JPS5829516B2 - Drive circuit for thin film EL display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves a drive circuit for a thin film EL display element.

In particular, the present invention relates to a circuit constructed by connecting the internal capacitance of a thin film EL display element and a coil forming a series resonant circuit.

Further, the present invention aims to reduce the power supply voltage for three-layer thin film EL display.

A thin film EL display element has a transparent electrode made of In2O3 on a transparent substrate such as glass, a dielectric material layer such as Y2O3, 813N4, an EL layer made of ZnS doped with an activator such as Mn,
Same as above <Dielectric material layer such as Y2O3, Si3N4, A
It is constructed by sequentially stacking back electrodes made of l2O3.

The two dielectric material layers and the EL layer are formed into extremely thin layers using thin film techniques such as vapor deposition and sputtering.

For example, the dielectric material layer is 0.2 μm, and the EL layer is 0.01 to 0.
．． It is 5 μm.

At least one of the transparent electrode and the back electrode is divided into a plurality of segments according to the displayed characters.

For example, it is divided into the Japanese character shape and the Japanese character shape.

Since a thin film EL display element has an EL layer sandwiched between a transparent electrode and a back electrode with a dielectric material layer, it has an equivalently large capacitive component.

By connecting a coil in series with this capacitive component to form a series resonant circuit, and driving the thin film EL display element with an AC power source having a frequency equal to the resonant frequency, it is possible to reduce the power supply voltage.

Generally, the resonant frequency f in a series resonant circuit is given by the following equation.

Here, L is the inductance of the coil, and co is the total capacitance.

By the way, in the LC resonance drive circuit shown in FIG. 1, which uses one coil in common for all segments, 1 is used, for example, when driving 7 segments in a Japanese character shape, 1 is turned on (
Connection) The value of co changes depending on the number of segments, so the resonant frequency differs, and if an excitation electromotive force with a certain frequency is applied to the LC circuit, it will deviate from resonance and the voltage value required for a 1-light display will not be obtained, causing inconvenience. .

In addition, in FIG. 1, 1a...1n are coils, and each EL segment 3 arranged in a sun or field shape is a coil.
Reference numeral 4 indicates an excitation electromotive power drive circuit, and reference numerals 5a, . . . , 5n indicate switch circuits consisting of transistors and diodes.

In view of the above-mentioned drawbacks, the present invention provides a drive circuit that can drive the display without causing the resonant frequency and external excitation frequency to differ even when the number of lighting segments differs depending on display content, such as day-shaped segments.

When making a three-layer thin film EL element emit light, the applied voltage is:
A certain voltage value of about 160 to 180 cm (hereinafter referred to as light emission starting voltage 1 h) or more is required.

Therefore, the drive circuit according to the present invention applies bipolar excitation pulses having a frequency equal to the resonant frequency determined by the total capacitance of the display segments such as the sun-shaped segment and the inductance of the coil, and having a phase difference of 180° to each segment and the resonant frequency. applied to the coil to maintain resonance in all segments.

At this time, the voltage value of the excitation pulse is set so that the voltage across the segment for which lighting is desired is driven resonantly at a light emission starting voltage of 1 h or more, and the voltage across the segment for which lighting is not desired is driven resonantly at a light emission starting voltage Vth or lower. The voltage value of the excitation pulse is set to .

FIG. 2 shows a drive circuit according to an embodiment of the present invention, and FIG. 3 shows a voltage waveform time chart at each point of the implemented circuit.
A detailed explanation of this circuit will be given below.

Input terminal IN1 of the excitation pulse drive section 24 and resonance maintenance excitation pulse drive sections 25 and 26 in FIG.

Figure 3 A and B for IN4, IN2, and IN3, respectively.
The coil 23 and the plurality of EL segments are turned on and off by applying input signals with 1800 phases different from each other and turning on and off each driver transistor as shown in FIG.
Excitation electromotive force is applied to 21a...21n.

