JPS60151992A - 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 electroluminescent (EL) X-sons.

[Prior art]

In conventional EL elements, the brightness varies depending on the applied voltage or 1
It is well known that it changes depending on the frequency.

Therefore, in order to obtain a stable brightness output even when the DC power supply voltage or load fluctuates, the applied voltage and frequency A driving power supply method that stabilizes the sound is being considered.

However, even when driven by such a driving power supply method, for example, a pure sine wave constant frequency/constant voltage 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 the use of EL elements.

As shown in Figure 1, the time tlA required for the initial brightness Bo to reach Bo/2 is called the half-life and is a parameter of lifespan. It's on point. If the EL element during lighting is exposed to high temperature or irradiated with ultraviolet rays, this reduction in brightness will be further accelerated.

[Summary of the invention]

The present invention was made in view of these circumstances.
The purpose is to provide an electroluminescent device that can compensate for the long-term decline in brightness, which is currently the biggest obstacle to putting EL devices into practical use in a wide range of fields.

In order to achieve this purpose, the present invention provides
Focusing on the fact that there is a positive correlation between the current flowing through the L resistor and the brightness G', negative feedback is sent to the circuit that detects the entire current and its detection chip drive circuit, and in the second generation 1j, El , S
, and a drive control circuit for controlling the primary voltage output of the primary fill of the step-up transformer whose child is disconnected.

That's 9. When an EL element is viewed as an electrical impedance circuit, it is a distributed constant circuit of resistance and capacitance.

1 impedance is determined by the material and manufacturing method of the EL transducer C.
When specifying the female EL capacitor unique to Cz, it is a function of the applied voltage V and frequency f, similar to the brightness, but
On the other hand, if we fix either the applied voltage or the frequency and change the credit, and look at the correlation between 1+iB and the current i per unit area, for example, as shown in Figure 2, B and i fit non-linearly, but it becomes positive. It was found that there is a correlation. Furthermore, the second
In the figure, f+ < fz < fs, and Vup
■ indicates the direction of increase. It was also revealed that there is a positive correlation between the changes in B and i in lighting durability at constant voltage and constant frequency. From the above results, it is clear that the current, that is, the decrease in admittance (constant V) greatly contributes to the decline in luminance over time.
This can be compensated for by using foot current drive. As the admittance decreases, the applied voltage increases because it drives the current. For example, if the admittance is 2/3 of the initial value when the brightness is 0, then it is sufficient to increase the applied voltage to 2/3 of the initial value, for example, about 150 V compared to the initial value of 100 V. Demeru. Hereinafter, the present invention will be explained in detail using Examples.

〔Example〕

FIG. 3 is a block diagram showing one embodiment of the present invention. In the figure, 1 is a signal generator, which may be any device that generates a signal of a constant frequency. 2 is a drive circuit that is turned on and off by the input signal from the signal generator 1, thereby completely cutting off the current flowing through the primary coil of the step-up transformer 3. 4 is an EL element, which is caused by the voltage ■ induced in the secondary coil of the step-up transformer 3! l1 emits light. 5 is a current detection circuit that detects the current flowing through the EL element 4. 6 is the detection output '? from the current detection circuit 5Vc. i: Drive circuit 2V This is a drive control circuit that provides negative feedback, and when the detected current is increased U, the drive voltage output of the primary coil of the step-up transformer 3 is produced.When the detected current is decreased, VC is reversed and the above drive voltage output is It has the function of increasing the current ηt flowing through the EL element 4 and making it constant.

For example, if the signal generator 1 generates a sine or C triangular wave, the drive circuit 2, current detection circuit 5, and drive control circuit 6 can be realized by a circuit as shown in FIG. . That is, in FIG. 4, drive tooth #12 is a class A amplifier consisting of a transistor Q1, a resistor R, and a DC blocking capacitor C1. In addition,
The circuit power supply Vcc is, for example, a commercial power supply (ACI 00 V
.

