JPH037116B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electroluminescent display device in which a luminescent electroluminescent display element is used as an ambient light sensing element.

Generally, electroluminescent display elements are used on instrument dials and
It is used as a night illumination member or light-emitting display member for light-receiving elements such as LCDs, but in order to automatically turn on or off the light-emitting display member in the ambient light condition, it has conventionally been necessary to It was necessary to provide another sensing element.

In consideration of the above points, the present invention uses an electroluminescent display element as a light emitting element and also as an ambient light detection element, and detects the state of ambient light with the electroluminescent display element itself. The present invention provides an electroluminescent display device in which the voltage applied to the display device is variably controlled to turn on and off the light.
Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 shows a cross-sectional view of the electroluminescent display element of the present invention, in which a transparent electrode 2 is formed on a transparent insulating substrate 1 such as glass or plastic, and a ZnS :Mn phosphor is formed as a light emitting layer 3, and aluminum [Al] is formed as a reflective conductive film 4 on this light emitting layer 3. The electroluminescent display element 5 configured as described above is connected in series to the current detection section 6 and the AC power supply 7, and when the current detection section 6 detects the current flowing through the electroluminescence display element 5, the electroluminescence display element 5 emits light. Compared to the case at night when there is no ambient light (see Figure 2 A),
During the daytime when ambient light is input to the electroluminescent display element 5 (see Figure 2B), the peak value of the current flowing through the circuit varies from I ₁ to I ₂ as shown by A and B in Figure 3.
This change is approximately proportional to the intensity of the ambient light. This phenomenon occurs in the light emitting layer.
It is thought that electrons in the impurity level formed in the forbidden band are excited by the incident light, rise to the conduction band, become conduction electrons, and increase the current. Further, this current is not affected by the light emission of the electroluminescent display element 5, and this increase/decrease change is not affected by the light emission of the electroluminescent display element 5.
does not affect the light emission.

FIG. 4 shows a block diagram of an electroluminescent display device according to an embodiment of the present invention, in which 5 is an electroluminescent display element, 8 is a current detection section, 9 is a power supply section, 10 is a voltage control section, 11 is a switch, and the current detection section 8
detects the current in the circuit, and has three detection levels IA,
The voltage control unit 10 determines the relationship between IB and IC, and
For example, it is composed of a microcomputer, and outputs a switching signal to output two voltage levels V ₁ and V ₂ to the power supply section 9 according to the relationship between the circuit current i and each detection level IA, IB, and IC. In addition, i ₁ is the current when voltage V ₁ is applied, i ₂ is the current when voltage V ₂ is applied, Vth is the emission starting voltage, Ith is the current when the emission starting voltage Vth is applied, and V ₂ < Vth < V ₁ There is a relationship between

Next, the operation of this embodiment will be explained with reference to FIG. 5, which shows the relationship with the current _i3 of the electroluminescent display element 5, which increases or decreases depending on the ambient brightness L, and FIG. 6, which shows the switching range of the voltage V. This will be explained by. First, switch 1
1, the power supply unit 9 outputs voltage V ₁ ,
When the brightness around the electroluminescent display element 5 is L, a current of i ₁ + i ₃ flows in the circuit (see curve G in Figure 6),
Also, at this time, the electroluminescent display element 5 emits light. Then, as the ambient light increases and becomes brighter, the current i ₃ increases, resulting in a current i ₃ up for a certain brightness Lup,
The circuit current becomes i ₁ +i ₃ up (see curve H in Figure 6).
At that time, the voltage control section 10 instructs the power supply section 9 to change the voltage to _V2 , and the electroluminescent display element 5 turns off. Thereby, the circuit current is i ₂ + i ₃ up
(See curve C in Figure 6). When the ambient light decreases and becomes dark, the current i ₃ decreases to a certain brightness
The current corresponding to low becomes i ₃ low, and the circuit current becomes i ₂
+i ₃ low (see curve B in Figure 6). At that time, the voltage control section 10 instructs the current to be changed to _V1 , and the electroluminescent display element 5 emits light. Therefore, the circuit current becomes i ₁ +i ₃ low (see curve F in FIG. 6). Repeat the same operation below.

Note that the current curves A to J in FIG. 6 are as shown in the table below.

[Table 1] A: i ₂ + i ₃ min B: i ₂ + i ₃ low = IC (light emission switching level) C: i ₂ + i ₃ up D: i ₂ + i ₃ max E: i ₁ + i ₃ min = IB ( F: i ₁ + i ₃ low G: i ₁ + i ₃ H: i ₁ + i ₃ up = IA (light-off switching level) J = i ₁ + i ₃ max The voltage switching range is shown in Table 2 below. It will be as shown.

[Table 2] Range [] i≧IA (curves H, J) V ₁ →
_V2 range [] IB≦i<IA (curves E, F, G)
V ₁ range [] IC<i<IB (curves C, D) V ₂ range [] IC≧i (curves A, B) V ₂
→V ₁ As explained above, according to the present invention, the electroluminescent display element can automatically turn on and off depending on the surrounding brightness, and in this case, an ambient light detection sensor is required. By further setting the detection level arbitrarily, there is an advantage that the light emission/extinction point can be arbitrarily set with respect to the amount of light.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an electroluminescent display element of the present invention and a circuit diagram for detecting a current flowing through the electroluminescent display element, and FIG. 2 is an explanatory diagram illustrating the characteristics of the electroluminescent display element of FIG. 1. FIG. 3 is a diagram showing a current waveform flowing through the electroluminescent display element of FIG. 1, FIG. 4 is a circuit diagram of an electroluminescent display device according to an embodiment of the present invention, and FIG. FIG. 6, which is a diagram showing the relationship between the current flowing through the element and the surrounding brightness, is a diagram showing the voltage switching range of the power supply section in FIG. 4. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Transparent electrode, 3... Light emitting layer, 4... Reflective conductive film, 5... Electroluminescent display element, 6... Current detection section, 7... AC power supply, 8 …
...Current detection unit, 9...Power supply unit, 10...Voltage control unit, 11...Switch.

Claims (1)

[Claims] 1. An electroluminescent display element that emits light in response to the application of voltage and whose current changes depending on the state of ambient light, and two types of voltages, one higher and one lower than the light emission starting voltage of the electroluminescent display element. a power supply unit that selectively outputs the power to the electroluminescent display element;
a current detection unit connected to form a closed circuit with the electroluminescence display element and the power supply unit so as to detect a current flowing in a connection circuit between the electroluminescence display element and the power supply unit; and current detection in the current detection unit. is connected to output a selection signal to the power supply in response to the state, and controls the output of the power supply unit to a low voltage when the detected current of the current detection unit reaches a predetermined high light-off switching level; An electroluminescent display device comprising: a voltage control section that controls the output of the power supply section to a high voltage when the detected current reaches a predetermined low light emission switching level.