JP2799972B2 - EL drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL driving circuit.

[0002]

2. Description of the Related Art At present, there is a light emitting display device using a plurality of EL elements on a display surface. As shown in FIG. 2, an EL drive circuit used in this type of light-emitting display device has three EL elements 33 to 35 at both ends of a coil 32 of an inverter circuit 31 that generates an AC voltage. The transistors are connected in parallel via 36 to 38, and each of the transistors 36 to 38 is selectively turned on and off by a selection circuit 39, thereby causing each EL element to emit light selectively.

[0003]

However, in such a device, when the area of each of the EL elements 33 to 35 is different, the light emission depends on the area of the EL element which emits light when each light emitting element emits light individually. The brightness will be different. That is, for example, assuming that the area of each of the EL elements 33 to 35 is determined to become smaller in order, in an EL driving circuit that causes the EL element 33 having the largest area to emit light with appropriate luminance, a smaller area is used instead of the EL element 33. EL element 34
When light is emitted, since the capacitance value connected to the coil 32 decreases, the driving voltage increases and the luminance increases.
When the EL element 35 having a smaller area emits light instead of the EL element 34, the emission luminance further increases. For example, each of the EL elements 33 to 35 has an area of 900 cm.
As a result of actual measurement of the drive voltage value when each of the general thick-film EL elements of ² , 600 cm ² and 300 cm ² was driven independently using the appropriate EL drive circuit having the above configuration, the EL element was measured. The relationship between the area and the voltage value is as shown in FIG. 3A, and the relationship between the area of the EL element and the emission luminance at that time is as shown in FIG. 3B.

Accordingly, an object of the present invention is to enable an individual EL element to emit light with a desired emission luminance in an EL drive circuit for driving a plurality of EL elements. When emitting light independently, each EL
The object is to make the light emission luminance of the element substantially equal.

[0005]

A coil connected to an AC voltage source and having a plurality of taps, a plurality of EL elements having different capacities, and each of the EL elements is connected to one terminal of the coil and each EL element. The above object is achieved by an EL driving circuit including a control circuit selectively connected to a unique tap determined according to the capacitance of the element.

Here, it is preferable that the number of turns between one terminal of the coil and a unique tap increases as the capacity of each EL element increases. In particular, when each of the EL elements emits light alone,
It is preferable to determine a unique tap of each EL element so that the light emission luminance of the L element becomes substantially equal.

[0007]

Next, an embodiment of the present invention will be described. FIG. 1 is an explanatory diagram showing the configuration of the present example.
Is an AC power supply, and 2 is a coil. The coil 2 has taps 2b and 2c in order from one terminal 2a. Here, as the AC power supply 1, although not shown, the above-mentioned known inverter circuit may be used, and in this case, the coil 2 may be a coil constituting the inverter circuit. 3a, 3b and 3c are EL elements.
The areas of the L elements 3a to 3c are reduced in this order. E
L element 3a is connected between one terminal 2a of coil 2 and the other terminal 2d via transistor 4a. EL
The element 3b is connected between the other terminal 2d and the tap 2b via the transistor 4b. The EL element 3c is connected between the terminal 2d and the tap 2c via the transistor 4c. 5 is a selection circuit, and transistors 4a to 4c
Are selectively turned on and off to cause the EL elements 3a to 3c to emit light selectively. A control circuit is composed of the transistors 4a to 4c and the selection circuit 5.

Next, the operation of this embodiment will be described. First,
When the transistor 4a is turned on by the selection circuit 5, EL
The element 3a emits light. At this time, since the EL element 3a is connected to both ends of the coil 2, it receives the maximum drive voltage.
Next, when the transistor 4b is turned on instead of the transistor 4a, the EL element 3b emits light. At this time, since the EL element 3b is connected between the terminal 2d of the coil 2 and the tap 2b, the number of coil turns connected to both ends of the EL element 3a is reduced as compared with the case of the EL element 3a. As a result, the increase in the driving voltage corresponding to the difference in capacitance between the EL element 3a and the EL element 3a is canceled out, and the light emission luminance becomes almost equal to that of the EL element 3a.
Similarly, when the transistor 4c is turned on instead of the transistor 4b, the EL element 4c emits light. At this time, EL
The number of turns of the coil connected to the element 3c is further reduced. As a result, a rise in the driving voltage due to a further decrease in the capacitance is offset, and a change in the light emission luminance is suppressed.

As described above, in this embodiment, the coils connected to both ends of each EL element according to the decrease in capacitance when switching from the EL element 3a to the EL element 3b and from the EL element 3b to the EL element 3c. The positions of the taps are set so as to increase the decrease in the number of turns, whereby the light emission luminance of each of the EL elements 3a to 3c becomes substantially equal.

In the present embodiment, the positions of the taps are set so that the light emission luminances of the EL elements 3a to 3c are substantially equal. However, the present invention is not limited to this, and light is emitted at a desired light emission luminance by changing the position of the taps. be able to. For example, each E
A plurality of taps are provided for the L element to selectively connect E between one terminal of the coil and any of the plurality of terminals.
The light emitting luminance of the EL element may be selectively changed by connecting the L element.

[0011]

According to the present invention, it is possible to cause each EL element to emit light with a desired emission luminance. In particular, if the number of turns between one terminal of the coil and the unique tap is increased as the capacity of each EL element increases, when each EL element emits light alone, Can be made substantially equal in light emission luminance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an EL driving circuit according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a conventional technique.

FIG. 3 is an explanatory diagram for explaining the operation of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Coil 2b, 2c Tap 2d Terminal 3a-3c EL element 4a-4c Transistor (control circuit) 5 Selection circuit (control circuit)

Claims (3)

(57) [Claims] 1. A coil connected to an AC voltage source and having a plurality of taps, a plurality of EL elements having different capacities, and each of the EL elements being connected to one terminal of the coil and a capacity of each EL element. An EL drive circuit comprising: a control circuit selectively connected to a unique tap determined accordingly. 2. The EL drive according to claim 1, wherein the number of turns between one terminal of the coil and a unique tap increases as the capacitance of each EL element increases. circuit. 3. The unique tap of each EL element is determined such that when each EL element emits light independently, the emission luminance of each EL element becomes substantially equal. EL drive circuit.