JP2013104926A - Power supply device, liquid crystal module and method for controlling power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a temperature rise in an internal circuit of a liquid crystal module and reduce cost in the liquid crystal module while maintaining the display quality.SOLUTION: A power supply device 10 that supplies power to a source driver 3 in a liquid crystal module 1 reduces a voltage value of an output voltage supplied to the source driver 3 and supplies the power to the source driver 3 when a current value of a current supplied to the source driver 3 exceeds a predetermined detection threshold.

Description

  The present invention relates to a power supply device that supplies power to a source driver in a liquid crystal module, a liquid crystal module, and a power supply method.

  Currently, in order to improve the display quality of moving images, the liquid crystal module is realized with double speed drive or quadruple speed drive. In the future, the development of “4k × 2k” displays having a pixel count of 4000 × 2000 and “8k × 4k” displays having a pixel count of 8000 × 4000 will advance, and the definition of liquid crystal panels will increase.

  In such a liquid crystal module, the processing load of the liquid crystal driver, particularly the source driver, the panel load driven by the source driver, and the increase in the number of source drivers increase the power consumption of the internal circuit of the liquid crystal module. Since the loss of power consumption is converted into thermal energy, the temperature of the liquid crystal module rises as the power consumption increases. As the temperature of the liquid crystal module increases, the reliability of the internal circuit of the liquid crystal module decreases.

  Here, the configuration of a liquid crystal module having a conventional analog power supply circuit is shown in FIG. 17, and a specific example of the temperature rise of the liquid crystal module will be described. As shown in FIG. 17, the liquid crystal module 101 includes a liquid crystal panel 102, a source driver 103, a gate driver 104, a gate driver VGon power supply circuit 105, a gate driver VGoff power supply circuit 106, and a source driver AVDD power supply circuit 107. As shown in FIG. 17, the liquid crystal module 101 has K gate drivers 104 and L source drivers 103 (K and L are arbitrary natural numbers).

  As shown in FIG. 17, the source driver AVDD power supply circuit 107 supplies power to the L source drivers 103. When the liquid crystal module 101 performs double speed drive or quadruple speed drive, the number of transitions of each source driver output is doubled or quadrupled. That is, since the number of times of charging / discharging the panel load increases, the power consumption of the source driver 103 is doubled or quadrupled, and the temperature rise of the source driver 103 is drastically increased.

  As described above, the temperature of the source driver 103 rises, and the driver IC (Integrated Circuit), the TCP (Tape Carrier Package), or the like may be damaged by its own heat.

  Conventionally, in order to prevent the source driver from being destroyed, a heat dissipation measure such as releasing heat to the chassis has been adopted by attaching a heat dissipation sheet to the source driver IC.

  In addition, in order to suppress the temperature increase of the source driver, a technique for suppressing the power consumption of the source driver has been developed. For example, Patent Document 1 discloses an output of a source driver so as to detect display data in which the amplitude of a voltage signal output from the source driver is maximized and to output a voltage necessary for displaying the display data. A technique for varying the voltage is described.

JP 11-175028 A (released July 2, 1999)

  As described above, in a liquid crystal module that performs processing at double speed driving or quadruple speed driving or a liquid crystal module having a high-definition liquid crystal panel, the temperature of the source driver or the like becomes very high during operation. In the case of suppressing the increase, there is a problem that the cost of the heat dissipation sheet or the like becomes very large.

  Further, even if the source driver is controlled to output the minimum necessary voltage using the technique described in Patent Document 1, it has a liquid crystal module or a high-definition liquid crystal panel that performs processing at double speed drive or quadruple speed drive. In the liquid crystal module, there is a problem that the source driver may be destroyed due to a temperature rise due to display processing of display data corresponding to the maximum drive voltage.

  Therefore, in order to suppress the temperature rise of the liquid crystal module, that is, to reduce the power consumption of the internal circuit of the liquid crystal module, it is conceivable to permanently reduce the power supply voltage supplied to the source driver. If the power supply voltage is permanently reduced, the luminance specification may not be satisfied, and the above problem cannot be solved simply by reducing the power supply voltage.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply that suppresses the temperature rise of the internal circuit of the liquid crystal module and reduces the cost of the liquid crystal module while maintaining display quality. It is to realize a method for controlling the apparatus, the liquid crystal module, and the power supply apparatus.

