JP2005202139A - Light emitting display device, and portable equipment having the light emitting display device, and method for driving the light emitting display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting display device with high light emission efficiency capable of suppressing the occurrence of intermittent operations of a boosting means in the light emitting display device having the boosting means, and to provide a portable equipment having the light emitting display device, and a method for driving the light emitting display device. <P>SOLUTION: The light emitting display device having an LED, a power source for outputting the voltage to drive the LED and the boosting means for boosting the power source voltage outputted from the power source, the portable equipment having the light emitting display device, and the method for driving the light emitting display device are provided, wherein a voltage detection means for detecting a first voltage which is the prescribed voltage value of the power source voltage and a second voltage which is the prescribed voltage difference between the power source voltage and the voltage outputted from the boosting means is arranged. The boosting means is constituted to start operation to boost the power source voltage so as to attain the least possible voltage value necessary for driving the LED when the first voltage is detected and to stop the operation when the second voltage is detected after the start of the operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting display device having a plurality of LEDs (Light Emitting Diodes), a portable device including the light emitting display device, and a driving method of the light emitting display device.

  Recently, portable devices such as mobile phones and various toys and gaming machines have built-in light-emitting display devices composed of a plurality of LEDs, and the LEDs to be used are red, green, Light emitting in each color such as blue and white is used as appropriate. By emitting each light at a predetermined timing, it is possible to display a predetermined state by a light emission pattern or the like.

  In such an LED, the forward voltage required for each light emission is different for each color LED. That is, the forward voltage of the red LED is about 2.0V, the forward voltage of the blue LED and the green LED is about 3.0V, and the forward voltage of the white LED is about 3.5V.

  Therefore, in order to make each color LED emit light while saving power, it is desirable to apply a driving voltage according to the forward voltage of each LED to each LED. Specifically, a voltage detection circuit is provided at the cathode of each LED. By connecting and detecting the voltage applied to the LED with this voltage detection circuit and controlling the detected value to be a predetermined voltage value, the operation of the light-emitting display device with power saving is enabled. (For example, refer to Patent Document 1).

  When such a light-emitting display device is built in a portable device, an output-variable power source whose output voltage decreases with the use of a battery, a dry cell, or the like is used as a power source for operating the light-emitting display device.

With this output-variable power supply, the output voltage gradually decreases as the mobile device is used, and the necessary voltage required to operate the mobile device cannot be output, but the output voltage is thus lower than the required voltage. Even after that, since the power supply can output at a voltage lower than that, a booster composed of a booster circuit that boosts this voltage and outputs it as a necessary voltage is provided so that the portable device and the light-emitting display device can be It can be used for a long time.
JP 2000-347613 A

  However, when the boosting device is provided as described above, the non-boosting operation is performed in the vicinity of the output voltage value at which the non-boosting operation state where the boosting device is not operated and the boosting operation state where the boosting device is operated are switched. There has been a problem that intermittent operation of the boosting device that alternately repeats the state and the boosting operation state occurs.

  In other words, the output voltage output from the output variation type power supply does not decrease with a substantially constant attenuation rate, but actually depends on the operating state of each circuit provided in the light emitting display device or booster device. Therefore, when the fluctuation occurs in the vicinity of the output voltage value for switching between operation / non-operation of the booster, the booster is operated intermittently.

  In particular, when a battery is used as the power source, the battery voltage largely fluctuates due to fluctuations in current consumption in various circuits including the booster connected to the battery due to the internal resistance of the battery. In addition, it is easy to induce intermittent operation of the booster.

  In addition, when the booster operates, an oscillation operation may occur if the power supply voltage input to the booster and the boosted voltage output from the booster are substantially the same voltage. When the oscillation operation or the intermittent operation of the boosting device described above occurs, there is a possibility that the operation of the light emitting display device, the boosting device, and peripheral devices may be adversely affected as a noise source inside the device.

  In addition, since a circuit such as a booster circuit generally consumes a large amount of circuit current at the time of starting, the booster circuit repeats a large amount of current consumption by repeating operation / non-operation, thereby increasing the power consumption of the power supply. There was a risk of inviting.

