JP4247003B2 - Light control device and liquid crystal display device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light control device for a liquid crystal display and a liquid crystal display device using the same.
[0002]
[Prior art]
Conventionally, in a liquid crystal display, a backlight composed of a fluorescent lamp or the like is used on the back of the display. The backlight is connected to a drive circuit, and drive power from a power source such as a battery is supplied through the drive circuit.
In addition, in some cases using a reflective liquid crystal display, a front light made of a fluorescent lamp or the like is provided in front of the reflective liquid crystal display, and the light is similarly turned on using a drive circuit.
[0003]
Such a drive circuit includes an inverter circuit, generates a pulse lighting signal with a cycle of 100 to 400 Hz based on the drive power supplied from the power supply, and the inverter circuit during a period when the pulse signal is at a high level. To generate a high-frequency voltage with a period of 40 K to 200 KHz. Thereafter, the high frequency voltage is input to the backlight.
[0004]
As an example of such a light control device, in the light control device for a flat lamp disclosed in Patent Document 1, a logical product of a pulse lighting signal with a cycle of 100 to 1000 Hz and a duty signal output from a duty signal generation circuit. The driving voltage of the flat lamp is adjusted by the duty pulse lighting signal taking the above. As a result, it is possible to expand the light control range of the flat lamp and save power consumption.
[0005]
Further, in the backlight control device disclosed in Patent Document 2, the on / off signal of the switch circuit for turning on / off the supply voltage of the inverter circuit and a fraction to one tenth of the transmission frequency of the inverter. The switch circuit is turned on / off at the timing of the logical sum with the on / off signal of the switch circuit that is turned on / off at the frequency of. Thereby, even when the fluctuation of the power supply voltage is large, it is possible to supply a stable voltage to the inverter circuit and to perform wide-range dimming.
Further, Patent Literature 3 and Patent Literature 4 disclose contents relating to a pulse charging method as a battery charging method.
[0006]
[Patent Document 1]
JP 2002-100496 A [Patent Document 2]
Japanese Patent Laid-Open No. 11-122937 [Patent Document 3]
JP 2000-23382 [Patent Document 4]
Japanese Laid-Open Patent Publication No. 8-241735
[Problems to be solved by the invention]
By the way, liquid crystal displays are often used for portable devices and the like. However, such devices are typically provided with a battery so that they can operate for a certain period of time even without a power source. Therefore, when the liquid crystal display is connected to the power source and used, the battery is charged at the same time.
[0008]
However, in the conventional liquid crystal display, since the backlight dimming circuit and the battery charging circuit operate independently, as shown in FIG. 7, for example, the battery is charged at a constant voltage (or constant current). Even if the dimming pulse, which is a pulse lighting signal, is turned on / off, the power load on the liquid crystal display increases at the timing when the charging voltage on period and the dimming pulse on period overlap. It was fluctuating.
[0009]
On the other hand, in general, a secondary battery such as a lithium ion battery is used for a battery of a liquid crystal display, and in charging such a battery, in order to prevent overcharging, charging and pause are performed at regular intervals. Repeated pulse charging is performed.
[0010]
In the pulse charging methods disclosed in Patent Documents 3 to 4, it is described that the battery voltage of the secondary battery is maintained within a predetermined set voltage range by a pulse charging method with various devices. .
[0011]
Also in the liquid crystal display that performs such pulse charging, as described above, the power load applied to the liquid crystal display varies greatly depending on whether the dimming pulse is turned on or off and the charging pulse is turned on or off.
[0012]
Thus, when the power load applied to the liquid crystal display fluctuates greatly, the power source generates noise, which causes problems such as beat disturbance on the display screen and noise in the sound.
[0013]
In particular, in the case where the backlight dimming circuit and the battery pulse charging circuit are operating independently, there is a problem in that each pulse causes frequency interference, resulting in a beat.
[0014]
Therefore, in view of the above situation, the present invention prevents the power supply load of the entire liquid crystal display from fluctuating greatly even when the backlight dimming circuit and the battery pulse charging circuit are operating simultaneously. It is an object of the present invention to provide a light control device that can be controlled in an automatic manner and a liquid crystal display device using the same.
