JP5421695B2 - Lighting control device, mobile phone - Google Patents

Description

  The present invention relates to a technique for changing the brightness when a backlight is turned on in stages.

  Conventionally, in a backlight provided in a portable device or the like, the luminance is changed based on ambient brightness or the like (Patent Document 1).

JP 2009-105871 A

By the way, when trying to change the brightness | luminance of a backlight provided with several LED (Light Emitting Diode) as a light source in steps especially among backlights, the following circuit structures can be considered, for example.
In the first circuit configuration, as shown in FIG. 9, three LEDs 104a, 104b, 104c are connected in parallel to the power source 102, and an LED control IC 108 controlled by the CPU 106 is connected to the output side of the LEDs 104a, 104b, 104c. Has been.

In order to make the backlight a uniform surface light source, it is necessary to pass the same current to each LED 104a, 104b, 104c. The LED control IC 108 can correct the variation of the LEDs 104a, 104b, and 104c (particularly, the variation of the VI characteristic curve) and change the luminance stepwise.
However, the LED control IC 108 as shown in FIG. 9 has a problem that the cost of parts is high.

  In the second circuit configuration, as shown in FIG. 10, three LEDs 124 a, 124 b, and 124 c are connected in series via a booster circuit 126 on the output side of the power source 122. Two resistors of a resistor R11 and a resistor R12 that is turned on / off by the switch 128 are connected in parallel to the output side of the LEDs 124a, 124b, and 124c. By controlling on / off of the switch 128, the current flowing in the LEDs 124a, 124b, 124c can be controlled to change the luminance.

In the circuit of FIG. 10, the drive voltage (for example, 3.5V per LED) of the LEDs 124a, 124b, and 124c is boosted by the booster circuit 126 because the voltage of the power supply 122 (for example, 4.2V) is insufficient.
However, the circuit shown in FIG. 10 has a problem that if the luminance is changed in more stages, more resistors and switches are required and the number of parts increases.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a lighting control device capable of changing the luminance in multiple stages with a simple circuit configuration in a backlight having a plurality of LEDs as light sources. .

  The lighting control device according to the present invention is connected to a plurality of LED elements connected in series and a current output side of the plurality of LED elements, and is turned on by a pulse signal having a first signal level. A first transistor that becomes non-conductive by a pulse signal having a second signal level different from the signal level, and is connected in parallel to the first transistor on the current output side of the plurality of LED elements; A second transistor that is turned on by a pulse signal of a third signal level and is turned off by a pulse signal of a fourth signal level different from the third signal level; and a pulse signal is sent to the first transistor A CPU including a first port for outputting and a second port for outputting a pulse signal to the second transistor, wherein the CPU outputs a period for outputting the third signal level; It is characterized by controlling the luminance of the plurality of LED elements by controlling the ratio of the time period for outputting the serial fourth signal level.

  According to the lighting control device according to the present invention, it is possible to control currents flowing to a plurality of LED elements (luminances of the plurality of LED elements), and it is possible to change the luminance in multiple steps with a simple circuit configuration.

External view of mobile phone housing Table showing flip status and on / off status of both displays Functional block diagram of mobile phone 1 The figure which shows the outline | summary of the circuit of the mobile telephone 1 Table showing relationship between lighting mode, backlight surface brightness, signals output by port 1 and port 2, and CPU power saving mode The figure which shows the waveform output from the port 2 of CPU24 The figure which shows the modification of the circuit of the mobile telephone 1 The figure which shows the modification of the circuit of the mobile telephone 1 FIG. 3 is a diagram of a circuit configuration example 1 for changing the luminance of the backlight in stages. The figure of the circuit structural example 2 which changes the brightness | luminance of a backlight in steps

Hereinafter, an example in which a backlight of a mobile phone is turned on as a lighting control device will be described with reference to the drawings.
FIG. 1 is a diagram showing an appearance of a housing 2 of the mobile phone 1. The casing 2 of the mobile phone 1 is a foldable type, and includes an upper casing 2a, a lower casing 2b, and a hinge portion 2c.
The casing 2 is in a state in which the upper casing 2a and the lower casing 2b are opened to the left and right (open) and the upper casing 2a and the lower casing 2b are overlapped and closed by the rotation of the hinge portion 2a. There are two (closed) flip states.

