JP2007108545A - Light emitting element driving apparatus and portable device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep driving a system and also obtain stable brightness even in such a situation that a power supply voltage is reduced when light is emitted from an LED, regarding a light emitting element driving apparatus and portable device. <P>SOLUTION: Regarding the driving apparatus for a white LED 18 loaded to a portable telephone 1, the driving apparatus includes: a light source part 22 having the white LED 18 and an LED driver 21 for driving the white LED 18 with a constant current; a CPU 23 for controlling the whole system of the portable telephone 1; a Li-ion secondary battery 24 provided to supply power to the light source part 22 and the CPU 23; and a condenser element 25 charged by the Li-ion secondary battery 24 so as to supply the power to the light source part 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light-emitting element driving device that drives an LED that functions as a flash when photographing with a camera function, for example, and a portable device such as a mobile phone including the light-emitting element driving device.

  In recent years, many mobile devices such as mobile phones have a digital camera function, and some have a light source that emits light during shooting and functions as a flash. In such mobile phones, rechargeable lithium ion secondary batteries (hereinafter referred to as Li ion secondary batteries) are used as a power source, and white LEDs (Light Emitting Diodes) are mainly used as light sources. It is used for. Here, a Li-ion secondary battery used as a power source is usually used to drive a control circuit that is built in a mobile phone and controls the entire system of the mobile phone.

Since the Li ion secondary battery emits an LED used as a light source with a sufficient amount of light as a flash at the time of shooting, it is necessary to allocate a large amount of power at the time of shooting.
In view of this, a device has been proposed that reduces the number of LEDs required by supplying a current exceeding the LED rating to the LEDs to increase the amount of light, thereby reducing power consumption (see, for example, Patent Document 1). .
Japanese Patent Laying-Open No. 2004-77597 (Claims, FIG. 1)

  However, the following problems remain in the LED flash technology in the conventional portable device. That is, in the above-mentioned conventional, since the Li ion secondary battery used as a power supply has an internal resistance, the power supply voltage decreases as the current to be released increases. For this reason, when the LED, which is the light source, is driven with a large current at the time of flashing, there is a possibility that the system drive of the portable device cannot be maintained due to a voltage drop and a shutdown occurs. Li-ion secondary batteries used in mobile phones and the like have a maximum current value of about 1 A, and a large-capacity battery is required to reduce the voltage drop. For this reason, the battery volume is increased. There was a problem that the size would increase. Further, in Patent Document 1, the LED directly emits light with a capacitor charged from a battery. However, since the luminance characteristics of the LED vary with respect to the driving voltage, when a voltage is directly applied by the capacitor, There was a disadvantage that the brightness of each LED varied.

  The present invention has been made in view of the above-described problems, and provides a light-emitting element driving device and a portable device capable of maintaining system driving and obtaining stable luminance even when the power supply voltage is reduced during LED emission. The purpose is to do.

  The present invention employs the following configuration in order to solve the above problems. That is, the light emitting element driving device of the present invention is a light emitting element driving device mounted on a portable device, and includes a light source unit including the light emitting element and a driving unit that drives the light emitting element at a constant current, and the portable device. A control unit that controls the entire system, a battery power source that can supply power to the light source unit and the control unit, and a storage element that is charged by the battery power source and supplies power to the light source unit. It is characterized by.

  In this light emitting element driving apparatus, when the light source unit emits light, the power storage element supplies power to the driving unit instead of the battery power source to cause the light emitting element to emit light at a constant current. Thus, the system is not shut down, and uniform and stable luminance can be obtained by constant current driving even if the luminance characteristics of the light emitting elements vary. In addition, since a large current can flow through the light emitting element, brighter luminance can be obtained.

  In the light emitting element driving device of the present invention, it is preferable that the power storage element is an electric double layer capacitor. That is, in this light-emitting element driving device, it is possible to rapidly charge and discharge and has a large number of times of charge and discharge, and contributes to the miniaturization of the entire portable device by using a small and high voltage electric double layer capacitor, Even in long-term repeated use, the system can be driven stably when the light emitting element emits light.

A light-emitting element driving device of the present invention is a portable device on which a light-emitting element is mounted, and includes the light-emitting element driving device of the present invention.
Since the portable device includes the light emitting element driving device of the present invention, the entire system of the portable device can be stably driven even when a large current is supplied to the light emitting element to emit light.

  In addition, the portable device of the present invention has a camera mechanism, and the light emitting element driving device causes the light emitting element to emit light as a flash during photographing by the camera mechanism. That is, in this portable device, a light emitting element is mounted as an LED flash, and in the light emitting element driving device of the present invention, power is supplied to the light source unit by the power storage element at the time of flashing, thereby preventing the entire system from being shut down. The camera function can be stably maintained, and a uniform and stable flash light amount can be obtained between frames.