[0015]
[Means for Solving the Problems]
As a result of diligent research in view of the above problem, the present inventor has found that the dimming pulse of the dimming circuit and the charging pulse of the battery charging circuit have substantially the same frequency, and the other pulse It was conceived that it is possible to stabilize the power load by synchronizing so that is turned off.
[0016]
That is, the present invention provides a dimming pulse generating means for generating a dimming pulse for adjusting the voltage supplied to the light, and a charging pulse generating means for generating a charging pulse for adjusting the voltage supplied to the battery. And the dimming pulse and the charging pulse have a phase opposite to each other.
[0017]
As a result, the dimming pulse is turned off when the charging pulse is on, and the dimming pulse is turned on when the charging pulse is off, so that it is possible to suppress fluctuations in the power supply load of the entire dimming device. .
[0018]
In the light control device according to the present invention, the light control pulse and the charge pulse are rectangular pulses. As a result, the total power source load of the dimming pulse and the charging pulse having phases opposite to each other can be made substantially constant.
[0019]
In the present invention, the frequency of the dimming pulse and the charging pulse is in the range of 100 to 400 Hz. When dimming is turned on / off within this frequency range, no change is perceived by the human eye.
[0020]
In the present invention, the dimming pulse and the charging pulse are both different in frequency from either the vertical synchronization frequency or the horizontal synchronization frequency of the video signal. Thereby, it is possible to prevent the pulse signals from interfering with the vertical / horizontal synchronization frequency, and to eliminate the screen flicker.
[0021]
Furthermore, the present invention provides a liquid crystal display device that suppresses occurrence of flicker, beat interference, audio noise, and beat noise on the display screen by realizing a liquid crystal display having the above-described light control device. It is to provide.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the embodiment of the light control device of the present invention described below is incorporated as a backlight light control device in various liquid crystal displays.
[0023]
FIG. 1 is a block diagram schematically showing a configuration of a light control device according to an embodiment of the present invention.
[0024]
In FIG. 1, a light control device according to the present embodiment includes a liquid crystal panel 102 including a backlight 101 that constitutes a display screen unit, an AC adapter 103 that converts an external commercial power source into an appropriate DC power source, and a lithium battery. A battery 104 made of an ion storage battery and a microcomputer (microcomputer) 105 that incorporates a microprocessor and controls each component in the apparatus are included.
[0025]
The light control device of the present embodiment further includes a switch circuit 111 for turning on / off the voltage supplied from the AC adapter 103 to the battery 104, driving of the device by an external power source by the AC adapter 103, and a battery by the battery 104. A power switch 112 for switching between driving and a regulator 113 for rectifying the voltage supplied from the AC adapter 103 or the battery 104 to be used for the liquid crystal panel 102, by the AC adapter 103 or the battery 104. Electric power for driving the liquid crystal panel 102 is supplied.
[0026]
The light control device according to the present embodiment further includes an inverter for converting the high frequency voltage of several tens of kilohertz to several hundreds of kilohertz and supplying the same to the backlight 101 using the direct current voltage supplied from the AC adapter 103 or the battery 104 as a trigger. Circuit 114 and a dimming pulse generation circuit 115 for adjusting the voltage supplied to the backlight 101 by inputting the dimming pulse to the inverter circuit 114. The dimming function can be used.
[0027]
The light control device of the present embodiment further supplies the battery 104 with the battery voltage detection means 116 for detecting the voltage of the battery 104 and the voltage value of the battery 104 detected by the battery voltage detection means 116. Includes a control means 117 for controlling the charging voltage to be generated in the switch circuit 111 and a charging pulse generation circuit 118 for generating a charging pulse for performing pulse charging on the battery 104, and pulse charging the battery 104. By doing so, the charging voltage is maintained within a predetermined range.
[0028]
The operation of the light control device of the present embodiment configured as described above will be described.