An LCD (Liquid Crystal Display) display 4 is disposed on the front surface (the surface that is inside when folded closed) of the upper housing 2a, and the organic EL display is disposed on the back surface (the surface that is outside when folded closed). 6 is arranged.
Although a specific mechanism will be described later, when the flip state is open, the display on the LCD (Liquid Crystal Display) display 4 is turned on, and the display on the organic EL display 6 is turned off. On the contrary, when the flip state is closed, the display on the LCD display 4 is turned off and the display on the organic EL display 6 is turned on.

FIG. 3 is a functional block diagram of the mobile phone 1.
The mobile phone 1 includes an organic EL display 6, an LCD display 4, an LCD backlight LED 10, an LED controller 12, an open / close detection unit 14, a key operation unit 16, a camera unit 18, a speaker unit 20, a call unit 22, a CPU 24, and a memory. 26.
The LCD backlight LED 10 (hereinafter sometimes simply referred to as “LED 10”) is a light source of the backlight of the LCD display 4 and constitutes a backlight unit. Although not shown, the backlight unit in the present embodiment is a general edge light system (light guide plate system), for example, an acrylic light guide plate, and three white LEDs placed on the side of the light guide plate (Rated voltage is, for example, 3.5 V), and is made up of various optical sheets that are attached to the surface of the light guide plate to increase the light extraction efficiency or to increase the light uniformity. The light emitted from the three LEDs serving as the light source passes through the light guide plate and the optical sheet, and uniformly shines on the surface of the backlight unit.

The LED controller 12 controls the current flowing through the LED 10. Details will be described later with reference to FIG.
The open / close detection unit 14 includes, for example, a magnet provided in the upper housing 2b of the housing 2 and a magnetic sensor provided at a position facing the magnet when folded, and a magnetic field detected by the magnetic sensor. Based on the strength of the power (open is weak, close is strong), whether it is open or closed is detected and output to the CPU 24.

The key operation unit 16 includes a dial key for calling and receives an input from the user of the mobile phone 1.
The camera unit 18 captures various images. The speaker unit 20 outputs sound. The call unit 22 includes a high frequency circuit and realizes a call function.
The CPU 24 executes computations and controls devices and devices.

Further, the CPU 24 includes two ports 1 and 2 (see FIG. 5) that output a GPIO (General Purpose Input / Output) signal that is either High or Low. The output voltage of High is 2.7V, for example, and the output voltage of Low is 0V, for example.
The port 1 outputs a High or Low GPIO signal.
Port 2 can output either a High or Low GPIO signal and can output a pulse density (High / (High + Low)) at a specified density, that is, pulse density modulation (PDM). This is a port that outputs a signal.

The CPU has a power saving mode (sleep mode) in which the operation clock is stopped. In the power saving mode, a pulse density modulated signal cannot be output from the port 2. However, the High or Low GPIO signal output from the port 1 and the port 2 before entering the power saving mode can be maintained as it is.
The memory 26 stores a program executed by the CPU 24 (a control program related to changing the luminance of the LED 10 in multiple stages) and provides a work area for executing the program.

In this control program, the lighting mode indicating the brightness of the backlight unit (the brightness of the LED 10) is changed stepwise in accordance with the user's preference via the key operation unit 16. There are six lighting modes from the darkest lighting mode 0 to the brightest lighting mode 5.
In the lighting mode 1 to the lighting mode 4, information indicating the prescribed pulse density for each lighting mode is stored in the memory 26, and the CPU follows the prescribed pulse density from the port 2 based on the stored contents. A signal is output (see FIG. 6).

FIG. 4 is a diagram showing an outline of the circuit of the mobile phone 1.
As shown in FIG. 4, a booster circuit 32 that boosts the voltage to 14 V is disposed on the output side of the battery 30 (the voltage when fully charged is 4.2 V, and the value slightly decreases as the discharge progresses). . The output side of the booster circuit 32 is connected to the organic EL display 6 via the switch 34 by the line L1. Further, the output side of the booster circuit 32 is also connected to the LED 10 by a line L2 led out from the branch point P of the line L1 from the booster circuit to the organic EL display 6.

  The organic EL display 6 has an operating voltage of, for example, 10V or higher and lower than 14V. A switch 34 is provided on the input side of the organic EL display 6. The switch 34 is on / off controlled by the CPU 24 and is in an off state while the open / close detection unit 14 detects open, and the organic EL is not lit (not displayed). On the other hand, while the open / close detection unit 14 detects the close, the on-state is turned on and the organic EL is turned on.