60750 H2) may be used after full-wave rectification, or if it is used in a vehicle, a DC power source such as a battery may be used. The current detection circuit 5 includes a diode DIN which branches all of the current flowing to the EL element 4 from the connection point between the resistors R2, R, and the EL element 4 and the resistor R3, and extracts the current from the diode DIN. This is a peak hold circuit consisting of a holding capacitor C2 and a voltage follower connected arithmetic circuit 1m'JE OP1 which receives the peak value as input. The drive control circuit 6 is a DC analog inverting amplifier circuit using an operational amplifier OPZ, and the difference between the peak voltage and the reference voltage Lr is 'ar! The voltage is amplified and fed back to the base input of the transistor Q1 of the drive circuit 2. Furthermore, R4-R
7 is resistance. That is, when the current detected by the current detection circuit 5 is less than a predetermined value, the output of the operational amplifier OP2 increases, and the drive voltage of the primary coil of the step-up transformer 3 by the transistor Q1 increases and is applied to the EL element 4. As the output voltage increases and the detection current increases,
Conversely, by lowering the output voltage applied to the EL element by one level, the current flowing through the EL resistor 4 is always kept constant.

The signal generator 1 is the switching light source 1.
Although it is easy to configure a waveform with one path, in such a case, for example, in the case of a 50% duty square wave, the 51st wave
It can be configured as shown in 21. That is, the drive circuit 2 includes one coil of the step-up transformer 3 (a drive u'M+ +- transistor Q that cuts off the flowing current);
The output of the HIR amplifier OP2 constituting the drive control circuit 6 is connected to the input side of the transistor Q2 which controls the base current of the transistor Ql. As mentioned above, if the current flowing through the EL element 4 decreases as shown in q, the output of the operational amplifier OP2 increases, and the voltage on the primary coil side of the step-up transformer 3 increases via the transistors Q+ and (h, 4, the output voltage increases. Note that R8 to It+z are resistors.

In order to eliminate distortion of the drive voltage waveform of the primary fill of the step-up transformer 3 and improve its symmetry, a push-pull switching type drive circuit 2 as shown in FIG. 6 may be used. In the same figure, transistor Q 1' + Q 2
' are transistors similar to Ql and Q2, respectively, and RI
O' to R12' are the same resistances as Rlo-RI2, but the output signal from the signal generator 1 is directly input to the transistor Q2 side;
A signal inverted by the logic inversion circuit 7 is input to the transistor 2' side. The logic inversion circuit 7 may be configured using a transistor Q3, for example, as shown in FIG. 7(a), or Same figure (b)
Even if the inverter element IVI is used as shown in Figure Ce), ! : Alternatively, it may be constructed with an inverting amplifier using an operational amplifier OP3. In addition, R13 to R1s
is a resistance, and EOO is a reference voltage.

Instead of using the logic inversion circuit T, a push-pull switching type drive circuit 2 can also be realized by using a flip-flop circuit 8 as shown in FIG.

Here, the signal generator 1 can be configured as shown in FIG. 9, for example. In the figure, OF2 is an operational amplifier,
R13 to R1s are resistors, and C3 is a capacitor. In this case, the output (m has a duty of approximately 50%).

In the embodiment described above, such an output signal was input to the drive circuit 2 as is. However, in this case the frequency is 4
00 Hz, the step-up transformer 3 must have a large external size because heat is generated due to iron loss. For example, when used in a vehicle, it is necessary to suppress the amount of heat generated in order to reduce the external size, and an effective method for this purpose is to reduce the on-duty of the electric current 61F flowing through the primary coil.

Figure 10 shows this as one-shot multi-pipe lake 9,
This is an example realized using 10. In other words, the figure shows the sixth
This is an example in which the inverting amplifier shown in FIG. 7(C) VC is used as the logic inverting circuit 7, but the one-shot multivibrator 9 The output of .10 is shown in the same figure (b).
, As shown in (c), the current flowing through the primary coil of the step-up transformer 3 can be reduced.

Similarly, FIG. 12 shows an example in which capacitors C4 and C4' are connected to form a differential circuit together with resistors R1o and RIO', thereby reducing the on-duty. Note that the inverter element IVI shown in FIG. 7(b) is used as the inverting amplifier 7. Furthermore, in FIG. 13, the drive circuit 2 is configured using a flip-flop circuit 8 and a NAND circuit 11. In this example, in response to the input signal from the signal generator 1 as shown in FIG. 14(a), the flip-flop circuit 8 outputs a higher Q value as shown in FIG. ) can be obtained, and as the output of the NAND circuits 11 and 1.2, outputs with an on-duty of less than 50 cm can be obtained as shown in (d) and (,) of the figure. In the examples shown in FIGS. 10 and 12, a symmetrical switching waveform could not be obtained unless the duty of the input signal from the signal generator 1 was 50, but in the example shown in FIG. (Even at t2, a push-pull switching circuit can be configured, and the on-duty of the current flowing through the primary coil of the step-up transformer 30 can be freely set depending on the ratio of tl and t2. The signal generator 1 that generates a signal can be configured, for example, as shown in FIG. 15. That is, in FIG. 15, diodes Dz and Ds are used as the feedback impedance of the operational amplifier OP4 in FIG. are connected in parallel with opposite polarity to
Each diode D2. Resistor R2 (+
, The duty of the rainbow output can be changed by changing the resistance ratio of R21.

