JP4094018B2 - Portable device - Google Patents

Description

  The present invention relates to a portable device using a light emitting element driving device that drives a plurality of light emitting elements having different driving voltages.

For portable devices such as mobile phones, light emitting diodes (LEDs) as a plurality of light emitting elements having different emission colors are used to perform light emission as a backlight of an image display device composed of, for example, an LCD (Liquid Crystal Device), or display an incoming call. Light Emitting Diode (hereinafter referred to as LED) is provided.
Current portable devices are generally equipped with a red (R) LED, a green (G) LED, a blue (B) LED, and a white LED.

  These various LEDs have different so-called forward voltages (Vf). For example, the forward voltage Vfr of the red LED is set to approximately 2.0V, the forward voltages Vfg and Vfb of the green and blue LEDs are set to approximately 3V, and the forward voltage Vfw of the white LED is set to approximately 3.5V.

Thus, the portable device carrying various LEDs having different forward voltages has an LED driving device for driving these LEDs.
The output voltage in this LED driving device is set by selecting a value that satisfies the maximum forward voltage in order to correspond to various LEDs having different forward voltages.
For example, when a red LED with a forward voltage Vfr of 2.0 V and a white LED with a forward voltage Vfw of 3.5 V are driven by the same power source, the voltage required for the constant current source and the forward voltage Vfw of the white LED In general, the output voltage of the LED driving device is fixed to 4.5 V to 5.0 V in consideration of variations.

However, when an LED drive circuit in which the output voltage is matched to the LED having the highest forward voltage is used, for example, a red LED having a low forward voltage is driven at a voltage close to 2.0V higher than the required drive voltage. . As a result, there is a very large power loss.
In addition, as described above, the margin is included in consideration of variations in LEDs having a high forward voltage, and this margin is one factor of power loss.

This power loss problem significantly reduces the luminous efficiency of the LED. Since the portable device is battery driven due to its portability, this power loss shortens the actual use time of the portable device.
For this reason, in conventional LED drive circuits, studies have been made to increase the efficiency of charge pumps and DC-DC converters that serve as power sources. However, the efficiency of these circuits has already exceeded 90%, and it has become difficult to extend the actual use time even if the efficiency is further increased.

On the other hand, as a solution to the above problem, there is a method in which several LEDs are connected in series and driven by a boost power source.
By using this method, the output of the LED drive circuit is controlled to the minimum necessary voltage, so that high efficiency (high light emission efficiency) can be expected.
However, this method has the following problems.

First, since the output voltage becomes high, a high breakdown voltage process is required.
Second, in order to output within the withstand voltage, driving of 3 to 4 LEDs is the limit.
The third is series connection, so that independent control of each LED is difficult.

  In particular, the third problem is a big problem and does not satisfy the function of “many LEDs emit various ways” expected in recent portable devices.

  The present invention has been made in view of such circumstances, and an object thereof is to eliminate the need for a high breakdown voltage process, to increase the number of light-emitting elements that can be driven, and to independently control each of a plurality of light-emitting elements. Needless to say, even if the brightness of a plurality of light emitting elements is individually adjusted, or even when a plurality of light emitting elements having different driving voltages are simultaneously driven, it is possible to always output the lowest voltage that satisfies the driving conditions. An object of the present invention is to provide a portable device using a light emitting element driving device with high light emission efficiency and low power loss.

In order to achieve the above object, a first aspect of the present invention is a portable device having a battery as a power supply voltage source, and is illuminated by a plurality of light emitting elements having different driving voltages necessary for light emission and the light emitting elements. A plurality of display devices as an illuminated portion and a plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, and one light emission that drives one or a plurality of light emitting elements of the plurality of light emitting elements A plurality of drive circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with luminance based on a set value; Based on the drive states of the plurality of drive circuits, a drive voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is driven to the at least the determined value. And a power supply circuit for supplying to the plurality of light emitting elements as a voltage, the power supply circuit, a power supply voltage is supplied, when the value of the power source voltage is larger than the voltage value above determination is the supplied power supply voltage A driving voltage is supplied to the plurality of light emitting elements, and the plurality of light emitting elements that illuminate the plurality of display devices are driven by one light emitting element driving device.

  Preferably, at least one of the plurality of display devices includes a display device that is backlit by the light emitting element.

  Preferably, upon receiving a predetermined blinking operation instruction command, the power supply circuit fixes the output drive voltage of the power supply circuit to a predetermined set voltage regardless of the driving state of the light emitting element.

  Preferably, when the value of the power supply voltage is larger than the determined voltage value, the power supply circuit steps down the supplied power supply voltage to any value up to the determined voltage value, and decreases the power supply voltage. Is supplied to the plurality of light emitting elements as the driving voltage.

  Preferably, when the value of the power supply voltage is smaller than the determined voltage value, the power supply circuit boosts the supplied power supply voltage to at least the determined voltage value, and uses the boosted power supply voltage as the drive voltage. Supply to the plurality of light emitting elements

  Preferably, when the value of the power supply voltage is larger than the determined voltage value, the power supply circuit steps down the supplied power supply voltage to any value up to the determined voltage value, and decreases the power supply voltage. Is supplied to the plurality of light emitting elements as the driving voltage, and when the determined voltage value and the value of the power supply voltage are substantially equal, the supplied power supply voltage is supplied to the plurality of light emitting elements as the driving voltage, When the value of the power supply voltage is smaller than the determined voltage value, the supplied power supply voltage is boosted to at least the determined voltage value, and the boosted power supply voltage is supplied to the plurality of light emitting elements as the drive voltage.

  Preferably, the power supply circuit is configured so that a drive voltage value required for light emission is smaller than the power supply voltage value, and the supplied power supply voltage is any one up to a drive voltage value required for light emission of the light emitting element. And a step-down power supply that supplies the reduced power supply voltage to the target light emitting element as the drive voltage.

  Preferably, the power supply circuit boosts the supplied power supply voltage to at least a drive voltage value necessary for light emission of the light emitting element to a light emitting element whose drive voltage value necessary for light emission is larger than the power supply voltage value. And a boosted power supply that supplies the boosted power supply voltage to the target light emitting element as the drive voltage.

  Preferably, the power supply circuit is configured so that a drive voltage value required for light emission is smaller than the power supply voltage value, and the supplied power supply voltage is any one up to a drive voltage value required for light emission of the light emitting element. A step-down power supply that supplies the reduced power supply voltage to the target light-emitting element as the drive voltage, and a power supply that is supplied to the light-emitting element that has a drive voltage value required for light emission greater than the power supply voltage value. And a boosting power source that boosts the voltage to at least a driving voltage value necessary for light emission of the light emitting element and supplies the boosted power supply voltage to the target light emitting element as the driving voltage.