  In order to solve the above problems, a power supply device according to the present invention is a power supply device that supplies power to a source driver in a liquid crystal module, and a current value of a current supplied to the source driver has a predetermined detection threshold value. And detecting an active level while the current value exceeds the detection threshold, while generating an inactive level signal while the current value is below the detection threshold. It is characterized by comprising: current detection means for generating a detection signal; and voltage drop means for lowering the voltage value of the output voltage supplied to the source driver while the detection signal generated by the current detection means is in an active level. .

  According to another aspect of the present invention, there is provided a control method for a power supply device that supplies power to a source driver in a liquid crystal module in order to solve the above problem. A current value determination step for determining whether or not the current value exceeds a predetermined detection threshold; and when the current value determination step determines that the current value exceeds the detection threshold, the current value is supplied to the source driver And a voltage drop step for dropping the voltage value of the output voltage to be output.

  According to the above configuration, the power supply device reduces the voltage value of the output voltage supplied to the source driver when the current value of the current supplied to the source driver exceeds a predetermined detection threshold, and Supply power to the source driver. At this time, the source driver drives the liquid crystal panel based on the dropped output voltage.

  Here, the detection threshold is a current value that flows when the power consumption of the source driver becomes very large, such as when displaying a solid white image. In this case, when the power supply device decreases the voltage value of the output voltage when the current value exceeds the detection threshold, the voltage applied to the liquid crystal panel by the source driver decreases. Therefore, it is possible to suppress the power consumption of the source driver when displaying a white solid image. By suppressing the power consumption of the source driver, the temperature rise of the internal circuit of the liquid crystal module such as the source driver can be suppressed. Note that since the voltage applied by the source driver to the liquid crystal panel is reduced, the luminance is also reduced. However, the effect on the user's viewing is small in displaying a white solid image.

  Therefore, by changing the power supply voltage of the source driver according to the amount of supply current, the temperature rise of the internal circuit of the liquid crystal module is suppressed, and the cost of the liquid crystal module is reduced while maintaining the display quality. . Moreover, since the temperature rise of the internal circuit of the liquid crystal module can be suppressed, damage to the internal circuit due to heat can be prevented, and the reliability of the liquid crystal module as a product can be improved.

In addition, the power supply device according to the present invention, at a certain point in time, when the output level of the output maintenance signal generated by itself is an inactive level and the detection signal transitions from the inactive level to the active level, Output maintaining means for generating an output maintaining signal whose output level is an active level for a predetermined output maintaining time from a certain point in time,
The voltage drop means preferably drops the voltage value of the output voltage supplied to the source driver during a period when either the detection signal or the output maintenance signal is at an active level.

  According to the above configuration, the voltage drop unit is configured to at least the period of the output maintenance time when the current value of the current supplied to the source driver exceeds a predetermined detection threshold in a state where the voltage is not dropped, The state where the voltage value of the output voltage supplied to the source driver is lowered is maintained.

  Therefore, even when the current value of the current supplied to the source driver fluctuates in the vicinity of the detection threshold or when the current value changes periodically, the voltage drop means is connected to the source driver. The voltage value of the output voltage to be supplied is not frequently lowered or raised. Therefore, the flicker display can be prevented from occurring by changing the power supply voltage of the source driver in accordance with the supply current amount.

  The liquid crystal module according to the present invention preferably includes the power supply device and a source driver that receives power from the power supply device.

  According to said structure, the said liquid crystal module has an effect similar to the said electric power supply apparatus.

  A television receiver including the liquid crystal module is also included in the scope of the present invention.

  As described above, the power supply device according to the present invention detects whether or not the current value of the current supplied to the source driver exceeds a predetermined detection threshold, and the current value exceeds the detection threshold. On the other hand, an active level detection signal is generated, while a current detection means for generating an inactive level detection signal while the current value is below the detection threshold, and a detection signal generated by the current detection means Voltage drop means for dropping the voltage value of the output voltage supplied to the source driver during the active level period is provided.

