JPH0845661A - Electroluminescence driving device - Google Patents

Abstract

PURPOSE:To reduce the power consumption by turning on and off a switching element for discharging electroluminescence at a cyclic period longer than that of a switch element for feeding current to a voltage boosting means, and varying the on-time of the latter named switch element in compliance with the output of a light receiving element. CONSTITUTION:The gate of the first switch element 9 is fed with a pulse signal A to turn off current feed to a choke coil 11 when a lighting switch is put on, and electric charges are accumulated in an EL element 5 by the electromotive force of the coil 11. When a pulse signal R actuates the second switch element 10, the electric charges accumulated in the EL element 5 are discharged. Thin procedure is repeated so that the EL element 5 emits light continuously. A control device 4 controls the duty ratio of signals A in accordance with the brightness of an external light from a light sensing circuit part 3 including a light receiving element, 13 so that the current feed time to the coil 11 is shortened in a dark place to drop the brightness and also, during out of lighting, the third switch element 16 is turned off, the light sensing circuit part 3 is stopped, the current consumption is reduced, and the EL element is driven efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence driving device.

[0002]

2. Description of the Related Art Conventionally, a chopper type EL drive device shown in FIG. 3 is known as an electroluminescence (hereinafter abbreviated as EL) drive device.

This EL driving device rectifies the current boosted by the choke coil 33 and a power source 32 for supplying a driving current to the EL 31, a choke coil 33 for boosting the current from the power source 32, and supplies the rectified current to the EL 31. And a first switch element (nMOS transistor) 3 for turning on / off the power supply to the choke coil 33.
5, and a second switch element (nMOS transistor) 3 for turning on / off the discharge of the charges accumulated in the EL 31.
6 and a control device 37 for controlling ON / OFF of the first and second switch elements 35 and 36.

As shown in FIG. 4, the controller 37 generates a pulse signal A having a short cycle and a pulse signal B having a long cycle, and the pulse signal A is applied to the gate of the first switch element 35 and the pulse signal B is applied. To the gate of the second switch element 36,
Output each.

The pulse signal A is for turning on / off the current flowing through the choke coil 33. When the pulse signal A is H (High), the first switch element 35 is turned on, and the current from the power source 32 to the choke coil 33 is turned on. Flows. Further, when the pulse signal A is L (Low), the first switch element 35 is turned off and the power supply to the choke coil 33 is stopped. At that moment, counter electromotive force is generated at both ends of the choke coil 33,
The current due to the boosted voltage passes through the diode 34 and passes through the EL 31.
Flows to Every time this is repeated, electric charge is accumulated in EL31, and the voltage applied to EL31 becomes high. EL3
In No. 1, the light emission starts from the moment the energization is started, and the brightness becomes higher as the voltage becomes higher.

Next, when the pulse signal B is H, the second switch element 36 is turned on, the charge accumulated in the EL 31 is discharged, and the voltage of the EL 31 drops to the voltage of the power supply 32. By repeating this, a large amplitude AC voltage is applied between both electrodes of EL 31, and EL 31 emits light continuously.

Since this chopper type EL drive device is easier to miniaturize than a transformer type device or the like,
Recently, it has been used in a driving device for a backlight EL that illuminates the dial of an analog electronic wrist watch from the back surface and displays a display mark such as an hour character in a silhouette.

[0008]

However, in the conventional EL drive device, since the EL 31 is always emitted with a constant brightness regardless of the ambient brightness, the display mark can be clearly displayed even in a weak brightness. Even in a dark place where a silhouette can be displayed, the EL 31 emits light more brightly than necessary and consumes a large amount of power. Further, in a bright place, the brightness of the EL 31 was insufficient with respect to the surrounding brightness, and the visibility was poor.

Further, in the conventional EL drive device, the minimum luminance of the EL 31 is ensured by setting the drive voltage of the EL 31 to a high value in consideration of the variation of parts for each device. Therefore, depending on the device, EL3
The brightness of No. 1 becomes higher than necessary, which causes a further increase in power consumption.