  Therefore, in the light emitting display device of the present invention, in a light emitting display device having an LED, a power source for driving the LED, and a boosting means for boosting the power supply voltage output from the power source, the light emitting display device has a predetermined power supply voltage value. Voltage detecting means for detecting a first voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means is provided, and the boosting means detects the first voltage. When the operation starts, the power supply voltage is boosted so that the required minimum voltage value can drive the LED. After the operation starts, the operation stops when the second voltage is detected. Configured to do.

  Further, the voltage detection means includes a first voltage detection means connected to the cathode of the LED and a second voltage detection means connected to the power source and the boosting means, and the first voltage detection means detects the first voltage. In addition, the second voltage detection means has a feature that the second voltage detection means detects the second voltage, and the first voltage detection means switches between the operation and non-operation of the boosting means based on the detection of the first voltage. The first detection signal to be output and the second detection signal output from the second voltage detection means based on detection of the second voltage are input to the switching control means, and the switching control means includes The first detection signal and the second detection signal obtained by delaying the first detection signal and the second detection signal by a predetermined time are input, respectively. is there.

  Further, in the driving method of the light emitting display device of the present invention, in the driving method of the light emitting display device having the LED, the power source for driving the LED, and the boosting means for boosting the power source voltage output from the power source. Voltage detecting means for detecting a first voltage that is a predetermined voltage value of the first voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means. When the voltage of 1 is detected, the power supply voltage is boosted so that the boosting means operates and the LED can be driven, and the voltage detecting means When the voltage of 2 is detected, the operation of the boosting means is stopped.

  Further, in the portable device of the present invention, in the portable device comprising a light emitting display device composed of a plurality of LEDs, a battery for driving these LEDs, and a boosting means for boosting the power supply voltage output from the battery, Voltage detecting means for detecting a first voltage, which is a predetermined voltage value of the power supply voltage, and a second voltage, which is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means, is provided. The power supply starts to operate when the first voltage is detected so that the LED having the maximum forward voltage value among the LEDs emitting light can be driven to have the minimum voltage value necessary. The voltage is boosted, and the operation is stopped when the second voltage is detected after the operation is started.

  According to the first aspect of the present invention, in a light emitting display device having an LED, a power source for driving the LED, and a boosting unit for boosting a power source voltage output from the power source, the light emitting display device has a predetermined voltage value of the power source voltage. Voltage detecting means for detecting a first voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means is provided, and the boosting means detects the first voltage. When the operation starts, the power supply voltage is boosted so that the required minimum voltage value can drive the LED. After the operation starts, the operation stops when the second voltage is detected. With this configuration, the value of the power supply voltage at which the boosting means is switched from the non-operating state to the operating state can be made different from the value of the power supply voltage at which the boosting means is switched from the operating state to the non-operating state. ,Power supply Even if fluctuations in the up / down in pressure is generated, boosting means can be prevented to perform frequent intermittent operation. Therefore, noise reduction and power saving in the light-emitting display device can be achieved.

  According to a second aspect of the present invention, the voltage detecting means comprises a first voltage detecting means connected to the cathode of the LED and a second voltage detecting means connected to the power source and the boosting means. By detecting the first voltage and detecting the second voltage with the second voltage detection means, the first voltage detection means can also be used as the detection means for detecting the application state of the voltage in the LED. The voltage detection means can be configured simply. In addition, since the second voltage detection means can detect the second voltage without being affected by other circuits or the like, it is possible to accurately switch the operation of the boosting means from non-operation.

  According to the third aspect of the present invention, the switching between the operation and the non-operation of the boosting means is performed by detecting the first detection signal output from the first voltage detection means based on the detection of the first voltage and the detection of the second voltage. And the second detection signal output from the second voltage detection means is input to the switching control means, and the switching control means receives the first detection signal and the second detection signal for a predetermined time. The first delay detection signal and the second delay detection signal that are delayed by an amount of time are input to increase or decrease the power supply voltage in the vicinity of the first voltage and in the vicinity of the second voltage. Even if a momentary fluctuation occurs, it can be made less susceptible to the influence, and the light-emitting display device can be operated more stably.

