JPH0313987A - Driving circuit for fluorescent display tube - Google Patents

Abstract

PURPOSE:To settle the light emission brightness of each display part by providing a means which varies the pulse width of the grid signal of the fluorescent display tube according to the instantaneous value of an applied AC voltage. CONSTITUTION:The pulse width setting part 9 of a microcomputer 6 varies the pulse widths t1 and t2 of grid signals G3 and G4 of the fluorescent display tube 11 according to the voltage level of the AC driving voltage 31 of the display tube 11, namely, widens the pulse widths at the timing where the control voltage between the cathode and grid is low to make the illumination time of a display part long, thereby correcting the brightness difference. Therefore, each anode is made substantially equal in light emission energy to eliminate the light emission brightness variance among the respective display parts.

Description

DETAILED DESCRIPTION OF THE INVENTION ■Presentation process■ The present invention relates to a drive circuit for a fluorescent display tube that displays patterns such as numbers and symbols.

Traditionally, as home appliances such as microwave ovens become more sophisticated, products equipped with a data display function that displays various data have been put into practical use. Display tubes are often used.

As is well known, this fluorescent display tube includes a plurality of anodes serving as a display body, a cathode that emits electrons to the anode, and a plurality of grids that individually control the emission of electrons from the cathode to the plurality of anodes. Data is displayed using fluorescent display tubes arranged in parallel with the desired digits, or by a composite tube in which the desired digits are integrated.

To drive such a fluorescent display tube, as shown in FIG. 3, an AC drive voltage 31 is directly applied to the cathode, and a grid signal G with the same pulse width t is applied to the grid of each digit.
etc. was applied.

In the conventional device described above, an alternating current voltage is applied to the cathodes, so the grid signals G, , Gx for the cathodes of each digit are
The level of the above changes depending on the timing of application of the alternating current voltage applied to the cathode. Therefore, if grid signals of the same level are applied, there is a problem in that brightness differences occur between each display portion of the display tube.

In view of these points, it is an object of the present invention to provide a drive circuit for a fluorescent display tube that prevents luminance differences between digits from occurring.

In order to achieve the above-mentioned object, the invention of the present invention adjusts the emission brightness of each anode according to the instantaneous value of the AC voltage applied to the fluorescent display tube during the pulse of the grid signal of the fluorescent display tube driven by AC. The configuration is such that the value is changed so that it is substantially constant at all times.

Therefore, for example, a grid signal applied to the grid at a high timing of the AC drive voltage applied to the cathode of a fluorescent display tube has a lower level to the cathode than a grid signal applied at a low timing, but the grid signal The width of the pulse increases depending on the voltage value of the AC drive voltage. In this way, the emission energy of each anode becomes substantially the same, and the emission brightness becomes constant.

彉jfl FIG. 1 is a circuit diagram of an embodiment of the present invention.

In the figure, 1 is a power transformer for a control circuit, and the transformer 1 has a primary winding connected to an AC power source 12 and a first secondary winding S connected to a cathode of a fluorescent display tube 11. A second secondary winding S2 is connected to a full-wave rectifier circuit 2 consisting of a diode bridge D. The output of the full-wave rectifier circuit 2 is passed through a smoothing capacitor 3, and further via a voltage stabilizing circuit 4 and a capacitor 5 to a microcomputer 6.
connected to provide a stable DC voltage.

Also, from the smoothed voltage, a Zener diode ZD
A negative DC voltage vo is obtained, and this voltage is applied to the cathode of the fluorescent display tube and connected to the secondary winding S.

It forms the center voltage of the AC voltage given by The microcomputer 6 includes a control program storage section 7, a control section 8. It consists of a pulse setting section 9 and a display register 10, and a power synchronization circuit 13 consisting of resistors R5 and R2 is connected to the control section 8, and the microcomputer 6 drives the fluorescent display tube 11 in half cycles of AC power. The power synchronization circuit 13 is also connected to the pulse width setting section 9 so that the pulse width of the grid signal of the fluorescent display tube 11 can be set to a predetermined value according to the voltage level of the AC power supply voltage. I have to.

Therefore, the AC voltage from the AC power source 12 is applied to the first voltage of the transformer 1.
The voltage is stepped down to a desired value by the secondary winding S of the fluorescent display tube 11.
A cathode consisting of a filament of On the other hand, the AC voltage stepped down to a desired value by the second secondary winding S of the transformer 1 is converted to a DC voltage Vp by the full-wave rectifier circuit 2 and the smoothing capacitor 3, and then converted to the DC voltage Vp by the voltage stabilizing circuit 4 and the smoothing capacitor 3. The capacitor 5 converts the voltage into a stable DC voltage Vt111, which is supplied to the micro combinator 6 as a power source. The microcomputer 6 has a control program storage section 7 stored in advance.
The control section 8 is operated according to the program, and the display register 10 generates grid signals IG to 6G of the fluorescent display tube 11 at timings corresponding to the pattern to be displayed.The control section 8 consists of resistors R, , R1. Since the power synchronization circuit 13 controls the AC waveform applied to the cathode of the fluorescent display tube 11 in half cycles, the fluorescent display tube 11 is driven every half cycle of the AC waveform.

FIG. 2 is an explanatory diagram of the operation of the present invention, showing the relationship between the AC drive waveform of the fluorescent display tube and the grid signal waveform of the fluorescent display tube.

The cathode of the fluorescent display tube 11 is supplied with the AC drive voltage 31 as described above, and the grid of the fluorescent display tube 11 is supplied with grid signals Gs, Ga, etc. from the display register 10 of the microcomputer 6. grid signal G,
(c) AC driving voltage 31 applied to the cathode of the fluorescent display tube 11
Therefore, the control voltage applied between the cathode and the grid is lower than the grid signal G4 by X (V), but
The pulse width setting section 9 of the microcomputer 6 sets the pulse 11t1 of the grid signal G to 1.1 among the pulses of the grid signal G4. The brightness of the display portion corresponding to each anode is made constant by setting it wider and lengthening the lighting time using the grid signal G.

That is, the pulse width setting section 9 of the microcomputer 6 generates the grid signal G3. During the pulse of G, F+h is changed according to the voltage level of the AC drive voltage 31, and the cathode
At the timing when the control voltage between the grids is low, the pulse is spread out to lengthen the lighting time of the corresponding display portion to correct the brightness difference and make the brightness of each display portion constant.

Although the above embodiment has been described with the pulse width setting section 9 provided independently in the microcomputer 6, the pulse width of the grid signal can be set to the instantaneous voltage level of the AC voltage using software using a program. It is best to change it accordingly.

Since the present invention has the above-described configuration, even when the fluorescent display tube is driven with alternating current, it is possible to eliminate unevenness in the luminance of each display portion.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is an explanatory diagram of a conventional example. 6.--Microcomputer. 9-Pulse width setting unit, 11-.- Fluorescent display tube. 12-AC power supply.

Claims (1)

[Claims] (1) In a drive circuit for a fluorescent display tube that controls a grid signal of a fluorescent display tube that applies an alternating voltage to the cathode to display a desired pattern by combining display parts that selectively emit light, the grid signal 1. A drive circuit for a fluorescent display tube, comprising means for changing the pulse width of the voltage according to the value of the alternating current voltage.