Further, in the conventional EL driving device,
When the EL is driven, the choke coil 33 is always energized / de-energized by the pulse signal A having a constant period. Therefore, when the EL 31 is discharged, a current flows through the choke coil 33 in the same manner as during the charge accumulation. The current boosted by the choke coil 33 when the EL 31 is discharged is
Since it is discharged as it is without contributing to the emission of light, the power loss is large.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an EL drive device capable of driving an EL with appropriate brightness and low power consumption.

[0012]

The EL drive device according to the first invention of the present application discharges the charges charged in the electroluminescence at a predetermined cycle while supplying the charges to the electroluminescence. Assuming an electroluminescence driving device that emits light, boosting means for accumulating electric charges in the electroluminescence by using counter electromotive force generated when power supply to the coil is cut off, and energization of the boosting means are turned on. A first switch element for turning on / off, a second switch element for turning on / off the electroluminescence discharge, and a second switch element while turning on / off the first switch element at a predetermined cycle. ON / OFF at a predetermined cycle longer than that of the first switch element, and the ON time of the first switch element A control device for varying, due to the provision of the, have achieved the above object (claim 1).

An EL drive device of a second invention according to the present application is an electroluminescence drive device which supplies electric charges to electroluminescence and discharges the charges charged to the electroluminescence at a predetermined cycle to emit light. Based on the premise, a boosting means for accumulating electric charges in the electroluminescence by using a counter electromotive force generated when the power supply to the coil is cut off, and a first for turning on / off the conduction to the boosting means. 1
A switch element, a second switch element for turning on / off the electroluminescence discharge, a light receiving element for detecting external brightness, and a first switch element being turned on / off at a predetermined cycle. , Turning on / off the second switching element at a predetermined cycle longer than that of the first switching element
The above object is achieved by including a control device that is turned off and that changes the on time of the first switch element according to the output of the light receiving element (claim 2).

Further, the EL drive device of the third invention according to the present application supplies the electric charge to the electroluminescence, and at the same time, discharges the electric charge charged to the electroluminescence at a predetermined cycle to emit the electroluminescence. In the drive device, a boosting unit that accumulates electric charges in the electroluminescence by using a back electromotive force generated when power supply to the coil is cut off, and a first for turning on / off the powering to the boosting unit. One switching element, a second switching element for turning on / off the electroluminescence discharge, a light receiving element for detecting the luminance of the electroluminescence, and a first switching element for turning on / off at a predetermined cycle. At the same time, the second switch element has a predetermined cycle longer than that of the first switch element. On / off and, and, by that and a control device for varying the ON time of the first switching element in response to an output of the light receiving element, and achieve the above object (claim 3).

In the EL drive devices of the second and third inventions, the control device controls the first switch element so that the energization time to the choke coil is shortened while the second switch element is on. It is desirable to have a function of changing the on-time (Claim 4).

In the EL drive device of the above invention, output amplifying means for amplifying the output of the light receiving element, and a signal for converting the signal from the output amplifying means into a digital signal and outputting the digital signal to the control device. The control device includes a conversion unit and a third switch element for turning on / off the drive of the output amplification unit and the signal conversion unit, and the control device turns on / off the first switch element at the predetermined cycle. It is desirable to have a function of turning on the third switch element only during the operation (Claim 5).

[0017]

In the EL drive devices of the first, second, and third inventions, each control device turns on / off the first switch at a predetermined cycle to boost the voltage when the first switch element is on. The means is energized and the energization is cut off when the first switch element is off. Then, the electric charge is supplied to the EL by the counter electromotive force generated in the coil at the moment when the energization is cut off. Each time this is repeated, electric charge is accumulated in EL, and the voltage applied to EL becomes higher. The EL starts to emit light at the moment when the energization is started, and the brightness becomes higher as the applied voltage becomes higher.

Then, each control device turns on / off the second switch element at a predetermined cycle longer than that of the first switch element.
By turning off, the charge accumulated in EL is
While the switch element is ON, it is discharged and the voltage of EL drops to the voltage of the power supply. By repeating this, E
A large amplitude AC voltage is applied to L, and EL continuously emits light.