  According to a fourth aspect of the present invention, in a driving method of a light-emitting display device having an LED, a power source for driving the LED, and a boosting means for boosting a power source voltage output from the power source, a predetermined voltage value of the power source voltage is provided. Voltage detecting means for detecting the first voltage and the second voltage, which is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means, is provided, and the first voltage is detected by the voltage detecting means. In this case, the power supply voltage is boosted so that the boosting means operates to drive the LED, and the voltage detecting means detects the second voltage after the boosting means starts operating. In this case, by stopping the operation of the boosting means, the power supply voltage value at which the boosting means is switched from the non-operating state to the operating state and the boosting means are operated as in the first aspect of the invention. Since the value of the power supply voltage that is switched from the state to the non-operation state can be made different, it is possible to prevent the boosting means from performing frequent intermittent operation even if the power supply voltage fluctuates up or down. . Therefore, noise reduction and power saving in the light-emitting display device can be achieved.

  According to a fifth aspect of the present invention, in a portable device comprising a light emitting display device comprising a plurality of LEDs, a battery for driving these LEDs, and a boosting means for boosting the power supply voltage output from the battery, Voltage detection means for detecting a first voltage, which is a predetermined voltage value of the voltage, and a second voltage, which is a predetermined voltage difference between the power supply voltage and the voltage output from the boosting means, is provided. The operation starts when the first voltage is detected, and the power supply voltage is set to a minimum necessary voltage value capable of driving the LED having the maximum forward voltage value among the light-emitting LEDs. And the operation is stopped when the second voltage is detected after the operation is started, so that the boosting means is changed from the non-operating state to the operating state. Switch Since the value of the source voltage and the value of the power supply voltage at which the booster is switched from the operating state to the non-operating state can be made different, the booster is frequently intermittent even if the power supply voltage fluctuates up or down. The operation of the portable device can be stabilized by suppressing the operation.

  In the light emitting display device of the present invention, the portable device including the light emitting display device, and the driving method of the light emitting display device, the light emitting display device includes at least an LED, a power source that outputs a voltage for driving the LED, and the power source. And a booster that boosts the power supply voltage output from the power supply voltage, and a first voltage that is a predetermined voltage value of the power supply voltage, and a predetermined voltage of the power supply voltage and the voltage output from the booster Voltage detecting means for detecting the second voltage which is the difference is provided, and the operation / non-operation of the boosting means is switched using the first voltage and the second voltage.

  That is, the boosting unit starts operation when the first voltage is detected by the voltage detecting unit, boosts the power supply voltage so as to obtain a minimum necessary voltage value capable of driving the LED, After the operation is started, the operation is stopped when the second voltage is detected by the voltage detection means.

  As described above, when the operation control / non-operation switching control of the voltage boosting unit is performed using the first voltage and the second voltage, the power supply voltage detected by the voltage detection unit fluctuates. However, as long as there is no voltage fluctuation corresponding to a predetermined voltage difference, it is possible not to switch the operation / non-operation of the boosting means, so that it is possible to suppress frequent operation of the boosting means. .

  Therefore, generation of noise and power consumption can be reduced with the suppression of frequent intermittent operation of the boosting means, and the light emitting display device can be stably operated with power saving.

  In addition, when the boosting means is operated, the power supply of a predetermined magnitude is used so that the necessary minimum voltage value capable of driving the LED having the maximum forward voltage value among the light emitting LEDs is driven. By boosting the voltage, it is possible to prevent the power supply voltage and the boosted voltage boosted by the boosting means from being substantially coincident with each other, thereby suppressing the occurrence of an oscillation operation.

  The voltage detection means described above includes a first voltage detection means connected to the cathode of the LED and a second voltage detection means connected to the power source and the boosting means. The first voltage detection means uses the first voltage detection means. , And the second voltage detecting means detects the second voltage.

  The second voltage detection means is connected to the power source and the boosting means, so that the second voltage detection means can detect the second voltage without being influenced by other circuits provided in the light emitting display device. By detecting the voltage, it is possible to improve the accuracy of switching control from the operation of the boosting means to the non-operation.

