JPH0156398B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display lighting device for small electronic equipment that uses a battery as a power source, and more specifically to an electroluminescent display lighting device for illuminating a display surface in a dark place. This invention relates to an improvement of an EL board drive circuit when the device (hereinafter referred to as an EL board) is used as a light source.

Conventionally, as a method of lighting the display screen of small electronic devices such as electronic watches at night, luminous paint containing a radioactive isotope is applied to the display surface, or a radioactive isotope is sealed in a glass tube whose inner surface is coated with a fluorescent substance. It has been put into practical use to have a built-in light emitter to illuminate the display surface.

However, lighting using this method cannot be used extensively because it uses radioactive isotopes that are harmful to the human body, and not only does it not provide sufficient lighting effects, but it also causes problems during the manufacturing process and during use. There is always a risk of environmental pollution.

On the other hand, there is a method in which a small incandescent power source is built into a part of the display device and the display surface is illuminated by energizing it by operating a switch. In recent years, this method has come into widespread use in so-called electronic watches that use batteries as their power source.

However, since the incandescent light source is close to a point or line light source, a brightness gradient occurs on the display surface, making it difficult to read the display at certain points.

In addition, because incandescent lights consume a lot of power when lit, they also have the disadvantage of accelerating battery consumption when used in small, portable electronic devices powered by batteries. However, it was not suitable as a display lighting device for small electronic equipment.

An object of the present invention is to realize an EL drive circuit that uses an EL board that has an excellent lighting effect as an illumination light source, and that can drive the EL board with small power consumption using a built-in battery as a power source.
An object of the present invention is to provide a display lighting device for a small electronic device that achieves improved lighting effects and reduced power consumption at the same time.

The present invention will be described in detail below with reference to the drawings.

Figure 1 is an example showing the cross-sectional structure of an AC EL board used in the present invention, and is generally a distributed AC EL board.
It has a known structure called. 1 in the figure is an appropriate amount
It is a light-emitting layer with a thickness of several microns to several tens of microns, made of ZnS (zinc sulfide) crystals mixed with Cu (copper) as an activator and hardened with an appropriate binder.

Although such a light emitting layer 1 is electrically close to an insulator, an insulating film 2 containing a white pigment is arranged in a laminated manner to further increase the insulation property. The white pigment has a reflective effect to effectively convert the light emitted from the light emitting layer 1 into external irradiation light. A first electrode 3 made of a transparent conductor is arranged in a stacked manner on one surface of the light emitting layer 1. Generally, the transparent first electrode 3 on the light emitting surface side is formed on the surface of a transparent base material 4 such as a glass plate or a polyester film.

For example, a glass plate or polyester film with a thin film of In ₂ O ₃ (indium oxide) formed on its surface, a special vapor deposition of Pd (palladium) on a polyester film, or a metallized polyester film by etching the metal. A material with a fine mesh structure is used. A second electrode 5 is arranged in a stacked manner on one surface of the insulating film 2 . Since the second electrode 5 is on the non-light emitting surface side, it may be made of an opaque material, and metal foil, vapor-deposited metal thin film, or conductive paint coated and cured has been put into practical use. The transparent first electrode 3 and second electrode 5 are completely insulated, and each of the electrodes 3 and 5 constitutes a capacitor whose dielectrics are the light emitting layer 1 and the insulating film 2. The capacitance of this capacitor ranges from several hundred picofarads to several thousand picofarads per square centimeter, and is closely related to the current consumption of the EL board. Basically, distributed AC EL is composed of the above-mentioned laminated structure, but currently in practical use there is a structure in which the outer periphery has a protective structure to protect the light-emitting layer 1 from moisture and to increase mechanical strength. has been done.

When a suitable alternating current voltage is applied between the two electrodes of such an EL plate, the light emitting layer 1 emits beautiful green light. By selecting an appropriate type of activator from among Mn (manganese) and rare earth elements, it is possible to obtain luminescent colors such as red, blue, and white.
AC voltage is generally used as the voltage applied to the EL board, but one of the important features of distributed AC EL boards is that the DC component superimposed on the AC voltage hardly contributes to the light emission of the EL board. It is known.

That is, if the AC component included in the drive voltage is constant, the brightness of the EL board is constant. This means that EL
This means that a DC pulse voltage can be used as the drive voltage waveform for the board, which is an especially important property when the EL board is built into a small electronic device powered by a battery.

However, in general, when a DC voltage is superimposed on an AC voltage, the maximum value of the voltage applied between two electrodes becomes large, so it is necessary to increase the withstand voltage between the electrodes in manufacturing the EL board.

