JP2826630B2 - EL element 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 a driving circuit for an EL device.

[0002]

2. Description of the Related Art Currently, there is an EL element drive circuit as shown in FIG. This is a battery 8 as a DC power supply
1 to the EL elements 83 to 85 using the inverter circuit 82.
And an AC power source for driving the battery.
An AC voltage of 1 OOV is generated from a voltage of 1.5 V at both ends of 1 to drive the EL elements 83 to 85. In such an inverter circuit 82, output terminals 87 and 88 are provided at both ends of a step-up transformer 86, and one output terminal 88 is provided.
Is grounded, and an AC voltage is generated based on the output terminal 88 on the ground side. In such an EL element driving circuit,
The EL elements 83 to 85 are connected to the back electrodes 8a, which are the segment electrodes of the respective EL elements, by the drive control transistors 89 to
Output terminal 8 on the ground side via a switching element such as 91
8 and a transparent electrode 8b serving as a common electrode for each EL element
Is connected to the output terminal 85 on the non-ground side for driving. This is because the bias coil 9 of the step-up transformer 86
A current (shown by an arrow 8A) in the direction of the output terminal 88 on the ground side always flows through the transistor 2 when the transistor 93 is on. Therefore, the non-grounded output terminal 87 has a DC positive potential with respect to the grounded output terminal 88, that is, the average voltage obtained by averaging the AC voltage during this period is positive. The reason is that when a high voltage of 100 V is applied between the transparent electrode and the back electrode with the transparent electrode being DC negative with respect to the back electrode, the ITO indium film is formed on the transparent film.
In a general EL device in which a light emitting layer is interposed between a transparent electrode formed by evaporating tin oxide) and a back electrode, ITO (which constitutes the transparent electrode is electrolyzed with moisture contained in the EL device, The transparent electrode is corroded, so that the potential of the transparent electrode needs to be DC-positively maintained with respect to the potential of the back electrode.

[0003]

However, when the EL element is used for illumination or decoration, the transparent electrode is mounted so as to be in front. In such a driving circuit for an EL element, the transparent electrode side of the EL element always has a high voltage of 100 V. Therefore, when a metal decoration is applied to the front of the EL element, if the metal part and the transparent electrode are not strictly insulated, a short circuit may occur. There is a danger. For example, a pachinko machine has a high risk of driving many nails. Therefore, in order to provide the EL element over a wide area on the front of the base, it is necessary to provide the EL element so as to wipe the nail portion, which causes an increase in cost.

[0004]

Therefore, the transparent electrode is grounded in an alternating current manner, and the transparent electrode is made to be positive with respect to the back electrode in direct current.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION An EL element in which a light emitting layer is interposed between a transparent electrode formed by depositing ITO (indium tin oxide) on a transparent film and a back electrode,
A driving voltage generating circuit for generating an AC voltage for driving the EL element between a pair of output terminals and grounding one of the output terminals, and applying a driving voltage to the transparent electrode side of the EL element. Connected to one of the grounded output terminals of the generation circuit, a switching element is provided between the back electrode side and the other output terminal of the drive voltage generation circuit, and the transparent electrode is DC-connected to the back electrode. And a driving circuit for the EL element that is held at a positive potential and grounded in an alternating current manner.

On a transparent film, ITO (indium.
An EL element in which a light emitting layer is interposed between a transparent electrode formed by evaporating tin oxide) and a back electrode, and an AC voltage for driving the EL element generated between a pair of output terminals. A drive voltage generating circuit having an output terminal grounded, and a switching element and a DC component cutoff differentiating circuit provided between the output terminal and the rear electrode on the non-ground side are connected in series in this order. A series circuit, a clamp circuit provided between the output terminal on the ground side and the transparent electrode, for clamping a voltage directed from the output terminal to the transparent electrode, a pull-up resistor for pulling up the transparent electrode, A ground resistance for grounding the back electrode, and a potential control circuit that holds the transparent electrode at a positive potential with respect to the back electrode in a DC manner and grounds in an AC manner. Constituting the driving circuit.