In the EL drive device of the first invention, the control device enables the power consumption to be suppressed by changing the ON time of the first switch element. In the EL drive device of the second invention, , EL is bright when the surrounding area is EL
The brightness of the EL is increased, and the brightness of the EL is decreased when the surrounding area of the EL is dark, so that the brightness of the EL is changed according to the external brightness, and the EL can be efficiently driven with an appropriate brightness at all times.

Further, according to the EL drive device of the third aspect of the invention, the light receiving element detects the brightness of the light emitting surface of the EL, and in accordance with the output of the light receiving element, the control device makes the first control.
By changing the on-time of the switch element, the brightness of the EL can be made constant by controlling the energization time to the choke coil even when there are variations in the components of each device. Therefore, according to the EL drive device of the third invention, the EL drive voltage is set to a high value so that the minimum brightness of the EL can be secured in consideration of the variation in the components of each device as in the conventional device. Since it is not necessary to do so, the EL can be driven efficiently.

In the EL drive devices of the second and third inventions, the control device controls the first switch element so that the energization time to the choke coil is shortened while the second switch element is on. By changing the ON time, the power loss at the time of discharging the EL can be reduced and the EL can be driven more efficiently.

Further, in the EL drive device of the above invention, the control device turns on the third switch element only while the first switch element is turned on / off at the predetermined cycle, so that the EL device When is not lit, the third switch element is turned off, and the operation of the output amplification means and the signal conversion means is stopped. This can prevent unnecessary power consumption when the EL is not lit.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. 1 is a schematic configuration diagram showing a first embodiment of an EL drive device of the present invention, and FIG. 2 is a timing chart of the device shown in FIG. First, the configuration of this embodiment will be described.
The EL drive device 1 shown in FIG. 1 has an EL drive circuit unit 2 configured similarly to the circuit unit of a conventional device, a photodetection circuit unit 3 connected to the EL drive circuit unit 2, and both circuit units 2. 3 and a control device 4 for controlling 3.

The EL drive circuit section 2 includes a power source 6 for supplying electric power to the EL 5, a boosting means 7 for accumulating electric charges in at least one electrode of the EL 5 to expand a potential difference between the two electrodes, and a boosting means 7. First for turning on / off the energization of
It is composed of a switch element (nMOS transistor) 9 and a second switch element (nMOS transistor) 10 for turning on / off discharge of charges accumulated in the EL 5.
The booster 7 includes a choke coil 11 and a diode 8 which is a rectifying element for rectifying a current due to a back electromotive force generated when the power supply to the choke coil 11 is cut off and flowing the EL5.

The photodetector circuit section 3 includes a photodiode 13, which is a light receiving element for detecting external brightness, and an operational amplifier 1 for amplifying the output of the photodiode 13.
4, an A / D converter 15 for converting the output of the operational amplifier 14 into a digital signal, and a third switch element (nMOS for operating the operational amplifier 14 and the A / D converter 15).
A transistor 16 and three resistors 17, 18, 19 inserted between them.

In this case, the photodiode 13 is arranged so that the light receiving surface is exposed to the outside of the device equipped with the EL 5 so that the brightness of the external light can be detected.
The output of the photodiode 13 is amplified by the operational amplifier 7, converted into a digital signal by the A / D converter 14, and input to the control device 4.

As shown in FIG. 2, the controller 12 generates a pulse signal A having a short cycle and a pulse signal B having a long cycle, and the pulse signal A is applied to the gate of the first switch element 9.
The pulse signal B is output to the gate of the second switch element 10, and the brightness of extraneous light is detected based on the signal from the A / D converter 15, and according to the detection result,
It has a function of changing the duty ratio of the pulse signal A in three stages.

In FIG. 2, the section L shows that the external light is very dark, the section M shows that the external light is slightly dark, and the section H shows that the external light is bright. In this example, the duty ratio of the pulse signal A is set so that the ON duty (ON time / pulse cycle) of the pulse signal A is 60% in the section M, 80% in the section H, and 40% in the section L. Is set to change. In addition, the control device 4 is configured such that while the pulse signal B is H (section S),
It has a function of changing the duty ratio of the pulse signal A so that the ON duty of the pulse signal A becomes smaller than the ON duty of the pulse signal A in the section L.