On the output side of the LED 10, a resistor R1 (8 kΩ) and a bipolar transistor (hereinafter simply referred to as “transistor”) Q1, and a resistor R2 (300Ω) and a transistor Q2 are connected in parallel.
The port 1 of the CPU 24 is connected to the base of the transistor Q1. Therefore, the conduction of the transistor Q1 can be controlled by the output of the port 1. Similarly, since the port 1 of the CPU 24 is connected to the base of the transistor Q2, the conduction of the transistor Q2 can be controlled by the output of the port 2.

FIG. 5 is a table showing the relationship between the lighting mode, the brightness of the backlight surface, the signals output by the ports 1 and 2, and the CPU power saving mode.
(1) Lighting mode 5 (highest)
When the GPIO signal output from the port 1 is Low, the transistor Q1 is non-conductive because the potential difference between the base and emitter of the transistor Q1 is small.

When the GPIO signal output from the port 2 is high, the potential difference between the base and emitter of the transistor Q2 is large, and the transistor Q2 becomes conductive. At this time, since the resistance R2 is as relatively small as 300Ω, a large current flows through the LED 10, so that the brightness of the surface of the backlight becomes as bright as 320 (cd / m ² ).
(2) Lighting mode 0 (dim)
Contrary to the lighting mode 5, when the GPIO signal output from the port 1 is High and the GPIO signal output from the port 2 is Low, the transistor Q1 is turned on and the transistor Q2 is turned off. In this case, since a relatively small current flows through the LED 10 due to the relatively large resistance R1 of 8 kΩ, the luminance of the surface of the backlight is 13.5 (cd / m ² ), so that a faint light can be seen.

(3) Lighting mode OFF
When both GPIO signals output from port 1 and port 2 are low, both the transistor Q1 and the transistor Q2 are in a non-conductive state, no current flows through the LED 10, and the brightness of the surface of the backlight is almost zero. .
(4) Lighting mode 4 (high)
When the GPIO signal output from the port 1 is Low, the transistor Q1 is turned off. As shown in FIG. 6A, a high level signal is repeatedly output from the port 2 for 210 ns during a certain period (210 ns + 420 ns).

The transistor Q2 is turned on during the High level pulse width (210 ns), and the transistor Q2 is turned off during the Low level pulse width (420 ns). The LED 10 is turned on and off at high speed by this high-speed switching between conduction and non-conduction. Therefore, the brightness of the surface of the backlight is 238 (cd / m ² ), which is slightly lowered from 320 (cd / m ² ). Since the LED 10 is turned on and off at a very high speed, there is almost no sense of incongruity such as flickering from the human eye (the lighting modes 1 to 3 are the same).

(5) Lighting mode 3 (medium)
When the GPIO signal output from the port 1 is Low, the transistor Q1 is turned off. As shown in FIG. 6B, a high level signal is repeatedly output from the port 2 for 210 ns in a certain period (210 ns + 830 ns). The luminance of the surface of the backlight is 154 (cd / m ² ).

(6) Lighting mode 2 (low)
When the GPIO signal output from the port 1 is Low, the transistor Q1 is turned off. As shown in FIG. 6C, a high level signal is repeatedly output from the port 2 for 210 ns in a certain period (210 ns + 1.03 μs). The luminance of the surface of the backlight is 101 (cd / m ² ).

(7) Lighting mode 1 (lowest)
When the GPIO signal output from the port 1 is Low, the transistor Q1 is turned off. As shown in FIG. 6D, a high level signal is repeatedly output from the port 2 for 210 ns in a certain period (210 ns + 2.09 μs). The luminance of the surface of the backlight is 61 (cd / m ² ).

As described above, according to the present embodiment, the PDM signal output from the port 2 of the CPU 24 is used to switch the conduction / non-conduction at a high speed by turning on / off Q2 at a high speed, and a current is supplied to the LED 10. Whether to flow or not can be switched at high speed, and the luminance can be adjusted in four stages of lighting modes 1 to 4 by changing the density of the PDM signal.
Further, since the LED 10 and the organic EL display 6 share one booster circuit 32, the circuit scale and cost can be reduced. The booster circuit is a particularly expensive component, and it is particularly efficient that the booster circuit for the organic EL display can be used originally. In addition, either one can be displayed (lighted) according to the flip state as shown in FIG.