  Further, the method for controlling the power supply apparatus according to the present invention includes a current value determination step for determining whether or not a current value of a current supplied to the source driver exceeds a predetermined detection threshold, and the current value determination step. A voltage drop step of dropping the voltage value of the output voltage supplied to the source driver when it is determined that the current value exceeds the detection threshold.

  Therefore, by changing the power supply voltage of the source driver according to the amount of supply current, the temperature rise of the internal circuit of the liquid crystal module is suppressed, and the cost of the liquid crystal module is reduced while maintaining the display quality. . Moreover, since the temperature rise of the internal circuit of the liquid crystal module can be suppressed, damage to the internal circuit due to heat can be prevented, and the reliability of the liquid crystal module as a product can be improved.

1 is a block diagram illustrating a main configuration of a liquid crystal module according to a first embodiment of the present invention. FIG. It is a figure which shows an example of the correspondence of the voltage which the source driver contained in the said liquid crystal module applies to a liquid crystal panel, and the gradation value which a liquid crystal panel outputs. It is a figure which shows an example of the correspondence of the gradation value which the said liquid crystal panel outputs, and the luminance value which the said liquid crystal panel outputs. It is a figure which shows an example of the output waveform of the voltage which the said source driver applies to a liquid crystal panel, when the said liquid crystal panel displays a white solid image. It is a figure which shows an example of the output waveform of the electric current detection circuit contained in the said liquid crystal module. It is a figure which shows an example of the specific structure of the said current detection circuit. It is a figure which shows another example of the specific structure of the said current detection circuit. It is a figure which shows an example of the specific structure of the voltage switching control circuit contained in the said liquid crystal module. It is a figure which shows another example of the specific structure of the said voltage switching control circuit. It is a flowchart which shows an example of the process which the power supply apparatus for source drivers contained in the said liquid crystal module performs. FIG. 7 is a block diagram illustrating a main configuration of a liquid crystal module according to a second embodiment of the present invention. It is a figure which shows an example of a specific structure of the timer circuit contained in the said liquid crystal module. It is a figure which shows an example of the output waveform of the electric current detection circuit contained in the liquid crystal module which concerns on 1st Embodiment. It is a figure which shows an example of the output waveform of the said timer circuit. It is a figure which shows another example of the output waveform of the said timer circuit. It is a flowchart which shows an example of the process which the power supply apparatus for source drivers contained in the liquid crystal module which concerns on 2nd Embodiment performs. It is a block diagram which shows a prior art and shows the principal part structure of a liquid crystal module.

<Outline of the present invention>
In a normally black liquid crystal panel, the voltage applied by the source driver to the liquid crystal panel when displaying a white solid image is maximized. That is, in the normally black liquid crystal panel, the power consumption is maximized when displaying a solid white image, and the temperature rise of the source driver is also maximized. In a liquid crystal module that performs processing at double speed driving or quadruple speed driving or a liquid crystal module having a high-definition liquid crystal panel, the source driver or the like may be destroyed by heat when displaying a solid white image.

  In general video such as television broadcasting, it is considered that there are few cases where white solid images continue for a long time. Also, when displaying a white solid image, it is considered that there is almost no effect on the display quality of the video even if the brightness is slightly reduced.

  Therefore, in the present invention, the voltage supplied to the source driver (source voltage) is not lowered permanently, but the source voltage is lowered only when displaying a white solid image where heat generation is a problem. Specifically, a current detection circuit that detects that a current corresponding to white solid image display data has flowed into the source driver power supply line is inserted, and the voltage switching control circuit is configured based on the output of the current detection circuit. Reduce the output voltage of the driver power supply circuit.

  Thus, by changing the power supply voltage of the source driver according to the amount of supply current, it is possible to suppress the temperature rise of the internal circuit of the liquid crystal module and reduce the cost of the liquid crystal module while maintaining display quality. it can. Moreover, since the temperature rise of the internal circuit of the liquid crystal module can be suppressed, damage to the internal circuit due to heat can be prevented, and the reliability of the liquid crystal module as a product can be improved.

