JP3935058B2 - Backlight device and liquid crystal display device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lighting device capable of battery operation, and more particularly to a backlight device capable of ensuring a certain luminance.
[0002]
[Prior art]
There is a power supply control device that controls an inverter circuit for a backlight used in a liquid crystal display device or the like. In this device, when the voltage of the input power supplied to the power circuit of the inverter circuit fluctuates, the power circuit processes the conversion signal for converting the input power to the output power according to the fluctuation, and the output power A technique for preventing fluctuation and keeping the output of an inverter circuit constant is disclosed (for example, see Patent Document 1).
[0003]
Liquid crystal display devices that place importance on portability are also being developed by driving a battery (such as a rechargeable battery or a dry battery). As shown in FIG. 6, there is also an automatic dimming circuit that extends the operation duration of the backlight lighting circuit. This automatic dimming circuit includes an inverter circuit including a switching transistor Q1, oscillation transistors TR1 and TR2, a resonant capacitor C1, a transformer T1, and a lamp L, mainly a counter IC1, and a comparator. The light control circuit T including the IC 2 and the battery BT1 are configured.
[0004]
In this circuit, when a constant voltage is applied by the battery BT1, 2 of the transformer T1 is generated by an oscillation phenomenon including a resonance capacitor C1 and a primary side winding of the transformer T and the alternating switching of the oscillation transistors TR1 and TR2. An AC waveform is generated in the next winding. In order to cause oscillation drive, it is necessary to apply a predetermined voltage to the base terminals of the oscillation transistors TR12 and TR2. A general duty dimming control method can be realized by adjusting the base voltage application period ratio. Therefore, the timing at which oscillation drive is caused by applying a voltage signal having a desired duty ratio between the collector and base of the switching transistor Q1 (frequency is a frame frequency (about 60 Hz or more) at which human eyes do not feel flicker). The brightness of the backlight is controlled. That is, a pulse is output in accordance with a duty ratio at a constant voltage (Vout). Such a method is called a duty light control method. The duty ratio is 100% if it is illuminated all the time, and the duty ratio is 0% if it is extinguished all the time. For example, when the duty ratio is X, the pulse width: T is T = X × Tmax, where Tmax is the pulse period when X = 100%.
[0005]
The light control circuit determines the duty ratio X of this signal. As shown in FIG. 6, a reference voltage having a constant value is preliminarily applied to one terminal (+ terminal) of the comparator IC2, and the other terminal (− A voltage related to the battery BT1 is applied to the terminal. The output of the comparator IC2 is input to the clear CLR terminal of the counter IC1, and the QE terminal of the counter is input to the base terminal of the switching transistor Q1.
[0006]
According to the circuit configuration shown in FIG. 6, when the battery voltage value falls below the reference voltage value, the output of the comparator IC2 transitions from the low voltage state (Low) to the high voltage state (High), and the clear terminal of the counter IC1 By being input, the clock input of the counter IC 1 is divided, and the output of the QE terminal is output with a certain duty ratio. As a result, since the inverter circuit is driven in the low power consumption mode, a means for reducing the power consumption of the battery and extending its operation duration is also disclosed (for example, see Patent Document 2).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-308870
[Patent Document 2]
Japanese Patent No. 3256008
[0008]
[Problems to be solved by the invention]
In Patent Document 1 described above, a triangular wave signal whose voltage increase rate changes in accordance with voltage fluctuations of the input power supply is generated, and a driving pulse signal applied to the inverter circuit in accordance with the time when the voltage of this triangular wave signal reaches the threshold voltage. The luminance of the backlight is adjusted by changing the duty ratio.
[0009]
Specifically, two comparison signals of a DC signal that changes according to the duty ratio of the triangular wave signal and the dimming signal are created from the dimming signal, and the DC signal that changes according to the power supply voltage is used as a threshold in the comparator. A drive pulse of the inverter circuit is created by slicing a predetermined level of the triangular wave signal.
[0010]
However, Patent Document 1 does not describe how to generate a dimming pulse in accordance with individual changes in the power supply voltage, for example, changes with time or drop characteristics of the power supply voltage.