Further, as described above, even in the power saving mode in which the CPU operation clock is stopped, the CPU 22 can maintain the output of the High or Low GPIO signal output from the ports 1 and 2 as it is. is there.
The combination of High and Low makes it possible to use the brightest lighting mode 5 and the darkest mode 0 regardless of the power saving mode.

For example, before entering the power saving mode, High is output from the port 1 and Low is output from the port 2, and the mode is shifted to the power saving mode as it is. It can also be displayed.
As an example of usage, a lighting mode 5 can be provided to a user who wants to use the light of the LCD display 4 with the brightness of a flashlight, and to a user who wants to use the LCD display 4 so as to be thinly displayed. On the other hand, the lighting mode 0 can be provided.

<Supplement>
As mentioned above, although embodiment of this invention was described, this invention is not limited to said content, It can implement also in the various forms for achieving the objective of this invention, its related or incidental object, for example, The following may also be used.
(1) In the embodiment, as shown in FIG. 2, it has been described that either one of the LCD display 4 and the organic EL display 6 is turned on. However, for example, there is no key operation by the user from on to save battery power. It is also possible to switch off a display that is turned on under the condition that a certain time has passed.

  (2) In the embodiment, NPN transistors Q1 and Q2 are used as shown in FIG. 4, but PNP transistors Q3 and Q4 may be used as shown in FIG. In the case of the PNP type, since the polarity is opposite to that of the NPN type, the GPIO signal output from the ports 1 and 2 is Low, and the transistors Q3 and Q4 are turned on. Further, the load (resistors R3 and R4) is arranged on the output side of the transistors Q3 and Q4, and the resistance value of the resistor R3 is much higher than that of the resistor R4 as in the relationship between the resistors R1 and R2. .

  In the embodiment, bipolar transistors Q1 and Q2 are used. However, as shown in FIG. 8A, an N-channel TFT (Thin Film Transistor) or a P-channel transistor as shown in FIG. A TFT may be used. In the case of the N-channel TFT shown in FIG. 8A, the TFTs (Q5, Q6) are turned on (on) when the GPIO signal output from the ports 1 and 2 is at the high level, and are turned off (off) at the low level. . In the case of FIG. 9B, the TFTs (Q7, Q8) are turned on (on) when the GPIO signals output from the ports 1 and 2 are at the low level, and are turned off (off) at the high level.

  (3) In the embodiment, the signal output from the port 2 of the CPU 24 is pulse density modulation in which the pulse width is constant and the pulse density per unit time is changed. However, the present invention is not limited to this. . For example, pulse width modulation (PWM) may be used. In short, it is only necessary to be able to control the ratio of the periods during which high and low pulses are output.

  (4) In the embodiment, as illustrated in FIG. 5, in the lighting mode 5 and the lighting mode 0, it has been described that either one of the port 1 and the port 2 is set to High, but both may be set to High. . When both are set to High, the total resistance R of the resistors R1 and R2 connected in parallel is less than 300Ω of R2 (R = about 290Ω from 1 / R = 1 / R1 + 1 / R2), so it is brighter than the lighting mode 5 It becomes brightness.

(5) In the embodiment, it has been described that the specification of the luminance level is received from the user via the key operation unit 16, but the present invention is not limited to this. For example, an illuminance sensor is provided beside the LCD display 4 and However, if the illuminance is low, the brightness may be set to a brighter stage, and if the illuminance is high, the brightness may be set to a darker stage.
<Summary>
(1) A lighting control device according to the present invention is connected to a plurality of LED elements connected in series and a current output side of the plurality of LED elements, and is conducted by a pulse signal of a first signal level, A first transistor that is rendered non-conductive by a pulse signal having a second signal level different from the first signal level; and a current output side of the plurality of LED elements in parallel with the first transistor. A second transistor connected to be turned on by a pulse signal of a third signal level and turned off by a pulse signal of a fourth signal level different from the third signal level; and to the first transistor A CPU including a first port for outputting a pulse signal and a second port for outputting a pulse signal to the second transistor, and the CPU outputs the third signal level. And controlling the brightness of the plurality of LED elements by controlling the ratio of the time period for outputting the fourth signal level between.

According to this configuration, it is possible to change the luminance in multiple steps with a simple circuit configuration.
(2) The CPU has a mode for stopping the operation clock. When the operation clock is stopped, the signal level output from the first port and the second port is fixed before the operation clock is stopped. However, the brightness of the plurality of LED elements may be set.

