JP2000292775A - Luminance control unit of back light for display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the luminance of a back light so as to become constant over the entire in-use temperature range by varying the rate of variation in pulse width up to convergence on target pulse width according to the value of the target pulse width. SOLUTION: This control unit is equipped with a transistor 5 which controls the electric power supplied to the back light 4 for liquid crystal panel, a temperature sensor 8 which detects the temperature of the back light 4 or its circumference, and a one-chip microcomputer 9 which performs pulse-width modulation control over the electrification time of the transistor 5 so as to obtain specific target luminance according to the temperature detected by the temperature sensor. When the one-chip microcomputer 9 varies the electrification time according to the detected temperature, the rate of variation in DUTY ratio up to convergence on a target DUTY is suppressed in a range wherein the target DUTY ratio is nearly 10% or nearly 90%. The luminance of the back light 4 can be controlled by PWM control so as to obtain constant luminance in standard use environment irrelevantly to the temperature variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the brightness of a backlight for a display device such as a liquid crystal monitor for a vehicle or outdoors, and more particularly to a device for a vehicle or outdoors used in a low to high temperature environment. That can control backlight of LCD monitor for LCD to have constant brightness
The present invention relates to a luminance control device for a backlight for a display device of a (Pulse Width Modulation) control method.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a structure of a conventional luminance control device for a backlight for a voltage control type display device disclosed in Japanese Patent Application Laid-Open Nos. 5-53522 and 1-227131. is there. In the figure, 15 is a temperature compensation circuit, 16 is a lighting circuit, and 17 is a backlight.

Next, the operation will be described. When the temperature compensation circuit 15 changes and outputs the magnitude of the DC voltage input thereto according to the temperature, the lighting circuit 16 converts the DC voltage into an AC voltage, and the backlight 17 controls the magnitude of this voltage. The lamp is illuminated with a brightness corresponding to the power of the applied AC voltage. This makes it possible to lower the brightness of the backlight 17 at high temperatures and suppress the temperature rise.

[0004]

Since the conventional brightness control device for a backlight for a display device is configured as described above, the brightness control is performed only in a range corresponding to the setting range of the magnitude of the DC voltage and the resolution. Can't do it. Therefore, when the brightness of the backlight for a display device such as an in-vehicle or outdoor liquid crystal monitor is controlled using this technology, the brightness and the temperature of the surroundings greatly change, and the brightness of the backlight is correspondingly changed. Since it is necessary to control the brightness in a fine and wide range of brightness, there is a problem that the brightness cannot be controlled to be constant regardless of the brightness and temperature.

[0005] Therefore, as a method of controlling the power supplied to the backlight to be large and fine, a pulse width modulation signal is generated, and thereby, a transistor provided on a power supply path to the backlight is controlled. It is possible to solve the problem.

However, a backlight control device for a display device of the PWM control method is configured as described above,
If the brightness of the backlight is controlled by the PWM control so that a constant brightness can be obtained regardless of the temperature change in the standard usage environment, the target DUTY ratio is particularly 10% or 90% at low temperatures. There is a problem that, when the PWM control is performed in a range close to the vicinity, the luminance change is visually recognized as flickering or the like.

Therefore, in an in-vehicle or outdoor liquid crystal monitor which is expected to be used in such a temperature range from a low temperature to a high temperature, the PWM control can be performed without causing flicker or the like over the entire use temperature range. Therefore, it was not possible to control the brightness of the backlight to be constant.

Further, it is conceivable that the rate of the luminance change due to the PWM control is shifted from the above setting. However, in such a case, the convergence time to the target luminance becomes longer in the ordinary temperature control. The stability of luminance will be impaired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can be used for an in-vehicle or outdoor liquid crystal monitor without deteriorating luminance stability at normal temperature or causing flicker at low temperature. Even if this is the case, the PWM can control the brightness of the backlight to be constant over the entire operating temperature range.
It is an object of the present invention to obtain a brightness control device for a backlight for a control display device.

[0010]

SUMMARY OF THE INVENTION A backlight control device for a display device according to the present invention includes a transistor for controlling power supplied to the display device backlight, and a display device backlight or a temperature around the transistor. And a control means for performing pulse width modulation control of the energization time of the transistor so that a predetermined target luminance is obtained according to the temperature detected by the temperature sensor. When the energizing time is changed in accordance with the above, the rate of change of the pulse width until the pulse width converges on the target pulse width is changed in accordance with the value of the target pulse width corresponding to the target luminance.