  On the other hand, by connecting the first voltage detecting means to the cathode of the LED, the applied voltage to the LED detected for feedback control of the voltage applied to the LED can be simultaneously performed by the first voltage detecting means. The size of the apparatus can be reduced.

  The operation of the boosting means is switched between non-operation by the first detection signal output from the first voltage detection means based on the detection of the first voltage and the second voltage detection means based on the detection of the second voltage. The second detection signal to be output is input to the switching control means.

  In particular, the switching control means inputs the first detection signal and the second detection signal to the signal delay means, respectively, and the signal delay means receives the first detection signal and the second detection signal, respectively. A first delay detection signal and a second delay detection signal delayed by a predetermined time are generated, and the first delay detection signal and the second delay detection signal are respectively input.

  Therefore, even if a momentary increase / decrease in the power supply voltage occurs in the vicinity of the first voltage or the second voltage, it is possible to make the light-emitting display device more stable. It can be operated.

  Hereinafter, the portable device of the present embodiment will be described in detail based on the drawings. The mobile device of this embodiment is a mobile phone equipped with a light emitting display device, and uses a rechargeable battery as a power source. Note that the portable device is not limited to a cellular phone, and is a portable electronic device including a light emitting display device, such as a digital still camera, a portable game machine, a penlight, a portable music player, a PDA ( Personal Digital Assistant) or a mobile personal computer may be used. The power source is not limited to a rechargeable battery, but may be a dry battery that is used up as long as power can be supplied. Unless otherwise specified, “battery” refers to a power source of an output variation type in which the output voltage decreases with the use of a storage battery such as a battery or a dry battery.

  As shown in FIG. 1, the light emitting display device 10 incorporated in the portable device A of the present invention includes a battery 11 formed of a battery, a voltage supplied from the battery 11, that is, a voltage adjusting unit 12 for adjusting a power supply voltage, LED 13a, 13b,..., 13n each having an anode connected to the voltage adjusting unit 12, and the cathode of each LED 13a, 13b,..., 13n connected to drive each LED 13a, 13b,. .., 14n that performs control, and a light emission control circuit 15 that controls the LED light emission current driving circuits 14a, 14b,..., 14n.

  Further, the light emitting display device 10 is connected to the cathodes of the LEDs 13a, 13b,..., 13n to detect the voltage values applied to the respective LEDs 13a, 13b,. The lowest voltage detection circuit 16 for detecting the lowest voltage value is provided. Based on the lowest voltage value detected by the lowest voltage detection circuit 16, the LEDs 13a, 13b,... , The voltage applied to 13n is adjusted.

  Further, the light emitting display device 10 is connected to a first voltage detection circuit 17 which is a first voltage detection means connected to the lowest voltage detection circuit 16 to detect a first voltage, a battery 11 and a booster circuit 12b which will be described later. The second voltage detection circuit 18 as the second voltage detection means for detecting the second voltage, and the first detection signal and the second detection signal output from the first voltage detection circuit 17 and the second voltage detection circuit 18, respectively. A signal delay circuit 19 for inputting a signal and a switching control circuit 21 connected to the signal delay circuit 19 are provided.

  In FIG. 1, 22 is a coil for boosting the voltage output from the battery 11, and 23 is a capacitor for stabilizing the voltage output from the voltage adjustment unit 12.

  For convenience of explanation, the battery 11 is included in the light emitting display device 10, but the battery 11 is shared as a power source for devices other than the light emitting display device 10 of the portable device A. For convenience of explanation, the power supply voltage output from the battery 11 will be referred to as “battery output voltage”.

  The voltage adjustment unit 12 adjusts the voltage value of the boost in the through circuit 12a that outputs the input voltage as it is, the booster circuit 12b that is a booster that boosts and outputs the input voltage, and the booster circuit 12b Hysteresis adjusting circuit 12c and a switching circuit 12d for switching the input voltage to be input to either the through circuit 12a or the booster circuit 12b. Note that the voltage regulator 12 may be regarded as a single booster circuit as a whole.