[0011]
In addition, the above-mentioned Patent Document 2 is a document disclosing means for realizing a longer battery life and power saving in order to extend the battery operation duration in a battery-driven device. In the case of emphasis, there is a demand for ensuring sufficient luminance. As described in Patent Document 2, when a backlight drive control circuit that emphasizes the extension of the battery life is used, the impedance of the backlight drive circuit does not change so much, so that the input current also decreases as the battery voltage decreases. There is a problem that the tube current flowing in the fluorescent tube decreases and the luminance decreases sequentially. In addition, when designing so that the screen brightness does not decrease below the desired brightness even after long-term use, it is necessary to design the screen brightness at the initial stage of driving higher than the desired brightness. Accordingly, there is a problem that the power consumption of the battery increases as much as it is lit at a brightness higher than necessary, and it is difficult to use the battery efficiently.
[0012]
An object of the present invention is to provide a backlight device capable of preventing a decrease in luminance with respect to various changes with time accompanying a decrease in output voltage of a battery.
[0013]
[Means for Solving the Problems]
The illuminating device of the present invention controls the drive period of the light source lighting device by gradually increasing the duty ratio of the dimming signal in accordance with the time-dependent decrease in the detected output voltage value of the battery, thereby controlling the brightness of the light source. It has a function to maintain.
[0014]
According to one aspect of the present invention, a backlight unit including a light source, a light source lighting circuit that turns on the light source, a dimming pulse signal generating unit that generates a dimming pulse signal for controlling the light amount of the light source, A battery power source for driving the light source lighting circuit; a voltage detection circuit for detecting an output voltage from the battery power source; and a time-dependent output voltage drop of the battery power source detected by the voltage detection circuit. There is provided a backlight device including a control unit that sequentially varies a duty ratio of the dimming pulse signal so as to keep current consumption substantially constant.
[0015]
Further, the voltage detection circuit divides the drive voltage range of the battery power source into a plurality of voltage ranges, and selects a voltage range suitable for the current value of the battery power source among the divided voltage ranges. Setting means for setting the battery power supply voltage, a determination circuit for determining whether or not the battery power supply voltage is within the reference voltage range, and the battery power supply voltage when the current value of the battery power supply voltage is out of the reference voltage range. Reference voltage range switching means for switching to a new reference voltage range including the current value of the current, and the dimming pulse signal generating means generates a dimming pulse signal having a duty ratio corresponding to the new reference voltage range It is preferable to do this.
[0016]
According to the backlight device described above, since the duty ratio is appropriately selected according to the change with time of the battery power supply, the dimming signal can be finely adjusted.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In the present specification, the term “sequentially changing the duty ratio” means changing the duty ratio in order. In general, since the output voltage of the battery power supply changes in order (does not change discontinuously), it means that the duty ratio is changed (changed) in association with this.
[0018]
FIG. 2 is a diagram showing how the tube current fluctuates with the voltage drop (change) of the battery over time when the lighting device is driven by a battery, the horizontal axis is the drive time, and the vertical axis is the battery. Voltage. In general, a battery has a characteristic that an output voltage value decreases with time when used continuously (characteristic shown by a broken line in FIG. 2). Therefore, the tube current is also reduced and the luminance is lowered (characteristic indicated by the solid line L1 in FIG. 2).
[0019]
In order to reduce the change in luminance over time, the inventor considered the following technique. Hereinafter, a backlight device for liquid crystal display (illumination device) using the light control circuit according to the present embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of a backlight device including a light control circuit according to an embodiment of the present invention. As shown in FIG. 1, the dimming circuit according to the present embodiment includes a battery 1, an inverter circuit 2 used as a light source lighting device, a dimming signal generating means 3 for supplying a pulse waveform to the inverter circuit 2, and a battery. And a voltage detection circuit 4 for detecting the power supply voltage. The backlight device is a backlight unit 5 driven by the dimming circuit, and includes a backlight unit 5 having a light source (such as a fluorescent tube), an optical sheet, a light guide plate, and a housing (not shown). Yes.
[0020]
The feature of the dimming circuit shown in FIG. 1 is that means for compensating for a decrease in tube current of a fluorescent tube or the like due to a voltage drop accompanying a change with time explained in FIG. 2 is provided. More specifically, this means varies the duty ratio of the dimming signal in the dimming signal generating means 3 so as to maintain a certain tube current in accordance with the battery voltage value detected in the voltage detection circuit 4 ( FIG. 2 solid line L2). In this specification, the ratio of the period during which the inverter circuit 2 operates is defined as the duty ratio.
[0021]
Hereinafter, an example of a specific method of controlling the dimming signal will be described focusing on the function of the voltage detection circuit 4. The voltage detection circuit 4 includes a determination circuit 41, a control circuit 45, a control circuit 45 including a reference voltage range search circuit 42 / reference voltage range switching circuit 43, and an inverter 41 d provided therebetween. Contains.