Here, the switching element is preferably a triac.

The clamp circuit is connected to the ground-side output terminal via a resistor between the transparent electrode and the ground-side output terminal with the direction from the transparent electrode to the ground-side output terminal being a forward direction. And a diode connected between the transparent electrode and the output terminal on the ground side, with the direction from the output terminal on the ground side to the transparent electrode being the forward direction.

The series circuit and the ground resistor are provided for each of the plurality of EL elements having the light emitting layer and the back electrode which share the transparent electrode with each other and are independent of each other. It is also preferable to share an up resistance.

[0010]

Next, a description will be given of an EL element driving circuit according to an embodiment of the present invention.

FIG. 1 is an electric circuit diagram showing the configuration of this embodiment. First, the configuration of this embodiment will be described with reference to FIG. In FIG. 1, reference numerals 1A to 1C denote EL elements.
(A) and a transparent electrode 1b is formed by depositing ITO on a transparent film 1a as shown in FIG. 2 (b) showing a cross section taken along line AA of FIG. 2 (a), and an EL element 1A is formed on this surface. ~ 1
C, independent light emitting layers 1c to 1e are formed thereon, and a dielectric layer 1f is formed thereon, and independent back electrodes 1g to 1C to EL elements 1A to 1C corresponding to the light emitting layers 1c to 1e. 1i is provided. Reference numerals 1j to 1m denote lead lines of the transparent electrode 1b and the back electrodes 1g to 1i, respectively.

An inverter circuit 2 has an output terminal ou.
During t1 and out2, the AC voltage obtained by boosting the voltage across the battery 3 is generated. The inverter 2 generates an AC voltage by oscillating a transformer T having a bias coil 2a, a primary coil 2b, and a secondary coil 2c connected in series. Here, an output terminal out1 is provided at the other end of the secondary coil 2c, and the other end of the bias coil 2a is connected to the negative electrode of the battery 3 and the output terminal out.
2 is provided, and the output terminal out2 is grounded.
The inverter 2 has a transformer T, a collector connected to the positive pole of the battery 3, an emitter connected to a connection point between the bias coil 2a and the primary coil 2b via a resistor, and a base connected to a resistor. r1, Darlington-connected transistors tr1 and tr2 connected to the connection point between the primary coil 2b and the secondary coil 2c via the capacitor c1 (there may be a single transistor) and the collector and the base of the transistor tr1. A capacitor c2, a transistor tr3 and a resistor r2 connected in series between the collector and the base of the transistor tr1, an output terminal out1,
and a capacitor c3 connected between out2. The inverter circuit 2 starts operation by turning on the switch sw0 and grounding and turning on the base of the transistor tr3.

Reference numeral 4 denotes a snubber circuit, which has an output terminal out.
Bias coil 2a due to load fluctuation between 1 and out2
Is connected between both ends of the bias coil 2a in order to suppress an undershoot generated in the bias coil 2a. The snubber circuit 4 has a diode d1 and a capacitor c so that the forward direction of the current flowing through the bias coil 2a is reversed.
4 are connected in series, and the connection point between the diode d4 and the capacitor c4 is grounded via a resistor r3.

Reference numeral 5 denotes a triac as a switching element, and reference numeral 6 denotes a differentiating circuit. The triac 5 and the differentiation circuit 6 are connected in series, and the EL elements 1A to 1C
It is provided between each of the back electrodes 1g to 1i and the output terminal out1. The control terminal of each triac 4 is grounded via a series circuit formed by the corresponding diode d2, resistors r4 and r5, and transistor tr4. When the transistor tr4 is turned on, the triac 5 is activated. Each transistor tr4
Are turned on by turning on the switches sw1 to sw3 provided corresponding to the EL elements 1A to 1C and pulling up the base to the potential side of the positive pole of the battery 3 through the respective transistors tr5. Is done. The differentiating circuit 6 includes a capacitor c5 and a resistor r6 for grounding a terminal on the side opposite to the side connected to the back electrode of the capacitor c5.
The DC component of the voltage between the output terminals out1 and out2 applied via the triac 5 is cut off.