  The booster circuit 12b adjusts the voltage applied to each of the LEDs 13a, 13b,..., 13n by adjusting the boost amount based on the minimum voltage value input from the minimum voltage detection circuit 16, as will be described later. .

  The hysteresis adjustment circuit 12c can arbitrarily adjust a boosted voltage, which is a boosted voltage output from the booster circuit 12b, as will be described later, by inputting an adjustment signal (not shown). The voltage boosted and output by the booster circuit 12b based on the hysteresis adjustment circuit 12c will be referred to as “boosted voltage”.

  Based on the switching control signal input from the switching control circuit 21, the switching circuit 12d switches the mode by inputting the voltage input from the battery 11 to either the through circuit 12a or the booster circuit 12b. ing. That is, when the through circuit 12a is selected in the switching circuit 12d, the battery output voltage is output as the through mode, and when the boost circuit 12b is selected in the switching circuit 12d, the boost voltage is output as the boost mode. It is made to output.

  The LEDs 13a, 13b,..., 13n are provided in accordance with required purposes, and are connected in parallel to each other. In the case of the present embodiment, the LEDs 13a, 13b,..., 13n are specifically the backlight LED of the liquid crystal display device of the mobile device A composed of a mobile phone, the LED for incoming call display, etc. A plurality of LEDs that emit light in different colors are provided so as to intrigue the user. A plurality of LEDs are not necessarily provided, and only one LED may be provided. In that case, the minimum voltage detection circuit 16 is unnecessary.

  Each LED 13a, 13b,..., 13n is driven by an LED light emission current drive circuit 14a, 14b,..., 14n connected to each cathode, and the LED light emission current drive circuits 14a, 14b,. .., 14n are driven based on the drive control signal input from the light emission control circuit 15.

  A light emission output signal from a control circuit (not shown) of the portable device A provided outside the light emitting display device 10 is input to the light emission control circuit 15, and the light emission control circuit 15 is driven based on this light emission output signal. A control signal is generated.

  The lowest voltage detection circuit 16 connected to the cathode of each LED 13a, 13b,..., 13n detects the value of the voltage applied to each LED 13a, 13b,. The lowest voltage value is detected. The voltage value detected by the lowest voltage detection circuit 16 is a value corresponding to the difference between the voltage output from the voltage adjustment unit 12 and the forward voltage of each LED 13a, 13b,. When this voltage value is not a positive value, the LED is not supplied with a voltage corresponding to the forward voltage.

  Therefore, the minimum voltage detection circuit 16 is provided with a predetermined threshold value, and if the lowest voltage value among the detected voltage values is smaller than the threshold value, the voltage value is input to the booster circuit 12b. As described later, the booster voltage is output from the voltage adjustment unit 12.

  The first voltage detection circuit 17 is input with the lowest voltage value output from the lowest voltage detection circuit 16, and in the through mode, the battery output voltage is calculated from the voltage value and the battery output voltage is preset. The first detection signal is output when the first voltage is reached.

  The first voltage is necessary for operating each circuit constituting the light emitting display device 10 to the forward voltage of the LED having the maximum forward voltage among the LEDs 13a, 13b,. The voltage is the sum of the voltages.

  When the LEDs 13a, 13b,..., 13n are connected to the first voltage detection circuit 17 via the minimum voltage detection circuit 16, based on the voltage value output from the minimum voltage detection circuit 16 as described above. Thus, it is possible to detect the first voltage and to appropriately control the boosting in the boosting circuit 12b.

  In the present embodiment, the first voltage detection circuit 17 is connected to the cathodes of the LEDs 13a, 13b,..., 13n via the minimum voltage detection circuit 16, but the purpose is to detect the first voltage. Therefore, it is not always necessary to provide the minimum voltage detection circuit 16, and the first voltage detection circuit 17 may be connected to the cathodes of the LEDs 13a, 13b,..., 13n to detect the first voltage. Good. In this case, it is only necessary to connect to the cathode of any one of a plurality of LEDs 13a, 13b,..., 13n, and the cathodes of all the LEDs 13a, 13b,. There is no need to connect.