[0022]
In the dimming circuit, the battery voltage is managed for each of a plurality of predetermined reference voltage ranges. The reference voltage range will be described with reference to FIG. As shown in FIG. 3, a plurality of voltage ranges A to H are provided, for example, in a plurality of stages with respect to a preset battery driving voltage range (range from Vmax to Vmin). Among these voltage ranges A to H, the voltage range including the battery voltage value being driven is selected as the reference voltage range. The determination circuit 41 monitors the vertical relationship between the upper limit value, the lower limit value, and the battery voltage value in any of the selected reference voltage ranges A to H, and adjusts a constant duty ratio corresponding to the reference voltage range. An optical signal is generated in the dimming signal generating means 3. If a desired duty ratio is designed for each voltage range so that the tube current is maintained as described above, the duty ratio characteristic that increases stepwise as the battery voltage decreases as shown in FIG. Is given.
[0023]
As shown in FIG. 1, the determination circuit 41 includes a first comparator 41a, a second comparator 41b, and an AND circuit 41c. The maximum voltage value in the reference voltage range selected from the voltage ranges A to H is V1, and the minimum voltage value is V2. V1 is input to the + terminal of the first comparator 41a, and the battery voltage V is input to the-terminal. V2 is input to the negative terminal of the second comparator 41b, and the battery voltage V is input to the positive terminal.
[0024]
The outputs of the first and second comparators 41a and 41b are respectively input to the input terminals of the 2-input AND circuit 41c, and the output of the 2-input AND circuit 41c is input to the dimming signal generation circuit 3, The signal is output to the input of the reference voltage range search circuit 42 and the reference voltage range switching circuit 43 via the inverter 41d. The maximum voltage value V1 and the minimum voltage value V2 in the reference voltage range switched by the reference voltage switching circuit 43 are input to the first comparator 41a and the second comparator 41b, respectively.
[0025]
When the battery voltage V is within the currently selected reference voltage range (when V2 <V <V1), “1” is output from each of the first and second comparators 41a and 41b. The When “1” is input to either of the two inputs of the AND circuit 41c, the AND circuit 41c outputs “1”, the dimming signal generating means 3 is driven by the battery voltage V, and a signal is output from the inverter 41d. Inverted and “0” is output to the reference voltage search circuit 42 and the reference voltage range switching circuit 43, so that the state is maintained as it is.
[0026]
When the battery voltage V deviates from the currently selected reference voltage range (when at least one of V2> V or V> V1 is satisfied), the first and second comparators 41a , 41b, “0” is output from at least one of them. When “0” is input to at least one of the two inputs of the AND circuit 41c, the AND circuit 41c outputs “0”, and the drive of the dimming signal generating means 3 by the battery voltage V is stopped. Since the signal is inverted by the inverter 41d and “1” is output to the reference voltage search circuit 42 / reference voltage range switching circuit 43, the reference voltage search circuit 42 / reference voltage range switching circuit 43 starts its operation. In other words, when the battery voltage V deviates from the reference voltage range due to a decrease over time, the determination circuit 41 transitions to its own OFF state (“0”, “1” via the inverter), whereby the reference voltage Is searched for a new voltage range including the current battery voltage. A detailed search method will be described later.
[0027]
When the search is completed, the reference voltage range switching circuit 43 switches the reference voltage range to a new reference voltage range, and at the same time, the determination circuit 41 works on the dimming signal generating means 3 by returning to the ON state. Thus, the dimming signal generating means 3 changes the dimming duty ratio based on a new reference voltage range or a voltage value including the new reference voltage range, and the inverter circuit 2 starts driving at a duty ratio corresponding to the new reference voltage range.
[0028]
The series of processes described above is repeated by the voltage change (drop) of the output voltage V from the battery 1, and gradually decreases each time the battery voltage reaches a predetermined voltage value (marked with ●) as shown in FIG. The tube current that has been increased gradually with the increase of the inverter driving period, and by repeating these processes, a constant tube current is maintained (solid line L2).
[0029]
Based on the design philosophy of setting the duty ratio of the dimming signal so as to lower the backlight lighting period when the battery voltage at the time of initial lighting is high and eliminating unnecessary power consumption in the method described above, The advantage that can be used effectively is also obtained. Then, the duty ratio control according to the voltage drop of the battery over time is adjusted so that there is no luminance fluctuation with time, and at the same time, the pace of power consumption can always be kept constant.