In the embodiment described above, the pace voltage of the drive transistor Qr is controlled by the collector voltage of the transistor Q2, and the drive control circuit 6 uses a configuration in which the detection output from the current detection circuit 5 is negatively fed back to the transistor Q2. 16
As shown in the figure, the drive control circuit 6 is connected to the output terminal of the operational amplifier OP2 by a diode D4. By connecting the cathode of Da' and connecting the anode of the diode D 4 + D 4' to the pace terminal of the transistor Q2 to directly control the pace voltage, the Ml configuration of the drive circuit 5 can be simplified. It can be done. 16th 1 is 10th
Although this corresponds to the configuration shown in the figure, it can be applied in exactly the same way to cases such as those shown in FIGS. 12 and 13, for example. This is shown in FIGS. 17 and 18.

FIG. 19 is a circuit diagram showing an embodiment in which the present invention is applied to a vehicle-mounted electroluminescent device. In other words, the same figure (,
) correspond to each of the circuit configurations described above, and FIG. 14 is an ignition switch, and by closing this ignition switch 14, EOr El r
Each DC power supply voltage p, is supplied to each part of the circuit shown in FIG. D5 is dio )", ZDIidyx-) --
Diode, C5 and C6 are capacitors, R22 to R45
Mine resistance.

In FIG. 19(,), a rectangular wave oscillator with a duty of 50φ similar to that shown in FIG. 9 is used as the signal generator 1. In addition, as the logic inversion circuit I, the seventh
The driving circuit 2 uses an inverting amplifier as shown in FIG. 11(c) to adopt a push-pull switching system, and uses an RC differential circuit to reduce the current on the primary coil side of the step-up transformer 3. In addition, R'26 r 'R27
is resistance. A capacitor C7 is connected in parallel with the EL element 4 as a load for the step-up transformer 3, but the inductance of the step-up transformer 3 and this capacitor C7 are
The valley and valley portions of the L isolation element 4 create a resonance state, resulting in a waveform almost like a sine wave. In this case, the capacitance value of the capacitor C7 is set so that its impedance is approximately the same as the initial impedance of the EL element 4. For this reason,
It is possible to reduce the change in the load impedance of the external pressure transformer 3 to approximately 1/2 with respect to the change in the impedance of the EL element 4 over time, and to suppress the change in the waveform of the current flowing through the EL element 4.

Also, resistors R28 and R29 are connected in parallel to the capacitor C7.
A voltage divider consisting of a series circuit is connected, and a diode D6 is connected between the connection point of both resistors and the operational amplifier 0P10 input terminal of the current detection circuit 5. When the output voltage induced in the output voltage increases beyond a certain level, a bypass consisting of diode D6 causes a large current to flow into the input side of the operational amplifier OPI to suppress the rise in output voltage. be. That is, as mentioned above, the present invention
Since the device 4 is controlled so that a constant current always flows regardless of the increase in impedance of the element 4 over time, the output voltage increases in proportion to the increase in impedance. If this output voltage is allowed to rise indefinitely, there is a risk of dielectric breakdown of the step-up transformer 3 and the F and L elements 4. Therefore, in the above-mentioned configuration,! An earth limit of the output voltage is set, and from then on, constant voltage control is used to prevent dielectric breakdown. Note that Zn2 is a Zener diode, but due to the delay time of negative feedback, when the power is turned on (negative feedback does not work)
The transient output increases abnormally, and as a result, the current peak value increases, which serves to prevent an excessive voltage exceeding the power supply voltage E1 from being input to the input of the operational amplifier OPz.