  A second aspect of the present invention is a portable device having a battery as a power supply voltage source, and a plurality of light emitting elements having different driving voltages required for light emission, and a plurality of illuminated parts illuminated by the light emitting elements. A display device, the plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, one light emitting element driving device that drives one or a plurality of light emitting elements of the plurality of light emitting elements, and the plurality A control device that performs display control of the display device and drive control according to an operation mode of the light emitting element driving device, and a synchronization signal supply circuit that supplies a synchronization signal to the light emitting element driving device under the control of the control device And the light emitting element driving device is connected to a corresponding light emitting element of the plurality of light emitting elements, and drives the corresponding light emitting element with luminance based on a set value, and Based on the driving states of a plurality of driving circuits, a driving voltage value necessary for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is set as the driving voltage of the at least the determined value. A plurality of light emitting elements for illuminating the plurality of display devices by one light emitting element driving device.

  According to a third aspect of the present invention, there is provided a light emitting element driving apparatus in which a plurality of light emitting elements having different driving voltages required for light emission are connected in parallel and drives one or a plurality of light emitting elements among the plurality of light emitting elements. A plurality of drive circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with brightness based on a set value, and based on each driving state of the plurality of drive circuits A power supply circuit that determines a drive voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light, and supplies at least the determined drive voltage to the plurality of light emitting elements.

  A fourth aspect of the present invention is a portable device having a battery as a power supply voltage source, a plurality of light emitting elements having different driving voltages required for light emission, and at least one illuminated portion illuminated by the light emitting elements. A plurality of light emitting elements connected in parallel and driving one or a plurality of light emitting elements among the plurality of light emitting elements, and the light emitting element driving apparatus includes the plurality of light emitting elements. A plurality of driving circuits connected to the corresponding light emitting elements of the elements and driving the corresponding light emitting elements with brightness based on a set value, and one or more of which is driven to emit light based on each driving state of the plurality of driving circuits A power supply circuit that determines a drive voltage value required for the highest light emission among the plurality of light emitting elements and supplies the power supply voltage to the plurality of light emitting elements as the drive voltage of the at least the determined value.

According to the present invention, for example, light emission luminance is given as a set value to a desired drive circuit from a host device.
Accordingly, the corresponding light emitting element is driven by the drive circuit so as to emit light with luminance based on the set value.
At this time, in the power supply circuit, the drive voltage value required for the highest light emission among the one or the plurality of light emitting elements that are driven to emit light is determined based on the drive states of the plurality of drive circuits.
At least the determined driving voltage is supplied to the plurality of light emitting elements.
As a result, even when the luminance of the plurality of light emitting elements is individually adjusted or the plurality of light emitting elements are driven simultaneously, it is possible to always output the lowest voltage that satisfies the driving conditions. Therefore, the light emission efficiency can be improved and the power loss can be reduced.

According to the present invention, there is an advantage that a process with a high withstand voltage is unnecessary, the number of driveable light emitting elements can be increased, and each of the plurality of light emitting elements can be controlled independently.
According to the present invention, even when the brightness of a plurality of light emitting elements is individually adjusted or a plurality of light emitting elements having different driving voltages are simultaneously driven, the lowest voltage that always satisfies the driving conditions is output. Thus, there is an advantage that light emission efficiency can be improved and power loss can be reduced.

First Embodiment FIG. 1 is a diagram showing a basic configuration of a first embodiment of an LED (light emitting element) driving apparatus according to the present invention.

As shown in FIG. 1, the present LED driving device 10 includes a plurality of n (n is a positive integer) LEDs 20-1 to 20-n having different driving voltages, that is, forward voltages Vf required for light emission, in parallel. The LEDs 20-1 to 20-n are each driven with an arbitrary luminance (drive current).
At this time, the LED driving device 10 outputs an optimum voltage (for example, the lowest voltage) that can be driven by the set current of the LED having the maximum forward voltage Vf among the plurality of LEDs connected in parallel from the terminal TVO. Output to the anode of each LED 20-1 to 20-n.
The LED driving device 10 is supplied with a power supply voltage VCC via a terminal TVI by a power supply voltage source (PVS) 30 such as a battery.

  Hereinafter, a specific configuration and function of the LED driving device 10 will be described in order with reference to the drawings.

As shown in FIG. 1, the LED driving device 10 includes a serial / parallel conversion circuit (S / P) 11, a luminance (current) setting circuit (CSC) 12-1 to 12-n, and a current driving circuit (CDRV) 13-1. 13-n, an error amplifier (EAMP) 14, and a boost power supply (BST) 15.
The error amplifier 14 and the boost power supply 15 constitute a power circuit according to the present invention.

  The serial-parallel conversion circuit 11 converts the digital serial data relating to the current (luminance) values to be driven by the host device such as a CPU (not shown) and inputted through the terminal TDI into parallel data. The digital data ID1 to IDn related to the converted current (luminance) values are supplied to the corresponding current setting circuits 12-1 to 12-n.

  The current setting circuit 12-1 is configured by, for example, a digital / analog conversion circuit (DAC), and the digital data ID1 relating to the drive current (luminance) value supplied by the serial / parallel conversion circuit 11 is converted into a current setting signal IA1 which is an analog signal. It converts and supplies to the current drive circuit 13-1.

  The current setting circuit 12-2 is constituted by, for example, a digital / analog conversion circuit (DAC), and the digital data ID2 relating to the drive current (luminance) value supplied by the serial / parallel conversion circuit 11 is converted into an analog signal current setting signal IA2. It converts and supplies to the current drive circuit 13-2.

  Similarly, the current setting circuit 12-n is constituted by, for example, a digital / analog conversion circuit (DAC), and the digital data IDn relating to the drive current (luminance) value supplied by the serial / parallel conversion circuit 11 is set as a current setting which is an analog signal. It converts into the signal IAn and supplies it to the current drive circuit 13-n.

In the current driving circuit 13-1, the current source is connected to the cathode of the LED 20-1 to be driven through the terminal TL1, and the current setting signal IA1 is an analog signal supplied by the current setting circuit 12-1. The LED 20-1 is driven to emit light with a corresponding driving current.
Further, the current drive circuit 13-1 detects, for example, a voltage at a connection point between the terminal TL1 and the current source, that is, a voltage (VDRV−Vf1) obtained by subtracting the LED forward voltage Vf1 from the output drive voltage VDRV of the boost power supply 15. The voltage DV1 is output to the error amplifier 14.
The detection voltage DV1 is a signal indicating the driving state in the current driving circuit 13-1, but the signal indicating the driving state is not limited to this voltage.

In the current drive circuit 13-2, the current source is connected to the cathode of the LED 20-2 to be driven via the terminal TL2, and the current setting signal IA2 is an analog signal supplied by the current setting circuit 12-2. The LED 20-2 is driven to emit light with a corresponding driving current.
Further, the current drive circuit 13-2 detects, for example, the voltage at the connection point between the terminal TL2 and the current source, that is, the voltage obtained by subtracting the LED forward voltage Vf2 from the output drive voltage VDRV of the boost power supply 15 (VDRV−Vf2). The voltage DV2 is output to the error amplifier 14.
The detection voltage DV2 is a signal indicating a driving state in the current driving circuit 13-2, but the signal indicating the driving state is not limited to this voltage.