  The portable device of the present invention is characterized in that the camera mechanism includes a CMOS image sensor. That is, in the camera mechanism using the CMOS image sensor, when there is no shutter function, two or more frames are required at the time of capturing an image, and uniform brightness is required between the frames. Even with a CMOS image sensor, even brightness (flash light amount) can be obtained by the LED flash thus made, and good photographing can be performed.

The present invention has the following effects.
That is, according to the light emitting element driving device and the portable device according to the present invention, the power is supplied to the driving unit by the power storage element to cause the light emitting element to emit light at a constant current, so that even if a large current is consumed for light emission, the system Can be maintained, and a sufficient amount of light can be emitted without causing a shutdown. Therefore, even when a large amount of light such as an LED flash is required, the influence on the system during light emission can be eliminated, and a uniform and stable large amount of flash can be obtained.

Hereinafter, a light emitting element driving device according to an embodiment of the present invention and a portable device including the same will be described with reference to FIGS. 1 and 2.
A mobile phone (mobile device) 1 according to the present embodiment is a mobile phone equipped with a digital camera mechanism (hereinafter referred to as camera mechanism) CA having an LED flash function, as shown in FIGS. The first housing 2 and the second housing 4 are foldable via the first housing 2 and the hinge mechanism 3.

On the inner surface side when the cellular phone 1 of the first housing 2 is folded, an operation key unit 11 configured by numeric keys and the like for inputting operation of the cellular phone 1, and a microphone 12 for inputting transmission voice, Is provided. In addition, a sounder 13 for notifying the incoming state is provided on the outer surface side of the first housing 2 when it is folded.
A speaker 14 that outputs a received voice and a first display 15 that displays characters and images are provided on the inner surface side of the mobile phone 1 of the second housing 4 when folded. In addition, on the outer surface side of the second housing 4 when folded, a second display 16 that displays characters and images similarly to the first display 15, an objective lens 17 that is used for photographing, and this objective lens 17 are provided. A white LED (light emitting element) 18 for irradiating illumination light to the imaging range of the objective lens 17 at the time of imaging used is provided.

  The objective lens 17 is a member constituting the objective optical system of the camera mechanism CA shown in FIG. 2, and is applied to a CMOS (Complementary Metal Oxide Semiconductor) image sensor 20 provided in the second housing 4 from a subject. An image is formed. That is, as shown in FIG. 2, the camera mechanism CA includes an objective lens 17 and a CMOS image sensor 20 as an optical system and an imaging system. The camera mechanism CA does not have a shutter function such as a mechanical shutter or an electronic shutter.

  As shown in FIG. 2, the white LED 18 is driven at a constant current by an LED driver (drive unit) 21 provided in the second housing 4 and is used as an LED flash at the time of photographing, and also notifies the incoming call and the charged state. Is configured to do. The LED driver 21 is configured by an electric circuit using a semiconductor element such as a transistor, for example, and drives the white LED 18 with a predetermined constant current.

  As shown in FIG. 2, the cellular phone 1 includes the entire system and a white LED 18 driving system (light emitting element driving device) in the first housing 2 or the second housing 4, as shown in FIG. 2. A light source unit 22 comprising: a CPU (control unit) 23 which is a control circuit for controlling the functions of the entire system of the mobile phone 1, and a Li ion secondary battery (battery power source) capable of supplying power to the light source unit 22 and the CPU 23. ) 24, and a storage element 25 that is charged by the Li ion secondary battery 24 through the LED driver 21 and supplies power to the light source unit 22.

Further, the mobile phone 1 is provided with a memory (not shown) for recording captured images and an antenna (not shown) for transmitting and receiving radio waves.
The power storage element 25 is a large-capacity capacitor, and is formed of, for example, an electric double layer capacitor. Electric double layer capacitors do not use heavy metals such as lead and cadmium, so the load on the environment is small, and charging and discharging is performed by physical adsorption and separation, so that charging and discharging are performed by chemical reaction. In comparison, it has a feature of less deterioration.
In addition, although the electrical storage element 25 is charged via the LED driver 21 by the Li ion secondary battery 24, you may make it charge directly from the Li ion secondary battery 24 not via the LED driver 21.

The CPU 23 controls a system of the entire mobile phone such as a communication control circuit (not shown) that controls communication by the mobile phone 1 and photographing by the camera mechanism CA.
The camera mechanism CA includes the CMOS image sensor 20 and a DSP (Digital Signal Processor) 26 that performs ON / OFF control of the CMOS image sensor 20. The DSP 26 is connected to the CPU 23 and controlled by the CPU 23.

Next, a method for using the mobile phone 1 having such a configuration will be described.
First, the first and second housings 2 and 4 are expanded and a predetermined operation is performed with the operation key unit 11 to turn on the power. Here, when the mobile phone 1 is used as a telephone, a call operation is performed in this state. When the call processing is started, the audio signal input to the microphone 12 is transmitted as audio data from the antenna by the CPU 23 provided in the first housing 2. Also, audio data received by the antenna is output from the speaker 14 as an audio signal by the CPU 23. In this way, it is used as a telephone.

