JP2002108263A - Vacuum fluorescent display driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always keep effective voltage to be supplied to a filament constant irrespective of unevenness of elements, temperature changes and variations in power supply voltage in DC pulse driving of the filament of a vacuum fluorescent display. SOLUTION: The pulse width and voltage to be supplied to the filament is fed back to a microcomputer, and the width of the pulses outputted from the microcomputer is varied by the fed-back value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to DC pulse driving of a filament of a fluorescent display tube, and more particularly to a filament driving device for a fluorescent display tube suitable for supplying a constant effective voltage to the filament.

[0002]

2. Description of the Related Art Conventionally, a filament of a fluorescent display tube is DC.
In the case of driving with the pulse of (1), a constant pulse width was always output from the microcomputer to supply an effective voltage to the filament.

[0003]

However, in the conventional driving circuit, the microcomputer always outputs a constant pulse width and supplies an effective voltage to the filament. However, the effective voltage actually applied to the filament is
Since it fluctuates due to the responsiveness and variation of the element to be driven, temperature fluctuations, and power supply voltage fluctuations, the effective voltage supplied to the filament may fall outside the rated voltage of the filament even if the effective voltage supplied to the filament deviates from the rated voltage of the filament. There was no means for correcting the effective voltage. As a result, the display of the fluorescent display tube becomes dark, the filament becomes red, and the life of the fluorescent display tube is shortened.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide, in DC pulse driving of a filament of a fluorescent display tube, responsiveness, variation, temperature variation, and the like of a driving element. Even if there is a fluctuation in the power supply voltage, a constant effective voltage is always supplied to the filament.In particular, the pulse width and voltage supplied to the filament are detected by the microcomputer, and the pulse width output from the microcomputer is varied. The purpose is to always keep the effective voltage supplied to the power supply constant.

[0005]

In order to achieve the above object, a first aspect of the present invention is to make the pulse width of a voltage pulse applied to a filament detectable by a control means, and based on the detected pulse width. By varying the pulse width of the pulse output from the control means, a constant effective voltage can always be supplied to the filament of the fluorescent display tube regardless of the response, variation and temperature fluctuation of the driving element.

According to a second aspect of the present invention, the voltage applied to the filament is made detectable by the control means, and the pulse width of the pulse output from the control means is varied based on the detected voltage value, thereby driving the filament. It is possible to always supply a constant effective voltage to the filament of the fluorescent display tube regardless of the responsiveness and variation of the elements, temperature fluctuations and power supply voltage fluctuations.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contents of the present invention will be described below with reference to embodiments.

FIG. 1 is a diagram of claim 1 of the present invention, FIG. 2 is a diagram of claim 2 of the present invention, and FIG. 3 is a time chart of a pulse output from a microcomputer and a pulse applied to a filament. T in FIG. 3 is the period of the pulse applied to the filament when the filament is pulse-driven, ton is the pulse width of the pulse applied to the filament, and V is the voltage applied to the filament. FIG. 4 is a formula for calculating the effective voltage, and the effective voltage can be calculated from the above-described values. FIG. 5 is a flowchart of the embodiment of the present invention, showing a control flow of the embodiment.
First, an embodiment of the present invention will be described with reference to FIGS.

The microcomputer 1 supplies a pulse width of 3.75 μS to the drive circuit 2 from the Pout port at a constant frequency (30 KHz).
Is connected so that the driving circuit 2 is switched and a DC pulse is supplied from the power supply 4 (9.5 V) to the filament of the fluorescent display tube 5. The negative terminal of the filament is 2.0 V. It is connected to GND via a Zener diode 6. Further, the pulse applied to the filament is connected so as to be detectable by the microcomputer 1, and the width of the pulse output from the microcomputer 1 is varied based on the detected value. The rated voltage of the filament of the fluorescent display tube 5 is specified, and the rated effective voltage of the fluorescent display tube 5 used in the embodiment is 2.5 V ±
0.25 Vrms.

The microcomputer 1 has a preset frequency of 30K.
If a pulse having a pulse width of 3.75 μS and a pulse width of 3.75 μs is output, and if there is no variation in the drive circuit 2 or a variation factor, the pulse width applied to the filament at that time is the pulse width output from the microcomputer 1 and the effective voltage is as shown in FIG. It can be seen from the calculation formula that it is about 2.5 Vrms. However, in practice, the pulse width actually applied to the filament fluctuates due to variations in the drive circuit 2 and temperature fluctuations, and the effective voltage has a different value. Therefore, the pulse width output from the microcomputer 1 is 3.75 μS. However, the pulse width actually applied to the filament is not always 3.75 μS.

Assuming that the pulse width actually applied to the filament is 5 μS, the effective voltage actually applied to the filament is about 2.9 Vrms according to the calculation formula of FIG.
Thus, the rated voltage of the filament of the fluorescent display tube 5 is deviated. Therefore, the effective voltage applied to the filament in the ROM of the microcomputer 1 is rated at 2.5 V ± 0.25 Vrms.
The setting range of the pulse width is set so as to be within the range. Here, since the voltage of the power supply 4 is 9.5 V, the rating can be satisfied if the pulse width actually applied is in the range of 3 to 4.4 μS from the calculation formula of FIG. I do. The pulse width applied to the filament is detected by the microcomputer 1, and the detected pulse width is compared with the value in the above-mentioned set range. Since the detected pulse width is 5 μS (because it is larger than the set range). The pulse width outputted from the microcomputer 1 is reduced so that the detected pulse width falls within the above-mentioned set range, and the pulse width is controlled to be reduced until the detected pulse width falls within the above-mentioned range. I do. Conversely, when the detected pulse width is 2 μS (when it is smaller than the set range), the pulse width output from the microcomputer 1 is set so that the detected pulse width falls within the set range described above. The pulse width is controlled so as to increase until the detected pulse width falls within the above-described range.