Similarly, in the current drive circuit 13-n, the current source is connected to the cathode of the LED 20-n to be driven via the terminal TLn, and the current setting signal IAn that is an analog signal supplied by the current setting circuit 12-n The LED 20-n is driven to emit light with a driving current corresponding to the set value.
The current drive circuit 13-n detects, for example, the voltage at the connection point between the terminal TLn and the current source, that is, the voltage obtained by subtracting the LED forward voltage Vfn from the output drive voltage VDRV of the boost power supply 15 (VDRV-Vfn). The voltage DVn is output to the error amplifier 14.
The detection voltage DVn is a signal indicating the driving state in the current driving circuit 13-n, but the signal indicating the driving state is not limited to this voltage.

  FIG. 2 is a circuit diagram showing a configuration example of the current drive circuit according to the present embodiment.

  As shown in FIG. 2, the current drive circuit 13 (-1 to -n) includes an n-channel MOS (NMOS) transistor 131, a sense resistor element 132, a current detection amplifier 133, and a current control amplifier 134 as current sources. Have.

The drain of the NMOS transistor 131 is connected to the cathode of the corresponding LED 20 (−1 to −n) via the terminal TL (1 to n), and the source is one end of the resistance element 132 and the non-inverting input (+ of the current detection amplifier 133). And the gate is connected to the output of the current control amplifier 134.
The other end of the resistance element R132 is connected to the ground potential GND and the inverting input (−) of the current detection amplifier 133.
The inverting input (−) of the current control amplifier 134 is connected to the output of the current detection amplifier 133, and the non-inverting input (+) is a current setting signal IA (1) that is an analog signal by the current setting circuit 12 (−1 to −n). To n) supply lines.

2 drives the gate of the NMOS transistor 131 with the output of the current control amplifier 134, detects the current flowing through the NMOS transistor 131 with the sense resistor element 132, and detects the current. The amplifier 133 detects and amplifies.
Then, the gate voltage of the NMOS transistor 131 is controlled by the current control amplifier 134 so that the current flowing through the NMOS transistor 131 becomes a set current value by the current setting circuit 12 (−1 to −n).
As a result, the LEDs 20 (−1 to −n) to be driven emit light with a luminance corresponding to the set current.

  In the current drive circuit 13 (−1 to −n), the drain of the NMOS transistor 131 is supplied to the error amplifier 14 so that the drain voltage of the NMOS transistor 131 as the current source is supplied as the signal DV (1 to n). Are connected to corresponding input terminals of the error amplifier 14.

  In the current drive circuit 13 (-1 to -n), the minimum operating voltage of the NMOS transistor 131 and the sense resistor element 132 as current sources depends on the transistor size and the resistance value, but is set to about 0.5V to 1V, for example. The

The error amplifier 14 compares the detection voltages (drain voltages of the NMOS transistor 131) DV1 to DVn output from the n current driving circuits 13-1 to 13-n with the reference voltage Vref, and compares the lowest detection voltage with the reference voltage. A signal S14 corresponding to the difference from the voltage Vref is output to the boost power source 15.
In addition, the smallest detection voltage employed in the error amplifier 14 corresponds to the highest forward voltage Vf in other words.

  The step-up power supply 15 is constituted by a DC-DC converter, for example, and the power supply voltage VCC supplied from the power supply voltage source 30 supplied via the terminal TVI is DC-DC so as to have a value corresponding to the output signal S14 of the error amplifier 14. Conversion is performed, and the drive voltage VDRV is supplied in parallel from the terminal TVO to the n LEDs 20-1 to 20-n.

  An external capacitor C10 is connected between the terminal TVO and the ground potential GND.

  For example, when the reference voltage Vref of the error amplifier 14 is 1 V, the LED driving device 10 according to the first embodiment has a terminal voltage to which the cathode of the LED having the maximum forward voltage Vf is connected, in other words, a current. Feedback is applied to the boosted power supply so that the drain voltage of the NMOS transistor 131 constituting the current source of the drive circuit is 1V.

FIG. 3 is a circuit diagram in which a part of a specific configuration example of the boost power supply 15, the error amplifier 14, the detection voltage output unit of the current drive circuit, and the power supply voltage source 30 according to the present embodiment is omitted.
In FIG. 3, only the current drive circuit 13-2 is shown including the configuration of FIG. 2 for simplification of the drawing, and the other current drive circuits are shown with NMOS transistors 131 and sense resistor elements 132 as current sources. Only shows.

  As shown in FIG. 3, the boost power supply 15 includes a comparator 151, an oscillator 152, a pre-driver 153, a p-channel MOS (PMOS) transistor 154, and an NMOS transistor 155.

The comparator 151 has an inverting input (−) connected to the output of the error amplifier 14, a non-inverting input (+) connected to the output of the oscillator 152, and an output connected to the input of the pre-driver 153.
The PMOS transistor 154 has a drain connected to the terminal TVI to which the power supply voltage VCC from the power supply voltage source 30 is supplied, a source connected to the drive voltage output terminal TVO, and a gate connected to the first drive terminal of the pre-driver 153. It is connected.
The NMOS transistor 155 has a source connected to the ground potential GND, a drain connected to the connection point between the drain of the PMOS transistor 154 and the terminal TVI, and a gate connected to the second drive terminal of the pre-driver 153.

  The comparator 151 performs a comparison based on so-called PWM (Pulse Width Modulation), specifically, compares the output signal S14 of the error amplifier 14 and the oscillation signal of the oscillator 152, and preliminarily outputs a signal S151 corresponding to the comparison result. Output to the driver 153.

The pre-driver 153 outputs the drive signals SD1 and SD2 to the first drive terminal and / or from the second drive terminal to the gate of the PMOS transistor 154 and the gate of the NMOS transistor 155 according to the output signal S151 of the comparator 151, The drive voltage VDRV is supplied in parallel to the anodes of the LEDs 20-1 to 20-n from the terminal TVO by adjusting (through) or adjusting the value of the power supply voltage VCC supplied from the terminal TVI.
That is, as described above, the booster power supply 15 is configured such that the terminal voltage (drain voltage of the NMOS transistor 131 constituting the current source of the current driving circuit) to which the cathode of the LED having the maximum forward voltage Vf is connected is the error amplifier 14. The value of the power supply voltage VCC is adjusted so that the reference voltage Vref is set to be output as the drive voltage VDRV.

  As shown in FIG. 3, the power supply voltage source 30 includes, for example, a lithium ion battery 301 and an inductor 302 connected between the positive electrode of the battery 301 and the terminal TVI of the LED driving device 10.

  Next, the operation according to the above configuration will be described.

For example, digital serial data relating to current (luminance) values for the LEDs 20-1 to 20-n to be driven according to the operation mode is input from the host device to the serial-parallel conversion circuit 11 via the terminal TDI.
In the serial / parallel conversion circuit 11, digital serial data relating to the current (luminance) value to drive the supplied LEDs 20-1 to 20-n is converted into parallel data. Then, digital data ID1 to IDn related to the converted current (luminance) values are supplied to the corresponding current setting circuits 12-1 to 12-n.
The digital data ID1 to IDn also includes information that does not drive the corresponding LED.

  In the current setting circuits 12-1 to 12-n, the digital data ID1 to IDn related to the drive current (luminance) values supplied by the serial / parallel conversion circuit 11 are converted into current setting signals IA1 to IAn which are analog signals, and the corresponding Are supplied to the current drive circuits 13-1 to 13-n.