[0030]
Next, a backlight device including a dimming circuit according to a modification of the first embodiment of the present invention will be described with reference to FIGS. In the apparatus according to this modification, the operation start timing of the reference voltage range search circuit 42 is set after the battery voltage is detected a plurality of times. When this method is used, there is an advantage that the determination reliability of the determination circuit 41 is increased.
[0031]
When the battery voltage V reaches the lower limit value of the reference voltage range due to the drop of the battery voltage V, when the battery voltage V fluctuates up and down finely, an ON or OFF signal is output from the output terminal of the determination circuit 41. May be output irregularly, and the reference voltage range search circuit 42 may malfunction. It is necessary to increase the reliability of the determination circuit 41.
[0032]
Further, if extra power is consumed due to the extra operation of the reference voltage range search circuit 42, it is not efficient in terms of battery utilization efficiency. Therefore, the determination circuit 41 waits for a result of deviating from the reference voltage range with a certain certainty in a voltage fluctuation process such as a voltage drop of the battery, and the reference voltage switching function is operated. More specifically, a method is used in which the output signal of the determination circuit 41 is continuously read by a microcomputer or the like for a predetermined time, and the reference voltage range search circuit 42 is designed to operate when the output is OFF for a predetermined time or longer. be able to. This eliminates unnecessary operation of the reference voltage range search circuit 42 and allows the battery to consume power efficiently. The certain certainty here means that the certainty of deviating from the 100% reference voltage range is not required.
[0033]
Next, a backlight device including a light control circuit according to a second embodiment of the present invention will be described with reference to the drawings. In the present embodiment, the reference voltage range search circuit 42 (FIG. 1) uses a search method different from that of the first embodiment. In this embodiment, a region is sequentially searched from a reference voltage region that is close to the previous reference voltage region, and if there are two voltage regions that are the same distance from the previous reference voltage region, The search is started from the region on the low voltage side.
[0034]
As described with reference to FIG. 2, in the time variation characteristics of battery voltage in general battery driving, the voltage drops continuously. Therefore, even if the battery voltage does not have a discontinuous fluctuation characteristic such as a sudden fluctuation and the battery voltage deviates from the previous reference voltage range, the subsequent fluctuation target region is a region where the voltage range is adjacent to the immediately preceding reference voltage region. In particular, in many cases, the voltage range is one lower.
[0035]
Therefore, it is preferable that the search order when the reference voltage range search function operates is such that the voltage range close to the previous reference voltage range and a voltage range lower by one is the first. When searching for the previous reference voltage range first, the previous voltage range is searched second.
[0036]
With reference to FIG. 4, the search method (search order) according to the present embodiment will be specifically described. For example, when the battery voltage is detected in the voltage range C among the voltage ranges A to H in FIG. 3, the search order when the battery voltage is out of the voltage range C is as follows.
(C) (▲ 1 ▼) ⇒ D (▲ 2 ▼) ⇒ B (▲ 3 ▼) ⇒ E (▲ 4 ▼) ⇒ A (▲ 5 ▼) ⇒ F (▲ 6 ▼) ⇒ G (▲ 7 ▼) ⇒ H (▲ 8 ▼)
[0037]
There are two types of search methods: “jump search method” that specifies a voltage range to be searched so as to jump over the previous voltage range, and “order search method” that specifies an adjacent voltage range thereafter. is there. According to this embodiment, it is preferable that the former is performed first and the latter is performed later. In order to clarify this search order, a number from 1 to 8 is assigned to each voltage range A to H, and when the fluctuation of this number is seen, [“+1” → “−2” → “+3 "⇒" -4 "⇒" +5 "] ⇒ [" + 1 "⇒" +1 "], etc., [] on the left side of the arrow for jump search, and [] on the right side of the arrow for order search. The voltage range selected in this way depends on the regular variation of these numbers. Therefore, an example of a search order algorithm in which the search search order is performed in principle for every previous voltage range will be described with reference to FIG. As shown in FIG. 5, search means corresponding to all voltage ranges can be realized, and the search means can be controlled by software. A method of storing such a search order pattern uniformly in a memory for all voltage ranges or realizing it by an electric circuit (hardware) is also conceivable. However, when the number of voltage ranges is large, it is more preferable to control the search means by software in consideration of a memory shortage or an increase in the number of parts.
