JPH0731271Y2 - Fluorescent tube display - Google Patents

Description

[Detailed description of the device] [Industrial applications]

The present invention relates to a fluorescent tube type display device in which a display signal is supplied to a display electrode and a pulsed or alternating heating current is supplied to a filament electrode.

[Prior art]

As a conventional fluorescent tube type display device, there is one as shown in FIG. 7, for example. That is, in the figure, reference numeral 1 is a fluorescent display tube for displaying a vehicle speed, a traveling distance, etc., and has a filament electrode 1a, a grid electrode 1b and a segment electrode 1c. Reference numeral 2 denotes a fluorescent tube boosting power source which is a filament drive circuit for driving the filament electrode 1a, and is composed of a filament power source section and a filament center tap bias power source section, and outputs a heating current to the filament electrode 1a.
Reference numeral 3 is a drive circuit for driving the segment electrodes 1c. The drive circuit 3 includes, for example, a display data transfer signal which is signal-processed by a vehicle speed sensor (not shown), a lighting switch (not shown), and a dimming volume ( A PWM dimming signal according to the ambient brightness (not shown) is input. Reference numeral 5 is a battery, and 6 is an ignition switch. Next, the operation will be described. When a voltage is applied to the fluorescent display tube 1 from the fluorescent tube boosting power source 2, the filament electrode 1a emits electrons. The electrons are accelerated by the grid electrode 1b and travel toward the segment electrode 1c. On the other hand, the segment electrode 1c is on / off controlled based on the display data transfer signal and the PWM dimming signal, and when the segment electrode 1c is turned on, accelerated electrons from the filament electrode 1a reach and emit light. Become.

[Problems to be solved by the device]

However, in such a conventional fluorescent tube type display device, the filament drive frequency F _f and the dimming PWM frequency F _D
Since it was controlled asynchronously with, the interference condition is such that the dimming PWM frequency F _D is divisible by the filament driving frequency F _f , and the on-duty of the PWM waveform is controlled to a small value to achieve 1 / F _f (filament period). When the on-pulse width is reduced to several times or less, the filament frequency F _f
However, there is a problem in that the display brightness alternates between light and dark (beat) due to the frequency interference between the light control PWM frequency F _D and the light control PWM frequency F _D. The present invention has been made in view of such conventional problems, and an object thereof is to provide a fluorescent tube type display device in which frequency interference between the filament frequency and the dimming PWM frequency is eliminated.

[Means for Solving the Problems]

In the fluorescent tube type display device according to the present invention, a filament drive circuit for supplying a heating current to a filament electrode is provided with a frequency sweep circuit so that the heating current periodically repeats fluctuations within a predetermined frequency width. .

[Action]

In the fluorescent tube type display device according to the present invention, the heating current to the filament electrode is cyclically repeated within a predetermined frequency width by a frequency sweep circuit.
It is possible to eliminate the alternating phenomenon of the brightness of the display brightness caused by the frequency interference between the M frequency and the filament driving frequency.