Next, the operation of this embodiment will be described.
In the EL drive device 1, when a lighting switch (not shown) is turned on, the control device 4 operates, the pulse signal A is applied to the gate of the first switch element 9, and the pulse signal B is applied to the gate of the second switch element 10. Is added.

The pulse signal A is a signal for turning on / off the power supply to the choke coil 11, and the pulse signal A
When H is H, the first switch element 9 is turned on, a current flows from the power supply 6 to the choke coil 11, and when the pulse signal A is L, the first switch element 9 is turned off. Then, a counter electromotive force is generated at both ends of the choke coil 11 at the moment when the first switch element 9 is turned off, and a current due to the boosted voltage flows through the diode 12 to the EL5. Each time this is repeated, charges are accumulated in EL5, and the voltage applied between both electrodes of EL5 becomes high. The EL5 starts to emit light at the moment when the electric charge starts to be supplied, and the brightness becomes higher as the applied voltage between both electrodes becomes higher.

When the pulse signal B is H, the second switch element 10 is turned on, the charge accumulated in the EL5 is discharged, and the EL45 voltage drops to the voltage of the power supply 6. By repeating this, a large amplitude AC voltage is applied between both electrodes of EL5, and EL5 emits light continuously.

The control device 4 continues to apply the ON signal C shown in FIG. 2 to the gate of the third switch element 11 while applying the pulse signal A to the gate of the first switch element 9. As a result, while the EL5 is lit, the operational amplifier 14 and the A / D converter 15 are activated, the output of the photodiode 13 is amplified by the operational amplifier 14, and then the A
The signal is converted into a digital signal by the / D converter 15 and the control device 4
Is input to

The control device 4 detects the brightness of the external light based on the signal from the A / D converter 15, and determines the duty ratio of the pulse signal A according to the brightness of the external light as described above. Change in 3 steps.

As a result, the ON time of the first switch 9, that is, the energization time of the choke coil 11 constituting the booster 7 is long when the external light is bright (section L), and is very dark. It is controlled according to the brightness of the external light so that it is short in (section H) and has an intermediate length when it is slightly dark (section M).

Since the EL5 has higher brightness as the driving voltage becomes higher, the brightness becomes higher as the energization time to the choke coil 11 becomes longer. Therefore, the EL drive device 1 has an O level of the pulse signal A depending on the brightness of the external light.
By changing the N duty, E can be used in dark places.
L5 is made to emit light at a low brightness, EL5 is made to emit light at a high brightness in a bright place, and EL5 is made to emit light at an intermediate brightness in a slightly dark place.

In this way, the EL5
The brightness of EL5 can be reduced to reduce current consumption in a dark place where even a weak brightness is conspicuous, and conversely, in a bright place, the brightness of EL5 can be increased to improve visibility. it can.

Therefore, by applying the EL drive device 1 to the EL drive device for the backlight of the dial of the analog type electronic wristwatch, even when the ambient brightness changes, the display of the time scale, the hour characters, etc. The mark can always be displayed in a clear silhouette with a constant contrast. Since this kind of lighting function is usually used in a dark place and rarely used in a bright place, it is possible to reduce the current consumption by reducing the brightness of the EL in the dark place as described above.
It is possible to reduce the power consumption and drive the EL efficiently. As a result, it is possible to suppress the consumption of the built-in battery due to the mounting of the illumination function on the electronic wrist watch and the like, and to extend the battery life.

In the EL drive device 1 of this embodiment, E
When L5 is not lit, the control device 4 stops outputting the ON signal C, so the third switch element 16 is turned off, and the operational amplifier 14 and the A / D converter 15 stop operating. This can prevent unnecessary power consumption during non-lighting.