The light control device of this embodiment can be operated both when the external power supply is supplied and when it is not supplied. When the voltage is supplied from the AC adapter 103, the power switch 112 is connected to the terminal 112a on the AC adapter side. When the voltage is not supplied from the AC adapter 103, the power switch 112 is connected to the terminal 112b on the battery side. Assume that you are connected. The power switch 112 is switched by the microcomputer 105.
[0029]
Now, consider a case where the power switch 112 is connected to the terminal 112a on the AC adapter side and the liquid crystal display operates with power supplied from the AC adapter. The voltage supplied by the AC adapter is converted into a predetermined voltage by the regulator 113 through the power switch 112 and then supplied to the microcomputer 105 and the inverter circuit 114.
[0030]
Here, based on the output signal of the control means 119 inside the microcomputer 105, the dimming pulse generation circuit 115 generates a dimming pulse with a predetermined frequency (100 to 400 Hz in this embodiment) to control the inverter circuit 114. To do.
[0031]
The inverter circuit 114 uses the dimming pulse as a trigger to convert the DC voltage from the regulator 113 into a predetermined high frequency voltage (40 K to 200 KHz), and supplies this high frequency voltage to the backlight 101.
[0032]
FIG. 2 is a diagram illustrating a configuration example of the inverter circuit 114 of the present embodiment. The circuit shown in FIG. 2 is a generally known inverter circuit, and the inverter circuit 114 of the present embodiment is not limited to this configuration example.
[0033]
In FIG. 2, a power source 201 corresponds to the DC voltage supplied from the regulator 113 in FIG. 1, and a fluorescent tube 202 corresponds to the backlight 101 in FIG.
[0034]
Referring again to FIG. 1, in the dimming device of this embodiment, the dimming pulse generated by the dimming pulse generation circuit 115 is input to the inverter circuit 114, whereby the high-frequency voltage supplied to the backlight 101 is periodically changed. It can be turned on / off. In the present embodiment, the frequency of the dimming pulse on / off (dimming duty) is 100 to 400 Hz.
[0035]
This dimming pulse is input to the terminal S1 of the inverter circuit shown in FIG. 2 and passes through a PWM (Pulse Width Modulation) dimming circuit unit 203 based on the DC voltage from the power source 201 to the fluorescent tube 202 ( The high-frequency voltage supplied to the backlight 101) is turned on / off at a constant cycle.
[0036]
On the other hand, the DC voltage from the AC adapter 103 is also supplied to the battery 104 through the switch circuit 111. At this time, the battery voltage detection means 116 detects the charging voltage of the battery 104 and outputs the detected value to the control means 117. The control means switches on / off the voltage supplied to the battery 104 by controlling the switch circuit 111 in accordance with the detected charging voltage of the battery 104. Thus, the charging voltage of the battery 104 is maintained within a predetermined range.
[0037]
In the light control device of the present embodiment, the voltage supplied to the battery 104 is periodically turned on / off in the switch circuit 111 by inputting the charge pulse generated by the charge pulse generation circuit 118 to the control means 117. It can be made to. In the present embodiment, the on / off frequency of the charging pulse is 100 to 400 Hz, which is the same frequency as the dimming pulse.
[0038]
In this embodiment, the on / off frequency of the charging pulse is equal to the frequency of the dimming pulse, but at least when the dimming pulse is operating, the frequency of the charging pulse and the dimming The frequency of the pulse may be the same. For example, when the dimming pulse is not activated, such as when the backlight is turned off, the generation frequency of the charging pulse may be different from the frequency of the dimming pulse.
[0039]
FIG. 3 is a graph showing temporal changes in the voltage of the battery 104 and the charging current flowing through the battery 104 when the battery 104 is charged by the charging pulse in the light control device of the present embodiment.
[0040]
In FIG. 3, since the voltage of the battery 104 is equal to or lower than a predetermined reference value at the start of charging, the control unit 117 supplies the voltage from the AC adapter 103 to the battery 104 as it is. Thus, upon detecting that the voltage of the battery 104 has reached the start voltage value V _L of the ON period when pulse charging is performed, the control means 117 performs pulse charging based on the charging pulse input from the charging pulse generation circuit 118. The battery is charged until the battery voltage reaches the charge end voltage VH during the ON period when the battery voltage is pulse charged.
