JPH10261819A - Led driving circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driving circuit device in which a displaying section containing a driving circuit section can be mounted on one circuit board and can secure sufficiently high luminance. SOLUTION: A current limiting resistor R, an LED(light emitting diode) element P, and a field effect transistor Q are connected in series between a (+) power source and the ground GND and a capacitor C is connected between the gate G of the transistor Q and the ground GND. In addition, an analog switch AS is connected between a data input and the gate G. When data 1a are high at the timing when the analog switch AS is turned on by a distributing signal, the high voltage of the data 1a turns on the transistor Q and LED element P and, at the same time, charges the capacitor C. The voltage at the capacitor C continuously maintains the transistor Q and LED element P in the turned-on states.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED driving circuit device used for driving an LED such as a display board in which LEDs (light emitting diodes) are arranged in a matrix.

[0002]

2. Description of the Related Art In general, a traffic information board installed on a road or a display board for advertisement of a product or a store has a red dot per dot.
A plurality of dots including green, or red, green, and blue LED elements are arranged in a matrix, and an LED display board that is selectively turned on according to information data to be displayed is often used.

[0003] In order to drive each of the LED elements arranged in a matrix of this type of LED display board, data is written for each dot.
A static drive method that captures data at the capture timing, stores data in flip-flops, supplies a DC current to each LED, and drives the lighting, and a dynamic drive that drives a lighting by driving a pulse current to each LED element in a time-divisional manner for each row There is a method.

[0004]

The above-mentioned conventional LED
Among the driving methods, the static driving method requires a flip-flop for data storage for each LED, and the circuit including its peripheral circuit becomes complicated. As shown in FIG. Printed wiring board 2 to be mounted
_{In the case of -1} ,..., 2- _n, a plurality of sheets must be arranged vertically, and there is a problem that the display device becomes thick as a whole.

In the dynamic driving method, time-division driving is performed. If one row has, for example, 16 dots, the light is lit at a duty of 1/16, which is darker than the light at all times. In order to increase the brightness, it is sufficient to increase the current flowing through the LED.
There is a limit in terms of the D current capacity, and it is extremely difficult to flow a current 16 times higher, and there is a problem that there is always a limit in ensuring brightness.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an LE capable of mounting a display section including a drive circuit section on a single substrate and ensuring sufficient luminance (brightness) is provided.
An object is to provide a D drive circuit device.

[0007]

An LED drive circuit device according to the present invention connects a series circuit of a current limiting resistor, an LED, and a field effect transistor between a DC power supply voltage and a reference potential. A capacitor is connected between the input electrode of the transistor and the reference potential.

In this LED drive circuit device, when a high voltage indicating data is input to the input electrode of the field effect transistor, the capacitor is charged with the voltage, turns on the field effect transistor, and direct current flows through the LED. Emits light. While the LED is charging the capacitor,
Since the field effect transistor is kept ON by the charging voltage, the LED keeps lighting as it is.

When a low voltage indicating no data is applied to the input electrode of the field effect transistor, the charge voltage of the capacitor is discharged, the voltage applied to the input electrode of the field effect transistor is reduced, and the capacitor is turned off. LED does not light.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a diagram for explaining an information display board in which the present invention is implemented. In the information display board shown here, 16 × 16 dots are arranged in a matrix on the display board 1, and one dot is composed of six LEDs 3 ₋₁ , 3 ₋₂ ,
... formed of _3-6 . 2 out of 6 LEDs
Are red and four LEDs are green elements. However, the number of dots of the display panel 1, the number of elements of each dot, the arrangement of the dots, and the like may be appropriately selected according to the application.

In this information display board, data is sent to each dot with the passage of time, and an LED is turned on or off according to the data, and information such as characters, symbols, pictures, etc. is displayed as a still image or as a moving image. I do. FIG. 2 is a circuit diagram showing an LED drive circuit device according to one embodiment of the present invention.
The LED driving circuit device of this embodiment is used for driving the LEDs of the information display board. In this LED drive circuit device, 11a and 11b are red and green LED drive circuits of the first dot in the first row, and 21a is a red LED drive circuit of the second dot in the first column. Green LED drive circuit for the second dot in the first row, LED drive circuits for the third and subsequent dots in the first row, and LED for the second and subsequent rows
The drive circuit is not shown.