  In the present embodiment, the minimum voltage detection circuit 16 or the first voltage detection circuit 17 detects the voltage applied to each LED 13a, 13b,..., 13n, but each LED 13a, 13b,. As long as the value of the voltage applied to 13n can be detected, a configuration other than the minimum voltage detection circuit 16 and the first voltage detection circuit 17 may be used.

  The battery voltage output from the battery 11 and the boosted voltage output from the booster circuit 12b are input to the second voltage detection circuit 18, and a difference voltage between the boosted voltage and the battery output voltage is set in advance. The second detection signal is output when the voltage becomes equal to or lower than the second voltage. That is, the second voltage is a difference voltage between the boosted voltage and the battery output voltage (see FIG. 2). Since the second voltage detection circuit 18 is connected to the battery 11, it can accurately detect the second voltage from the battery output voltage regardless of the through mode and the boost mode, and is not affected by other circuits. The second voltage can be detected.

  As another embodiment, the voltage output from the battery 11 is input to the second voltage detection circuit 18 to detect the battery output voltage. When the battery output voltage becomes a preset voltage, the second detection signal May be output.

  The signal delay circuit 19 delays each of them by a predetermined time based on the first detection signal input from the first voltage detection circuit 17 and the second detection signal input from the second voltage detection circuit 18. The first delay detection signal and the second delay detection signal are generated, and the first delay detection signal and the second delay detection signal are output.

  The switching control circuit 21 outputs a switching signal for switching the switching circuit 12d of the voltage adjusting unit 12 based on the first delay detection signal and the second delay detection signal input from the signal delay circuit 19. Based on this switching signal, the voltage adjustment unit 12 outputs either the battery output voltage or the boosted voltage.

  Hereinafter, the operation of the booster circuit 12b will be described based on the correlation diagram of the LED driving input voltage with respect to the power consumption state in the battery 11 shown in FIG.

  First, as shown in FIG. 2, the battery output voltage of the battery 11 decreases according to a predetermined characteristic curve P as the power is consumed. Here, for convenience of explanation, it is assumed that the battery output voltage is appropriate power in the through mode without performing extra output adjustment for power saving in the through circuit 12a.

  In the light emitting display device 10, in the through mode, the required LEDs 13a, 13b,..., 13n are caused to emit light based on the battery output voltage output from the through circuit 12a, and the power of the battery 11 is consumed.

  When the battery output voltage approaches the first voltage due to the consumption of the battery 11, the first voltage is reached along the first path R1 on the characteristic curve P.

  When the battery output voltage reaches the first voltage, the first voltage detection circuit 17 outputs the first detection signal and switches the connection state of the switching circuit 12d to enter the boost mode.

  At this time, the first detection signal is converted into the first delay detection signal by the signal delay circuit 19 and input to the switching control circuit 21, so that even if an instantaneous voltage fluctuation occurs in the vicinity of the first voltage, Can be less affected.

  When the through mode is switched to the boost mode, the voltage output from the voltage adjusting unit 12 becomes a boosted voltage boosted along the second path R2 by the boosting circuit 12b, and the voltage adjusting unit 12 outputs this high voltage. The boost amount α when switching to the boost mode is set by the hysteresis adjustment circuit 12c, and the battery output voltage output from the voltage adjustment unit 12 before and after boosting by setting the boost amount α relatively large. And the boosted voltage can be made different from each other, and generation of an oscillation operation when the mode is switched can be suppressed.

  When the battery output voltage further decreases after entering the boost mode, the voltage adjustment unit 12 boosts the voltage by the boost circuit 12b based on the voltage value input from the minimum voltage detection circuit 16, and the third path R3 A boosted voltage is output along

  On the other hand, when the battery output voltage rises due to charging of the battery 11 after entering the boost mode, the boost mode is maintained until the difference voltage between the boost voltage and the battery output voltage becomes the second voltage or less. The voltage adjustment unit 12 outputs the boosted voltage along the fourth path R4.

  When the difference voltage between the boosted voltage and the battery output voltage becomes equal to or lower than the second voltage, the second voltage detection circuit 18 outputs the second detection signal to switch the connection state of the switching circuit 12d, thereby setting the through mode.

