JPS5828597B2 - Drive circuit for thin film electroluminescent panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film electroluminescent panel (hereinafter referred to as E
To provide a drive circuit configured with one DC voltage source having a voltage far lower than a light emission start voltage when driving a display element having a hysteresis characteristic between light emission brightness and applied voltage, such as an LP. It is something.

First, a cross-sectional configuration diagram of the ELP is shown in FIG.

A transparent electrode 2 made of In2O3 is provided on a glass substrate 1.

A dielectric material layer 3 such as Y2O3 is deposited on top of this, and a fluorescent layer 4 of ZnS doped with Mn is further applied thereon, and the same dielectric material 31 as described above is deposited by vapor deposition, sputtering, etc. It has a three-layer structure, on which a back electrode 5 made of AI or the like is arranged.

ELPs with such a structure have superior characteristics in terms of brightness, lifespan, and stability compared to conventional distributed EL elements.
The historical phenomenon shown in the figure is shown.

To explain this characteristic according to Fig. 2, when a pulse of voltage amplitude v1 is first applied as shown in Fig. 2a, the brightness will be as shown in Fig. 2a.
It is at level 81 as shown in c.

Here, vl is vl>vt, where vth is the emission threshold voltage.
It is h.

When a write voltage v2 is applied to this, the brightness increases all at once to B3.
Even if the voltage value is then returned to the maintenance voltage v1, the brightness settles to B2, which is higher than B1.

When the erase voltage V3 is applied to this, the brightness level decreases rapidly, and when it is returned to the sustaining voltage V1 again, the brightness settles to B1 (.

These temporal relationships are indicated by the symbols 1. ,
13......t21 are shown by corresponding to the positions of the same symbols in C of the same figure.

As shown by the thin line in FIG. 2, this hysteresis phenomenon can take any small loop depending on the amplitude and pulse width (not shown) of the write voltage.

That is, it is also possible to display halftones.

Once a write voltage is applied, E continues to emit light without losing the gradation given by the sustain pulse.
This is a major feature not found in other LP display elements.

The above voltages vary depending on the composition, film thickness, and applied waveform, but in the prototype example, Vth = 200 V.

V=210V, ■2-210~280V, V3=190
It is V.

As described above, thin film EL having hysteresis characteristics can be electrically written, but optical writing as described below is also possible.

That is, first, consider the case where light is irradiated from the outside only during the T2 period while constantly applying an alternating current sustaining pulse to both ends of the ELP as shown in FIG.

Then, the ELP will have a brightness of B during the T1 period before light irradiation.
1, the brightness increases to B3 during the T3 period after light irradiation.

Of course, this brightness level B3 largely depends on the length of the T2 period, the amplitude Vs and pulse width τ of the sustain pulse, and the intensity and wavelength of external light.

In this case, when light is irradiated from the outside, a polarization electric field is generated by optical writing during +V8 and v8 when the sustain pulse is applied, and this polarization electric field is relaxed during the Ov period when no sustain pulse is applied.

The relationship between the wavelength dependence of the optical writing source, the irradiation time, and the emission spectrum of the ELP is shown in FIG.

It can be seen that optical writing is most sensitive to light with a wavelength of 3,500 per person, and that the emission spectra of ELP are far from large values.

On the other hand, the brightness level B2 after optical writing on the amplitude Vs and width τ of the sustain pulse shows dependence as shown in FIG.

That is, the larger the sustain voltage and pulse width, the higher the brightness level B2.

The present invention relates to a drive circuit in which an ELP having the above characteristics is applied to, for example, an optical writing blackboard.

As shown in FIG. 6, the optical writing blackboard is an ELP with the above-mentioned configuration.
5, a light pen 7, a housing 8 containing a peripheral drive circuit, and a variable maintenance voltage dial 9.

The ELP 5 may have a shape in which the transparent electrodes 2 and 5 extend uniformly over the entire surface of the ELP as described above, or one electrode 2 or 5 may be arranged in parallel in a striped manner, and the other electrode 5 or 2 may be arranged in parallel with the above electrode. may be arranged in parallel stripes in orthogonal directions, or may be formed in a so-called matrix.

Sustain pulses are simultaneously applied to the entire surface of the ELP, and alphanumeric characters and symbols are arbitrarily written with a light pen.

If you want to erase the data, turn the variable volume 9 to the low voltage side.

Also, if you use a tungsten lamp instead of a special light source, you can get a compact and inexpensive pen, which has great practical value.

By the way, the emission peak wavelength of a tungsten lamp is on the long wavelength side even in visible light, and in relation to Figure 4, it is E.
The optical writing sensitivity is quite low compared to LP.

