JPH02190893A - Driving method for fluorescent display tube - Google Patents

Abstract

PURPOSE:To omit a transformer of a power supply circuit to reduce the cost of an electronic calculator or the like by specifying relations among the value of the duty ratio of an applied pulse signal, a filament voltage, and a grid/ segment voltage and varying them in accordance with the each display digit. CONSTITUTION:When the pulse signal having a prescribed duty ratio is applied to grid electrodes 31 and 32 and segment electrodes 41 and 42 and a DC voltage V is applied to a filament 2 of a fluorescent display tubed 1 of many digits to drive respective digits, the duty ratio is varied in accordance with each display digit so that the product (V<alpha>.Du; alpha=2.5 to 3) of the value of the duty ratio and the value obtained by multiplying the difference between the filament voltage and the grid/segment voltage of each display digit by 2.5 to 3 is fixed. That is, the duty ratio of the voltage pulse signal applied to grid electrodes 31 and 32 and segment electrodes 41 and 42 of each digit is so varied that the luminance of respective digits is made uniform. Thus, the luminance of respective digits is uniform, and the transformer used in the power supply circuit of the filament 2 is omitted to reduce the cost of the electronic calculator or the like.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for driving a multi-digit fluorescent display tube used for displaying electronic desktop calculators, measuring instruments, clocks, etc. Using DC voltage,
The present invention relates to a method for driving a fluorescent display tube in which the brightness of each digit is made uniform during dynamic driving.

[Conventional Example] Conventionally, this type of multi-digit fluorescent display tube has a structure shown in FIG. 5, for example.

In this figure, a fluorescent display tube 1 has a two-digit display, and this fluorescent display tube 1 includes a filament 2 that emits thermoelectrons,
It is provided with a grid electrode 3 that accelerates the thermoelectrons, and a segment electrode 4 that has a light emitter that emits light by collision of the accelerated thermoelectrons. Further, an AC voltage e from an AC ft source 5 is applied to the filament 2 via a transformer 6,
A pulse signal of a predetermined duty ratio output from the control circuit 7 is applied to each grid electrode 3 and segment electrode 4, respectively. Furthermore, the fluorescent display tube 1 is
Since it is a digit display, the transformer 6 is provided with a center tap 6a, and this center tap 6a is set to a level obtained by multiplying the potential of the grid segment by a bias EK corresponding to the cutoff by the Zener diode 8. ing.

Here, if the fluorescent display tube 1 is dynamically driven and the two digits are turned on, the control circuit 7 sends the seventh
Pulse signals shown in FIGS. (a) to (d) are output. At this time, the potential of the center tap 6a of the transformer 6 is at a level equal to the OFF potential of the grid segment with a cutoff bias applied, and both ends Fa of the filament 2,
The potential between Fb is within the shaded range shown in FIG. Furthermore, as is clear from FIG. 7, the grid electrodes 31, 3
The pulse signals applied to □ and the segment electrodes 4□, 4□ have the same duty ratio t/T (=Du). In this way, the potential difference at a predetermined position of the filament 2 is suppressed to a small value, and thermionic can be released uniformly. In addition, grid electrodes 3□, 3o and segment electrodes 4. ．． 4. Assuming that the duty ratio of the pulse signal is the same,
The brightness of each digit of the fluorescent display tube 1 can be made uniform.

[Problems to be Solved by the Invention] Incidentally, the above-mentioned method for driving a multi-digit fluorescent display tube requires a transformer 6 for applying an alternating voltage to the filament 2, and moreover, in the case of a multi-digit display, the transformer 6 is required. transformer 6
It is necessary to provide a center tap etc. In other words, a total of 3I8 electronic desktop calculators that require low cost! For appliances, watches, etc., the cost of transformers and the like is also an issue.

This invention was made in view of the above points.