In the current driving circuits 13-1 to 13-n, the LEDs 20-1 to 20 have driving currents corresponding to the set values of the current setting signals IA1 to IAn, which are analog signals supplied from the current setting circuits 12-1 to 12-n. -N is driven. As a result, the LEDs 20-1 to 20-n emit light with a luminance corresponding to the set current value, or are held off.
Further, in the current drive circuits 13-1 to 13-n, the voltages at the connection points between the terminals TL1 to TLn and the current source, that is, the voltages obtained by subtracting the LED forward voltages Vf1 to Vfn from the output drive voltage VDRV of the boost power supply 15. (VDRV−Vf1) to (VDRV−Vfn) are output to the error amplifier 14 as detection voltages DV1 to DVn.

  In the error amplifier 14, the detection voltages (drain voltage of the NMOS transistor 131) DV1 to DVn output from the n current drive circuits 13-1 to 13-n are compared with the reference voltage Vref. As a result of the comparison, a signal S14 corresponding to the difference between the smallest detection voltage and the reference voltage Vref is output to the boost power supply 15.

In the step-up power supply 15, DC-DC conversion is performed so that the power supply voltage VCC supplied from the power supply voltage source 30 supplied via the terminal TVI becomes a value corresponding to the output signal S14 of the error amplifier 14. Then, the driving voltage VDRV is supplied in parallel to the n LEDs 20-1 to 20-n from the terminal TVO.
Specifically, the comparator 151 of the boost power supply 15 compares the output signal S14 of the error amplifier 14 with the oscillation signal of the oscillator 152, and outputs a signal S151 corresponding to the comparison result to the pre-driver 153.
In the pre-driver 153, the drive signals SD1 and SD2 are output to the gate of the PMOS transistor 154 and the gate of the NMOS transistor 155 from the first drive terminal and / or from the second drive terminal according to the output signal S151 of the comparator 151. As a result, the value of the power supply voltage VCC supplied from the terminal TVI is directly (through) or adjusted (boosted), and the drive voltage VDRV is supplied in parallel to the anodes of the LEDs 20-1 to 20-n from the terminal TVO. Supplied.
That is, in the booster power supply 15, the terminal voltage (drain voltage of the NMOS transistor 131 constituting the current source of the current drive circuit) to which the cathode of the LED having the maximum forward voltage Vf is connected is the reference voltage set in the error amplifier 14. The value of the power supply voltage VCC is adjusted so as to be Vref and is output as the drive voltage VDRV.

The specific operation of the booster power supply 15 with respect to light emission (lighting) of each color LED is as follows.
Here, it is assumed that the LEDs 20-1 to 20-n include one or a plurality of red (R) LEDs, green (G) LEDs, blue (B) LEDs, and white LEDs.
The forward voltage of each color LED is as follows.
The forward voltage Vfr of the red LED is set to 1.9V, the forward voltages Vfg and Vfb of the green and blue LEDs are set to about 3.1V, and the forward voltage Vfw of the white LED is set to 3.5V.
Further, assuming that the power supply voltage source 30 is a lithium ion battery, the power supply voltage VCC is used in the range of 3.2V to 4.2V.
Further, the minimum operating voltage α required for the LED current drive circuits 13-1 to 13-n is set to 0.5V.
In the following description, “through” refers to turning on the PMOS transistor 154 and turning off the NMOS transistor 155 constituting the output stage of the boost power supply 15 (the operation of the DC-DC converter operates at 100% duty). )

In order to light a white LED whose forward voltage Vfw is 3.5V, a voltage required as the drive voltage VDRV is 4V (= 3.5V + 0.5V).
The operation of the boost power supply 15 in this case is “through” when the power supply voltage VCC is in the range of 4.0 V <VCC <4.2 V.
On the other hand, when the power supply voltage VCC is in the range of 3.2 V <VCC <4.0 V, the operation is to “boost” to 4 V, for example.

In order to turn on the green LED and the blue LED whose forward voltages Vfg and Vfb are 3.1 V, the voltage required as the drive voltage VDRV is 3.6 V (= 3.1 V + 0.5 V).
The operation of the boosting power supply 15 in this case is “through” when the power supply voltage VCC is in the range of 3.6 V <VCC <4.2 V.
On the other hand, when the power supply voltage VCC is in the range of 3.2 V <VCC <3.6 V, for example, the operation is “boosted” to 3.6 V, for example.

In order to light a red LED having a forward voltage Vfr of 1.9V, a voltage required as the drive voltage VDRV is 2.4V (= 1.9V + 0.5V).
The operation of the step-up power supply 15 in this case assumes that the power supply voltage VCC is in the range of 3.2 V <VCC <4.2 V, and the first embodiment does not include the step-down power supply. “Through” in all ranges.

  That is, the operation of the boosting power supply 15 is “through” when the output of the boosting power supply 15 expected by applying feedback through the error amplifier 14 is equal to or lower than the power supply voltage (battery voltage) VCC. The LED is directly driven by the voltage VCC.

Here, power loss will be considered.
For example, when only a blue LED having a power supply voltage VCC of 4.0 V and a forward voltage Vfb of 3.1 V is lit, the necessary drive voltage VDRV is 3.6 V (= 3.1 V + 0.5 V). 4.0V-3.6V) × (driving current) is a loss.

As described above, according to the first embodiment, the current source is connected to the cathodes of the LEDs 20-1 to 20-n to be driven via the terminals TL1 to TLn, and the current setting signals IA1 to IAn are set. The current driving circuit 13 that drives the LEDs 20-1 to 20-n with the driving currents according to the values to emit light, and outputs the voltages at the connection points of the terminals TL1 to TLn and the current sources as the detection voltages DV1 to DVn. -1 to 13-n and the detection voltages DV1 to DVn output from the n current drive circuits 13-1 to 13-n are compared with the reference voltage Vref, and the difference between the smallest detection voltage and the reference voltage Vref is compared. The power supply voltage VCC from the error amplifier 14 that outputs the signal S14 according to the power supply voltage source 30 and the power supply voltage source 30 supplied via the terminal TVI becomes a value corresponding to the output signal S14 of the error amplifier 14. Since the boosting power supply 15 that performs DC-DC conversion and supplies the drive voltage VDRV in parallel to the n LEDs 20-1 to 20-n from the terminal TVO is provided, the boosting power supply 15 has the maximum forward voltage. The value of the power supply voltage VCC can be adjusted and output as the drive voltage VDRV so that the terminal voltage to which the cathode of the LED having Vf is connected becomes the reference voltage Vref set in the error amplifier 14.
As a result, it is possible to increase the number of light emitting elements that can be driven without requiring a high withstand voltage process, and to individually control the brightness of each of the plurality of light emitting elements. In addition, even when a plurality of LEDs having different forward voltages are driven at the same time, the lowest voltage that always satisfies the driving condition can be output.
Therefore, there is an advantage that light emission efficiency can be improved and power loss can be reduced.

  In actual calculations, the conventional device has a luminous efficiency of about 50%, whereas the device according to the present embodiment can achieve a luminous efficiency of about 70%.