Reference numeral 7 denotes a clamp circuit.
Is a diode d3 connected to the output terminal out2 via the resistor r7 between the transparent electrode 1b and the output terminal out2 with the direction from the transparent electrode 1b to the output terminal out2 as a forward direction, and transparent in a direction opposite to the diode d3. The diode d4 is connected between the electrode 1b and the output terminal out2. The transparent electrode 1b side of the clamp circuit 7 is pulled up to the potential side of the positive pole of the battery 3 via a pull-up resistor r8. The back electrodes 1g to 1i of the EL elements 1A to 1C are grounded via grounding resistors r9 provided correspondingly. These clamp circuit 7, pull-up resistor r8 and ground resistor r9 constitute a potential control circuit, which holds transparent electrode 1b at a positive potential with respect to back electrodes 1g-1i in a DC manner and is grounded in an AC manner. It is.

Next, the operation of the driving circuit for the EL element of the present embodiment configured as described above will be described. First, the boosting operation of the inverter circuit 2 will be described. Inverter circuit 2
Is turned on, the switch sw0 is turned on.
As a result, the transistor tr3 is turned on, and the resistance r
2, the transistor tr1 is turned on. The transistor t which is turned on when the transistor tr1 is turned on
The emitter current of r2 flows to the bias coil 2a via the resistor r10. As a result, a feedback voltage is generated in the primary coil 2b, and the base current of the transistor tr1 is increased via the resistor r1 while charging the capacitor c1, thereby further increasing the emitter current of the transistor tr2. Thereby, the charging of the capacitor c1 is continued. When the feedback voltage decreases due to the saturation of the transformer T, the voltage of the capacitor c1 becomes a reverse bias voltage, and the transistors tr1 and tr2 are turned off. In this off state, the charge of the capacitor c1 is reversely charged in the path indicated by the arrow A passing through the primary coil 2b, the bias coil 2a, the battery 3, the transistor tr3, the resistor r2, and the resistor r1 until the base current of the transistor tr1 flows. Continue. By such a series of oscillating operations, a boosted voltage is generated in the secondary coil 2c and applied to the capacitor c3 and the terminal f of the triac 5. This voltage is as shown in FIG. 3 when viewed between the output terminals out1 and out2.
The drawing is based on the output terminal out2.

Next, the operation of causing the EL elements 1A to 1C to emit light will be described with reference to the case where the EL element 1C emits light.
The switch sw3 is turned on corresponding to the EL element 1C (hereinafter, the configuration indicated by the reference numeral common to the EL elements 1A to 1C, for example, the triac 5, the transistor tr4, and the like refer to the element corresponding to the EL element 1C). And As a result, the transistors tr5 and tr4 are turned on, a gate current flows to the triac 5 via the diode d2 and the resistors r4 and r5, and the triac 5 is turned on. Thereby, the EL is connected via the triac 5 and the capacitor c5.
The EL element 1C is charged along the path indicated by an arrow B reaching the element 1C and further reaching the output terminal out2 via the diode d3 and the resistor r7. Further, in the inverter circuit 2, the transistors tr1 and tr2 are turned off, and the secondary coil 2
When a back electromotive voltage is generated at the point c, the diode d4 and the EL element
C, arrow C leading to the triac via capacitor c5
The EL element 1C is charged through the path shown in FIG. Thus, FIG.
The alternating current flows through the EL element 1C along the paths indicated by arrows B and C, and the EL element 1C emits light. At this time, EL
An AC voltage as shown in FIG. 4A is applied to both ends of the element 1C. This drawing is based on the output terminal out2. Here, the current that has started flowing through the triac 5 is the EL element 1C
When the applied voltage (i.e., the average voltage shown in FIG. 4B) is the maximum, the minimum is the minimum, the triac 5 is turned off, and the on and off are repeated. 4A shows a state in which the triac 5 is turned off and the charge of the EL element 1C is discharged.

