JPH01593A - display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [0002] Field of Application for Additional Work This invention relates to display devices such as fluorescent display tubes and light emitting diodes.

2. Description of the Related Art When driving a multi-digit display, a dynamic driving method has become mainstream in order to save on the number of wiring lines and driving elements.

FIG. 2 shows the main part of the circuit of the display device using the dynamic drive method. Figure 2 shows a 4-digit 7-segment display 1.
This is an example of a display device that drives 1 to 1d. Display 1a
A microcomputer 2 is used for control of 1d, and the microcomputer 2 operates based on a clock signal from a clock circuit 3. The wt source is a commercial wt source 4 that is stepped down by a transformer 5, half-wave rectified by a diode 6, and then connected to a capacitor 7.
It is smoothed. Although it is not possible to obtain a complete direct current with this power supply circuit, it is a method that is often used because it is cost-effective.The microcomputer 2 periodically uses digit scanning pulses sequentially to apply one pulse to the digit to be lit. Select 4 for ~, and output a signal to the segment required at that time) @ -y g to light it up. Each segment 1 to 9 is connected in parallel, but only the digit selected by 1 to 4 in the digit scan is lit. Therefore, only one digit is lit at a given moment, but because the digits are switched at high speed by scanning, it appears as if all digits are lit at the same time due to the afterimage effect of the human eye. . The power applied to the displays 1a to 1d is not a complete direct current and contains ripples as shown in Figure 3. Therefore, if the commercial power supply 4 is used to scan the digits asynchronously, it will be affected by the ripples. hand,
The voltage applied to one digit constantly fluctuates, and this appears as flickering. In order to prevent this, there is a method of shortening one period of digit scanning and scanning at high speed, but there are limitations due to the performance of the microcomputer 2 and constraints on the software program, and it is difficult to take a complete countermeasure. Ta. Conventionally, one period of the digit scan pulse is synchronized with the frequency of the input commercial power supply 4 as shown in the timing diagram of Fig. 4, and the same digit is always displayed with the same power supply phase, thereby reducing the influence of ripple. Measures were taken to remove the problem. When the commercial power supply 4 is 50 Hz, the period is 20m5''cs, and 4 digits are scanned during this 20m.The scan pulse width of the corresponding period can be set to a maximum of 5ms, but please allow The scan pulse width is set to 4ms.

It is set by counting the number of timer interrupts that occur inside the microcomputer 2 every 0.5 ms, so it can be set to an integral multiple of 0.5 ms, but the cycle of the timer interrupt depends on the clock of the microcomputer 2. However, since the oscillation frequency of the clock circuit 3 fluctuates depending on the accuracy of the oscillation frequency, if the scan pulse width is set to 5 ms, the scan for 4 digits will be approximately 20 m, and the commercial power supply It is also possible that the synchronization with 4 is lost. Therefore, the single-digit scan pulse width is set to 4 ms, taking into consideration a margin.

Since the scan pulse width is 4 ms, the total pulse width when scanning four digits is 18 m5, leaving 4 ms, during which the entire display is blank.

Problems to be Solved by the Invention The conventional display device described above has the following problems. Is the pulse width of the scan pulse a constraint on the setting accuracy?5
ms instead of 4 ms, the display is blank for 4 ms out of one cycle of 20 m5 of the commercial power supply 4. Therefore, there is a problem in that the duty ratio is reduced and the display brightness is reduced compared to the case where the scanning pulse width is 5 ms.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the display device of the present invention variablely changes the pulse width of the digit scan of the display driven by the dynamic scan method for each digit. The total scan pulse width applied to each digit in one period or a period proportional to it is made equal in all digits.

Function The display device of the present invention changes the pulse width of the digit scan of the display for each digit, and the total of the scan pulse widths applied to each digit in one period of the scan or a period proportional to the period is Since the configuration is such that the values are the same, the duty that affects display brightness is maximized and display flickering is prevented.

Embodiment Hereinafter, a display device which is an embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram of a commonly used display device. 1 is a display with 4 digits.

The display 1 is controlled by a microcomputer 2. The microcomputer 2 operates based on the clock signal from the clock oscillation circuit 3. The display 1 is controlled by a dynamic lighting method, and each segment aNg of the display 1 is connected in parallel.
It is connected to the segment output a-9 of the microcomputer 2.

Digits 1 to 4 of the display 1 are connected to the digit scan output of the microcomputer 2, thereby selecting the digit to be displayed.

The wl source is obtained by stepping down the commercial power supply 4 with a transformer 5, half-wave rectifying it with a diode 6, and smoothing it with a capacitor 7.

FIG. 1 is a control timing diagram of a display device in a display device according to an embodiment of the present invention.
4 represents the digit scan pulse for dynamic driving. The scan starts from 1 to 2. 3°K4 and then return to 1 again. One period of 20 m5 of the commercial power supply frequency of 50 Hz is synchronized with one period of the scan. There are two types of scan pulse width: 5ms and 4.5ms.
For the same digit, 5 ms and 4.5 ms are alternated, and the scan widths are different from those of the immediately preceding digit and the immediately following digit. Although the width of the scan pulse is changed for the same digit, the switching is done at high speed in a short period of two cycles of the commercial power frequency 4, and flickering is not noticeable.

The total scan pulse width applied during two periods of 40 m3 at commercial power frequency 4 is 9.5 ms for every digit.
becomes. Therefore, there will be no variation in brightness between digits. Also, the time during which all digits disappear is 1 ms between the commercial power supply frequency and the cycle of 20 m5, which is half of that of the conventional example, and the display duty is increased by 5%.

As described in detail of the invention, according to the display device of the present invention, the pulse width of the dynamic drive scan of the display is made variable for each digit, and furthermore, during two periods of the commercial power supply, the pulse width is varied for each digit. Since the width of the scan pulses is made equal, it is possible to increase the display duty and therefore the brightness by setting the scan pulse width to the combination with the least number of display blanks. It is possible to provide an excellent display device with good display quality without display brightness variations or flickering due to changes in brightness of the same order of magnitude.

[Brief explanation of the drawing]

FIG. 1 is a timing diagram of a dynamic scan of a display device that is an embodiment of the present invention, FIG. 2 is a circuit diagram of the main parts of a general display device, FIG. 3 is a power waveform diagram of the same device,
The figure is a timing diagram of dynamic scanning of a conventional display device. 1...Display unit, 2...Microcomputer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure '20m5' 2D, ns l Figure 2 Figure 3 Drifting Cedar Figure 4 KI to 3 to 4 λ power supply 1 core, 1

Claims (1)

[Claims] The display device includes a display device having a plurality of digits, and a microcomputer that controls blinking of the display device, and the microcomputer controls the blinking of the display device by a dynamic lighting method that scans and selects digits, and controls the blinking of the display device by scanning and selecting the digits. The period of is synchronized with the input commercial power supply frequency, and the pulse width of the digit scan is made variable, so that the total pulse width of the scan applied to each digit in one cycle of the commercial power supply frequency or a period proportional to it is determined. is made equal in all digits.