Second Embodiment FIG. 4 is a circuit diagram showing the main configuration of a second embodiment of an LED (light emitting element) driving apparatus according to the present invention.

4, the same components as those in FIG. 1 are denoted by the same reference numerals.
Further, in FIG. 4, only the LED 20-1 is illustrated for simplification of the drawing, and only the current setting circuit 12-1 and the current driving circuit 13-1 A are illustrated correspondingly. 4, other current setting circuits 12-2 to 12-n and current driving circuits 13-2A to 13-nA (not shown) have the same configuration.

  The LED drive device 10A according to the second embodiment has a configuration in which a configuration in the case of blinking is added to the configuration of emitting (lighting) the LED of the first embodiment described above.

Specifically, the LED drive device 10A includes an inverter 16, a two-input AND gate 17, a second error amplifier 18, a switch circuit 19, and output voltage dividing resistance elements R11 and R12.
Further, each current drive circuit 13-1A (˜13-nA) has an NMOS whose source is connected to the ground potential GND, its drain is connected to the output of the current control amplifier 134, and its gate is connected to the output of the AND gate 17. A transistor 135 is provided.

In addition to the digital data related to the drive current (luminance) value, the serial / parallel conversion circuit 11A is supplied with a command indicating whether to perform a normal lighting operation or a blinking operation to the terminal TDI.
The serial / parallel conversion circuit 11A outputs a low-level signal S11 to the switch circuit 19 and a low-level signal S11 in the case of a command for performing a normal operation and a high-level signal in the case of a command to perform a blinking operation.

  The input of the inverter 16 is connected to an input terminal TSYNC of a pulsed synchronization signal SYNC supplied by an external synchronization signal supply circuit (such as a sound source IC) (not shown), and the output is connected to the other input of the AND gate 17. Yes. The output of the AND gate 17 is connected to the gate of an NMOS transistor 135 provided in each current drive circuit 13-1A (˜13-nA).

Resistance elements R11 and R12 are connected in series between the connection point of the source of the PMOS transistor 154 of the boosting power supply 15 and the terminal TVO and the ground potential GND, and the connection point of the resistance elements R11 and R12 is the second error amplifier 18. Is connected to the inverting input (−).
A reference voltage from the voltage source VSref is supplied to the non-inverting input (+) of the second error amplifier 18.

  The switch circuit 19 has a fixed output terminal a and switching input terminals b and c. The fixed output terminal a is connected to the inverting input (−) of the comparator 151 of the boost power supply 15 and the switching input terminal b is the first. Connected to the output of the error amplifier 14, the switching input terminal c is connected to the output of the second error amplifier 18.

When the switch circuit 19 receives the signal S11 from the serial / parallel conversion circuit 11A at a low level (normal lighting instruction), the switch circuit 19 connects the fixed output terminal a and the switching input terminal b, and outputs the output signal S14 of the first error amplifier 14. Input to the inverting input (−) of the comparator 151.
In this case, since the signal S11 is at the low level, the output of the AND gate 17 is also held at the low level. Therefore, the NMOS transistor 135 provided in each current driving circuit 13-1A (˜13-nA) is held in the off state.
That is, during normal lighting, the circuit is equivalent to the circuit according to the first embodiment described above.
This normal lighting operation is performed in the same manner as in the first embodiment described above. Therefore, detailed description thereof is omitted here.

When the switch circuit 19 receives the signal S11 from the serial / parallel conversion circuit 11A at a high level (blinking operation instruction), the switch circuit 19 connects the fixed output terminal a and the switching input terminal c, and compares the output signal S18 of the second error amplifier 18. Input to the inverting input (−) of the device 151.
In this case, since the signal S11 is at the high level, the output of the AND gate 17 is switched between the high level and the low level according to the inverted signal of the synchronization signal SYC.
Therefore, the NMOS transistor 135 provided in each current drive circuit 13-1A (˜13-nA) is turned on when the output of the AND gate 17 is at a high level. At this time, since the output of the current control amplifier 134 is connected to the ground potential, the NMOS transistor 131 as the current source is held in the off state, and the corresponding LED 20-1 (˜20-n) is in the non-light emitting state. Retained.
On the other hand, the NMOS transistor 135 provided in each current driving circuit 13-1A (˜13-nA) is turned off when the output of the AND gate 17 is at a low level. At this time, the NMOS transistor 131 as a current source is driven by the output of the current control amplifier 134, and the corresponding LED 20-1 (to 20-n) is held in the light emitting state.
That is, the LED 20-1 (˜20-n) performs a blinking operation.

During this blinking operation, the circuit configuration is such that the output voltage is fed back to the boost power supply 15 via the second error amplifier 18 as described above.
As a result, the output drive voltage VDRV of the boost power supply 15 is fixed to the internally set voltage regardless of the LED operating state.

  In the second embodiment, at the time of the blinking operation, the circuit configuration is such that the output voltage is fed back to the boost power supply 15 via the second error amplifier 18, and the output drive voltage VDRV is determined according to the operation state of the LED. The reason why the voltage is fixed internally is as follows.

For example, assuming an operation in which a red LED and a blue LED blink alternately, when pursuing efficiency, the output voltage of the boost power supply decreases when the red LED emits light, and the output voltage increases when the blue LED emits light. It is desirable to operate to increase the overall system efficiency.
However, in actuality, there is a concern that noise is generated due to fluctuations in the output of the boost power supply 15 in synchronization with the synchronization signal.
Therefore, during the blinking operation, the output voltage of the booster power supply 15 is fed back via the second error amplifier 18, and the output drive voltage VDRV is fixed to the internally set voltage regardless of the LED operating state. , Fluctuations in the output of the booster power supply 15 when the LED is blinking are suppressed.

  According to the second embodiment, in the normal lighting operation, in addition to obtaining the same effect as the first embodiment described above, the fluctuation of the output of the boost power supply 15 can be suppressed during the blinking operation. There is an advantage that a stable blinking operation can be performed without being affected by noise.

  In the second embodiment, when a predetermined blinking operation instruction command is received, the output voltage of the booster power supply 15 is fed back via the second error amplifier 18, and the output drive voltage VDRV is set to the LED operating state. However, for example, when there is no influence of noise in a blinking operation with a low frequency, the first error amplifier 14 is used as in the normal lighting operation. When a predetermined blinking operation with a high frequency is affected by noise, the output voltage is fed back to the boosting power supply 15 via the second error amplifier 18 and the output drive voltage VDRV is applied to the LED operation. It is also possible to configure to fix the voltage set internally regardless of the state.

Third Embodiment FIG. 5 is a diagram showing a basic configuration of a third embodiment of an LED (light emitting element) driving apparatus according to the present invention.

  The third embodiment differs from the first embodiment described above in that a step-up / down power supply (BDPS) 101 including a step-down function in addition to a step-up function is used instead of the step-up power supply as a power supply circuit for outputting a drive voltage. It is in providing.