The object of the present invention is to provide a method for driving a fluorescent display tube, which uses a DC voltage as a power source for a filament, makes the brightness of each digit uniform, and reduces the cost of electronic desktop calculators, measuring instruments, watches, etc.

[Means for Solving the Problems] In order to achieve the above object, the present invention accelerates thermoelectrons emitted from a filament at a grid electrode and collides with a phosphor on a segment electrode.
In a method for driving a multi-digit fluorescent display tube in which a pulse signal with a predetermined duty ratio is applied to the grid electrodes and segment electrodes to dynamically drive each digit, when applying a DC voltage V to the filament and dynamically driving each digit, The difference between the above duty ratio value, its filament voltage, and the grid segment voltage of each display digit is 2
．． Product of the value raised to the 5th or 3rd power<vCL・Du; α=2.
The gist of the present invention is that the duty ratio is varied according to each of the display digits so that 5 to 3) are kept constant.

[Operation] Since the above method is used, when a DC voltage is applied to the filament, the filament voltage has a slope and increases from the negative end Fa to the positive end Fb.

That is, the grid segment voltage Eas becomes higher in the digit that faces the end Fa, and the grid segment voltage EQ becomes lower in the digit that faces the end portion Ftl. Here, the brightness of each digit is proportional to the 2.5th to 3rd power of the difference between the filament level and the grid segment level,
In addition, the dynamic drive pulse signal duty ratio (D
u) is proportional to Therefore, the duty ratio of the voltage pulse No. 18 applied to the grid electrode and segment electrode of each digit is varied so that the brightness of each digit is made uniform. Therefore, when dynamically driving a fluorescent display tube,
The brightness of each digit is made uniform, and the transformer used in the filament power supply circuit can be omitted.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. In addition, in the figure, the same parts as in FIG. 5 are given the same reference numerals, and redundant explanation will be omitted.

In FIG. 1, a voltage Ef (filament voltage) from a DC power supply 10 is applied to a filament 2 of a fluorescent display tube 1. Then, as shown in FIG. 2, each voltage level of the filament 2 has a predetermined slope, and the grid segment voltage EG8 is applied to the column opposite the negative end Fa.
A high voltage is applied to the grid segment voltage EGg, and a low grid segment voltage EGg is applied to the digit facing the positive end Fb.

Here, the brightness of a general fluorescent display tube can be obtained from the following equation.

L=A−v−Du Note that ■ is the difference between the voltage level of filament 2 and the voltage Eas level of the grid segment, that is, the voltage applied to the grid segment with respect to the filament voltage, and D
u is a duty ratio representing the application time (pulse width of a pulse signal) for applying voltage to the grid and segment electrodes, and α is a value of 2.5 to 3. A is a constant, and the same voltage is applied to the grid electrode and the segment electrode.

That is, it is known that the brightness is proportional to the 2.5 to 3 power of the difference between the filament level and the grid segment level (grid segment applied voltage), and is proportional to the duty ratio Du of the dynamic drive pulse signal. There is.

So, to explain the case of a two-digit fluorescent display tube,
First, from the above formula, so that there is no difference in brightness between each display digit,
The duty ratio of the pulse signal that drives each display digit is calculated, and the pulse width of the pulse signal of the grid and segment electrodes is obtained based on this calculated value. At this time, as shown in FIG. 2, the brightness L1 of the digit opposite to the predetermined position a1 of the filament 2 is = A'Va: 'Du1, and the brightness L2 of the digit opposite to the predetermined position a3 is Ll'': A"Va2
・Du, and as shown in Figure 3,
The brightness of those digits is the same (constant; cor+8t
, ).

A grid in each display digit facing a predetermined position of the filament 2 at Du, /Du, = Va, /Va1.