  At this time, the second detection signal is converted into the second delay detection signal by the signal delay circuit 19 and input to the switching control circuit 21, so that even if an instantaneous voltage fluctuation occurs in the vicinity of the second voltage, Can be less affected.

  When the through mode is switched to the boost mode, the voltage output from the voltage adjustment unit 12 becomes the battery output voltage, and thus the voltage that has dropped along the fifth path R5 is output.

  Thus, by forming a hysteresis loop by the first path R1, the second path R2, the fourth path R4, and the fifth path R5, the booster circuit 12b is frequently used as the battery output voltage fluctuates. Repeated operation / non-operation can be suppressed, noise can be suppressed and power consumption can be reduced, and operation stability of the light emitting display device 10 and the portable device A including the light emitting display device 10 can be improved. In addition, the power supply voltage can be stably boosted only when necessary so as to obtain the minimum necessary voltage value that can drive the LED having the maximum forward voltage value among the LEDs that emit light. Therefore, highly efficient LED luminous efficiency can be obtained.

It is a schematic explanatory drawing of the portable apparatus which comprises the light emission display device which concerns on this invention. It is a correlation diagram of the input voltage for LED drive with respect to the power consumption state in a battery.

Explanation of symbols

A Mobile device
10 Light-emitting display device
11 batteries
12 Voltage regulator
12a Through circuit
12b Booster circuit
12c Hysteresis adjustment circuit
12d switching circuit
13a LED
13b LED
13n LED
14a LED light emission current drive circuit
14b LED light emission current drive circuit
14n LED light emission current drive circuit
15 Light emission control circuit
16 Minimum voltage detection circuit
17 First voltage detection circuit
18 Second voltage detection circuit
19 Signal delay circuit
21 Switching control circuit
22 coils
23 Capacitor

Claims (5)

In a light emitting display device having an LED, a power source that drives the LED, and a boosting unit that boosts a power supply voltage output from the power source.
Voltage detection means for detecting a first voltage that is a predetermined voltage value of the power supply voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and a voltage output from the boosting means;
The boosting unit starts operating when the first voltage is detected, boosts the power supply voltage so that the LED voltage can be driven, and starts operating. A light-emitting display device configured to stop operation when the second voltage is detected later.   The voltage detecting means includes a first voltage detecting means connected to the cathode of the LED, and a second voltage detecting means connected to the power source and the boosting means, and the first voltage detecting means includes the first voltage detecting means. The light emitting display device according to claim 1, wherein the second voltage is detected by the second voltage detecting means. The switching between the operation and non-operation of the boosting means is performed based on detection of the first detection signal output from the first voltage detection means based on detection of the first voltage and detection of the second voltage. The second detection signal output from the two voltage detection means is input to the switching control means, and is performed.
The switching control means is configured to input a first delay detection signal and a second delay detection signal obtained by delaying the first detection signal and the second detection signal by a predetermined time, respectively. The light-emitting display device according to claim 2. In a driving method of a light emitting display device having an LED, a power source that drives the LED, and a boosting unit that boosts a power supply voltage output from the power source.
Voltage detection means for detecting a first voltage that is a predetermined voltage value of the power supply voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and a voltage output from the boosting means;
When the first voltage is detected by the voltage detection means, the power supply voltage is boosted so as to obtain a minimum necessary voltage value capable of operating the boosting means to drive the LED, and the boosting When the voltage detection means detects the second voltage after the operation of the means is started, the operation of the boosting means is stopped. In a portable device comprising a light emitting display device composed of a plurality of LEDs, a battery for driving these LEDs, and a boosting means for boosting the power supply voltage output from the battery,
Voltage detection means for detecting a first voltage that is a predetermined voltage value of the power supply voltage and a second voltage that is a predetermined voltage difference between the power supply voltage and a voltage output from the boosting means;
The boosting means starts operation when the first voltage is detected, and the minimum voltage value necessary to drive the LED having the maximum forward voltage value among the light emitting LEDs. The portable device comprising the light emitting display device, wherein the power supply voltage is boosted so that the operation is stopped and the operation is stopped when the second voltage is detected after the operation is started.

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