When the switch sw3 is turned off, the transistors tr5 and tr4 are turned off, and the triac 5 is turned off.
, And the triac 5 is turned off. Here, the diode d2 is provided to prevent the triac 5 from being turned on by being triggered by the reverse bias current of the base and the emitter of the transistor tr4.

As described above, in the present embodiment, the DC component is cut off by the differentiating circuit 6, and the
The pull-up resistor r8 pulls up the transparent electrode 1b with respect to the DC component. That is, when a current flows through the path B, the voltage between the transparent electrode 1b and the ground is clamped by the voltage division of the pull-up resistor r8, the diode d3, and the resistor r7, and the current flows through the path C. In this case, the voltage is clamped by the forward voltage of the diode d4, and the voltage between the transparent electrode 1b and the ground becomes as shown in FIG. This allows
The average voltage of this AC voltage is set to + 1.3V. Further, a pull-up resistor r8, a diode d3,
The DC bias caused by the DC component flowing through the resistor r7 and the average bias generated by the AC components flowing through the resistor r7 and the diodes d3 and d4 do not reverse, that is, the transparent electrode 1b with respect to the back electrode 1i. The back electrode 1i is grounded via a ground resistor r9 so that the negative polarity does not become negative. Thereby, the transparent electrode 1b can be grounded for the AC component, and can be DC positive with respect to the back electrode 1i. Transparent electrode 1b
FIG. 6A shows the voltage across EL element 1C with reference to FIG.
The DC component, that is, the average voltage, is as shown in FIG.
As shown in FIG. 5, the back electrode 1i has a DC lower potential than the transparent electrode 1b. This prevents a DC component of a voltage as high as 100 V from being applied when the potential of the transparent electrode becomes DC negative with respect to the potential of the back electrode.

Further, when the triac 5 is turned on from the off state, the load on the transformer T sharply increases, so that the saturation excitation current of the transformer T does not increase. At the next excitation, the excitation current increases. When the magnetically stored energy is released, a large undershoot occurs. At this time, the undershoot generated in the bias coil 2a of the transformer T is absorbed by the capacitor c4 and the diode d1 of the snubber circuit 4. In the normal OFF state, the voltage generated between the bias coil 2a is a voltage determined by the capacitor c4 and the resistor r3, and does not repeatedly contribute to the amplitude. However, when a large abnormal peak value comes, it is absorbed by the capacitor c4 through the diode d1, Limit the peak value. Thereby, the abnormal voltage applied to the EL element 1C can be reduced. For example, FIG. 4C shows the voltage across the EL element 1C when the snubber circuit 4 is omitted from the configuration of the present example. It can be seen from the figure that the snubber circuit 4 has a large effect of suppressing undershoot. FIG. D shows the average voltage.

In the above, the case where the EL element 1C emits light has been described. However, the EL elements 1A and 1B operate similarly by turning on the corresponding switches sw1 and sw2.

As described above, according to this embodiment, the transparent electrode can be grounded. For this reason, even when the EL element is mounted using metal nails or screws, or when a metal decoration is put on the EL element and mounted with nails or screws, the transparent element is transparent when the decoration is provided through the transparent electrode. Even if the electrode and nail or screw are short-circuited, there is no danger of electric shock and safety is improved. In the past, holes for passing nails and screws were provided to insulate the transparent electrodes from the nails and screws, but in this example, nails and screws can be driven directly through the transparent electrode. In addition, it is possible to save the trouble of the conventional positioning and the trouble of insulating the through hole and the nail. Further, if the back electrode is avoided, the decoration can be easily attached, for example, the decoration can be screwed through the transparent electrode from behind.