At this time, the power supply voltage E1 s E2 +E3 is El-E
32E2 relationship, El-E3 and E2 are coil 2
3 and EL upper segments 1a, . . . , 21n as electromotive forces having opposite polarities.

Further, the frequency of the input signal is set equal to the resonance frequency determined by the inductance L of the coil and the total capacitance C of all EL segments.

In this case, the voltage values of (El-E3) and E2 are set so that the voltage across the EL segment is equal to or less than the light emission starting voltage 1h.

Input terminal lNA1, lNN1 or lNA2゜lN of lighting excitation pulse drive unit 27a...27n
The N2 input is kept at logic OXX when it is not desired to light up all EL segments.

Therefore, the voltage applied to the entire EL segment is (El-
E3) and E2, and this voltage is the emission starting voltage Vth
It is as follows.

When it is desired to light up all EL segments 1 For example, if only the upper EL segment 1a is to be lit, the input signal of logic 11 synchronized with the input signals of IN1 and IN4 is sent to terminal lNA2, and the logic % I synchronized with the input signals of IN2 and IN3 is applied.
By applying the input signal XX to the terminal INAl, the driver transistor is turned ON, OFFFL, and the excitation pulse voltage value of the upper EL segment 1a becomes IELL.

At this time, if the voltage value of El is set so that the voltage across the EL upper segment 1a is equal to or higher than the light emission starting voltage Vth,
It is possible to light only segment 1 on the EL without lighting other segments and without damaging resonance.

Figure 3C shows the input terminal lNA of the excitation pulse drive unit for lighting.
Input voltage waveform to l, lNN1, etc., input terminal lN to D
Input voltage waveform to A2, lNN2, etc.

E shows a time chart of the excitation electromotive force waveform, and F shows a time chart of the voltage waveform at both ends of the EL segment.

In the embodiment shown in FIG. 2, a reverse current prevention diode is added to the collector or emitter of the transistor to prevent reverse voltage from being applied to the transistor.

In the embodiment shown in FIG. 2, El r E2 is used as the power source.
Although three power supply voltages of +E3 are used, the resonance maintenance excitation pulse drive units 25 and 26 in Fig. 2 are modified to be authoritative using Zener diodes, and the modification is implemented when the drive circuit is authorized by only the -power supply E1. An example is shown in FIG.

If the Zener voltage value of the Zener diodes 29 and 30 in FIG. 4 is set to E3, the embodiment operates in exactly the same way as the embodiment shown in FIG. 2.

In addition, in Fig. 2, 23 is a coil, and in Fig. 4, 25.2 is a coil.
6 is an excitation pulse driver for maintaining resonance, and 31 and 32 are resistors for causing a current of a certain level or more to flow through the Zener diode.

As described above, the present invention provides a case in which LC series resonance is driven using a single coil and an EL upper segment capacitance C.
Regardless of the number of lit segments.

The LC resonance frequency can be kept constant and driven without deviation from the external excitation frequency.

The present invention also uses multi-digit display or katakana.

It can also be implemented when displaying alphabets, patterns, etc.

[Brief explanation of the drawing]

FIG. 1 is a drive circuit diagram according to the prior invention, FIG. 2 is a drive circuit diagram of one embodiment of the present invention, and FIG. 3 is a time chart of the circuit in FIG. 2. FIG. 4 is a diagram of another embodiment. FIG. 21a...21n is the EL upper segment 23 is a coil, 24 is an excitation pulse drive section, 25.26 is an excitation pulse drive section for maintaining resonance, and 27a...27n is an excitation pulse drive section for lighting. .

Claims (1)

[Claims] 1. A thin film EL display element having an electrode divided into a plurality of segments. One coil commonly connected in series to each segment. A drive circuit that excites the thin film EL display element at the resonant frequency of the series resonant circuit of the thin film EL display element and the coil;
A circuit that applies a voltage higher than the light emission start voltage of a display element and applies a voltage lower than the light emission start voltage to a segment that does not display a single display. A drive circuit for a thin film EL display element, characterized by comprising: