JP2001337638A - Display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress inrush current generated at the start of display and prolong the use time of a battery used as a system power supply. System voltage V _SYS supplied from A power supply circuit 22 boosts at boosting circuit 24, the boost voltages V ₁
Is supplied to the liquid crystal voltage generation circuit 28, and the display driving voltage V ₂
In the display device which performs display by generating a ~V _5, it provided a voltage level control circuit 27. This voltage level control circuit 2
7, the level of the reference voltage V _REF is lowered at the start of display and applied to the voltage comparison circuit 25, whereby the booster circuit 2
4, the output voltage (V ₁ ) is lowered. As a result, the occurrence of inrush current can be suppressed low, and the system voltage V
The use time of the battery 21 used as a system power supply can be extended while avoiding the influence on _SYS .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device used for a battery-driven portable device such as a notebook computer, a PDA (Personal Digital Assistant), and an electronic organizer.

[0002]

2. Description of the Related Art In a battery-powered portable device such as a notebook computer, a PDA, and an electronic organizer, for example, a liquid crystal display (LCD) is used as a display device.
y) is widely used. In this type of liquid crystal display device, after boosting a system voltage supplied from a power supply circuit to a level required for LCD display by a booster circuit, a plurality of liquid crystal driving circuits are driven by a liquid crystal voltage generation circuit based on the boosted voltage. The liquid crystal is driven by generating various kinds of voltage signals. In this case, in order to suppress current consumption as much as possible, the operation of each circuit is stopped during non-display, and each circuit is sequentially enabled according to a certain sequence at the time of startup.

[0003]

However, since the driving voltage of the liquid crystal is very high, when the liquid crystal is driven, the voltage on the system side may be affected. That is, as described above, in the liquid crystal display device, each circuit is enabled according to a certain sequence at the time of startup. However, the liquid crystal voltage generation circuit is enabled after the voltage is stabilized. ing. This is because the liquid crystal voltage generation circuit has a predetermined operating voltage range, and if enabled before boosting, the operation becomes unstable and the startup time becomes longer.

Here, when the liquid crystal voltage generation circuit is enabled at the start of display, a so-called inrush current is generated by the initial rise (startup) of the internal circuit, and the voltage instantaneously drops out (voltage drop) due to the inrush current. Phenomenon occurs. Since the voltage supplied to the liquid crystal voltage generation circuit is obtained by boosting the system voltage, if the boosted voltage drops out, the system voltage drops out even more.

[0005] Normally, in a battery-operated portable device, the voltage of a battery used as a system power supply is constantly monitored, and when the battery voltage falls below a predetermined level, it is determined that the terminal voltage has been reached. It is configured to issue a warning to the user. Therefore, due to the occurrence of the inrush current, when the battery voltage of the system drops out even below the predetermined level even instantaneously, it is determined that the voltage has been reached all the time, despite the remaining capacity of the battery. There was a problem that the battery could not be used for a long time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and suppresses an inrush current generated at the start of display.
It is an object of the present invention to provide a display device capable of extending the use time of a battery used as a system power supply.

[0007]

A display device of the present invention compares a boosted voltage for boosting a system voltage, a boosted voltage boosted by the boosted voltage and a reference voltage, and operates the booster according to the comparison result. Voltage comparing means for controlling a boosting ratio, voltage level controlling means for switching the level of the reference voltage in the voltage comparing means at a predetermined timing, and driving a display unit based on the boosted voltage supplied from the boosting means And a display voltage generating means for generating a predetermined voltage signal.

According to such a configuration, the output voltage of the boosting means can be controlled by switching the level of the reference voltage by the voltage level control means.
Therefore, at the start of display, the system voltage is boosted to a voltage lower than the voltage required for display by the voltage level control means, and after the operation of the display voltage generation means is stabilized, the system voltage is reduced to the voltage required for display. If the level of the reference voltage is switched to boost the voltage,
Inrush current generated at the start of display can be suppressed low, and the effect on the system voltage can be reduced.

Therefore, when a battery is used as a system power supply, the occurrence of the inrush current prevents the battery voltage from dropping out and being erroneously detected as reaching the end voltage, thereby extending the battery usage time. be able to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a portable device to which the display device of the present invention is applied.

The portable device 10 according to the present embodiment is, for example, a notebook computer, a PDA (Personal Digital Assis).
tant), an electronic organizer, and the like.
An input unit 13, a display unit 14, a communication control unit 15, a RAM 16, an external storage device 17, and the like are connected to the PU 11 via the system bus 12.

The CPU 11 controls the entire portable device 10, and reads a program stored in advance or a program stored in a recording medium provided through the external storage device 17 to read the program according to the program. Execute a predetermined process. The method of providing the program is not limited to the above-described recording medium, and may be provided from an external terminal via a network, for example.