The clamp circuit 7 of the above embodiment is composed of the diodes d3 and d4 and the resistor r7. However, the present invention is not limited to this. If the clamp circuit 7 can clamp the voltage between the transparent electrode and the ground as described above, Well, FIG. 7 (a)
As shown in (d), the capacitor is composed of a capacitor and a resistor ((a) and (b) in the same drawing), the diodes d3 and d4 are replaced with a Zener diode ((c) in the same drawing), and replaced with a photodiode. ((C) in the figure).

[0024]

According to the present invention, the transparent electrode is grounded in an alternating current manner and the transparent electrode is made positive in the direct current direction with respect to the back electrode. For this reason, it is easy to take insulation measures when attaching the EL element, and the disadvantages associated with the insulation measures can be eliminated. That is, for example, when the EL element is attached with nails or screws, it is only necessary to avoid contact with the back electrode, so that the attaching work is simplified and there is no danger of electric shock.

[Brief description of the drawings]

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

FIG. 2 is an electric circuit diagram showing a configuration of a main part of FIG.

FIG. 3 is a waveform chart for explaining the operation of FIG. 1;

FIG. 4 is a waveform chart for explaining the operation of FIG. 1;

FIG. 5 is a waveform chart for explaining the operation of FIG. 1;

FIG. 6 is a waveform chart for explaining the operation of FIG. 1;

FIG. 7 is a modified example of a main part of FIG. 1;

FIG. 8 is an explanatory diagram for explaining a conventional technique.

[Explanation of symbols]

Reference Signs List 1A-1C EL element 1b Transparent electrode 1g-1i Back electrode 2 Inverter circuit (drive voltage generation circuit) 5 Triac (series circuit) 6 Differentiator circuit (series circuit) 7 Clamp circuit (potential control circuit) r8 Pull-up resistor (potential control) Circuit) r9 Ground resistance (potential control circuit)

Claims (5)

(57) [Claims] 1. An EL device having a light emitting layer interposed between a transparent electrode formed by depositing ITO (indium tin oxide) on a transparent film and a back electrode, and a pair of output terminals, A drive voltage generating circuit that generates an AC voltage for driving the EL element and has one output terminal grounded, and the transparent electrode side of the EL element is connected to the grounded one of the drive voltage generating circuit. Connected to an output terminal, a switching element is provided between the back electrode side and the other output terminal of the drive voltage generation circuit, and the transparent electrode is DC-directly held at a positive potential with respect to the back electrode. A driving circuit for an EL element, which is grounded in terms of AC. 2. An EL element in which a light emitting layer is interposed between a transparent electrode formed by depositing ITO (indium tin oxide) on a transparent film and a back electrode, and said EL element is disposed between a pair of output terminals. A driving voltage generating circuit for generating an AC voltage for driving the EL element and having one output terminal grounded; and a switching element and a DC component provided between the output terminal on the non-ground side and the rear electrode. A series circuit in which a blocking differential circuit is connected in series in this order; and a clamp provided between the output terminal on the ground side and the transparent electrode, for clamping a voltage directed from the output terminal to the transparent electrode. A circuit, a pull-up resistor for pulling up the transparent electrode, and a grounding resistor for grounding the back electrode, for holding the transparent electrode at a positive potential DC with respect to the back electrode. And a potential control circuit that is grounded in an alternating current manner. 3. The EL element driving circuit according to claim 2, wherein said switching element is a triac. 4. The clamp circuit, wherein a direction from the transparent electrode to the output terminal on the ground side is a forward direction, and the clamp circuit is connected to the output terminal on the ground side via a resistor between the transparent electrode and the output terminal on the ground side. A connected diode, comprising a diode connected between the transparent electrode and the output terminal on the ground side, with the direction from the output terminal on the ground side to the transparent electrode being a forward direction. 3. The driving circuit for an EL element according to 2. 5. The output terminal and the clamp circuit, wherein the series circuit and the grounding resistor are provided respectively for a plurality of EL elements having the light emitting layer and the back electrode which share the transparent electrode with each other and are independent of each other. 3. The driving circuit for an EL element according to claim 2, wherein the driving circuit and the pull-up resistor are shared.