The duty ratio of the pulse signal of the segment electrodes 38, 3□tct4z is calculated. That is, as shown in FIG. 4, when V"·Du is constant, the above duty ratio is obtained such that the brightness of each display digit facing the filament 2 is constant. Then, as shown in FIG. ), as shown in
A low grid/segment voltage Eos is applied to the girders facing the end Fb, but the duty ratio Du1 (=t//
T1) is made high, and a high grid segment voltage EO8 is applied to the girder facing the one end Fa side.
The duty ratio DIJ= (== t 2 / T z ) of the pulse signals of the grid and segment electrodes is kept low. Note that the control circuit 7 calculates the duty ratio and obtains a pulse signal of the duty ratio.

In this way, when dynamically driving the two-digit fluorescent display tube, the duty ratio of the voltage pulse signal applied to the grid electrodes 3□, 3□ and the segment electrodes 41, 4□ is varied according to the above formula. Therefore, the difference in brightness between display digits caused by applying a DC voltage to the filament 2 is canceled out by changing the duty ratio.
The brightness of these display digits is kept uniform.

In the above embodiment, a two-digit fluorescent display tube was explained, but even for a fluorescent display tube with two or more digits, the brightness of each display digit of a large number of digits can be abbreviated using the above formula as described above. It can be kept even.

[Effects of the Invention] As explained above, according to the method for driving a fluorescent display tube of the present invention, DC power is applied to the filament, and the duty ratio value of the pulse signal of the grid and segment electrodes, the filament voltage, and each Since the duty ratio is varied according to each display digit so that the product of the grid segment voltage difference of the display digits to the 2.5th power to the third power is constant, the filament power supply circuit It is possible to eliminate the need for a transformer, thereby reducing the cost of electronic desktop calculators, measuring instruments, watches, etc. Further, according to this invention,
A high grid segment voltage is applied to the digit opposite to the negative side of the filament voltage, but the grid of that digit,
The duty ratio of the pulse signal of the segment electrode can be made low, while the grid segment voltage is applied low to the digit opposite to the positive side of the filament voltage.
Since the duty ratio of the pulse signals of the grid and segment electrodes of that digit can be increased, there is an effect that the brightness of each display digit in a multi-digit display can be made uniform.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a fluorescent display tube and its drive control circuit showing an embodiment of the present invention, FIG. 2 is a diagram for explaining the voltage level of the fluorescent display tube shown in FIG. 1, and FIG. 3@ is a characteristic diagram of the duty ratio Du of the driving pulse of the fluorescent display tube shown in FIG. 1 and the grid segment applied voltage V to the filament, and FIG. 4 is a pulse signal for dynamically opening the fluorescent display tube shown in FIG. 1. FIG. 5 is a schematic block diagram of a conventional fluorescent display tube and its vibration control circuit, and FIG. 6 is a diagram for explaining voltage levels of the fluorescent display tube shown in FIG. 5. FIG. 7 is a diagram for explaining the duty ratio of a pulse signal for driving the fluorescent display tube shown in FIG. In the figure, 1 is a fluorescent display tube, 2 is a filament, 31.3□
is a grid electrode; 4. ．． 42 is a segment electrode, 7 is a control circuit (CPU), 8 is a Zener diode, 10 is a DC power supply, and Fa and Fb are both ends of the filament 2. Patent Appearance Ceremony Takuya Ohara, Agent, Patent Attorney, Fujitsu General Co., Ltd. Figure VOI VO2 Voltage (V) Figure

Claims (1)

[Claims] (1) Dynamic drive by applying a pulse signal with a predetermined duty ratio to the grid electrode and segment electrode so that the hot electrons emitted from the filament are accelerated by the grid electrode and collide with the phosphor on the segment electrode. In a method for driving a multi-digit fluorescent display tube, when applying a DC voltage to the filament and dynamically driving the fluorescent display tube, the value of the duty ratio, the filament voltage, and the grid of each display digit are determined.
The product (
In order to keep V^α・Du; α=2.5 to 3) constant,
A method for driving a fluorescent display tube, characterized in that the duty ratio is varied according to each display digit.