FIG. 2 is a block diagram showing the main configuration when the lighting device according to the present invention is applied to an electronic timepiece. A battery 6 built into the timepiece is connected to a booster circuit 8 via a switch 7 that is closed by operating a member provided on the outer case of the timepiece. The booster circuit 8 converts the battery voltage given from about 1.5 volts to about 3 volts into a DC voltage of several tens of volts to more than 100 volts, which is necessary to drive the EL board.
The voltage is supplied to the EL board 10 having the structure explained in FIG. 1 via a switching device 9 that applies the voltage intermittently at a low frequency. The switching device 9 is a control signal generator 1 that generates a low frequency signal.
1. What is the low frequency signal referred to here?
It shows a frequency of 300 Hz or higher, and for example, a low frequency signal of 30 Hz is a frequency that can be sufficiently generated using mechanical methods, and is also a frequency that can be sufficiently tracked by the mechanical contact structure of the switching device. .

FIG. 3 is a block diagram showing a modified example of the basic configuration shown in FIG. 2, in which the battery 6 serves both as a power source for the clock circuit 12 of the clock device and as a power source for the EL board 10 for illumination. .

In such a configuration, the savings in watch space and battery costs are significant. Further, since the signal for controlling the switching device 9 is taken out from the clock circuit 12 of the timepiece device, the special control signal generating device 11 shown in FIG. 1 is not required. Recently, the timekeeping circuit in an electronic watch has a built-in circuit that sequentially divides a high frequency signal of 30 kilohertz or more into a lower frequency signal by cascading flip-flop circuits. It is possible to extract control signals.

In addition, such timekeeping circuits are integrated into large-scale integrated circuits, and even if an output buffer circuit is added by adding one external output terminal, there will be no significant increase in space or cost, so a special This is much more economical than providing a low frequency oscillation circuit.

Figure 4 shows an EL having the structure shown in Figure 1.
It is a graph showing relative values on the vertical axis of light emission brightness when the plate is driven with a rectangular wave voltage having a duty ratio of 50%. The horizontal axis of the graph indicates the voltage difference between the high level and low level of the rectangular wave voltage, and the unit is volts. The frequency of the square wave voltage is shown as a parameter in the figure. As is clear from the figure, the EL plate starts emitting light when the applied voltage range exceeds 40 volts, and the brightness increases linearly when it exceeds 60 volts. If the brightness indicated by the dotted line in the diagram is sufficient for practical use as a light source for night illumination of a watch, the range of change in applied voltage is 122 volts at 32 Hz, 100 volts at 64 Hz, 86 volts at 128 Hz, and 256 Hz. requires 75 volts at 512 hertz and 68 volts at 512 hertz. As mentioned above, the EL board can be considered a capacitor. Generally, when the voltage of a DC power supply is converted into a rectangular wave voltage by switching and applied to a capacitor, the current I is given by the following equation if the output impedance of the rectangular wave power supply is ignored.

I=kCVF where C is the capacitance of the capacitor, V is the transformation width of the square wave voltage, and F is its frequency. k is a constant determined by the method of the drive circuit, and is 2 in the case of a method in which the electric charge charged in the capacitor is discharged via a DC power supply, and is 1 if the discharge is performed in a separate bypass circuit.

According to the present invention, the high voltage for driving the EL board is
It is given by converting the battery voltage with a booster circuit, and if this conversion efficiency is η, the current consumption I _p of the EL board for the battery is given by the following equation.

I _p = ηkCV ² F/V _p where I _p means the voltage of the battery. In the above equation, k = 1, C = 2000 picofurads, V _p = 1.5
If the conversion efficiency η is 0.5 in volts and the voltage and frequency that provide the above-mentioned practical brightness are substituted, the current consumption of the EL board with respect to the power supply battery is as follows.

32 hertz 0.32 milliamps 64 hertz 0.43 milliamps 128 hertz 0.63 milliamps 256 hertz 0.96 milliamps 512 hertz 1.58 milliamps In other words, the battery current at 512 hertz is about five times that at 32 hertz. As is clear from this calculation example, the EL system converts the battery voltage into a high-voltage DC voltage using a booster circuit, and then converts the high-voltage DC voltage into a rectangular wave voltage using a switching means and applies it to the EL board. In the plate drive circuit, it is desirable to make the frequency of the rectangular wave voltage as low as possible and widen the voltage variation range.

Therefore, in the AC high voltage generating means constituting the booster circuit 8 of the present invention, by setting the resonance frequency to a relatively high frequency of several kilohertz or more, elements such as reactance can be miniaturized, and as a result, the booster circuit 8 can be made smaller. It has been miniaturized to a size that can be built-in.