[0011] In the backlight brightness control device for a display device according to the present invention, the control means controls the detected temperature at the target brightness and the target D of the pulse for controlling the energization time of the transistor.
A first table indicating a correspondence relationship with the UTY ratio, and a target DU
A second table indicating a correspondence relationship between the TY ratio and the control amount of the DUTY ratio per one control time, and setting a target DUTY ratio according to the detected temperature based on the first table; The control amount of the duty ratio per one control time is set based on the table, and the duty ratio is changed for each control amount of the duty ratio.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a backlight of an in-vehicle liquid crystal monitor and a brightness control device for controlling the backlight according to Embodiment 1 of the present invention.

In the figure, 1 is a DC voltage terminal to which a DC voltage is input, 2 is an inverter transformer for converting the DC voltage into an AC voltage, and 3 is an oscillation for setting the frequency of the AC voltage output from the inverter transformer 2. The circuit 4 is a backlight of a vehicle-mounted liquid crystal monitor to which the AC voltage is supplied (backlight for a display device), and 5 is a DC voltage terminal 1
A P-type transistor disposed on a DC voltage path between the inverter and the inverter transformer 2, a choke coil 6, and a ballast capacitor 7;

Reference numeral 8 denotes a temperature sensor which is disposed close to the backlight 4 and detects the temperature of the backlight 4 or its surroundings. A one-chip microcomputer (control means) for outputting an energization control pulse to the base terminal of 5, a resistance value of the temperature detection sensor (thermistor) is converted into a voltage, and the temperature can be captured by the one-chip microcomputer 9. This is a voltage dividing resistor for making

FIG. 2 shows Embodiment 1 of the present invention.
FIG. 4 is a characteristic diagram showing a correspondence relationship between a detected temperature and a target DUTY ratio of an energization control pulse. In the figure, the horizontal axis is the detected temperature (T), the vertical axis is the target duty ratio (DUTY [n]), 1
1 is a characteristic curve D at the maximum emission luminance of the backlight 4.
UTY [MAX], 12 is a characteristic curve DUTY [MID] at the standard light emission luminance of the backlight 4, and 13 is a characteristic curve DUTY [M at the minimum light emission luminance of the backlight 4.
IN]. Data equivalent to these characteristic curves is stored in the one-chip microcomputer 9 as a first table.

FIG. 3 shows Embodiment 1 of the present invention.
FIG. 7 is a characteristic diagram illustrating a correspondence relationship between a target DUTY ratio and a control amount of the DUTY ratio per one control time. In the figure,
The horizontal axis is the target duty ratio (DUTY [n]), and the vertical axis is the duty ratio control amount R per control (DUTY [n]).
Is a DUTY ratio change rate (%) normalized by the maximum DUTY ratio control amount R, and 14 is a change rate characteristic curve set based on the characteristics of the backlight 4. As shown in the figure, in the first embodiment, the change rate of the pulse width is set to be suppressed in a range where the target duty ratio is around 10% or 90%. Is stored in the one-chip microcomputer 9 as a second table.

Next, the operation will be described. When an energization control pulse according to the initial setting is output from the one-chip microcomputer 9, the P-type transistor 5 connects the DC voltage terminal 1 to the inverter transformer 2 during a period when the transistor 5 is at a low level. The inverter transformer 2 converts the DC voltage into an AC voltage at a cycle corresponding to the oscillation frequency of the oscillation circuit 3, and the backlight 4 is turned on by the AC voltage. The choke coil 6 separates the oscillation signal of the inverter transformer 2 from the output voltage of the transistor 5 in an AC manner, and the ballast capacitor 7 supplies a high voltage to the backlight at the start of the backlight lighting, and after the backlight is turned on, It has a function to supply lighting sustaining voltage.

When the backlight 4 is turned on at a predetermined brightness, the one-chip microcomputer 9 operates the backlight 4 detected by the temperature sensor 8.
The pulse width control of the energization control pulse is started in accordance with the temperature of the liquid crystal panel and the brightness around the liquid crystal panel.

FIG. 4 is a flowchart showing a pulse width control operation executed at predetermined intervals in the one-chip microcomputer 9 according to the first embodiment of the present invention.
In the figure, ST1 acquires information such as the temperature detection signal and the brightness of the surroundings, and sets a target duty ratio DUTY [n] and a control amount R at the target DUTY ratio in light of the characteristic diagrams of FIGS. (DUTY [n]) is an initial setting step for specifying the duty ratio D [n] of the current energization control pulse at the target DUTY.
ST3 is a control direction judging step for judging whether or not the current energization control pulse is equal to or more than the target energization control pulse. ST4 is a subtraction processing step of subtracting the control amount from the DUTY ratio, and ST4 is a subtraction completion confirmation determining step of determining whether the DUTY ratio after the subtraction is still smaller than the target DUTY ratio. The above steps ST1 to ST4 are repeated until it is determined in the determination step ST4 that the duty ratio after the subtraction is equal to or more than the target duty ratio.

