JPS6211314B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electroluminescent device (hereinafter referred to as an EL board) used as a light source for a display illumination device of a portable electronic device such as a watch powered by a battery. This invention relates to improvements in plate drive circuits.

Conventionally, methods for illuminating the time display surface of a wristwatch, such as a liquid crystal display element, include coating the time display surface with luminous paint containing a radioactive isotope.
A glass tube coated with a fluorescent substance on its inner surface contains a luminous body containing a radioactive isotope, which has been put into practical use to illuminate the time display. However, since lighting using this method uses radioactive isotopes that are harmful to the human body, not only can it not be used extensively and cannot achieve sufficient lighting effects, but also during the manufacturing process of watches. However, there is always a risk of environmental pollution. On the other hand, there is a method in which a small incandescent light bulb is built into the watch and the time display is illuminated by energizing it by attaching 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 incandescent light bulbs are close to point or line light sources, a brightness gradient occurs on the time display surface, resulting in areas where the display is difficult to read. In addition, incandescent light bulbs require more than 15 milliwatts of power to turn on, and if the power is less than that, not only will it not be possible to obtain a sufficient lighting effect, but there will be an inrush current immediately after lighting, so the batteries used as a power source will require a large amount of power. It must have a special specification that has a high capacity and can withstand sudden discharge. Silver peroxide batteries, which use KOH (potassium hydroxide) as an electrolyte, have been put into practical use as such batteries;
Compared to silver peroxide batteries or silver oxide batteries that use NaOH (sodium hydroxide) as an electrolyte, they have superior rapid discharge characteristics, but are inferior in light load long-term discharge characteristics or storage characteristics, and internal short-term or , accidents such as electrolyte leakage are likely to occur. Batteries used in wristwatches are required to be small due to space limitations, but on the other hand, they are also required to have a long battery life, which requires savings in power consumption and long-term battery stability. There is. However, as mentioned above,
It is difficult to meet this requirement in a wristwatch that has a built-in lighting device that uses a small incandescent light bulb.

The present invention is an electronic watch that uses an EL plate as a light emitting body and reduces the driving power to 1 to 2 milliwatts or less, thereby reducing the load on the built-in battery of the wristwatch and achieving a sufficient lighting effect. The purpose is to provide lighting devices. 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 actively disposed to further increase insulation. 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, this transparent first electrode 3 is made of a transparent substrate 4 such as a glass plate or a polyester film.
is formed on the surface of For example, surface In ₂ O ₃
A glass plate or polyester film with a thin film of indium oxide (indium oxide) formed on it, a special vapor deposition of Pd (palladium) on a polyester film, or a metallized polyester film with a fine mesh structure formed by etching the metal, etc. is used. Insulating film 2
A second electrode 5 is arranged in a stacked manner on one surface. The second electrode may be made of an opaque material, and metal foil, a vapor-deposited metal thin film, or a 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 4 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 it is necessary to protect the light emitting layer 1 from moisture.
A type with a protective structure on the outer periphery is currently in practical use to increase mechanical strength. EL like this
When a suitable alternating current voltage is applied between the two electrodes of the plate, the light emitting layer 1 emits a 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. Alternating 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 a DC pulse voltage can be used as the drive voltage waveform for the EL board, which is an especially important property when the EL board is built into a wristwatch. 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 basic configuration of the present invention. A battery 6 built into the watch supplies power to a booster circuit 7 whose operation is controlled by a control signal A. The booster circuit 7 has a function of converting the voltage of the battery 6 into a high voltage of several tens of volts to a hundred and more volts. The high voltage output of the booster circuit 7 is connected to the rectifier circuit 8.
EL plate 9 having the structure shown in FIG.
is connected to one electrode of the discharge circuit 10.
It is connected to the. The discharge circuit 10 receives a control signal B.
The operation is controlled by The two control signals A and B are a number 10 suitable for driving the electrostatic discharge of the EL board 9.
This signal has a relatively low frequency of Hz, is given by the control signal generation circuit, and causes the booster circuit 7 and the discharge circuit 10 to operate alternately and exclusively. In such a configuration, when the booster circuit 7 is operated by the control signal A, a high voltage is generated at the output of the booster circuit 7, and the EL board 9 is charged with a high voltage charge via the rectifier circuit 8. Even if the booster circuit 7 stops operating due to the control signal A, the charge on the EL board 10 will not flow back to the booster circuit due to the function of the rectifier circuit 8, so the EL board 9 will remain biased at a high voltage. be. Next, in response to the control signal B, the discharge circuit 10 is operated to discharge the charge stored in the EL board 9, and the terminal voltage of the EL board drops. Even if the discharge circuit 10 stops operating due to the control signal B, the terminal voltage of the EL board 9 does not rise until the booster circuit 7 starts operating again. As the booster circuit 7 and the discharge circuit 10 operate alternately, the terminal voltage of the EL board 9 is
It becomes a DC square wave. As mentioned above, distributed exchange
In the EL board, the DC voltage superimposed on the AC voltage does not contribute to the light emission of the EL board, so if the peak value of the DC rectangular wave voltage is sufficiently large, the EL board 9 emits light. If the charge/discharge cycle frequency is set to 30 hertz or higher, beautiful EL board light emission can be obtained due to the afterglow effect of the EL board and the afterimage effect of the observer's eyes.