Although the frequency is set to 30 KHz here, the frequency is set to 20 KHz which is generally said to be higher than the audible band.
If it is above, it is not limited to the frequency. or,
Here, the reason why the frequency is not varied is that if the frequency is too low when the effective voltage is lowered, there is a possibility of entering the audible band, so that only the pulse width is varied. Further, although the pulse width is set in the microcomputer 1, an effective voltage may be set and the effective value may be calculated in the microcomputer 1 for comparison. The frequency may also be varied within a range where there is no influence.

Next, claim 2 of the present invention will be described with reference to FIG. The microcomputer 1 sends a pulse width of 3.75 μm to the drive circuit 2 from the Pout port at a constant frequency (30 KHz).
It is connected so as to output an S pulse, switch the drive circuit 2 and supply a DC pulse from the power supply 4 (9.5 V) to the filament of the fluorescent display tube 5. The negative terminal of the filament is 2.0 V. Zener diode 6
Is connected to GND. Further, the pulse applied to the filament is connected so as to be detectable by the microcomputer 1, and the width of the pulse output from the microcomputer 1 is varied based on the detected value. Also, the fluorescent display tube 5
The rated voltage is specified for the filament No., and the rated effective voltage of the fluorescent display tube 5 used in the embodiment is 2.5 V
± 0.25 Vrms.

The microcomputer 1 has a preset frequency of 30K.
If a pulse having a pulse width of 3.75 μS and a pulse width of 3.75 μs is output, and if there is no variation in the driving circuit 2 or a variation factor, the pulse width applied to the filament at that time is the pulse width output from the microcomputer 1 and the effective voltage is as shown in FIG. It can be understood from the calculation formula that it is about 2.5 Vrms. However, in practice, the pulse width actually applied to the filament fluctuates due to variations in the drive circuit 2, temperature fluctuations, power supply voltage fluctuations, etc., and the effective voltage has a different value.
Even if the output pulse width is 3.75 μS, the pulse width actually applied to the filament is 3.75 μS.
The power supply 4 is not limited to 75 μS, and the power supply 4 is not constant at 9.5 V but slightly fluctuates. Further, when the voltage loss in the drive circuit 2 is taken into consideration, the effective voltage actually applied to the filament further differs.

Here, assuming that the pulse width actually applied to the filament is 2.5 μS, the effective voltage actually applied to the filament is about 2.1 Vrms according to the calculation formula of FIG. Further, assuming that the voltage of the power supply 4 is 9.3 V and the voltage loss of the driving circuit 2 is 0.2 V, the effective voltage actually applied to the filament is further reduced to about 1.9 Vrms, and the rating of the filament is reduced. It will come off even more. Therefore, in order to detect the effective voltage actually applied to the filament,
A voltage detection circuit is provided to smooth the pulse voltage applied to the filament, and the microcomputer 1 detects the smoothed voltage. The effective voltage applied to the filament in the ROM of the microcomputer 1 is rated 2.5V ± 0.25Vrm.
A set range of the voltage value within the range of s is provided, and the detected voltage value is compared with the value of the set range. If the detected voltage value is smaller than the set range, the detected pulse width is set as described above. Is controlled so as to increase the pulse width output from the microcomputer 1 so that the detected pulse width falls within a preset range. Conversely, if the detected pulse width is larger than the set range, the pulse width output from the microcomputer 1 is reduced so that the detected pulse width falls within the set range, and the detected pulse width is detected. Control is performed so that the pulse width is reduced until the pulse width falls within a preset range. Since the setting range of the voltage value differs depending on the fluctuation range of the power supply 4 to be used and the voltage loss of the driving circuit 2, the setting range may be set using the calculation formula in FIG.

Although the frequency is set to 30 KHz here, the frequency is set to 20 KHz which is generally said to be higher than the audible band.
If it is above, it is not limited to the frequency.

[0017]

According to the present invention, the following effects are exhibited by the above configuration. The pulse and voltage applied to the filament are detected by the microcomputer, and the pulse width output from the microcomputer is varied, so that an appropriate effective voltage is supplied to the filament regardless of the responsiveness and variation of the drive element, temperature fluctuations, and power supply voltage fluctuations. You can do it.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a microcomputer and a fluorescent display tube according to the present invention.

FIG. 2 is a circuit block diagram of a microcomputer, a fluorescent display tube, and voltage detection according to the present invention.

FIG. 3 is a diagram showing a relationship between an output pulse of a microcomputer and a period of a pulse applied to a filament in the present invention.

FIG. 4 Formula for calculating effective voltage of output pulse

FIG. 5 is a flowchart of an embodiment of the present invention.

[Explanation of symbols]

 1: microcomputer 2: filament drive circuit 3: voltage detection circuit 4: DC power supply 5: fluorescent display tube 6: zener diode

Claims (2)

[Claims] 1. A fluorescent display tube for applying and displaying a voltage on a filament, a pulse driving unit for pulse-controlling the applied voltage, a control unit for applying a pulse to the pulse driving unit, and a pulse applied to the filament. Detecting means for detecting a pulse width of the voltage, wherein the control means varies the pulse width of the pulse based on the pulse width detected by the detecting means. 2. A fluorescent display tube for applying and displaying a voltage on a filament, pulse driving means for pulse-controlling the applied voltage, control means for applying a pulse to the pulse driving means, and detecting the pulse applied voltage. A fluorescent display tube driving device, comprising: detecting means, wherein the control means changes a pulse width of the pulse based on a voltage detected by the detecting means.