FIG. 6 is a diagram for explaining the configuration and function of the step-up / down power supply 101 according to the third embodiment.
In the example of FIG. 6, nine (n = 9) LEDs 20-1 to 20-9 are provided in parallel.
Of the nine LEDs, two of LEDs 20-1, 20-4 are red LEDs, two of LEDs 20-2, 20-5 are green LEDs, two of LEDs 20-3, 20-6 are blue LEDs, LED 20- Three of 7-20-9 are white LEDs.
Also, current setting circuits 12-1 to 12-9 and current driving circuits 13-1 to 13-9 are provided corresponding to the respective LEDs 20-1 to 20-9. In FIG. 6, the drawing is simplified. Therefore, only the current setting circuit 12-1 and the current driving circuit 13-1 are illustrated.

  As shown in FIG. 6, the step-up / down circuit 101 includes a step-down power supply drive circuit 1011, a power supply through circuit drive circuit 1012, a step-up power supply drive circuit 1013, a step-down power supply (DPS) 1014, a power supply through circuit (PTR) 1015, and a step-up power supply. (BST) 1016.

  The step-down power supply driving circuit 1011 receives the output signal S14 of the error amplifier 14 and sets the maximum forward voltage Vf of the LED being driven to the minimum operating voltage required for the current driving circuits 13-1 to 13-9 of the LED. The step-down power supply 1014 is driven when the value obtained by adding α (for example, 0.5 V) is smaller than the value of the power supply voltage VCC by the power supply voltage source 30.

  The power supply through circuit drive circuit 1012 receives the output signal S14 of the error amplifier 14, and attains the minimum forward operation required for the LED current drive circuits 13-1 to 13-9 to the maximum forward voltage Vf of the LED being driven. When the value obtained by adding the voltage α is equal to the power supply voltage VCC by the power supply voltage source 30, the power supply through circuit 1015 is driven.

  The boosting power supply driving circuit 1013 receives the output signal S14 from the error amplifier 14, receives the maximum forward voltage Vf of the LED being driven, and the minimum operating voltage required for the current driving circuits 13-1 to 13-9 of the LED. When the value obtained by adding α is larger than the value of the power supply voltage VCC by the power supply voltage source 30, the boost power supply 1016 is driven.

  When the step-down power supply 1014 is driven by the step-down power supply driving circuit 1011, the step-down power supply 1014 steps down the power supply voltage VCC from the power supply voltage source 30 by a predetermined voltage and outputs the stepped-down voltage from the terminal TVO as the drive voltage VDRV.

  When driven by the power supply through circuit drive circuit 1012, the power supply through circuit 1015 passes through the power supply voltage VCC from the power supply voltage source 30 as it is and outputs it as the drive voltage VDRV from the terminal TVO.

  When the boost power source 1016 is driven by the boost power source drive circuit 1013, the power source voltage VCC from the power source voltage source 30 is boosted by a predetermined voltage, and the boosted voltage is output from the terminal TVO as the drive voltage VDRV.

  The specific operation of the step-up / down power supply 101 for the light emission (lighting) of each color LED is as follows.

The forward voltage of each color LED is as follows as in the case of the first embodiment.
The forward voltage Vfr of the red LED is set to 1.9V, the forward voltages Vfg and Vfb of the green and blue LEDs are set to about 3.1V, and the forward voltage Vfw of the white LED is set to 3.5V.
Further, assuming that the power supply voltage source 30 is a lithium ion battery, the power supply voltage VCC is used in the range of 3.2V to 4.2V.
Further, the minimum operating voltage α required for the LED current drive circuits 13-1 to 13-n is set to 0.5V.

In order to light a white LED whose forward voltage Vfw is 3.5V, a voltage required as the drive voltage VDRV is 4V (= 3.5V + 0.5V).
The operation of the step-up / down power supply 101 in this case is a “step-down” operation when the power supply voltage VCC is in the range of 4.0 V <VCC <4.2 V. Specifically, the step-down power supply 1014 is driven by the step-down power supply driving circuit 1011. As a result, the power supply voltage VCC is stepped down to any value of 4V or up to 4V, and is output from the terminal TVO as the drive voltage VDRV.
When the power supply voltage Vcc is equal to the voltage required for driving, it is “through”. Specifically, the power supply through circuit 1015 is driven by the power supply through circuit drive circuit 1012. As a result, the power supply voltage VCC of 4V is passed through and output from the terminal TVO as the drive voltage VDRV.
On the other hand, when the power supply voltage VCC is in the range of 3.2V <VCC <4.0V, the “boost” operation is raised to 4V. Specifically, the boost power source 1016 is driven by the boost power source drive circuit 1013. As a result, the power supply voltage VCC is boosted to a value of 4 V or higher and output from the terminal TVO as the drive voltage VDRV.

In order to turn on the green LED and the blue LED whose forward voltages Vfg and Vfb are 3.1 V, the voltage required as the drive voltage VDRV is 3.6 V (= 3.1 V + 0.5 V).
The operation of the step-up / down power supply 101 in this case is a “step-down” operation when the power supply voltage VCC is in the range of 3.6 V <VCC <4.2 V. Specifically, the step-down power supply 1014 is driven by the step-down power supply driving circuit 1011. As a result, the power supply voltage VCC is stepped down to either 3.6V or 3.6V and output from the terminal TVO as the drive voltage VDRV.
When the power supply voltage Vcc is equal to the voltage required for driving, it is “through”. Specifically, the power supply through circuit 1015 is driven by the power supply through circuit drive circuit 1012. As a result, the power supply voltage VCC of 3.6 V is passed through and output from the terminal TVO as the drive voltage VDRV.
On the other hand, when the power supply voltage VCC is in the range of 3.2 V <VCC <3.6 V, the “boost” operation is raised to 3.6 V. Specifically, the boost power source 1016 is driven by the boost power source drive circuit 1013. As a result, the power supply voltage VCC is boosted to a value of 3.6 V or higher and is output from the terminal TVO as the drive voltage VDRV.

In order to light a red LED having a forward voltage Vfr of 1.9V, a voltage required as the drive voltage VDRV is 2.4V (= 1.9V + 0.5V).
The operation of the step-up / down power supply 101 in this case is a “step-down” operation over the entire range because the power supply voltage VCC is assumed to be in the range of 3.2 V <VCC <4.2 V.
Specifically, the step-down power supply 1014 is driven by the step-down power supply driving circuit 1011. As a result, the power supply voltage VCC is stepped down to either 2.4 V or 2.4 V and is output from the terminal TVO as the drive voltage VDRV.

  That is, the operation of the step-up / down power supply 101 is “step-down” when the output of the boost power supply 15 expected by applying feedback through the error amplifier 14 is equal to or lower than the power supply voltage (battery voltage) VCC. In the above case, it becomes “boost”.

  According to the third embodiment, there is an advantage that the light emission efficiency can be further improved and the power loss can be reduced as compared with the first embodiment described above.

  Needless to say, a circuit with noise countermeasures corresponding to the blinking operation described in the second embodiment can also be applied to the LED driving device 10B according to the third embodiment.

Fourth Embodiment FIG. 7 is a circuit diagram showing the main configuration of a fourth embodiment of an LED (light emitting element) driving apparatus according to the present invention.