Further, the EL drive device 1 of this embodiment is shown in FIG.
As shown in, while the pulse signal B is H (section S), that is, the second switch element 10 is turned on,
While the charge accumulated in 5 is being discharged, the control device 4 controls the pulse signal A so that the ON duty of the pulse signal A becomes smaller than the ON duty of the pulse signal A in the section L. Change the duty ratio. As a result, the power loss during discharge of EL5 is suppressed, and EL can be driven more efficiently.

However, even when the EL5 is turned on at the lowest brightness, the consumption of the built-in battery is inevitably increased compared to when the EL5 is not turned on.
It is desirable that the photodetection circuit unit 3 including the operation amplifier 3, the operational amplifier 14, the A / D converter 15 and the like be configured to consume as little current as possible.

Next, as a second embodiment of the EL drive device of the present invention, a case where the brightness of EL5 is controlled to be constant will be described. In this case, the photodiode 13 of the EL drive device 1 is provided such that its light-receiving surface faces the light-emitting surface of EL5 so that the brightness of EL5 can be detected. In addition, it is arranged that no external light is incident on the light receiving surface of the EL5.

In the control device 4, the first switch element 9 is turned on / off at a predetermined cycle, and the second switch element 10 is turned on / off at a predetermined cycle longer than that of the first switch element 9. Moreover, the brightness of EL5 is detected based on the signal from the A / D converter 15, and E is detected according to the detection result.
In order that the brightness of L5 becomes a preset constant brightness,
A function of changing the ON duty of the pulse signal given to the first switch element 9 is provided.

E of the second embodiment constructed as described above
According to the L drive device, even when there are variations in the components forming each device, the ON time of the first switch element 9, that is, the energization time of the choke coil 11 is controlled by the control device 4, and the brightness of the EL 5 is reduced. Adjusted to constant. Therefore, the EL 5 can be driven more efficiently than in the case where the minimum luminance of the EL 5 itself is ensured in consideration of the variation of the components of each device as in the conventional device.

Therefore, the EL drive device of the second embodiment is used for the backlight E of the dial of an analog electronic wrist watch.
EL5 itself and EL
Even if there are variations in the components that make up the drive, E
The L5 can be made to efficiently emit light with a constant brightness, and the display marks such as the time scale and hour characters can be displayed in a clear silhouette.

Also in the EL drive device of the second embodiment, the operational amplifier 14 and the A / D converter 1 are turned off by turning off the third switch element 16 when the EL 5 is not lit.
It is possible to stop the driving of No. 5 and prevent unnecessary power consumption.

Also in the EL drive device of the second embodiment, while the second switch element 10 is turned on and the charge accumulated in EL5 is being discharged (corresponding to the section S in FIG. 2). Changes the ON duty of the pulse signal applied to the first switch element 9 so that the energization time to the choke coil 11 is as short as possible.
Suppresses power loss during discharge of EL
Can be driven.

Although the invention made by the present inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Needless to say.

For example, in the first embodiment, the case where the duty ratio of the pulse signal for turning on / off the first switch element 9 is changed in three steps according to the brightness of the external light has been described. May be changed in multiple stages, or may be changed continuously.

Also in the second embodiment, the duty ratio of the pulse signal for turning on / off the first switch element 9 may be changed stepwise according to the brightness of EL5.

Further, in the above-mentioned embodiments, the case of applying to the driving device of the EL for backlight of the dial of the analog type electronic wrist watch has been exemplified, but the EL driving device of the present invention is the back of the display portion of the digital wrist watch. It can also be applied to a drive device for a light EL.

Further, the EL drive device of the present invention can be applied to a drive device for illumination EL other than the backlight system.

Further, the EL driving device of the present invention is not limited to the lighting EL, but can be applied to other EL driving devices which require low power consumption.

[0053]

According to the display device of the present invention, as described in claim 1, the power consumption can be controlled by changing the on / off time of the first switch element.

Further, as described in claim 2, while the light receiving element for detecting the external brightness and the first switch element are turned on / off at a predetermined cycle, the second switch element is changed to the first switch. A control device that turns on / off in a predetermined cycle longer than the element and that changes the on-time of the first switch element in accordance with the output of the light receiving element, according to the ambient brightness. By changing the brightness of the EL, the EL can be efficiently driven.