The input unit 13 is an input device composed of, for example, a keyboard, a mouse, a pen, and the like, and is used for inputting data and giving various instructions. The display unit 14
For example, it is a display device such as an LCD (Liquid Crystal Display), and displays various data. The communication control unit 15 performs wired or wireless communication with another information device. The RAM 16 stores various information necessary for the processing of the CPU 11. The external storage device 17
For example, in addition to a magnetic disk device, a floppy (registered trademark) disk device, and a small storage device such as an IC card, it stores various types of information including programs.

Next, a display device of the present invention used for the display unit 14 provided in the portable device 10 will be described by taking a liquid crystal display device as an example.

FIG. 2 is a block diagram showing the configuration of the display device of the present invention.

In FIG. 2, reference numeral 21 denotes a battery serving as a drive source, which is used as a common power supply for the entire system including the display device. A power supply circuit 22 generates a system voltage _VSYS using the battery 21 as a drive source.

Here, this device includes a control circuit 23, a booster circuit 24, a voltage comparison circuit 25, a regulator circuit 26,
A voltage level control circuit 27, a liquid crystal voltage generation circuit 28, a liquid crystal driver circuit 29, and a liquid crystal panel 30 are provided.

The control circuit 23 comprises a microprocessor, and the system voltage V _SYS supplied from the power supply circuit 22 is provided.
In response to this, here, a switch signal S for driving and controlling each circuit in the display device according to a predetermined sequence is provided.
W1 to SW4 are output. The switch signal SW1 is a signal for driving and controlling the booster circuit 24, the switch signal SW2
Is a signal for driving and controlling the voltage level control circuit 27;
The switch signal SW3 is a signal for driving and controlling the liquid crystal voltage generation circuit 28, and the switch signal SW4 is a signal for driving and controlling the liquid crystal driver circuit 29.

The booster circuit 24 receives the system voltage _VSYS as an input and outputs a switch signal S output from the control circuit 23.
In accordance with W1, the system voltage _VSYS is boosted to a level required for LCD display. Voltage comparator circuit 25 compares the reference voltage V _REF output from the boosted voltage V ₁ and the voltage level control circuit 27 to be output from the booster circuit 24 controls the boosting ratio of the booster circuit 24 in accordance with the comparison result .

The regulator circuit 26 adjusts the system voltage _VSYS supplied from the power supply circuit 22 to a predetermined voltage with little fluctuation. The voltage level control circuit 27 is a feature of the present invention, and generates a reference voltage V _REF to be applied to the voltage comparison circuit 25 based on the voltage adjusted by the regulator circuit 26.
3 switches the level of the reference voltage V _REF in accordance with the switch signal SW2 output from the switch 3. The voltage level control circuit with the level switching of the reference voltage V _REF by 27, dividing ratio of the booster circuit 24 is changed, the level of the boost voltages V ₁ which is the output voltage is adjusted.

The liquid crystal voltage generating circuit 28 generates a liquid crystal driving voltage V ₂ based on the boosted voltage V ₁ supplied from the boosting circuit 24.
To generate a ~V _5. The boosted voltage V _1, the voltage V ₂ ~V ₅ generated by the liquid crystal voltage generating circuit 28 is supplied to the liquid crystal driver circuit 29 as a voltage signal for driving the liquid crystal,
When the switch signal SW4 is output from the control circuit 23, the liquid crystal driver circuit 29 drives the liquid crystal panel 30 based on these voltage signals. Since the driving method of the liquid crystal panel 30 is well known, the description thereof is omitted here.

FIG. 3 shows a booster circuit 24 in the display device.
It is a figure which shows the specific circuit configuration of a periphery.

As shown in FIG. 3, the voltage level control circuit 2
7, a regulator circuit 26 is provided. The regulator circuit 26 adjusts the system voltage _VSYS to a predetermined voltage with little fluctuation, and then adjusts the voltage level control circuit 27.
Has given to. The voltage level control circuit 27 supplies the voltage adjusted by the regulator circuit 26 to the voltage comparison circuit 25 as a reference voltage _VREF . Here, a TFT 31 is provided in the voltage level control circuit 27 and this TFT 3
1 is turned on / off by a switch signal SW2 to switch the level of the reference voltage V _REF .