According to this configuration, a plurality of LED elements can be caused to emit light even in a mode in which the operation clock of the CPU is stopped, that is, in a power saving mode. For example, a plurality of LED elements can be turned on even in the power saving mode. An LCD backlight unit as a light source can be turned on.
(3) The pulse signal output from the first port by the CPU is a signal that is not pulse-modulated, and the first signal level of the pulse signal output from the first port by the CPU and the second signal As for the signal level, one may be High and the other may be Low.

  (4) The battery further includes a battery, a booster circuit that boosts the voltage of the battery, and an organic EL display connected to a line on the output side of the booster circuit, and the plurality of LED elements are outputs of the booster circuit. It may be connected to a line drawn from a branch point of the side line, and may further include a switch element installed on a line from the branch point to the organic EL display.

According to this configuration, the organic EL display and the plurality of LED elements can share a circuit configuration such as a booster circuit, which can contribute to, for example, reduction in the number of parts.
(5) A mobile phone according to the present invention is a mobile phone having a folding housing including the lighting control device, and an upper housing and a lower housing, and the housing is not folded. A detection unit that detects whether it is in a folded state or a closed state; an LCD display that emits light from a backlight unit that uses the plurality of LED elements as light sources; and a back surface of the upper housing. Comprises an organic EL display, and when the detection unit detects a closed state, the CPU outputs a pulse signal of the second signal level to make the first transistor non-conductive, The organic EL display may be lit by turning off the plurality of LED elements and turning on the switch elements.

According to this configuration, the LCD display and the organic EL display can be suitably turned on / off according to whether the open state or the closed state.
Even if both the first transistor and the second transistor are made non-conductive, such as outputting the pulse signal of the fourth signal level from the CPU to make the second transistor non-conductive. Good.

  The lighting control device according to the present invention is useful because the luminance can be changed in multiple stages with a simple circuit configuration.

DESCRIPTION OF SYMBOLS 1 Mobile phone 2 Case 2a Upper case 2b Lower case 2c Hinge part 4 LCD display 6 Organic EL display 10 LCD backlight LED
12 LED Controller 14 Open / Close Detection Unit 24 CPU
30 battery (power)
L1 line L2 line P Branch point Q1, Q2, Q3, Q4 Transistor (bipolar transistor)
Q5, Q6, Q7, Q8 TFT
R1, R2, R3, R4, R5, R6, R7, R8 resistance

Claims (4)

A plurality of LED elements connected in series;
The first LED is connected to the current output side of the plurality of LED elements, is turned on by a pulse signal having a first signal level, and is turned off by a pulse signal having a second signal level different from the first signal level. Transistors
A current output side of the plurality of LED elements is connected in parallel to the first transistor, is conducted by a pulse signal having a third signal level, and is different from the third signal level. A second transistor that is turned off by a pulse signal at a signal level;
A CPU including a first port that outputs a pulse signal to the first transistor and a second port that outputs a pulse signal to the second transistor;
The CPU controls the luminance of the plurality of LED elements by controlling a ratio between a period for outputting the third signal level and a period for outputting the fourth signal level ,
The CPU has a mode for stopping the operation clock,
When stopping the operation clock, before stopping the operation clock, the signal levels output from the first port and the second port are fixed, and the brightness of the plurality of LED elements is set. Lighting control device. The pulse signal output from the first port by the CPU is a signal not subjected to pulse modulation,
2. The lighting control according to claim 1, wherein one of the first signal level and the second signal level of the pulse signal output from the first port by the CPU is High and the other is Low. apparatus. Battery,
And a booster circuit for boosting a voltage of said battery,
An organic EL display is connected to the output-side line of the booster circuit,
The plurality of LED elements are connected to a line drawn from a branch point of the output side line of the booster circuit,
The lighting control device according to claim 1, further comprising a switch element installed on a line from the branch point to the organic EL display. A mobile phone having a folding housing including the lighting control device according to claim 3 and an upper housing and a lower housing,
A detection unit that detects whether the housing is in an unfolded open state or a folded closed state;
An LCD display that emits light from a backlight unit that uses the plurality of LED elements as light sources on the front surface of the upper housing;
On the back of the upper housing and a said organic EL display,
When the detection unit detects a closed state, the CPU outputs a pulse signal of the second signal level to make the first transistor non-conductive and turn off the plurality of LED elements. And the organic EL display is turned on by turning on the switch element.

Images