Next, a photographing method using the camera function of the mobile phone 1 will be described.
First, the power is turned on by performing a predetermined operation with the operation key unit 11, and the camera mechanism CA is activated. At this time, the CPU 23 sends a control signal to the DSP 26, and the DSP 26 sets the CMOS image sensor 20 in a preparation state. In addition, the electrical storage element 25 is charged by the Li ion secondary battery 24 in a normal state.

Next, similarly, a predetermined operation is performed with the operation key unit 11 to perform photographing by the camera mechanism CA. At this time, the LED driver 21 to which power is supplied from the power storage element 25 drives the white LED 18 at a constant current for a certain period of time, and the white LED 18 performs flash emission. At this time, electric power is supplied from the Li ion secondary battery 24 to the CPU 23.
The light reflected from the object to be photographed by flash emission and incident on the objective lens 17 is projected onto the CMOS image sensor 20 that is ON / OFF controlled by the DSP 26 and converted into an electrical signal by the CMOS image sensor 20.

The DSP 26 sends an electrical signal from the CMOS image sensor 20 to the CPU 23 as image data, and the CPU 23 performs predetermined data processing. For example, the CPU 23 performs processing for displaying captured image data on the first display 15. In addition, by performing a predetermined operation with the operation key unit 11, the CPU 23 stores the image data in the memory.
Thereafter, the storage element 25 whose voltage has been reduced due to the light emission of the white LED 18 is charged again by the Li ion secondary battery 24.

  As described above, according to the mobile phone 1 of the present embodiment, when the light source unit 22 emits light, the power storage element 25 supplies power to the LED driver 21 instead of the Li ion secondary battery 24 and the white LED 18 is supplied with a constant current. Since it emits light, the power supply voltage of the Li-ion secondary battery 24 does not drop during light emission, causing a system shutdown, and even if the luminance characteristics of the white LED 18 vary, a uniform and stable flash by constant current driving The amount of light (the brightness of the white LED 18) can be obtained. In addition, since a large current can be passed through the white LED 18 during flash, a brighter flash can be obtained.

  In addition, the use of an electric double layer capacitor that is capable of rapid charge / discharge, has a large number of charge / discharge lifetimes, is small and has a high voltage for the electric storage element 25 contributes to downsizing of the entire mobile phone 1 as well as long-term use. Even in repeated use, the system can be driven stably when the white LED 18 emits light.

  Further, in the mobile phone 1, even with a camera mechanism CA using a CMOS image sensor 20 having no shutter function as an image pickup device by the flash of the white LED 18 driven at a constant current by the power storage device 25 and the LED driver 21, the brightness is equal ( Flash light quantity) can be obtained, and good shooting can be performed.

  In addition, this invention is not limited to said each embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

For example, in the above-described embodiment, the mobile phone 1 is applied as a mobile device. However, the mobile phone may be a mobile device and may be applied to other mobile terminals such as a PDA (Personal Digital Assistant). Or may be applied to a digital camera.
Moreover, although white LED18 is used as a light emitting element, LED which discharge | releases the light of another wavelength may be used individually or in combination, and another light emitting element may be applied.

Moreover, although the Li ion secondary battery 24 is used as a battery power source, other portable battery power sources such as a primary battery such as a nickel metal hydride battery or a dry battery may be applied.
In addition, as described above, it is preferable to use an electric double layer capacitor suitable for downsizing as the power storage element 25. However, even if another rechargeable power source is applied, for example, a storage battery that charges and discharges by a chemical reaction. A replaceable primary battery may be applied.
Further, an imaging device such as a CCD (Charge Coupled Device) may be employed instead of the CMOS image sensor 20, but the present invention is applied to a CMOS image sensor that does not have a shutter function as described above. Is particularly preferred.

1 shows a mobile phone according to an embodiment of the present invention, in which (a) is a perspective view and (b) is a perspective view seen from a direction different from (a). It is a block diagram which shows the supply state of the electric power in an LED drive system in the mobile telephone of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mobile phone (mobile device), 18 ... White LED (light emitting element), 20 ... CMOS image sensor, 21 ... LED driver (drive part), 22 ... Light source part, 23 ... CPU (control part), 24 ... Li ion Secondary battery (battery power supply), 25 ... electric storage element, CA ... camera mechanism

Claims (5)

A drive device for a light emitting element mounted on a portable device,
A light source unit having the light emitting element and a driving unit for driving the light emitting element at a constant current;
A control unit for controlling the entire system of the portable device;
A battery power source capable of supplying power to the light source unit and the control unit;
And a power storage element that is charged by the battery power source and supplies power to the light source unit. The light-emitting element driving apparatus according to claim 1, wherein the power storage element is an electric double layer capacitor. A portable device equipped with a light emitting element,
A portable device comprising the light emitting element driving device according to claim 1. Having a camera mechanism,
The portable device according to claim 3, wherein the light emitting element driving device causes the light emitting element to emit light as a flash during photographing by the camera mechanism. The portable device according to claim 4, wherein the camera mechanism includes a CMOS image sensor.

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