JPS61156692A - El element driving circuit - 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 [Industrial Application Field] The present invention relates to an EL (electroluminescence) element that emits light by application of an alternating current voltage, and particularly to a drive circuit for an EL element.

[Conventional technology and its problems]

Generally, as shown in FIG. 3, an EL element is manufactured using a transparent electrode 2 made of a transparent conductive material such as ln=0- by using an appropriate method such as vapor deposition or sputtering on a transparent substrate 1 made of glass or the like.
A first dielectric layer 3 made of an insulating material such as Y or 03 is formed on it to prevent dielectric breakdown, and a luminescent center such as Mn is roughly doped into the matrix material such as ZnS. A light emitting layer 4 is formed, and a first dielectric layer 3 is formed thereon.
A second dielectric layer 5 made of the same material is formed, and a back electrode 6 made of a conductive material such as A1 is formed thereon as the other electrode, and is used as a surface light source. .

In this EL device, electrons are excited to the conduction band by an electric field generated in the light-emitting layer 4 made of a semiconductor such as Zn 8, and are accelerated to obtain sufficient energy. Electrons directly excite the Mn light-emitting center, and the excited Mn When the luminescent center returns to the ground state, a luminescent output is obtained, and a high pulse voltage 7 of about 100 V must be applied between the transparent electrode 2 and the back electrode 6 to generate an electric field. Normally, this pulse voltage is pulses of alternating polarity as shown in FIG. 4, and a rest period t in which the voltage becomes O is set between the pulses. If a voltage is constantly applied to an EL element, the life of the element will be very short, but the inventors of the present application found that by applying a pulse voltage with a rest period, the life of the element becomes longer. Known through experiment.

By the way, as a conventional technique for applying such a pulse voltage to an EL element via a switching circuit,
There is an invention described in Publication No. 45466. This prior art is based on a first switching element in which two switching elements are connected in series. The second switching circuit is connected in parallel to the power supply, and the first switching circuit is connected in parallel to the power supply. A thin film EL element is connected between the connection points of both switching elements in the second switching circuit, and the pulse voltage is applied to the switching element to drive the EL element. The generation of a pulse voltage with a period has not been sufficiently disclosed, and since the generation of a pulse voltage with a rest period usually has a complicated circuit because it affects the life of the EL element, it is not stable. There remained a technical R issue that would make it difficult to obtain a break.

[Purpose of the invention]

The present invention has been made in view of the above problems, and
It is an object of the present invention to provide a drive circuit for an EL element that can stably obtain a rest period of an AC pulse voltage applied to the element with a simple circuit configuration.

[Means for solving problems]

In order to achieve the above object, the present invention includes an inverter that inverts the phase of the pulse voltage and a first differentiation circuit that differentiates the inverted pulse voltage, between an oscillator that generates a pulse voltage and the EL element. , and a second differentiating circuit for differentiating the pulse voltage.In the drive circuit for an EL element that applies a pulse voltage to emit EL, the pulse voltage is differentiated by the pulse voltage. It is characterized by narrowing the width and providing a stable pause period between pulses.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 shows a drive circuit that drives the EL element 11, and the oscillator 12 generates a pulse voltage of, for example, about 5V, and this pulse voltage is used to set the rest period t as shown in FIG. These oscillators 12
The pause period setting circuit 13 constitutes a circuit that generates a pulse voltage for driving the EL element 11.

The rest period setting circuit 13 is branched to generate two polarity voltages of the AC pulse voltage applied to the EL element 11, and includes an inverter 14 for inverting the pulse voltage, a notch buffer 15A for waveform shaping, 15B, CR differentiation circuit 16A, 16B, and buffer 17A, 1
7B.

These pulse voltages having pause periods and different phases are sent to noise removal circuits 18A and 18B which slow the rise of the pulse voltage applied to the EL element 11 to remove high frequency component noise 6.

Noise removal circuits 18A and 18B are CR integration circuits 19A and 19B and switching transistor 2O, respectively.
A, 20B.

Two transistors 21 for amplifying the pulse voltage.
22 connected in series, and a first amplifier circuit 23 having two
A second amplifier circuit 26, which has transistors 24 and 25 connected in series, is connected in parallel to the power supply +V, and a pulse voltage from the transistor 2OA is applied to the base terminal of the transistor 22 and 24. , the pulse voltage of the transistor 20B having the opposite phase to the pulse of the transistor 2OA is applied to the transistors 21 and 25.

The connection point of transistors 21 and 22 and the transistor 24
．． A series circuit of a resistor 27 that slows down the rise of the pulse voltage applied to the EL element 11 and the EL element 11 is inserted and connected between the connection point 25 and the EL element 11. Furthermore, E
A resistor 28 having a resistance value sufficiently smaller than the non-conducting resistance of the transistors 21 and 24 is connected in parallel to the L element 11.

A power supply circuit 29 supplies a power supply voltage +V, and is composed of a commercial power supply 30, four diodes 31, and a full-wave rectifier circuit 35 formed by 32°33.34.

The operation of the embodiment of the present invention constructed as described above will be explained in detail based on the waveform diagram of FIG.