ST5 is a control direction determination step ST.
2 is an addition process step in which the control amount is added to the DUTY ratio of the current energization control pulse when the DUTY ratio of the current energization control pulse is equal to or greater than the target DUTY ratio. Is an addition end confirmation judging step for judging whether or not the DUTY ratio after the addition is still equal to or more than the target DUTY ratio. In this addition end confirmation judging step ST6, the DUTY after the addition is determined.
The above steps ST1, ST2, ST5, ST6 are repeated until it is determined that the ratio is smaller than the target duty ratio.

Further, ST7 is a step executed every time the above addition processing or subtraction processing is completed. When a power-off signal for a liquid crystal monitor or the like is input, ST7 is executed.
This is an end determination step for ending the PWM control.

Next, in the initial setting step ST1, the target duty ratio DU is referred to with reference to the characteristic diagrams of FIGS.
TY [n] and the control amount R (D
UTY [n]) will be described in detail.
First, the one-chip microcomputer 9 specifies a target brightness in a selection table set in advance according to the surrounding brightness and the like, and is shown as a plurality of characteristic curves 11, 12, and 13 in FIG. Select characteristic data from the first table. Next, a DUTY ratio at a temperature that matches the detected temperature (T) is selected from the characteristic data, and set as a target DUTY ratio DUTY [n].

Further, a DU matching the target DUTY ratio
The duty ratio change rate of the TY ratio is selected based on the characteristic curve of FIG. 3, and is set as the control amount R (DUTY [n]) based on this.

Accordingly, when the target duty ratio DUTY [n] is determined according to the current brightness and temperature, the control amount R (DUTY [n]) is automatically set accordingly, and the energizing time of the transistor 5 is set. Will change for each control amount. In particular, in the first embodiment, as shown in FIG. 3, the change rate (R (DUTY) of the pulse width in the range where the target duty ratio is around 10% or 90%.
Since [n]) / R) is set to be suppressed, the pulse width of the energization control pulse changes slowly at the target DUTY ratio within such a range, unlike in other cases. That is, the rate of change of the pulse width until the pulse width converges on the target pulse width changes according to the value of the target pulse width.

As described above, according to the first embodiment, the transistor 5 for controlling the power supplied to the backlight 4 for the liquid crystal panel, and the temperature sensor 8 for detecting the temperature of the backlight 4 or its surroundings. And a one-chip microcomputer 9 that performs pulse width modulation control of the energization time of the transistor 5 so that a predetermined target luminance is obtained according to the temperature detected by the temperature sensor 8. When the energization time is changed according to the detected temperature, the target DUT
In a range where the Y ratio is close to 10% or 90%, the rate of change (control amount) of the DUTY ratio until it converges to the target DUTY ratio is suppressed. While the brightness of the backlight 4 is set to be controlled by PWM control so that a constant brightness is obtained, the range in which the setting is visually recognized as flickering, that is, the target DUTY ratio is 10%
In the range of about 90%, there is an effect that the rate of change can be suppressed and the occurrence of the flicker can be suppressed.

Therefore, even when the brightness control device of the backlight 4 is used for a vehicle-mounted or outdoor liquid crystal monitor as in the first embodiment, flickering or the like occurs over the entire wide operating temperature range. And the backlight 4 can be controlled to have a constant brightness by PWM control.

Further, since the rate of change of the pulse width during the PWM control is not uniformly suppressed, the convergence time to the target luminance does not become long in the ordinary temperature control, and the luminance is controlled in a stable state. There is an effect that can be changed.

According to the first embodiment, the one-chip microcomputer 9 stores the first table indicating the correspondence between the detected temperature at the target luminance and the target DUTY ratio of the energization control pulse for controlling the energization time of the transistor 5. A second table showing a correspondence relationship between the target DUTY ratio and a control amount (change rate) of the DUTY ratio per one control time, and a target DUTY ratio corresponding to a detected temperature is determined based on the first table. The control amount (change rate) of the DUTY ratio per one control time is set based on the second table, and the control amount is set in a range where the target DUTY ratio is around 10% or 90%. Is reduced, so that the brightness of the backlight 4 is controlled by the PWM control so that a constant brightness can be obtained regardless of a temperature change in a standard use environment. While setting as Gosuru, there is an effect that can be controlled so as not to be visually recognized as such flicker luminance change when carrying out the PWM control at low temperatures.