Furthermore, in the drive control circuit 6, the operational amplifier OPz
Generally, the reference voltage value applied to the non-inverting input terminal of EL can be determined according to the value of current detection resistor R3.
Due to the temperature characteristics of the element 4, even when constant current driving according to the present invention is performed, the brightness decreases as the temperature changes as shown in FIG. 20 (solid line) compared to constant voltage driving (dashed line). It will change, albeit slowly. Therefore, taking into consideration the temperature characteristics of the diode D1 of the current detection circuit 5, the reference voltage t
1 and the diode → “Dt terminal is voltage VF temperature change △V
By setting the ratio with F to an appropriate value, the brightness-temperature characteristic abstract line can be created as shown in Figure 21, a curve that has a brightness peak at approximately room temperature T and gently descends almost symmetrically from side to side. and minimize changes in brightness due to temperature. For this reason, in the above embodiment, the resistance values of the resistors R, 4 and R25 are set to 0.4 to 0.6 V, which is about the same as or less than the terminal voltage of the diode D1, with respect to the terminal voltage vzD of the Zener diode ZD. This is achieved by setting the capacitor C8 to about 0. The capacitor C8 forms an integration circuit with the resistor R2m to slow down the rise in the reference voltage 11. This is to prevent abnormal voltage from being applied to the EL element 4 and to gradually increase the brightness.In addition, D7 is a diode to ensure the above-mentioned soft start even when the power is suddenly turned on. , C9 is a capacitor.

【Effect of the invention〕

As explained above, according to the present invention, a circuit that detects the current flowing through the EL element and a drive control circuit that negatively feeds back the detection output to the drive circuit are provided, so that a constant current always flows through the EL element. By doing so, it is possible to compensate for the decrease in brightness and extend the life of the EL element despite the increase in impedance over time. As mentioned above, the relationship between brightness and current is non-linear, so it is not possible to keep brightness completely constant with simple constant current driving, but it has the advantage of being able to perform a considerable degree of compensation with a simple circuit configuration. According to Jikkyo, compared to conventional constant voltage drive, the life span has been significantly improved, with the half-life being 1/2 and doubling.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the luminance change over time of the EL element, Fig. 2 is a diagram showing the luminance-current characteristics, Fig. 3 is a block diagram showing an embodiment of the present invention, and Figs. 4 and 5 are diagrams showing the luminance-current characteristics. FIG. 6 is a circuit diagram showing a configuration example of a drive circuit using a push-pull switching method, and FIG. 7 is a circuit diagram showing a specific configuration example.
Figures (a), (b), and (c) are diagrams showing configuration examples of logic inverting circuits, Figure 8 is a circuit diagram showing another configuration example of a drive circuit using a push-pull switching method, and Figure 9 is a circuit diagram showing a configuration example of a drive circuit using a push-pull switching method. Figure 10 is a circuit diagram showing an example of the configuration of a drive circuit designed to reduce the current on the primary coil side of the step-up transformer, Figure 11 (IL) + (b) +
(c) is a time chart showing its operation), Thxz diagram and FIG.
) to (e) are time charts showing the operation of the circuit in Fig. 13, Fig. 15 is a circuit diagram showing other configuration examples of the signal generator, and Figs. 16 to 18 are a drive circuit and a drive control circuit, respectively. Circuit diagram showing another configuration example, No. 19
Figures (,) and (b) are circuit diagrams showing other embodiments of the present invention, Figure 20 is a diagram showing the brightness-temperature characteristics of an EL element when temperature compensation is not performed, and Figure 21 is a diagram showing the temperature FIG. 7 is a diagram showing brightness-temperature characteristics when compensation is performed. 1. φ. Signal generator, 2.. Drive circuit, 3. φ.. Step-up transformer, 4.. EL element, 5.
... Current detection circuit, 6... Drive control circuit. Patent applicant: Koito Manufacturing Co., Ltd. Agent Masaki Yamakawa (and 2 others)? i (Figure 1 2 is 1 Ni +til -t+L - 2,43Figure 1 8Ha5Figure 6Figure 7Figure 2 (Figure 18ε310FigureKff11Giant 1 (C) 8112FigureR13FigureKun14: e)

Claims (1)

[Claims] A drive circuit that repeatedly conducts and deconducts the current flowing through the primary coil of the step-up transformer in accordance with the input frequency (m), and a drive circuit that repeatedly turns on and off depending on the frequency, and a voltage that generates a current that flows through the secondary coil of the external pressure transformer. an EL resistor, a current detection circuit that detects the current flowing through the EL resistor, and a detection output of the current detection circuit that is negatively fed back to the drive circuit to generate the voltage of the step-up transformer.
An electroluminescent device characterized by comprising a drive control circuit that controls a drive voltage output of a secondary coil.