First, a pulse voltage of about 5V (FIG. 2A) is output from the oscillator 12, branched into two, and sent to the pause period setting circuit 13. In order to obtain one polarity of the AC pulse voltage that drives the EL element 11, the pulse voltage whose phase is inverted by the inverter 14 is differentiated by the CRI dividing circuit 16A via the buffer 15A. After being differentiated, the voltage is passed through the buffer 17A again to generate a pulse voltage (FIG. 2B) having a narrower pulse width than the pulse voltage output by the oscillator 12. Similarly, in order to obtain a pulse voltage of the other polarity, the pulse voltage output from the oscillator 12 is differentiated by the CR differentiation circuit 16B via the buffer 15B, and then passed through the buffer 717B to obtain the pulse voltage output from the oscillator 12. A narrow pulse voltage (FIG. 2C) is generated. In this way, pulse voltages are generated which have different phases and have a pause period t in which they are simultaneously in the OFF state. Note that the pause period t can be varied by changing the CR time constant.

These pulse voltages having different phases are sent to the subsequent noise removal circuits 18A and 18B, respectively. Noise removal circuits 18A and 18B are CR integration circuits 19A and 19B.

When the pulse voltage rises, it takes time to charge the capacitor to the switching voltage of the transistors 20A and 20B, and when the pulse voltage rises, the capacitor discharges and the pulse voltage is completely turned off. As a result, a pulse voltage (E in the second diagram) with a steep rise and a slow fall is output.

When point D is ON, transistors 22 and 24 are conductive and F
The potential at the point becomes approximately 0, the potential at the point G becomes approximately +V, and a voltage of V is applied to the EL element 11. Since the EL element 11 can be considered as a kind of capacitor and the resistor 27 is connected in series, the pulse voltage is integrated and applied to the EL element 11. Therefore, the pulse voltage rises and falls slowly.

On the other hand, when the point E is ON, the transistors 21 and 25 are conductive, and similarly the potential between F and G becomes approximately -, but in this case, the polarity is opposite. In this way, a high AC pulse voltage (FIG. 2, FG) is applied to the EL element 11.

The high-voltage power supply voltage element (2) is supplied from the power supply circuit 29, and by using a full-wave rectifier circuit, the rectified waveform of the commercial power supply 30 is chopped at the frequency of the pulse voltage generated by the oscillator 12. A necessary high driving voltage is supplied to the EL element 11. Therefore, a high power supply voltage of about 100V can be generated from the commercial power supply 30 without requiring a transformer or the like.

In this way, it is equipped with an oscillator 12 that generates a pulse voltage, an inverter 14 that branches this pulse voltage into two and inverts one phase, and CR differentiation circuits 16A and 16B that differentiate each pulse voltage. With a simple configuration, pulse voltages having different phases each having a pulse width narrower than that of the pulse voltage generated by the oscillator 12 are generated, and these pulse voltages are applied to the amplifier circuits 23 and 26 for driving the EL element 11. A high pulse voltage having a rest period t as shown in FIG. 2 is applied to both ends of the element 11. Note that the fall of this pulse voltage is caused by the EL element 11
Since the resistor 28 connected in parallel with the EL element 11 discharges the electric charge stored in the EL element 11, the voltage falls more reliably and steeply.
It is possible to stabilize the downtime period t. Therefore, a stable rest period can be obtained, and the amplifier circuit 23.26
The transistors within the E
It is possible to extend the life of the L element 11 and prevent destruction of the transistor.

In addition, since the rise of the pulse applied to the EL element 11 is slow due to the integration circuit of the noise removal circuits 18A and 18B and the resistor 27, harmonic component noise is removed and the pulse applied to the EL element drive circuit and EL element Noise generated from the connection cord is reduced.

[Other implementation examples]

Although the above embodiments are about thin film type EL elements,
Since a distributed type EL element similarly generates noise when emitting light, the present invention can also be applied to a classified type EL element.

〔Effect of the invention〕

As detailed above, according to the present invention, an inverter that inverts the phase of the pulse voltage and a first differential that differentiates the inverted pulse voltage are provided between an oscillator that generates a pulse voltage and the EL element. A pause time setting circuit consisting of a circuit and a second differentiation circuit for differentiating the pulse voltage is inserted and connected to the first differentiation circuit. By applying the pulse voltage differentiated by the second differentiating circuit to the EL element via the amplifier circuit, an AC pulse voltage with a stable rest period is supplied to both ends of the EL element, extending the life of the EL element. In addition, it is possible to prevent the transistors of the amplifier circuit from being destroyed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
Figure 3 is a voltage waveform diagram of the main parts in the circuit diagram, and Figure 3 is a general E
A cross-sectional view of the L element, and FIG. 4 is a waveform diagram of a general pulse voltage for driving an EL element. 11... EL element 12... Oscillator 13... Shutdown period setting circuit 14... Inverter 16
A, 16B...differentiation circuit 18A, 18B...noise removal circuit 19A, 19B...integration circuit 23.
26... Amplifier circuit 27... Integrating resistor 28... Differentiating resistor 29... Power supply circuit patent applicant
Nippon Seiki Co., Ltd. Figure 2 Figure 3

Claims (1)

[Claims] In an EL element drive circuit that applies a pulse voltage to both ends of the EL element to emit EL, an inverter that inverts the phase of the pulse voltage is provided between an oscillator that generates the pulse voltage and the EL element, and an inverter that inverts the phase of the pulse voltage. 1. A driving circuit for an EL element, characterized in that a rest time setting circuit comprising a first differentiating circuit for differentiating a pulse voltage and a second differentiating circuit for differentiating the pulse voltage is inserted and connected.