The voltage comparison circuit 25 includes a comparator 32
Is provided. One input terminal of the comparator 32
The terminal (+ terminal) has a booster voltage,
Pressure V ₁Is input, and the other input terminal (-terminal)
The reference voltage V which is an output signal of the level control circuit 27_REF
Is entered. In this comparator 32, the boosted voltage V ₁
And reference voltage V_REFAnd according to the comparison result
The signal is output to the booster circuit 24. The booster circuit 24
Control circuit 33, resistor 34, transistor 35, coil
36, a diode 37, and the like.
And the output signal of the voltage comparison circuit 25 is
System voltage V at the voltage division ratio determined by the_SYSof
It is configured to perform boosting.

Next, the operation of the display device of the present invention will be described.
The operation will be described in comparison with the operation of a conventional display device.

FIG. 4 is a diagram for explaining a display processing operation in the display device of the present invention in comparison with a conventional example.
(A) is a flowchart showing a display processing operation in a display device of the present invention, and (b) is a flowchart showing a display processing operation in a conventional display device. FIG.
Is a timing chart of each signal in the display device of the present invention, and FIG. 6 is a timing chart of each signal in the conventional display device. In each of the timing charts, all elements except for the switch signal SW2 in FIG. 5 are shown as low active.

The conventional display device does not have a voltage level control function, and the voltage level control circuit 27 shown in FIG.
It has a configuration excluding W2.

That is, in the conventional display device, FIG.
As shown in the flowchart of FIG.
First, the switch signal SW1 is turned on and the booster circuit 24 is turned on.
The power supply circuit 22 is enabled (step B11).
System voltage V supplied from_{S YS}Up to a certain level
(Step B12). In this case, LCD display
It is set to boost the voltage to the level required for Continued
And turns on the switch signal SW3 to turn on the liquid crystal voltage.
The path 28 is enabled (step B13), and the voltage is increased.
Boosted voltage V output from circuit 24₁For driving LCD based on
Voltage V₂~ V₅Is generated (step B14). Soshi
And turns on the switch signal SW4 to turn on the liquid crystal driver circuit.
29 (step B1).
5), boosted voltage V obtained from booster circuit 24₁And LCD
Voltage V generated by pressure generation circuit 28 ₂~ V₅Based on
To drive the liquid crystal panel 30 to perform display (step B1).
6).

As described above, in the conventional display device, the display is opened.
At the beginning, the system voltage V_SYSRequired to drive the LCD
To boost the voltage immediately to the bell, the timing chart in FIG.
As shown in FIG.
When the voltage generation circuit 28 is enabled, an inrush current
And the boost voltage V₁Is instantaneous
Drop out to system voltage V_SYSAffect
You. That is, the boost voltage V ₁Has dropped out
Receiving system voltage V_SYSIs even bigger
Go out. As a result, the battery 21 serving as the system power supply ends.
False detection that the stop voltage has been reached,
Time is shorter than the time corresponding to the capacity of
Was.

On the other hand, in the display device of the present invention, FIG.
As shown in the flowchart of FIG.
First, the switch signal SW2 is turned on (step A1).
1), the system voltage V supplied from the power supply circuit 22
_{SYS is set} by the booster circuit 24 so as to be boosted below the voltage necessary for the original LCD display (step A1).
2). For example, it is set near the lower limit of the operation voltage of the liquid crystal voltage generation circuit 28. Specifically, by turning on the switch signal SW2, as shown in the circuit diagram of FIG. 3, the TFT 31 of the voltage level control circuit 27 is switched to the ON state, and the voltage level control circuit 27 Of the reference voltage V _REF to be output is lower than a predetermined level required for LCD display.

In this state, the switch signal SW1 is turned on to enable the booster circuit 24 (step A1).
3), the system voltage V supplied from the power supply circuit 22
_SYS is boosted (step A14). In this case, LC
The boosting operation is performed at a level lower than the level required for D display. Subsequently, the switch signal SW3 is turned on to enable the liquid crystal voltage generation circuit 28 (step A1).
5), to produce a voltage _V 2 ~V ₅ for driving liquid crystal based on the boosted voltage _{V 1} output from the booster circuit 24 (step A1
6).

Here, the liquid crystal voltage generation circuit 28 is enabled.
Inrush current occurs when the
As shown in FIG.
Pressure V ₁Rush current is low
System voltage V_SYSWhat
Influence (dropout). Therefore,
Due to the occurrence of the inrush current, the battery 21 as the system power supply
There is no erroneous detection that the end voltage has been reached.

After the operation (voltage V ₁ ) of the liquid crystal voltage generation circuit 28 is stabilized, the switch signal SW2 is turned off (step A17), and the system voltage V _SYS supplied from the power supply circuit 22 is supplied to the booster circuit 24. LCD
The voltage is set so as to increase to a voltage required for display (step A18). Then, (step A19) by the switch signal SW4 is turned ON to a liquid crystal driver circuit 29 and the enable state, the voltage V generated by the booster circuit boosting voltages V ₁ obtained from 24 and the liquid crystal voltage generating circuit 28
Performs display by driving the liquid crystal panel 30 based on ₂ ~V ₅ (step A20).

