors Tr ₁ and Tr The delay time t _{4 of 2} is set to be substantially equal.

The operation will be described based on the above configuration.

Now, during daytime driving, lighting switch (not shown)
When is off, the dimming signal is not generated and the L level is input to the BLK terminal of the drive circuit 1. Since the drive voltage V ₁ of the this order from the drive circuit 1 to the blue-green segment 5b is Hi level not any modulation, blue green segment 5b emits light with the highest intensity. Similarly, since the voltage V ₂ applied to the emitter of the transistor Tr ₂ is applied to the color segment 5a without being modulated, the color segment 5a emits light with the highest brightness.

Next, when the lighting switch is turned on during night driving or the like, at this time, a predetermined frequency (20
A dimming signal having a predetermined duty ratio (T ₁ / T) of ˜50 KHz) is input to the BLK terminal of the drive circuit 1. With this dimming signal, the drive circuit 1 modulates its output signal (voltage V ₁ ) into a dimming pulse signal with a constant dimming rate as shown in FIG. 2B. The blue-green segment 5b directly driven by this dimming pulse signal reduces the light emission time to T ₁ and emits dimmed light.

Further, the color segment 5a is corrected by the drive circuit 1, the correction circuit 3, and the transistors Tr ₁ and Tr ₂ so as to emit light at a predetermined extinction rate. Here, since the ON time (T ₁ ) of the dimming pulse signal during dimming is around 10 μs,
The influence of the delay of the transistors Tr ₁ and Tr ₂ cannot be ignored. The switch delay of the transistors Tr ₁ and Tr ₂ can be ignored when the transistors are turned on, but it is turned off.
In this case, it takes about 2 to 3 μs due to the charge accumulation time. This delay is corrected by the correction circuit 3. That is, the dimming pulse signal from the drive circuit 1 is transmitted to the inverter I
It is inverted by N (FIG. 2C) and input to the base terminal of the transistor Tr ₃ . The voltage of this inverted pulse signal is L
When the level becomes the level, the transistor Tr ₃ is turned off with a delay of a predetermined time t ₃ due to the charge accumulation time, so that the collector terminal of the transistor Tr ₃ becomes H level with a delay of the predetermined time t ₃ , but an inversion pulse. When the signal becomes H level, the transistor Tr ₃ is turned on immediately, so that the collector terminal of the transistor Tr ₃ is immediately turned to L level.
Become a level. Therefore, the H level time of the collector terminal voltage of the transistor Tr ₃ becomes shorter than the dimming pulse signal waveform from the drive circuit 1 by the predetermined time t ₃ . Therefore, by making the switching delay time t _{4 of} the transistors Tr ₁ and Tr ₂ substantially equal to the correction time t ₃ ,
Since color segments 5a of the light emission pulse time width T ₂ and Blue green segment 5b and an emission pulse time width T ₁ can be made substantially equal, both segments 5a, 5
The dimming rate (T ₁ / T, T ₂ / T) of b can be adjusted to the same dimming level to emit dimmed light. The switching delay of the inverter IN is negligible as compared with the transistor.

Next, a second embodiment will be described with reference to FIG. In the second embodiment, as the correction circuit 3 of the previous embodiment, two inverters IN ₁ and IN ₂ for inverting one output signal, a diode D,
A correction circuit 3'comprising a resistor R and a capacitor C is used. Explaining the operation at this time, the light emission pulse signal from the drive circuit is inverted by the inverter IN ₁ .
This inverted signal passes through a circuit including a resistor R, a capacitor C, and a diode D, is inverted again by the inverter IN ₂ , and is input to the base terminal of the transistor Tr ₁ . When the voltage of the inverted pulse signal from the inverter IN ₁ becomes H level, the capacitor C is immediately charged by the current passing through the diode D, and the input terminal of the inverter IN ₂ immediately becomes H level, but the inverted pulse signal becomes L level. When the voltage reaches the level, the electric charge of the capacitor C is discharged through the resistor R, so that the input terminal of the inverter IN ₂ is delayed to become the L level. Therefore, when the inverter IN ₂ inverts the signal, the base terminal voltage of the transistor Tr ₁ is delayed from becoming H level, and when it becomes L level, it immediately becomes L level. Accordingly, H-level time of the base terminal voltage of the transistor Tr ₁ becomes to shrink compared to the pulse signal waveform from the driving circuit 1, so that the delay due to the transistors Tr _1, Tr ₂ is corrected.

First described above, in the second embodiment, since the number of color segments 5b of the fluorescent display tube 5 is less than the number of blue-green segments 5a, transistor Tr _1, Tr ₂ of the correction circuit 3 for correcting the switching delay, 3'is provided in each path connected to the color segment 5b. Therefore, the correction can be performed with a small number of correction circuits 3 and 3 '.

When the number of blue segments 5b is less than the number of color segments 5a in the above-described embodiment, they are connected to the blue green segments 5b. For each line,
A correction circuit for extending the dimming pulse signal width may be provided to correct the switching delay of the transistors Tr ₁ and Tr ₂ .

〔The invention's effect〕

As described above, according to the present invention, when the emission control of the fluorescent display tube having the first and second light emitting portions respectively driven by the first and second different voltages is controlled by the dimming pulse signal. By correcting the pulse widths of the dimming pulse signals applied to the two light emitting units so that they match, it is possible to control the dimming of the first and second light emitting units during dimming while maintaining the harmony of the co-owners. Therefore, there is an excellent effect that it is possible to perform a display with good brightness and good appearance.

[Brief description of drawings]

1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram showing waveforms at respective points in the circuit diagram shown in FIG. 1, and FIG.
FIG. 4 is a circuit diagram showing the second embodiment, FIG. 4 is a conventional circuit diagram,
FIG. 5 is a waveform diagram showing waveforms at various points in the circuit diagram shown in FIG. 1 ... Fluorescent display tube drive circuit, 2 ... Microcomputer, 3 ... Correction circuit, 5 ... Fluorescent display tube, 5a ... Color segment, 5b ...
Blue green segment.

Claims (1)

[Claims] 1. A driving device for a fluorescent display tube having first and second light emitting portions which are respectively driven by different first and second voltages, each of which is connected to the first and second light emitting portions. The driving pulse signal of the first voltage is sent to the first and second lines, and the basic pulse signal is sent during normal operation, and the dimming pulse signal whose on-time is shorter and whose frequency is higher than that of the basic pulse signal during dimming. Driving means, switch means provided in the middle of the second line for applying a second voltage to the second light emitting section, and provided in at least one of the first and second lines to provide the first and second lines. (2) A driving device for a fluorescent display tube, comprising: a correction unit configured to match pulse widths of dimming pulse signals applied to the light emitting unit at the time of dimming.