FIG. 3 is a circuit diagram showing a specific embodiment of the present invention. In this circuit, the booster circuit 7a is composed of a blocking oscillator consisting of a transformer having two windings 11 and 12, a capacitor 13, a transistor 14 and a resistor 15, and a battery 6.
is connected as a power source for the blocking oscillator. Control signal A is applied as a base bias voltage to transistor 14, and when control signal A is at a voltage level of approximately 1 volt or higher, it starts the blocking oscillator and generates a high voltage pulse at the collector of transistor 14. Control signal A
When the voltage level reaches a voltage level below about 0.4 volts, the blocking oscillator stops oscillating and the pulsed voltage is not generated. At this time, the power consumption of the battery 6 by the booster circuit 7a is approximately zero. Above control signal 7
When a is incorporated into a small electronic device such as an electronic watch, it is necessary to use elements such as transformers and capacitors as small as possible, so blocking oscillators are boosted at a relatively high frequency of several KHz to several tens of KHz. It is something that performs an action.

The high pulse voltage generated at the collector of the transistor 14 of the booster circuit 7a is applied to the EL board 9 as a DC high voltage via the rectifier circuit 8, and the EL
Charge the plate 9 with electric charge. The rectifier circuit 8 is a diode, and prevents the charge charged in the EL board 9 from flowing back to the booster circuit 7a. Therefore
The charges charged in the EL board 9 are discharged only by the discharge circuit 10a. The discharge circuit 10a is composed of resistors 16, 18 and a transistor 17. The control signal B is given as the base input of the transistor 17, and when the control signal B has a voltage level of approximately 1 volt or more, the transistor 17 becomes conductive and discharges the charge stored in the EL board 9 via the resistor 16. . Transistor 17 is non-conducting when control signal B is at a voltage level of approximately 0.4 volts or less. The resistor 16 is used to limit the current flowing from the battery 6 through the winding 11 of the booster circuit 7a and the rectifier circuit 8 when the transistor 17 is turned on.

In such a circuit, if the control signals A and B are pulse train voltages as shown by A and B in FIG.
The EL
The terminal voltage of the plate 9 becomes the DC pulse train voltage shown in FIG. 4C. If the peak value of this voltage is sufficiently large and the frequency is appropriate, the EL plate 9 emits light.

FIG. 5 shows a second embodiment of the EL plate driving circuit according to the present invention. The only difference from the circuit shown in FIG. 3 is the method of the booster circuit, and the structure of the other parts is the same. Boosting circuit 7b shown in the embodiment of FIG.
is composed of a coil 19, a transistor 20, and a base resistor 21 of the transistor 20. The control signal A that controls the operation of the booster circuit 7b is a group of DC pulses as shown in FIG.
The transistor 20 is controlled on and off at a high frequency using a zero base drive signal. At this time, since the current in the coil 19 changes rapidly, a high pulse voltage is generated at the collector of the transistor 20.
When control signal A is at a voltage level of 0.4 volts or less, transistor 20 is always non-conductive and booster circuit 7b stops operating. The high voltage output voltage of the booster circuit 7b charges the EL board 9 via the rectifier circuit 8, and the discharge circuit 10a is controlled by the control signal B.
The discharge process is the same as in the circuit example shown in FIG.

In the EL board drive circuit according to the present invention described above, the control signal A that controls the boosting operation of the booster circuit and the control signal B that controls the discharging operation of the discharge circuit share important roles. These signals must be in a state that minimizes the power consumption of the watch's built-in battery under normal circumstances, that is, when the EL plate is not emitting light. In the example circuits shown in FIGS. 3 and 5, control signals A and B must both be at a level of zero volts.
The two control signals are configured to become active only by operating a member provided on the outer case of the watch when the EL plate emits light.
The control signal generation circuit not only generates periodic pulse signals, but also includes the above-mentioned functions. Such a control signal generation circuit is expected to require a fairly complex structure, but by incorporating the control signal generation function into the integrated circuit that constitutes the clock circuit of the clock device, the circuit can be easily constructed. It is possible to save space and reduce component costs.

As described above, according to the present invention, it is possible to incorporate a lighting device that obtains sufficient brightness with low power consumption into a portable electronic device such as a wristwatch, without using dangerous radioactive substances. The fact that the power used for lighting is low and overload currents such as the inrush current of incandescent bulbs are eliminated means that there are no restrictions on the types of batteries that can be built into watches, and this improves storage characteristics and long-term low current load characteristics. This makes it possible to use superior types of batteries and at the same time significantly extend battery life. On the other hand, if the battery life is kept constant, the battery can be made smaller, and wristwatches can be designed with more elegance. Furthermore, since the EL board is capable of emitting light in many different colors and is a planar light emitter with uniform brightness, it can further improve the illumination effect of the display device of a watch and significantly increase the product value.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure of the EL board used in the present invention, Figure 2 is a block diagram showing the basic configuration of the present invention, and Figures 3 and 5 are the EL board drive circuit of the present invention. 4 is a waveform diagram showing the control signal waveform and the terminal voltage of the EL board in the circuit of FIG. 3, and FIG. 6 is a waveform diagram showing the control signal in the circuit of FIG. 5. be. 6... Battery, 7... Boost circuit, 8... Rectifier circuit, 9... EL board, 10... Discharge circuit.

Claims (1)

[Claims] 1. A portable electronic device incorporating a display lighting device using an electroluminescent device as a light source includes a booster circuit that operates at a relatively high frequency and converts the voltage of the built-in battery into a high voltage, and a booster circuit that converts the voltage of the built-in battery into a high voltage. A rectifying circuit that rectifies and charges the electroluminescent device, a discharging circuit that discharges the charge charged in the electroluminescent device, and two sets of intermittent pulses having relatively low frequencies and different phases. It is characterized by comprising a control signal generation circuit that generates a control signal, and by supplying the two sets of control signals to the booster circuit and the discharge circuit, the booster circuit and the discharge circuit operate alternately and exclusively. Lighting devices for portable electronic devices.