Further, as described in claim 3, the light receiving element for detecting the luminance of electroluminescence and the first switch element are turned on / off at a predetermined cycle while the second switch element is turned on and off. A control device that turns on / off at a predetermined cycle longer than the element and that changes the on-time of the first switch element according to the output of the light receiving element, so that the parts of each device vary. Even if there is, the brightness of the EL can be made constant by controlling the energization time to the choke coil. Therefore, considering the variation of parts of each device,
Since it is not necessary to set the EL drive voltage to a high value so as to ensure the minimum luminance of the EL, the EL can be efficiently driven.

Further, as described in claim 4, a control device is provided for changing the ON time of the first switch element so that the energization time to the choke coil is shortened while the second switch element is ON. As a result, the power loss during EL discharge can be reduced and the EL can be driven efficiently.

Further, as described in claim 5, for operating the output amplifying means and the signal converting means of the light receiving element only while the first switch element is turned on / off in the predetermined cycle. By including the control device that turns on the third switch element, it is possible to prevent unnecessary power consumption when the EL is not lit.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an EL drive device of the present invention.

FIG. 2 is a timing chart of the device shown in FIG.

FIG. 3 is a schematic configuration diagram showing a conventional EL drive device.

FIG. 4 is a timing chart of the device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 electroluminescence drive device 4 control device 5 electroluminescence 6 power supply 7 boosting means 9 first switching element 10 second switching element 11 choke coil 13 photodiode (light receiving element) 14 output amplification means 15 signal conversion means 16 third switching element

Claims (5)

[Claims] 1. An electroluminescence drive device for supplying electric charge to electroluminescence while emitting the electric charge charged to the electroluminescence at a predetermined cycle to generate light when the coil is de-energized. Boosting means for accumulating charges in the electroluminescence by using the counter electromotive force, a first switch element for turning on / off the energization to the boosting means, and turning on / off the discharge of the electroluminescence. A second switch element for turning on / off the first switch element at a predetermined cycle, while turning on / off the second switch element at a predetermined cycle longer than the first switch element, and A controller for changing the ON time of the first switch element; Toro luminescence drive. 2. An electroluminescence drive device that supplies electric charge to electroluminescence while discharging the electric charge charged to the electroluminescence at a predetermined cycle to generate light when the energization of a coil is cut off. Boosting means for accumulating charges in the electroluminescence by using the counter electromotive force, a first switch element for turning on / off the energization to the boosting means, and turning on / off the discharge of the electroluminescence. And a light receiving element for detecting the external brightness, and the second switch element more than the first switch element while turning on / off the first switch element at a predetermined cycle. It is turned on / off in a long predetermined cycle and the first switch element is turned on / off according to the output of the light receiving element. Electroluminescent driving apparatus characterized by comprising a control device for varying the time. 3. An electroluminescence drive device for supplying electric charge to electroluminescence while discharging the electric charge charged to the electroluminescence at a predetermined cycle to generate light when the current to the coil is cut off. Boosting means for accumulating charges in the electroluminescence by using the counter electromotive force, a first switch element for turning on / off the energization to the boosting means, and turning on / off the discharge of the electroluminescence. And a light receiving element for detecting the luminance of the electroluminescence; and a second switch element from the first switch element while turning on / off the first switch element at a predetermined cycle. ON / OFF with a long predetermined cycle, and depending on the output of the light receiving element Electroluminescent driving apparatus characterized by comprising a control device for varying the ON time of the first switching element. 4. The control device changes the on-time of the first switch element so that the energizing time to the boosting means is shortened while the second switch element is on. 2. The electroluminescence drive device according to 2 or 3. 5. An output amplification means for amplifying an output of the light receiving element, a signal conversion means for converting a signal from the output amplification means into a digital signal and outputting the digital signal to the control device, the output amplification means, and A third switch element for turning on / off the drive of the signal conversion means, and the controller is configured to control the third switch element only while the first switch element is turned on / off at the predetermined cycle. The electroluminescence drive device according to claim 2, wherein a switch element is turned on.