[0041]
Certain time the voltage of the battery 104 from reaching the V _L (T _1), for supplying a voltage from the AC adapter 103 to the battery 104 (charging pulse ON). When the voltage of the battery 104 reaches V _H after the lapse of a certain time (T ₁ ), the voltage supply to the battery 104 is stopped for a certain time (T ₂ ) (charging pulse off). After the elapse of a certain time (T ₂ ), the voltage of the battery 104 has become _VL again. Therefore, the charging pulse is turned on again, and the voltage is supplied for a certain time (T ₁ ). Subsequently, the charging pulse is turned off again, and the voltage supply is stopped for a certain time (T ₂ ).
[0042]
By repeating the above operation, the voltage of the battery 104 is maintained between _VL and _VH , and the deterioration of the battery capacity due to overcharging is suppressed. Note that, for a certain period of time (T ₁ and T ₂ ), the charging voltage of the battery 104 is within a desired range (between V _L and V _H) based on the voltage supplied from the AC power source or the charging characteristics of the battery 104. ) To be a predetermined value.
[0043]
Next, the phase of the dimming pulse for dimming the backlight 101 and the charging pulse for charging the battery 104 will be described.
[0044]
FIG. 4 is a graph showing the waveforms of the dimming pulse and the charging pulse (charging current) generated in the dimming device of this embodiment along the time axis. In the light control device of the present embodiment, both the light control pulse and the charge pulse are rectangular pulses, the frequencies are equal, and each pulse has the same ON time and OFF time (light control duty 50%). It is an example. .
[0045]
As shown in FIG. 4, in the dimming device of the present embodiment, the phase of the dimming pulse and the phase of the charging pulse (shown in FIG. 4 as a charging current for easy understanding of the phase relationship between the two) These pulses are generated so that they are just inverted. Therefore, operate each pulse generation circuit so that the dimming pulse is turned off when the charging pulse is on (T ₁ ) and the dimming pulse is turned on when the charging pulse is off (T ₂ ). I am letting.
[0046]
Specifically, the control means 119 shown in FIG. 1 reads the voltage of the battery 104 detected by the battery voltage detection means 116, and when the charging pulse of the battery 104 is turned off, that is, the battery voltage in FIG. The dimming pulse generation circuit 115 is controlled so that the dimming pulse is turned on when _VH is reached.
[0047]
FIG. 5 is a diagram showing the relationship between each pulse phase and the power load applied to the entire dimming device when the phase of the dimming pulse and the charging pulse is controlled as described above. In the dimming device of this embodiment, as described above, the phase of the dimming pulse and the phase of the charging pulse are just inverted, so that the power load applied to the entire dimming device has a substantially constant value. I understand.
[0048]
According to the light control device of the present embodiment described above, it is possible to greatly suppress fluctuations in the power load applied to the entire light control device by inverting the phases of the light control pulse and the charge pulse. Thereby, generation | occurrence | production of the noise by the fluctuation | variation of a power supply load can be suppressed, and generation | occurrence | production of the beat by the frequency interference of a light control pulse and a charge pulse can be prevented.
[0049]
In addition, since fluctuations in the power supplied to the light control device are reduced, it is possible to save power and to reduce the size of the AC adapter.
[0050]
In the above embodiment, the dimming pulse and the charging pulse are rectangular pulses having the same frequency. However, the dimming pulse and the charging pulse used in the dimming device of the present invention are not limited thereto.
[0051]
For example, as shown in FIG. 6, the falling of the charging pulse may be made gentle and the rising of the dimming pulse that follows this may be made gentle. (Takes longer delay time).
[0052]
Thereby, it is possible to suppress the fluctuation of the power supply load when shifting from the falling edge of the charging pulse to the rising edge of the dimming pulse. In the rectangular waveform as shown in FIG. 4, for example, when the falling edge of the charging pulse and the rising edge of the dimming pulse are slightly overlapped, a very large power load is applied to the entire dimming device. However, if the example shown in FIG. 6 is used, such a situation can be avoided.
[0053]
FIG. 6 shows an example in which the falling edge of the charging pulse and the rising edge of the subsequent dimming pulse are moderated. Similarly, the falling edge of the dimming pulse and the subsequent rising edge of the charging pulse are shown. It can be considered to be loose. Therefore, both the charging pulse and the dimming pulse may have waveforms that rise and fall gently.
[0054]
In the dimming circuit of this embodiment, the dimming pulse and the charging pulse are both set at a frequency different from either the vertical synchronizing frequency or the horizontal synchronizing frequency of the video signal. This suppresses interference between the vertical / horizontal synchronization signal applied to the liquid crystal panel and the dimming and charging pulses, thereby preventing flickering and improving the quality of the liquid crystal display device.
[0055]
The light control device of the present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the gist of the present invention.
[0056]
In particular, the light control device of the present invention can be applied to a backlight type or front light type liquid crystal display device having a liquid crystal display, or any electric device that performs light control and lighting control of a general lamp. The liquid crystal display device using the light control device of the invention can suppress the occurrence of screen flicker, beats on the screen, and the generation of voice noise and beat sound.
[0057]
In a battery-driven electric device equipped with a dimmer, dimming is possible over a wide driving range from when the output voltage of the battery drops from a high voltage value immediately after charging to a low voltage value near where the electric device shuts down. It is possible to provide a stable electric device that is not affected by the influence of a pulse.
[0058]
【The invention's effect】
As described above, according to the light control device of the present invention and the liquid crystal display device using the same, in the light control device of the liquid crystal display, the backlight light control circuit and the battery pulse charging circuit operate simultaneously. Even when the power is on, it is possible to control so that the power supply load of the entire liquid crystal display does not fluctuate greatly.
[0059]
In addition, in a liquid crystal display device that is equipped with a battery and is driven by the battery alone or driven by the battery alone, by suppressing fluctuations in the power supply, stable adjustments that suppress the generation of screen flicker, screen beats, audio noise, and roaring noise. It is possible to provide an optical device and a high-quality liquid crystal display device using the same.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing a configuration of a light control device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of an inverter circuit of a light control device according to an embodiment of the present invention.
FIG. 3 is a graph showing changes over time in battery voltage and charging current when the battery is charged by a charging pulse in the light control device according to the embodiment of the present invention.
FIG. 4 is a graph showing waveforms of a dimming pulse and a charging pulse generated along a time axis in the dimming device according to the embodiment of the present invention.
FIG. 5 is a diagram illustrating a relationship between a pulse phase of each of a pulse and a charge pulse and a power load applied to the entire device in the light control device according to the embodiment of the present invention.
FIG. 6 is a diagram illustrating waveforms of a dimming pulse and a charging pulse used in a dimming device according to another embodiment of the present invention.
FIG. 7 is a diagram showing the relationship between the phase of each charging voltage and dimming pulse and the power load applied to the entire device in a conventional liquid crystal display device.
[Explanation of symbols]
101 Backlight
102 LCD panel
103 AC adapter
104 battery
105 microcomputer
111 Switch circuit
112 Power switch
112a, 112b Power switch terminal
113 Regulator
114 Inverter circuit
115 Dimming pulse generator
116 Battery voltage detection means
117 Control means
118 Charge pulse generator
119 Control means
201 power supply
202 fluorescent tube
203 PWM dimming circuit

Claims (5)

A dimming pulse generating means for generating a dimming pulse for adjusting a voltage supplied to the light;
Charging pulse generating means for generating a charging pulse for adjusting the voltage supplied to the battery,
The dimming device in which the dimming pulse and the charging pulse have phases opposite to each other. The dimming device according to claim 1, wherein the dimming pulse and the charging pulse are rectangular pulses. The dimming device according to claim 1 or 2, wherein the frequency of the dimming pulse and the charging pulse is within a range of 100 to 400 Hz. 4. The device according to claim 1, wherein each of the dimming pulse and the charging pulse has a frequency different from any of a vertical synchronization frequency and a horizontal synchronization frequency of the video signal. Dimmer. A liquid crystal display device comprising the light control device according to claim 1.

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