Therefore, considering the characteristics shown in Figure 5, for the same light source, either increase the amplitude of the sustaining voltage by 1 vsl (although if it increases too much, the contrast ratio will deteriorate as seen in Figure 2), or The width τ may be increased.

Ultimately, from the point of view of optical writing, an applied waveform with a duty ratio of 50% is most preferable under the condition of a constant frequency.

FIG. 7 shows a circuit diagram for supplying sustain pulses to ELP,
In FIG. 7, 10.・・・・・・・・・・・・13
is a transistor, 14.・・・・・・・・・・・・17
Diode 18 is inductance, 19 is EL, 20
is a variable voltage source.

Transistor 10 in FIG.・・・・・・・・・・・・
The timing for turning ON and OFF 13 is as shown in FIG.

That is, when the signal shown in FIG. 8a is at bi level, the transistors 11 and 13 in FIG. 7 are turned on, and when it is at low level, they are turned off.
It is.

Also, when the signal in Figure 8 is at bi level, transistor 1
0.12 is ON, and OFF when it is low level.

The pulse subt t in FIGS. 8a and 8b is selected so that the inductance of the coil 18 in FIG. 7 is LCH), and the capacitance of EL 19 is CCF).

If there is no loss in the circuit system, the voltage of the power supply 20 in FIG. 7 is E.

Then, the voltage applied across the ELP 19 increases by +2Eo and -4E each time a and b in Fig. 8 alternately become bi-level.
o, +6Eo, . . . , the amplitude increases, and theoretically it should reach an infinite amplitude.

However, as a practical problem, there are various resistance losses such as the ON resistance of the transistor, the forward resistance of the diode, the electrode resistance of the EL, and the saturation phenomenon of the inductance core due to the increase in current as the amplitude increases. As shown in , the amplitude of the EL applied voltage reaches the saturation value.

The voltage at this time is set to be the maintenance voltage V1.

Therefore, after a certain transient time, the duty ratio of constant amplitude becomes 5.
A 0% bipolar pulse will be applied across the EL.

By the way, in our prototype, the capacitance is about 30,000P.
F's ELPK vs. 1. -CV.

=40V, an applied voltage with a duty ratio of 50% of ±200μ was obtained.

Further, while applying the above-mentioned alternating voltage (300 Hz) to the EL, sufficient optical writing was possible with a 1 watt tungsten lamp.

The optically written characters, symbols, or patterns are different in the sensitivity of the ELP during optical writing and the emission spectrum of the ELP as shown in Figure 4, and the emission time of the ELP is different from the pulse width of the sustain pulse. Of course, if the electrodes 2 and 5 are in a matrix shape, the voltage application parts are independent of each other, and even if the electrodes 2 and 5 are formed to extend uniformly over the entire surface, the light-emitting area is the non-light-emitting area. It never bleeds.

Furthermore, in order to erase a panel that has been optically written, by rotating the dial 9 in FIG. 6 and lowering the power supply voltage 20 in FIG. 7, an erase voltage pulse is applied to both ends of EL.

Since the thin film EL has a large capacitance, it can be combined with an inductance to form a resonant circuit, and the switching element can be turned on and off at appropriate timing.
In this way, an optical writing device can be configured with one power supply voltage that is much lower than the light emission starting voltage.

Although all the transistors used in FIG. 7 are of the NPN type, it goes without saying that a PNP type may also be used.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the ELP, Figure 2 is a diagram of the relationship between the ELPO applied voltage and luminance, Figure 3 is a voltage waveform diagram applied to the ELP during optical writing, and Figure 4 is the ELP's light sensitivity wavelength and luminescence. 5 is a diagram showing the relationship between ELP applied waveform and luminance; FIG. 6 is a perspective view of an optical writing plate constituting an embodiment of the present invention; FIG. 7 is a diagram showing an embodiment of the present invention. FIG. 8 is a time chart of the circuit shown in FIG. 7. 2 is an electrode, 3, 3' is a dielectric material layer, 4 is a fluorescent layer, 10-
13 is a transistor, 18 is a coil, and 20 is a power supply.

Claims (1)

[Claims] 1. In a drive circuit for a thin film electroluminescent panel in which a dielectric material layer and an electrode are provided on both sides of a fluorescent layer, the thin film electroluminescent panel has 1
A series resonant circuit is formed by connecting several coils, and when performing optical writing, a switching element is connected to the series resonant circuit to alternately connect one DC power source in the reverse direction to apply an AC sustaining pulse. Features a drive circuit for thin-film electroluminescent panels.