[0029]

As described above, according to the present invention, a transistor for controlling power supplied to a display backlight, a temperature sensor for detecting the temperature of the display backlight or its surroundings, and Control means for performing pulse width modulation control of the energization time of the transistor so as to obtain a predetermined target luminance in accordance with the temperature detected by the temperature sensor, and the control means changes the energization time in accordance with the detected temperature In this case, the rate of change of the pulse width until the pulse width converges on the target pulse width is changed according to the value of the target pulse width corresponding to the target luminance, so that the target DUTY ratio becomes, for example, around 10% or 90%. By setting so that the rate of change of the pulse width is suppressed in such a range, a constant brightness can be obtained regardless of temperature changes in a standard usage environment. While set to control the brightness of the backlight by the PWM control to be an effect which can be controlled so as not to be visually recognized as such flicker luminance change when carrying out the PWM control at low temperatures.

Therefore, even when used in an in-vehicle or outdoor liquid crystal monitor which is expected to be used in such a temperature range from a low temperature to a high temperature, flickering or the like occurs over the entire use temperature range. Without happening, and
There is an effect that the brightness of the backlight can be controlled to be constant by the PWM control.

Further, since it is not necessary to uniformly suppress the rate of change of the pulse width during the PWM control, the convergence time to the target luminance does not become long in the ordinary temperature control, and the luminance is maintained in a stable state. There is an effect that can be changed.

According to the present invention, the control means includes the first table indicating the correspondence between the detected temperature at the target luminance and the target DUTY ratio of the pulse for controlling the energization time of the transistor; DUT per hour
A second table indicating a correspondence relationship between the Y ratio and the control amount, a target DUTY ratio corresponding to the detected temperature is set based on the first table, and one control time per control time is set based on the second table. Since the DUTY ratio control amount is set and the DUTY ratio is changed for each DUTY ratio control amount,
For example, by setting the second table so as to suppress the rate of change of the pulse width in a range where the target duty ratio is around 10% or 90%, a constant brightness can be maintained regardless of temperature changes in a standard use environment. That the brightness of the backlight is controlled by the PWM control so that the brightness can be obtained, and the brightness change when the PWM control is performed at a low temperature can be prevented from being visually recognized as flickering or the like. There is.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a backlight of a vehicle-mounted liquid crystal monitor and a brightness control device for controlling the backlight according to Embodiment 1 of the present invention;

FIG. 2 is a characteristic diagram showing a correspondence relationship between a detected temperature and a target DUTY ratio of an energization control pulse in the first embodiment of the present invention.

FIG. 3 shows a target DU according to the first embodiment of the present invention.
FIG. 9 is a characteristic diagram illustrating a correspondence relationship between a TY ratio and a control amount of a DUTY ratio per one control time.

FIG. 4 is a flowchart showing a pulse width control operation executed at predetermined intervals in the one-chip microcomputer according to the first embodiment of the present invention;

FIG. 5 is a block diagram illustrating a configuration of a conventional luminance control device for a backlight for a voltage control type display device.

[Explanation of symbols]

4. Backlight (backlight for display device), 5 transistor, 8 temperature sensor, 91 chip microcomputer (control means).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA10 NC44 NC50 NC57 NC59 NC65 ND02 ND07 ND37 ND44 ND49 NE10 3K098 CC23 DD21 DD35 EE08 EE31 EE32 EE37 FF06 FF13 5C006 AF52 BB29 BF15 BF31 BF37 BF38 FA41

Claims (2)

[Claims] 1. A transistor for controlling power supplied to a display device backlight, a temperature sensor for detecting a temperature of the display device backlight or its surroundings, and a predetermined target according to a temperature detected by the temperature sensor. And control means for performing pulse width modulation control on the energization time of the transistor so as to obtain luminance. When the energization time is changed in accordance with the detected temperature, the control means controls a target corresponding to the target luminance. A brightness control device for a backlight for a display device, wherein a change rate of a pulse width until the pulse width converges to the target pulse width is changed according to a value of the pulse width. 2. A control unit comprising: a target DU of a pulse for controlling a detected temperature at a target luminance and a conduction time of a transistor;
A first table showing the correspondence with the TY ratio, and a target DUT
A second table indicating a correspondence relationship between the Y ratio and a control amount of the duty ratio per one control time, wherein a target duty ratio corresponding to a detected temperature is set based on the first table; 2. The luminance of a backlight for a display device according to claim 1, wherein a control amount of a duty ratio per one control time is set based on a table, and the duty ratio is changed for each control amount of the duty ratio. Control device.