On the other hand, it is known that the lifetime characteristics of distributed AC ELs largely depend on the frequency of the drive voltage waveform. That is, when the initial brightness is constant, the higher the frequency of the drive voltage waveform, the more pronounced the brightness decay due to aging.

For example, an EL board driven at 10 kHz is approximately 5
After an hour, reduce its brightness by half. Electronic devices are required to have stable reliability over a long period of time, and display lighting devices are no exception.
Driving the EL plate at frequencies above 1 kilohertz should be avoided, which will significantly shorten the life of the plate. Simply saving the current consumed by the EL board relative to the battery is not a method of the present invention.
It is possible to reduce the effective power consumption by constructing an LC resonant circuit in which the EL board is used as a capacitor and a coil is combined with it. The more the device is used, the more it becomes impossible to incorporate a sufficiently large reactance due to space limitations, and it becomes difficult to reduce the resonant frequency to several kilohertz or less.

On the other hand, when the frequency of the driving voltage of the EL panel falls below 30 hertz, it exceeds the limits of the human eye's afterimage phenomenon and the luminescent material of the EL panel, resulting in a flickering blinking phenomenon. This blinking phenomenon tires the observer's eyes and must be avoided.

For the three reasons mentioned above, namely, saving current consumption, preserving the life of the EL board, and preventing blinking, it is practical to set the frequency of the voltage that drives the EL board to a value of 30 kHz or more and 300 Hz or less. be. As shown in FIG. 3, when a clock circuit 12 is required to provide a signal that controls the switching device 9, a clock signal having a frequency of this n-th power series (n is a positive integer) exists inside the clock circuit. Therefore, the practical frequencies are 32 Hz, 64 Hz,
128 hertz and 256 hertz.

FIG. 5 is an embodiment showing a specific circuit configuration of the illumination device shown in FIG. and supplies current to the control signal generator 11a of the switching device 9a. The booster circuit 8a rectifies the collector voltage of a known blocking oscillator composed of a transistor 13, a transformer having two windings 16 and 17, a resistor 18, and a capacitor 19 with a diode 14 and filters it with a capacitor 15. battery 6
voltage to a DC voltage of several tens of volts to more than 100 volts.

That is, in this embodiment, the booster circuit 8a is composed of a blocking oscillator that converts the voltage of the power supply battery 6 into a spike-like high voltage, a rectifier circuit that converts the spike-like high voltage into a DC high voltage, and the like. The control signal generation circuit 11a is a well-known astable multivibrator, and outputs two output signals OUT1.
and OUT2 are complementary low-frequency signals of 30 to 300 Hz and opposite phase rectangular wave signals, each of which serves as a control signal for the switching circuit 9a. The transistors 20 and 25 of the switching circuit 9a constitute an inverter circuit having collector resistors 21, 26 and base resistors 22, 27, respectively, and the control signal generating circuit 1 operates with the voltage of the battery 6.
It constitutes an interface that converts output signals OUT1 and OUT2 of 1a into high voltage switching signals. As switch elements of the switching device 9a, two sets of complementary emitter follower circuits each include a pair of complementary first and second transistors 23 and 24 and third and fourth transistors 28 and 29, respectively. is used, and two electrodes of the EL board 10 are connected to each emitter output.

That is, the first and second transistors 2 described above
3, 24 and third and fourth transistors 28,
29 are respectively connected in series to the high voltage output side of the booster circuit, and the connection point between the first and second transistors and the connection point between the third and fourth transistors are EL. They are respectively connected to two electrodes of the plate 10.

In such a circuit, when switch 7 is closed, the blocking oscillator of booster circuit 8a starts oscillating, and a spike-like high voltage is generated at the collector of transistor 13. By storing this high voltage spike in the capacitor 15 via the diode 14, the terminal voltage of the capacitor 15 becomes
It reaches a value approximately equal to the peak value of the spike voltage.

On the other hand, the control signal generation circuit 11a also starts operating and generates a rectangular wave signal of opposite phase that is complementary to the two output signals OUT1 and OUT2. Now, when the output signal OUT1 is at a high level, the transistor 20 is conductive and its collector voltage is at a low level, the transistor 23 is non-conductive, and the transistor 24 is conductive. At this time, since the output signal OUT2 is at a low level, the transistor 25 is non-conductive, its collector voltage is at a high level, the transistor 28 is conductive, and the transistor 29 is non-conductive.