The internal circuit of the LED drive circuit 11a is such that a series circuit of a resistor R, an LED element P, and a field effect transistor Q is connected between the + power supply and the ground GND, and is connected between the gate G of the field effect transistor Q and the ground GND. And the capacitor C
Is connected. The data 1a is connected to the gate G of the field effect transistor Q via the analog switch AS.
Is added, and the analog switch AS
Are turned on / off by the distribution signal.

The other LED driving circuits 11b, 21a,.
The internal circuit has exactly the same connection as the LED drive circuit 11a. Data 1a is the first row of data for red, and data 1b is the first row of green data. The data 2a is red data in the second row, and although not shown, the data 2b is green data in the second row. The same applies to the data for the third and subsequent rows.

Next, the display operation of the LED drive circuit 11a will be described. When the distribution signal (pulse signal) for the first column is applied to the analog switch AS in a state where the data 1a for lighting the LED element P of the LED drive circuit 11a is high, the analog switch AS AS is turned on and the high of data 1a indicates that the field effect transistor Q
And charges the capacitor C. The field effect transistor Q is turned on by the input of a high signal to the gate G, a current flows through the LED element P,
The ED element P lights up. Distribution signal is analog switch A
No longer added to S, analog switch AS is OFF
Even so, a high signal is applied to the gate G of the transistor Q by the voltage charged in the capacitor C, and the transistor Q is kept on, so that the LED element P keeps lighting. When the next distribution signal is added and the analog switch AS is turned on again, if the data 1a is high, the capacitor C is charged again, the field effect transistor Q is kept on, and the LED element P is turned on. The lighting will be continued. That is, the LED element P performs DC lighting.

When the distribution signal is applied to the analog switch AS, if the input data 1a is low, the analog switch AS is turned on and discharged to the input side through the voltage analog switch AS charged in the capacitor C. Therefore, the potential of the gate of the field effect transistor Q becomes low, the field effect transistor Q is turned off, and LE
Since no current flows through the D element P, the LED element P is turned off.

This embodiment of the LED driving circuit device is shown in FIG.
As shown in FIG. 3, since the circuit is very simple, the entire circuit can be mounted on one printed circuit board. As shown in FIG. 3, the display board 1 and the circuit board 4 can be overlapped, and a thin information display board can be provided. realizable. In the above embodiment, the case where the present invention is applied to an information display board having a matrix dot arrangement is described. However, the present invention can also be applied to one row or one column or an arrangement of several dots.

[0017]

According to the present invention, by connecting a capacitor between the input electrode of the field-effect transistor for driving the LED element and the reference potential, the capacitor has a storage function. Lighting and sufficient luminance can be ensured. In addition, the configuration of the driving and storage circuit of one unit of the display is only one transistor and one capacitor, the circuit configuration is very simple, and mounting on the same circuit board as the LED can be realized more easily than before. Space can be saved. Further, since only one circuit board is required, a thin display panel can be obtained, and the manufacturing cost can be reduced as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an information display board in which the present invention is implemented.

FIG. 2 is a circuit diagram showing an LED drive circuit device according to one embodiment of the present invention.

FIG. 3 is a perspective view of an information display board using a circuit board on which the LED drive circuit device of the embodiment is mounted.

FIG. 4 is a perspective view showing a conventional information display board.

[Explanation of symbols]

 11a, 11b LED drive circuit R Current limiting resistor P LED element Q Field effect transistor C Capacitor AS Analog switch

Claims (1)

[Claims] 1. A series connection of a current limiting resistor, an LED and a field effect transistor is connected between a DC power supply voltage and a reference potential, and a capacitor is connected between an input electrode of the field effect transistor and a reference potential. An LED drive circuit device comprising: