JPS60151996A - Electric field light emitting device - 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 [Technical Field of the Invention] The present invention relates to an electroluminescent device using an electroluminescent (EL) element.

[Prior art]

It is well known that the brightness of conventional KL elements changes depending on the applied voltage or frequency.

Therefore, in order to obtain stable brightness output even when the DC power supply voltage or load fluctuates, the applied voltage and frequency can be adjusted by detecting the output voltage and feeding it back negatively to the drive circuit to stabilize the output voltage. A drive power supply method that stabilizes the power supply is being considered.

However, even when driven by such a driving power supply method, for example, a pure sine wave constant frequency/constant current AC power supply, the brightness of the EL element gradually decreases as the lighting time elapses, and this aging In other words, the problem of lifetime is currently the biggest problem in practical use of EL elements. As shown in Figure 1, the time t required for the initial brightness BO to reach B o/2
x/2'l: This is called the half-life and is used as a parameter of lifespan, and the value of t1/2 from the current value is generally several to several thousand hours. If the EL element is exposed to high temperatures or irradiated with ultraviolet rays during lighting, this reduction in brightness will be further accelerated.

[Summary of the invention]

The present invention was made in view of these circumstances, and
The purpose is to provide an electroluminescent device that can compensate for the long-term decline in luminance, which is currently the biggest obstacle to the practical application of E L l< in a wide range of fields. It is in.

In order to achieve such an object, the present invention focuses on the fact that there is a positive correlation between the current flowing through an EL element and brightness, and comprises a peak hold circuit that extracts and detects the current through a diode. A drive control circuit that compares the detected output with a reference voltage and feeds the difference back to the drive circuit to control the drive voltage output of the primary coil of a step-up transformer with an EL element connected to the secondary side. EL
The brightness of the element has a peak value at room temperature, and as the temperature increases
It is set to exhibit a temperature characteristic that gradually decreases symmetrically with respect to time as the temperature decreases. Hereinafter, the present invention will be explained in detail using Examples.

〔Example〕

FIG. 2 is a block diagram showing one embodiment of the present invention. In the figure, 1 is a signal generator, which may be any generator as long as it generates a signal with a constant frequency. Reference numeral 2 denotes a 1, 14 circuit that is turned on and off by the input signal from the signal generator 1, thereby intermittent current flowing through the primary coil of the step-up transformer 3. 4 is EL
When the transducer goes out, it emits light due to the voltage V induced in the secondary coil of the transformer 3. Reference numeral 5 denotes a current detection circuit consisting of a peak hold circuit which extracts and detects the current flowing through the EL element 4 via a diode as described later.

A drive circuit 6 compares the detection output from the current detection circuit 5 with a reference voltage EO and feeds back the difference negatively to the drive circuit 2. When the lJ closed circuit detection current increases, the drive voltage output of the primary coil of the step-up transformer 3 is lowered, and when the detection current decreases, the drive voltage output is increased to reduce the total current flowing through the EL curative 4. However, the reference voltage is the same as the brightness-temperature characteristic curve of the EL element in relation to the temperature change in the operating temperature range of the terminal box of the diode of the peak hold circuit. As shown in the figure, the curve was selected so that the brightness peaked at room temperature and gradually descended in a substantially symmetrical manner to the left and right.

As described above, the present invention increases the output voltage applied to the EL element 4 as the impedance of the EL element 4 increases over time, and supplies a constant total current to maintain a constant li.
However, the brightness of the EL element 4 varies depending on the current as described above, and at the same time,
Even a constant current changes with temperature as shown in FIG. Therefore, even if constant current control is performed as described above, if there is a change in temperature, the brightness will change in the same way as shown in FIG. 4. Therefore, in the present invention, the temperature percentage of the diode of the current detection circuit 5 is also included in the horsepower, and the drive control circuit 6
By setting the reference voltage to 31.1, a brightness-temperature characteristic as shown in FIG. 3 is obtained, and changes in brightness due to changes in direct position during normal use are kept as small as possible.

For example, if the signal generator 1 is an oscillator that generates a rectangular wave with a duty of 50%, the 1 drive circuit 2, the current detection circuit 5, and the drive control circuit 6 can be realized by a circuit as shown in FIG. The drive circuit 2 includes a drive transistor Q1 that intermittents the current flowing through the primary coil of the step-up transformer 3.
and a transistor Q2 that controls the base voltage of the transistor Q1.In order to eliminate distortion r of the drive voltage waveform and improve symmetry, a push-pull switching method is used, and the voltage is connected via a logic inversion circuit T. Transistors Qt', Q similar to the above transistors Ql, Qz
2' is connected. R1-R3+ R1'~R3'
is resistance.

Note that the circuit power supply VCC is, for example, a commercial power supply (AC100
V, 60150' Hz) may be used by flowing a full wave, or if it is used in an automobile, a DC power source such as a battery may be used.

The current detection circuit 5 includes resistors R4+R5, a diode D1 which takes out the current flowing to the EL element 4 from the connection point between the EL element 4 and the resistor R5, and a capacitor which is charged by the current and holds the entire peak value. Act 3 of voltage follower connection with input as input and amplifier OPI
This is a peak hold circuit consisting of: The drive control circuit 6 is a DC analog inverting amplifier circuit using an amplifier OPZ, and amplifies the entire left voltage of the peak voltage and the reference voltage EO to the transistors Q2 + Q2 of the drive circuit 2.
' returns to the input terminal. Note that R6 and R7 are resistors. In other words, when the current flowing through the EL element 4, that is, the '1L current detected by the current detection circuit 5, is less than a predetermined value, the output of the operational amplifier OP2 is not large. When the driving voltage of the next coil increases and the output voltage applied to the ELX element 4 increases, and the detection current increases, conversely, by decreasing the output voltage applied to the EL hydrogen element, the current flowing through the EL element 4 increases. always kept constant.

Here, a Zener diode ZDI and a resistor R8+ are connected to the non-inverting input terminal of the operational amplifier OP2 of the drive control circuit 6 in order to set the reference voltage to a predetermined level as described above.
R91RIOs capacitor C2 and diode D2
A reference voltage setting circuit consisting of the following is provided, DC voltages El and Ezk are applied, and the terminal voltage of Zener diode ZDI is set at point A, total VZD s, resistance value of resistor R8+R9 'f:
r8. r, so that a reference voltage of e1=vzD rB+rg is obtained. In this example,
By setting the value of this reference voltage e1 to about 0.4 to 0.6 V, which is about the same level or about 2/3 of the terminal voltage of the diode DI, all of the above conditions could be satisfied. The capacitor C2 forms an integration circuit with the resistor R8 to slow the rise in the reference voltage e1, thereby preventing abnormal voltage from being applied to the EL element 4 when the power is turned on, etc. The brightness increases gradually. Further, D2 is a diode that ensures the above-mentioned quick start even when the power is suddenly turned on.

In addition, in the above-mentioned embodiment, a reference voltage setting circuit was used which sets the reference voltage to the desired value by the resistors R8 and R9, but the present invention is not limited to this, and the terminal voltage of the diode DI is Any material may be used as long as it can absorb the voltage at point A so that the brightness-temperature characteristic shown in FIG. 3 can be obtained in relation to the temperature change. Also, a resistor R5 was connected in series with the EL element 4, and a diode Dl' was connected to the connection point, but this resistor R5? By setting 5p<resistance, even if the connected EL element 4 changes (that is, its impedance changes), it is possible to easily adjust the M"I BM so that the appropriate brightness (1) is obtained. Furthermore, the impedance connected in series with the EL element 4 may be a capacitor, and in this case, the input of the current detection circuit 5 is integrated to detect changes in the current peak value due to changes in the output voltage waveform when the impedance of the EL element 4 changes. is suppressed ft1l
It has the advantage of being stable and providing a stable /l JET' degree output.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a 'current detection circuit' comprising a peak hold circuit which takes out the 'kt current flowing through EL hydrogen atoms via a diode and detects its peak value, and its detection output and reference voltage. By providing a drive control circuit that feeds back the difference between
It is possible to compensate for a long-term reduction in brightness due to aging of the impedance of the 9EL element. In addition, by appropriately selecting the reference voltage of the drive control circuit in response to temperature changes in the terminal voltage of the diode constituting the peak hold circuit, the EL hydrogen brightness can be adjusted to its peak value at the given temperature. By adopting a temperature characteristic that gradually decreases in an almost symmetrical manner as the temperature increases, there is an advantage that a more stable luminance output can be obtained under normal usage conditions.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the secular change in EL hydrogen brightness, Fig. 2 is a block diagram showing an embodiment of the present invention, and Section 3 shows the brightness of the EL element versus temperature when temperature compensation is performed according to the present invention. FIG. 4 is a diagram showing the brightness-temperature characteristic when the above-mentioned compensation is not performed, and FIG. 5 is a circuit diagram showing a specific example of the configuration of FIG. 2. 1... Signal generator, 2@... Drive circuit, 3... External pressure transformer, 4... EL element, 5...
...Parent current detection circuit, 6...41 first i1j control circuit, DI...Diode that takes out the current flowing to the EL element. q) Hosoto Kide Koito Seisakusho Co., Ltd. Agent Kazuha Yamakawa (and 2 others) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] a drive circuit that repeats conduction and non-conduction in response to an input signal of a predetermined frequency, and an EL element that emits light by a voltage induced in the secondary coil of the step-up transformer; a current detection circuit that detects the current flowing through the EL resistor; and a drive control that controls the entire drive voltage output of the primary coil of the transformer by feeding back the difference between the detection output of this current detection circuit and a reference voltage to the drive circuit. The current detection circuit includes a diode that takes out the current flowing to the EL element, a capacitor that is charged by the current and holds the peak value, and a voltage follower connection calculation that takes the peak value as input. e) by a peak hold circuit equipped with an amplifier, and calculates the ratio of the change in the terminal voltage of the diode over temperature and the reference voltage of the drive control circuit so that the brightness of the EL element has a peak value at room temperature. An electroluminescent device characterized in that the temperature is set to a value that exhibits a temperature characteristic that gradually decreases in an almost symmetrical manner as the temperature rises and falls.