As described above, the system voltage _VSYS is temporarily raised to a low voltage at the start of display, and the liquid crystal voltage generation circuit 28 is enabled in that state, so that the occurrence of inrush current can be suppressed low. . This allows
It is possible to prevent the system voltage V _SYS from dropping significantly, thereby preventing the battery 21 as the system power supply from being erroneously detected as having reached the final voltage. As a result, the battery 21 can be made longer than before. Can be used.

As shown in the circuit diagram of FIG. 3, basically, the reference voltage V _REF is kept constant by the regulator circuit 26 even when the system voltage V _SYS drops out. Although the voltage V _REF is forcibly reduced by an external microcomputer control (control circuit 23), the system voltage V _SYS is supplied as the reference voltage V _REF by omitting the regulator circuit 26, for example. System voltage V _SYS
Since the output voltage (V ₁ ) of the booster circuit 24 also fluctuates in conjunction with the fluctuation (drop) of the voltage, the influence of the rush current can be suppressed low.

Further, when the inrush current is generated, the operation of the microcomputer (control circuit 23) is temporarily stopped, and the LCD display is started in a state where the power consumption of the entire system is low. Can be further reduced.

The present invention is not limited to the LCD, but can be applied to other display devices. In the same manner as described above, the rush current at the start of display is suppressed, and the power supply voltage of the system is greatly reduced. Can be prevented.

Further, the present invention is not limited to the above-described embodiment, and can be variously modified in an implementation stage without departing from the gist thereof. Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some components are deleted from all the components shown in the embodiments, the effects described in “Problems to be Solved by the Invention” can be solved, and the effects described in the “Effects of the Invention” section can be solved. In the case where a certain effect can be obtained, a configuration from which this configuration requirement is deleted can be extracted as an invention.

[0040]

As described above in detail, according to the present invention, the rush current generated at the start of display can be suppressed by controlling the output voltage of the booster circuit. Further, by suppressing the inrush current, it is possible to avoid a large dropout of the system voltage. Therefore, when a battery is used as a system power supply, it is possible to prevent the battery voltage from being erroneously detected as having reached the cutoff voltage despite having the capacity, and to extend the operating time of the battery as compared with the conventional case. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a portable device to which a display device of the present invention is applied.

FIG. 2 is a block diagram illustrating a configuration of a display device of the present invention.

FIG. 3 is a diagram showing a specific circuit configuration around a booster circuit in the display device of FIG. 2;

FIG. 4 is a diagram for explaining a display processing operation in the display device of the present invention in comparison with a conventional example. FIG. 4A is a flowchart showing a display processing operation in the display device of the present invention; 4B is a flowchart illustrating a display processing operation in the conventional display device.

FIG. 5 is a timing chart of each signal in the display device of the present invention.

FIG. 6 is a timing chart of each signal in a conventional display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Portable equipment 11 ... CPU 12 ... System bus 13 ... Input part 14 ... Display part 15 ... Communication control part 16 ... RAM 17 ... External storage device 21 ... Battery 22 ... Power supply circuit 23 ... Control circuit 24 ... Booster circuit 25 ... Voltage Comparison circuit 26 Regulator circuit 27 Voltage level control circuit 28 Liquid crystal voltage generation circuit 29 Liquid crystal driver circuit 30 Liquid crystal panel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/36 G09G 3/36 F-term (Reference) 2H093 NC03 NC49 NC58 ND37 ND60 5C006 AC02 AF67 AF69 BB11 BF25 BF31 BF36 BF37 BF45 BF46 FA47 5C080 AA10 BB05 DD26 DD30 FF03 FF09 GG02 JJ02 JJ03 JJ04 JJ07

Claims (2)

[Claims] A boosting means for boosting a system voltage; a voltage comparing means for comparing a boosted voltage boosted by the boosting means with a reference voltage; and controlling a boosting ratio of the boosting means in accordance with a result of the comparison. Voltage level control means for switching the level of the reference voltage in voltage comparison means at a predetermined timing; and a display voltage for generating a predetermined voltage signal for driving a display unit based on the boosted voltage supplied from the boosting means. A display device comprising: a generator. 2. The voltage level control means boosts the system voltage to a voltage lower than a voltage required for display at the start of display, and switches the system voltage to display after the operation of the display voltage generating means is stabilized. In order to boost to the required voltage,
2. The display device according to claim 1, wherein a level of said reference voltage in said voltage comparing means is switched.