[0038]
More specifically, processing is performed with an algorithm according to the flowchart shown in FIG. In the memory, the number of searches (finally the number of searches at the start of the order search) N and the jump / order search switching determination index I reference voltage range allocation number X are set as initial values. The output terminal (Z) is turned off. Then, by judging these N and I, X is sequentially changed to select a voltage range. In particular, after “J = 1” is input because it is determined that the skip search is no longer possible, if the number of searches N is not counted, the positive / negative directionality of the sequential search is determined by the odd / even number of the numbers. As a judgment material, memory can be used effectively.
[0039]
Finally, when the output terminal (Z) of the determination circuit 41 is turned on again by selecting the corresponding voltage range, the reference voltage range is determined, and the operation of the search circuit 42 ends.
[0040]
The above operation will be described in detail. Processing starts in step S0. In step S1, the number of searches is set to an initial value (N = 0). In step S2, the search method switching determination is set to an initial value (J = 0). In step S3, the previous reference voltage range is set to X = 1, for example. In step S4, the selection voltage range is input to the determination circuit. In step S5, it is determined whether or not the determination circuit is on, that is, whether or not the battery voltage is within the reference voltage range. If it is determined in step S that the battery voltage is within the reference voltage range (Y), the reference voltage range is determined in step S6, and the process returns to step S5. It is continuously detected whether or not it is within the reference voltage range.
[0041]
If it is determined in step S5 that the battery voltage is not out of the reference voltage range, the process proceeds to step S15 via step S6, and the process is terminated. If it is determined in step S5 that the battery voltage is out of the reference voltage range, the process proceeds to step S7, where J = 0 (jumps or not) is determined. If J = 0, the process proceeds to step S8, and N = N + 1, and the process proceeds to step S9. In step S9, Y {X + N × (-1) ^N-1 } Is 1 or more and 8 or less. In this case, it is determined whether or not the voltage range is not exceeded by jumping. If it is determined in step S9 that the voltage range is not exceeded by jumping, the process proceeds to step S10, where X = X + N × (−1). ^N-1 And return to step S4.
[0042]
If it is determined in step S9 that the voltage range is exceeded due to the jump, the process proceeds to step S12, and it is determined whether N is an odd number. If N is an odd number, the process proceeds to step S13, X = X-1 (negative) is substituted, and the process returns to step S4. If N is not an odd number, the process proceeds to step S14, X = X + 1 (positive) is substituted, and the process returns to step S4. Thereafter, the same processing is continued.
[0043]
As a result, the reference voltage range can be continuously searched. The value of the reference voltage range X is preferably stored for the next search. By such a method, the search time can be shortened, and at the same time, the search means is not always operated, so that it is possible to suppress wasteful power consumption of the battery power source as much as possible.
[0044]
Next, a backlight device according to a third embodiment of the present invention will be described.
The backlight device according to the present embodiment has means for ensuring the search for the optimum reference voltage range. The battery power supply voltage has a property of gradually decreasing with respect to the elapsed time. Therefore, when the battery voltage slightly fluctuates up and down near the reference voltage range, the output from the output terminal of the judgment circuit becomes irregular and it is difficult to determine whether or not the reference voltage range switching function should be operated. There is also.
[0045]
Therefore, in the backlight device according to the present embodiment, it is determined that the determination of the determination circuit performed a plurality of times in the voltage fluctuation process such as the voltage drop of the battery power supply is out of the reference voltage range with a certain certainty. It is characterized by actually operating the reference voltage range switching function after waiting.
[0046]
More specifically, it is designed so that the output signal of the determination circuit 41 (FIG. 1) is continuously read by a microcomputer or the like for a certain period of time, and the dimming signal generating means 3 operates when the output is on for a certain period of time or longer. . Thereby, switching of an unnecessary voltage range can be prevented and battery power can be used without waste. As in the case of the second embodiment, the term “certain certainty” used here does not necessarily require a condition that the voltage is out of the 100% reference voltage range.
[0047]
As described above, in the backlight device according to each embodiment of the present invention, even if the battery voltage decreases with time, the time-dependent decrease in backlight luminance can be detected and suppressed in stages. A finer dimming signal can be created according to the slope of the individual discharge characteristics of the battery voltage. Furthermore, the number of extra parts can be reduced by software control, and the battery capacity of the battery power source can be used efficiently.
[0048]
As mentioned above, although demonstrated along this Embodiment, it cannot be overemphasized that this invention is not limited to these examples, and various deformation | transformation are possible. In addition to the backlight device, the present invention can be applied to various lighting devices. The number of batteries is not limited to one.