【Example】

The invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 2 is an operation explanatory diagram of the frequency sweep circuit shown in FIG. 1. In FIG. 1, the same or equivalent components as in FIG. The same reference numerals are given and duplicate description is omitted. In the figure, 10 is a booster power supply for a fluorescent tube, which is a filament drive circuit that outputs a heating current to the filament electrode 1a, and is composed of a ringing choke converter type power supply circuit. 11 is a frequency sweep circuit connected to the center tap terminal 10a of the booster power supply 10 for the fluorescent tube. This frequency sweep circuit 11 is a load resistor.
Triangle wave generation circuit that sweeps the output voltage with a predetermined voltage width of 12
It is composed of 13 and. Reference numeral 14 is a microcomputer circuit which is a signal processing circuit.
Reference numeral 14 is an A / D converter 16 for converting the dimming signal from the dimming volume 15 which indicates the dimming rate into a digital amount, and a memory for storing the waveform data of the dimming characteristic for daytime and the dimming characteristic for nighttime Circuit 17, a waveform generation circuit 19 for generating a PWM waveform pulse based on the output value of the A / D converter 16 and the dimming characteristic for daytime or the dimming characteristic for night selected by the lighting switch 18, for example, the vehicle speed An arithmetic circuit 20 for arithmetically processing and decoding a vehicle speed signal from a sensor (not shown). Next, the operation will be described. Ringing choke converter type booster power supply for fluorescent tubes
The oscillation frequency of 10 changes with changing load conditions. That is, since the triangular wave generating circuit 13 outputs a voltage waveform as shown in FIG. 2, the load state of the resistor 12 changes continuously. For this reason, the booster power supply 10 for the fluorescent tube has a frequency that moves to a frequency corresponding to the amount of change in the load with respect to a change in the load, and the oscillation frequency also changes continuously. As described above, the blanking of the drive circuit 3 is performed by continuously changing the oscillation frequency of the booster power supply 10 for the fluorescent tube, that is, by sweeping the filament drive frequency F _f at a certain repetition frequency F _s in the width of ΔF _f. The relationship between the dimming PWM frequency F _D input to the terminal BI and the filament drive frequency F _f is that the frequency interference condition that F _f / F _D is divisible is not uniquely established as in the past, and there is no interference from the interference state. The state will exist, which is equivalent to the state where interference does not occur. In addition, under the condition of F _f << F _D << F _s , the larger the width ΔF _f of fluctuation of the filament drive frequency is, the larger PW
The ON pulse width of the M dimming signal can be reduced. According to the experiment, F _f = 80 KHz, F _D = 1 KHz, F _s = 256 Hz and ΔF _f =
At 30 KHz, the on-pulse width is 4 μs or less and the beat of the display luminance cannot be visually recognized, but at ΔF _f = 0 KHz, the on-pulse width is up to 50 μs, and when it is less than that, the display luminance beat is visually recognized. Next, a second embodiment will be described with reference to FIG. FIG. 3 shows an embodiment in which a separately excited type is used as the booster power source 21 for a fluorescent tube, and a triangular wave generating circuit 23 is connected to the control input of a voltage controlled oscillator circuit 22 to form a frequency sweep circuit 24. is there. In the filament power supply unit 21a, the input voltage of the voltage controlled oscillator circuit 22 is swept with a triangular wave, so if the input voltage-output frequency characteristic shown in FIG.
As shown in FIG. 5, the filament driving frequency F _f will be swept. In the above embodiment, the filament drive frequency F _f is swept using the triangular wave generating circuit, but the same effect as the above embodiment can be obtained by using the sawtooth wave generating circuit instead of the triangular wave generating circuit. Play. Further, as the booster power source for the fluorescent tube of the above embodiment, as shown in FIG. 6, only the filament power source unit may be constituted by an LC resonance type inverter (self-exciting type). In this case, the frequency sweep circuit is connected so as to continuously change the C condition of the LC resonance circuit, for example.

[Effect of device]

As described above, according to the present invention, a filament driving circuit that outputs a heating current, a signal processing circuit that outputs a display signal corresponding to a pulse width corresponding to a desired display brightness, and the filament are provided. In a fluorescent tube type display device including a fluorescent display tube having a filament electrode to which a heating current is supplied from a drive circuit and a display electrode to which a display signal from the signal processing circuit is supplied, in a predetermined frequency width Since the fluorescent tube type display device is characterized in that the filament drive circuit is provided with a frequency sweep circuit so as to output a heating current that repeatedly repeats fluctuations,
The frequency interference between the filament driving frequency and the dimming PWM frequency can be eliminated, so that the beat of the display brightness can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a fluorescent tube type display device according to the present invention, FIG. 2 is an operation waveform diagram of the frequency sweep circuit of FIG. 1, and FIG. 3 is a fluorescent tube type display of the present invention. Second of the device
FIG. 4 is a circuit configuration diagram showing an embodiment, FIG. 4 and FIG. 5 are operation explanatory diagrams of the frequency sweep circuit of FIG. 3, and FIG. 6 is a circuit configuration diagram showing a third embodiment of the fluorescent tube type display device of the present invention. FIG. 7 is a circuit configuration diagram showing an example of a conventional fluorescent tube type display device. 1 ... Fluorescent display tube, 1a ... Filament electrode, 10 ... Filament drive circuit, 11 ... Frequency sweep circuit, 14 ... Signal processing circuit.

Claims (1)

[Scope of utility model registration request] 1. A filament drive circuit for outputting a heating current, a signal processing circuit (14) for outputting a display signal corresponding to a pulse width corresponding to a desired display brightness, and a heating current from the filament drive circuit. A fluorescent tube type display device comprising a filament electrode (1a) supplied and a fluorescent display tube (1) having a display electrode supplied with a display signal from the signal processing circuit, wherein a cycle is provided between predetermined frequency widths. A fluorescent tube type display device characterized in that a frequency sweeping circuit (11) is provided in the filament drive circuit so as to output a heating current that repeatedly fluctuates.