Therefore, a high voltage, which is the output of the booster circuit 8a, is applied to the EL board 10 by the transistors 24 and 28. After that, when the output signals OUT1 and OUT2 of the control signal generation circuit 11a are inverted, the transistors 24 and 28 become non-conductive.
Transistors 23 and 29 conduct, and the EL board 10
is connected to the high voltage in the opposite direction. signal OUT
1. By repeating the inversion of OUT2, the two sets of complementary emitter follower circuits are alternately and exclusively connected to the high level and low level, so the EL
A rectangular alternating current voltage having a voltage variation range twice that of the output voltage of the booster circuit 8a is applied to the plate 10.

That is, in this embodiment, the first and fourth transistors 23 and 29 are
and third and second transistors 28 and 2
4 are controlled to alternately take a conductive state and a non-conductive state, and as a result, the high voltage from the booster circuit 8a is alternately applied to the two electrodes of the EL board. There is.

The above-mentioned switching device is composed of bipolar transistors, but bipolar transistors can easily have a structure that can withstand the high voltage required to drive the EL board 10, are small, and have a long life. It is most suitable as a switching element used in the invention.

In the future, if the driving voltage of the EL board 10 is further reduced or if high-voltage complementary MOS transistors appear due to advances in MOS FET technology, MOS FETs will be used as switching elements in the switching circuit of the present invention. Since this becomes possible, it is considered that, for example, it will become possible to incorporate the switching circuit itself into an integrated circuit that constitutes the timekeeping circuit of a timepiece device.

Further, in this embodiment, an emitter follower circuit configured by a pair of complementary transistors is shown as a switching circuit, but the emitter follower circuit is not limited to this, and for example, an emitter follower circuit configured by a pair of complementary transistors is used. Even if an inverter circuit is used, similar functions and effects can be obtained.

The present invention has been described in detail above, and according to the present invention, a display lighting device that obtains sufficient brightness with low power consumption without using dangerous radioactive materials is provided using a battery as a power source. It becomes possible to incorporate it into small electronic devices.

Furthermore, by alternately driving the electroluminescence device by two sets of switching circuits each composed of a pair of complementary transistors, a voltage twice the DC high voltage can be applied to the EL device as an effective voltage. This makes it possible to provide illumination with high luminance, and it is also a capacitive element.
Since the EL device can be driven alternately, there is no residual DC component, making it possible to extend the lifespan. Furthermore, by combining boosting with high frequency and alternating drive with low frequency of 30 to 300 Hz, the driving conditions of the EL device can be set to low frequency - high voltage driving, which prevents flickering of the lighting and reduces current consumption. At the same time, the life characteristics of the EL device can be significantly improved.

In addition, the fact that the power for lighting is low and overload currents such as the inrush current of incandescent electric currents are eliminated means that especially in ultra-small electronic devices such as electronic wristwatches, the type of built-in battery can be reduced. Eliminate restrictions,
This makes it possible to use a type of battery with excellent storage characteristics and long-term low current load characteristics, and at the same time, it makes it possible to significantly extend the battery life.

On the other hand, when the battery life is constant, it becomes possible to downsize the battery, and it becomes possible to design an elegant external appearance of a small electronic device.

Furthermore, since the EL board is capable of emitting light in many different colors and is a flat light emitter with uniform brightness, it can further improve the display illumination effect and significantly increase the product value.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of the EL board used in the present invention, FIGS. 2 and 3 are block diagrams showing the basic configuration of the display lighting device in the present invention, and FIG. 5 is a graph showing the relationship between the drive voltage of the EL board and the brightness of the EL board, and FIG. 5 is a circuit diagram showing a specific example of the configuration of the display lighting device shown in FIG. 6... Battery, 8, 8a... Boost circuit, 9a...
Switching circuit, 10...EL board, 11a...
Control signal generation circuit.

Claims (1)

[Claims] 1 Using an electroluminescent device as a light source,
In a display lighting device for a small electronic device using a built-in battery as a power source, an AC high voltage forming means converts the voltage of the built-in battery into a relatively high frequency AC high voltage, and the AC high voltage is converted into a DC high voltage. a booster circuit constituted by a rectifying means, two sets of complementary switching circuits each using a DC high voltage from the booster circuit as a power source and each composed of a pair of complementary transistors, and the two sets of complementary switching circuits. a control signal generator that generates a low frequency signal of 30 to 300 Hz to control the circuit so that the circuit alternately assumes a conducting state and a non-conducting state; and an electroluminescent device connected between the output terminals of the two sets of complementary switching circuits. by supplying the low frequency signal from the control signal generating device to each control terminal of the two sets of complementary switching circuits in opposite phases to the electroluminescence sensing device. A display lighting device for small electronic equipment characterized by applying a DC high voltage alternately at the cycle of a low frequency signal.