[0049]
For example, the backlight device described in the above embodiment can be applied to a portable liquid crystal television, a digital camera and a digital video camera provided with a liquid crystal monitor, a mobile phone, a PDA, and the like. Needless to say, the display form is not limited to the liquid crystal display device and can be applied to various display devices.
[0050]
【The invention's effect】
According to the present invention, it is possible to suppress a decrease in backlight luminance over time even when the battery voltage decreases over time.
[Brief description of the drawings]
FIG. 1 is a functional block diagram illustrating a configuration example of a backlight device according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of changes over time in battery voltage and tube current in the backlight device according to the embodiment of the present invention.
FIG. 3 is an example of a correspondence table between voltage ranges and dimming duty ratios used in the backlight device according to the embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of a reference voltage value search method for a backlight device according to an embodiment of the present invention.
FIG. 5 is a flowchart showing a flow of reference voltage value search processing of the backlight device according to the embodiment of the present invention.
FIG. 6 is a circuit diagram showing a configuration of an automatic dimming circuit for extending the operation duration of a conventional backlight lighting circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Battery, 2 ... Inverter circuit, 3 ... Dimming signal generation means, 4 ... Voltage detection circuit, 5 ... Backlight part, 41 ... Determination circuit, 41d ... Inverter, 42 ... Reference voltage range search circuit, 43 ... Reference voltage Area switching circuit, 45... Control circuit.

Claims (8)

A backlight unit including a light source;
A light source lighting circuit for lighting the light source;
A dimming pulse signal generating means for generating a dimming pulse signal for controlling the light amount of the light source;
A battery power source for driving the light source lighting circuit;
A voltage detection circuit for detecting an output voltage from the battery power supply;
The duty ratio of the dimming pulse signal is changed stepwise so as to keep the current consumption of the light source substantially constant according to the output voltage drop of the battery power supply with time detected by the voltage detection circuit. have a control unit,
Further, the voltage detection circuit includes:
A setting unit that divides the drive voltage range of the battery power supply into a plurality of voltage ranges, and sets a voltage range suitable for the current value of the battery power source as a reference voltage range among the plurality of divided voltage ranges;
A determination circuit for determining whether or not the battery power supply voltage is within the reference voltage range;
Reference voltage range switching means for switching to a new reference voltage range including the current value of the battery power supply voltage when the current value of the battery power supply voltage is out of the reference voltage range,
The backlight device, wherein the dimming pulse signal generating means generates a dimming pulse signal having a duty ratio corresponding to the new reference voltage range . 2. The backlight device according to claim 1 , further comprising optimum reference voltage range search means for searching for a reference voltage range suitable for the current value prior to the operation of the reference voltage range switching means. The optimum reference voltage range search means operates after the determination circuit repeatedly determines whether or not the battery power supply voltage has first deviated from the reference voltage range, and a similar result is obtained with a certain probability or more. The backlight device according to claim 1 or 2 . The optimum reference voltage region search unit, a backlight device according to claim 2 or 3, characterized in that the search operation for the optimum reference voltage region so as to sequentially away from the nearest reference voltage range. The backlight according to any one of claims 2 to 4, wherein the optimum reference voltage range search means performs a search operation for a voltage range that is next lower than the previous reference voltage range. apparatus. The search completion time of the optimum reference voltage range search means is the time when the voltage reference operation is confirmed with a certain certainty that may be the optimum reference voltage range as a result of performing the voltage detection work multiple times in each voltage range. The backlight device according to any one of claims 2 to 5 , wherein the voltage range can be reliably detected. The voltage-detection circuit includes a first comparator circuit for comparing the highest voltage and the battery voltage of said reference voltage region, and a second comparator circuit for comparing the lowest voltage and the battery voltage, the first and second When the battery voltage is between the lowest voltage and the highest voltage, a voltage in the current reference voltage range is supplied to the dimming signal generating means when the output of the comparison circuit of A determination circuit for determining whether or not a battery voltage deviates from between the lowest voltage and the highest voltage;
When the determination circuit determines that the battery voltage has deviated from between the lowest voltage and the highest voltage, the reference voltage range search unit is made to search for a new reference voltage range, and newly based on the search the highest voltage and the lowest voltage in any one of up to 6 claims 2, characterized in that it comprises a logic circuit portion for supplying to said second comparing circuit and the first comparator circuit in the obtained reference voltage range The backlight device described. The backlight device according to any one of claims 1 to 7 ,
A liquid crystal display device having a liquid crystal panel disposed in front of the backlight device.

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