  The fourth embodiment is different from the third embodiment described above in that the red LEDs 20-1 and 20-4 can only have a step-down operation. The error amplifier 102 and the step-down circuit 103 are provided, and the drive voltage obtained by stepping down the power supply voltage VCC to 2.4 V is separately supplied to the red LEDs 20-1 and 20-4.

Therefore, the detection voltage signals DV2, DV3, DV5 to DV9 are supplied to the error amplifier 14C by the current driving circuits 12-2, 12-3, 12-5 to 12-9 corresponding to the green LED, blue LED, and white LED. Is done.
Other configurations are the same as those in FIG.

  According to the fourth embodiment, the overall luminous efficiency can be increased as compared with the third embodiment.

  Needless to say, a circuit with noise countermeasures corresponding to the blinking operation described in the second embodiment can also be applied to the LED driving device 10C according to the fourth embodiment.

Fifth Embodiment FIG. 8 is a diagram for explaining a fifth embodiment of the present invention, and is a portable device (terminal) to which the LED driving device according to the first to fourth embodiments described above can be applied. It is a block diagram which shows the example of a structure.

The mobile device 40 is composed of a mobile phone device, for example, and as shown in FIG. 8, a CPU 41, a first image display device 42, a second image display device 43, an input device 44, an incoming call display unit 45, a synchronization signal supply, It has the circuit 46 and the LED drive device 47 which has the structure in any one of the 1st-4th embodiment mentioned above.
And the 1st image display apparatus 42, the 2nd image display apparatus 43, the input device 44, and the incoming call display part 45 comprise the to-be-illuminated part illuminated with LED.

  The CPU 41 controls the operation of the device based on the input data from the input device 44, the display control of the first image display device 42 and the second image display device 43 when the power is turned on, the drive control of the synchronization signal supply circuit 46, and the operation mode. Control of supply of the current (luminance) setting data and blinking operation command data to the LED driving device 47 according to the above is performed.

The first image display device 42 functions as a main display unit of the portable device 40 and is configured by a liquid crystal display device capable of color display.
In the vicinity of the first image display device 42, there are three white LEDs (LEDs 20-7 to 20-9 in the examples of FIGS. 6 and 7) connected in parallel to the LED drive device 47 as an illumination backlight. ) Is arranged.
Under the control of the CPU 41, the first image display device 42 displays a radio wave reception state, an icon menu and various images, a destination telephone number or a message input by the input device 44 or received.

The second image display device 43 functions as a sub display unit of the portable device 40 and is configured by a liquid crystal display device.
In the vicinity of the second image display device 43, LEDs for three colors of red, green, and blue connected in parallel to the LED drive device 47 for illumination (in the examples of FIGS. 6 and 7, LEDs 20-1 to 20-1) are used. 20-3, or 20-4 to 20-6).
The second image display device 43 displays the time, date and time under the control of the CPU 41, and one of the three colors of LEDs or any two of them is selected by the LED driving device 47 at the time of incoming call or transmission. Alternatively, all color LEDs are lit or blinked.

The input device 44 includes a power switch, a numeric keypad, and the like, and in the vicinity thereof, LEDs for three colors of red, green, and blue (FIGS. 6 and 7) connected in parallel to the LED driving device 47 for illumination. In the example, LEDs 20-1 to 20-3, or 20-4 to 20-6) are arranged.
When the power is turned on under the control of the CPU 41, the input device 44 is illuminated by one, three, or all of the three colors of LEDs by the LED driving device 47.

The incoming call display unit 45 has three colors of red, green, and blue LEDs connected in parallel to the LED driving device 47 (in the example of FIGS. 6 and 7, LEDs 20-1 to 20-3, or 20-4 to 20-6) is arranged.
In the incoming call display unit 45, when the incoming call is received, the LED driving device 47 turns on or blinks one of the three colors of LEDs, or any of the two colors or all of the LEDs.

  The synchronization signal supply circuit 46 is constituted by a sound source IC such as MIDI, and supplies a synchronization signal SYNC used for, for example, a blinking operation to the LED driving device 47 under the control of the CPU 41.

  In addition, the lithium ion battery is used for the power supply of this portable apparatus 40 similarly to the case of the 1st-4th embodiment mentioned above.

  In the portable device 40 having such a configuration, the first image display device 42, the second image display device 43, the first part where the incoming call display unit 45 is arranged, and the second part where the input device 44 is arranged, Is carried by the user in a folded state, for example, by the hinge mechanism.

When the user operates to open the first part and the second part, for example, when the power switch is turned on, the CPU 41 causes the LED driving device to illuminate the first image display device 42 with the backlight. 47 is supplied with current (luminance) setting data for driving the white LED.
As a result, the white LED is driven by the LED driving device 47, and the first image display device 42 is illuminated brightly in white.
At this time, for example, the CPU 41 supplies current (luminance) setting data for driving the green LED to the LED driving device 47 so that the input device 44 is illuminated by the green LED.
Thereby, the green LED is driven by the LED driving device 47, and the input device 44 is lightly illuminated in green.

Further, for example, when there is an incoming call in a state where the first part and the second part are folded when the power is turned on, the CPU 41 in order to turn on or blink the incoming call display unit 45 or the second image display device 43 by, for example, a red LED. Thus, current (luminance) setting data for driving the red LED is supplied to the LED driving device 47. When the mode for blinking operation is set, the blinking operation instruction command data is output to the LED drive device 47 by the CPU 41, and the synchronization signal SYNC is supplied from the synchronization signal supply circuit 46 to the LED drive device 47. To be controlled.
As a result, the red LED is driven by the LED driving device 47, and the incoming call display unit 45 and the second image display device 43 are displayed in red or blinking.

As described in the first to fourth embodiments, the operation of the LED drive device 47 during each of the above operations is performed by the terminal voltage to which the cathode of the LED having the maximum forward voltage Vf is connected to the error amplifier 14. The value of the power supply voltage VCC is adjusted so as to be the set reference voltage Vref, and is output as the drive voltage VDRV.
As a result, even if the brightness of the plurality of LEDs is individually adjusted or a plurality of LEDs having different forward voltages are simultaneously driven, the lowest voltage that always satisfies the driving condition is output.
Therefore, the luminous efficiency is high and the power loss is kept low.
Here, detailed operation of the LED driving device 47 is omitted.

  According to the portable device 40 according to the fifth embodiment, the illumination LED can always output the lowest voltage that satisfies the driving condition, can improve the light emission efficiency, and reduce the power loss. And, in turn, has the advantage of extending the battery life.

It is a figure which shows the basic composition of 1st Embodiment of the LED (light emitting element) drive device which concerns on this invention. It is a circuit diagram which shows the structural example of the current drive circuit which concerns on this embodiment. FIG. 5 is a circuit diagram in which a part of a specific configuration example of a boost power supply, an error amplifier, a detection voltage output unit of a current drive circuit, and a power supply voltage source according to the present embodiment is omitted. It is a circuit diagram which shows the principal part structure of 2nd Embodiment of the LED (light emitting element) drive device which concerns on this invention. It is a figure which shows the basic composition of 3rd Embodiment of the LED (light emitting element) drive device which concerns on this invention. It is a figure for demonstrating the structure and function of the buck-boost power supply which concern on 2nd Embodiment. It is a circuit diagram which shows the principal part structure of 4th Embodiment of the LED (light emitting element) drive device which concerns on this invention. It is a block diagram which shows the structural example of the portable apparatus (terminal) which employ | adopted the LED (light emitting element) drive device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10A-10C ... LED (light emitting element) drive circuit, 11 ... Serial parallel conversion circuit (S / P), 12-1 to 12-n ... Current setting circuit (CSC), 13-1 to 13-n ... Current Drive circuit (CDRV) 131 ... NMOS transistor 132 ... Sense resistor element 133 ... Current detection amplifier 134 ... Current control amplifier 14 ... Error amplifier (EAMP) 15 ... Boost power supply (BST) 151 ... Comparator DESCRIPTION OF SYMBOLS 152 ... Oscillator, 153 ... Pre-driver, 154 ... PMOS transistor, 155, 156 ... NMOS transistor, 16 ... Inverter, 17 ... 2 input AND gate, 18 ... 2nd error amplifier, 19 ... Switch circuit, 101 ... Buck-boost power supply 102 ... Error amplifier 103 ... Step-down power supply (DPS) 1011 ... Step-down power supply drive circuit 1012 ... Power supply Lou circuit drive circuit, 1013 ... Boost power supply drive circuit, 1014 ... Step-down power supply (DPS), 1015 ... Power through circuit (PTR), 1016 ... Boost power supply (BST), 20-1 to 20-n ... LED, 30 ... Power supply Voltage source (PSV), 40 ... portable device, 41 ... CPU, 42 ... first image display device, 43 ... second image display device, 44 ... input device, 45 ... incoming display unit, 46 ... synchronization signal supply circuit, 47 ... LED drive device.

Claims (9)

A portable device having a battery as a power supply voltage source,
A plurality of light emitting elements having different driving voltages required for light emission;
A plurality of display devices as illuminated parts illuminated by the light emitting elements;
A plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, and one light emitting element driving device that drives one or a plurality of light emitting elements of the plurality of light emitting elements;
Have
The light emitting element driving device is:
A plurality of driving circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with brightness based on a set value;
Based on each driving state of the plurality of driving circuits, the driving voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is the driving voltage of the at least the determined value. A power supply circuit for supplying to the plurality of light emitting elements,
The power supply circuit is supplied with a power supply voltage, and when the value of the power supply voltage is larger than the determined voltage value, the supplied power supply voltage is supplied to the plurality of light emitting elements as the drive voltage,
A portable device that drives a plurality of light emitting elements that illuminate a plurality of display devices by one light emitting element driving device. The portable device according to claim 1, wherein at least one of the plurality of display devices includes a display device that is backlit by the light emitting element. The portable device according to claim 1, wherein the power supply circuit fixes the output drive voltage of the power supply circuit to a predetermined set voltage regardless of a driving state of the light emitting element when receiving a predetermined blinking operation instruction command. When the value of the power supply voltage is smaller than the determined voltage value, the power supply circuit boosts the supplied power supply voltage to at least the determined voltage value, and uses the boosted power supply voltage as the drive voltage as the plurality of light emitting elements. The portable device according to claim 1, wherein the portable device is supplied to an element. The power supply circuit boosts a supplied power supply voltage to at least a drive voltage value necessary for light emission of the light emitting element to a light emitting element whose drive voltage value necessary for light emission is larger than the power supply voltage value, and boosted power supply The portable device according to claim 1, further comprising a boosting power source that supplies a voltage to the target light emitting element as the driving voltage. A portable device having a battery as a power supply voltage source,
A plurality of light emitting elements having different driving voltages required for light emission;
A plurality of display devices as illuminated parts illuminated by the light emitting elements;
A plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, and one light emitting element driving device that drives one or a plurality of light emitting elements of the plurality of light emitting elements;
Have
The light emitting element driving device is:
A plurality of driving circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with brightness based on a set value;
Based on each driving state of the plurality of driving circuits, the driving voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is the driving voltage of the at least the determined value. A power supply circuit for supplying to the plurality of light emitting elements
Including
When the value of the power supply voltage is larger than the determined voltage value, the power supply circuit steps down the supplied power supply voltage to any value up to the determined voltage value, and reduces the reduced power supply voltage to the drive voltage. To the plurality of light emitting elements,
When the determined voltage value and the power supply voltage value are substantially equal, the supplied power supply voltage is supplied to the plurality of light emitting elements as the drive voltage,
When the value of the power supply voltage is smaller than the determined voltage value, the supplied power supply voltage is boosted to at least the determined voltage value, and the boosted power supply voltage is supplied to the plurality of light emitting elements as the drive voltage.
Portable device . A portable device having a battery as a power supply voltage source,
A plurality of light emitting elements having different driving voltages required for light emission;
A plurality of display devices as illuminated parts illuminated by the light emitting elements;
A plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, and one light emitting element driving device that drives one or a plurality of light emitting elements of the plurality of light emitting elements;
Have
The light emitting element driving device is:
A plurality of driving circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with brightness based on a set value;
Based on each driving state of the plurality of driving circuits, the driving voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is the driving voltage of the at least the determined value. A power supply circuit for supplying to the plurality of light emitting elements,
The power supply circuit steps down the supplied power supply voltage to a value up to a drive voltage value necessary for light emission of the light emitting element to a light emitting element whose drive voltage value necessary for light emission is smaller than the power supply voltage value. A step-down power supply that supplies the stepped-down power supply voltage to the target light emitting element as the drive voltage;
A drive voltage value required for light emission is increased to a light emitting element greater than the power supply voltage value, and the supplied power supply voltage is boosted to at least a drive voltage value required for light emission of the light emitting element, and the boosted power supply voltage is increased to the drive voltage. The portable device according to claim 1, further comprising: a step-up power supply that supplies a target light emitting element as A portable device having a battery as a power supply voltage source,
A plurality of light emitting elements having different driving voltages required for light emission;
A plurality of display devices as illuminated parts illuminated by the light emitting elements;
A plurality of light emitting elements that illuminate the plurality of display devices are connected in parallel, and one light emitting element driving device that drives one or a plurality of light emitting elements of the plurality of light emitting elements;
A control device that performs display control of the plurality of display devices, and drive control according to an operation mode of the light emitting element driving device;
A synchronization signal supply circuit for supplying a synchronization signal to the light emitting element driving device under the control of the control device;
Have
The light emitting element driving device is:
A plurality of driving circuits connected to the corresponding light emitting elements of the plurality of light emitting elements and driving the corresponding light emitting elements with brightness based on a set value;
Based on each driving state of the plurality of driving circuits, the driving voltage value required for the highest light emission among one or a plurality of light emitting elements that are driven to emit light is determined, and the power supply voltage is the driving voltage of the at least the determined value. A power supply circuit for supplying to the plurality of light emitting elements,
A portable device that drives a plurality of light emitting elements that illuminate a plurality of display devices by one light emitting element driving device. The portable device according to claim 8 , wherein at least one of the plurality of display devices includes a display device that is backlit by the light emitting element.

Images