  Hereinafter, specific embodiments of the liquid crystal module of the present invention will be described with reference to the drawings. In addition, since the liquid crystal panel currently used for a general liquid crystal display device is a normally black system, in the following, it is assumed that the liquid crystal panel included in the liquid crystal module is a normally black system, but the present invention is not limited to this. . The liquid crystal panel included in the liquid crystal module may be a normally white system.

<First Embodiment>
The first embodiment of the present invention will be described with reference to FIGS. 1 to 10 as follows.

[Configuration of LCD module]
The configuration of the liquid crystal module according to the first embodiment will be described with reference to FIG. As illustrated, the liquid crystal module 1 includes a liquid crystal panel 2, a source driver 3, a gate driver 4, a gate driver VGon power supply circuit 5, a gate driver VGoff power supply circuit 6, and a source driver power supply device 10. The liquid crystal module 1 may include other members such as a light source (backlight), but the description is omitted because it is not related to the features of the invention.

  The liquid crystal module according to the present invention is mounted on a display device such as a television receiver, for example.

  In the liquid crystal panel 2, liquid crystal molecules are sandwiched between glass substrates having transparent electrodes. The liquid crystal panel 2 displays an image by changing the direction of the liquid crystal molecules according to the voltage applied to the transparent electrode and controlling the light transmittance.

  On the glass substrate of the liquid crystal panel 2, scanning lines (gate lines) and data lines (source lines) are two-dimensionally wired vertically and horizontally, and transparent electrodes are arranged at the intersections of the scanning lines and the data lines. . In addition, on the glass substrate, subpixels corresponding to the transparent electrodes are arranged in a grid pattern.

  The liquid crystal panel 2 in this embodiment operates by an active matrix driving method, and each pixel is provided with an active element such as a thin film transistor (TFT). That is, the active element is turned on by the voltage applied from the scanning line, and charges corresponding to the voltage applied to the data line are accumulated.

  However, the liquid crystal panel 2 is not limited to the above. As will be described later, the liquid crystal panel 2 may be of any type as long as the gradation value of the image to be displayed changes according to the voltage applied from the data line.

  The source driver 3 is a circuit or IC that drives the liquid crystal panel 2 and applies a voltage to the sub-pixels through the data line based on the power supplied from the power supply device 10 for source driver. Specifically, the source driver 3 applies, to each data line, a voltage that is gradation according to a video signal received from the outside in accordance with an instruction from a timing controller (not shown).

  The liquid crystal module 1 includes one or more source drivers 3, and in the example illustrated in FIG. 1, the liquid crystal module 1 includes M source drivers 3 (M is an arbitrary natural number). The source driver 3 is connected to one or a plurality of data lines.

  The gate driver 4 is a circuit or IC for driving the liquid crystal panel 2 and scans scanning lines based on the power supplied from the gate driver VGon power supply circuit 5 and the gate driver VGoff power supply circuit 6. Specifically, the gate driver 4 applies the voltage to the active element through the scanning line based on the power supplied from the gate driver VGon power supply circuit 5 according to the instruction of the timing controller (not shown), and is in the “ON” state. Or, based on the power supplied from the VGoff power supply circuit 6 for the gate driver, a voltage is applied to the active element through the scanning line to turn it off.

  The liquid crystal module 1 includes one or more gate drivers 4. In the example illustrated in FIG. 1, the liquid crystal module 1 includes N gate drivers 4 (N is an arbitrary natural number). The gate driver 4 is connected to one or a plurality of scanning lines.

  The gate driver VGon power supply circuit 5 supplies power to the gate driver 4 to turn on the active element.

  The gate driver VGoff power supply circuit 6 supplies the gate driver 4 with power for turning off the active element.

  The source driver power supply apparatus 10 supplies power to the source driver 3 with a set source driver drive voltage. Here, the voltage value of the source driver drive voltage set by the source driver power supply device 10 is AVDD (unit: volts (V)). That is, the voltage value of the output voltage of the source driver power supply apparatus 10 is AVDD. In the initial setting, AVDD is set to 15.6V. The value of AVDD may be an arbitrary value and can be set as appropriate based on the characteristics of the liquid crystal panel 2, the source driver 3, and the like.

(Relationship between the amount of current supplied by the power supply device for the source driver and the image displayed on the liquid crystal panel)
Next, a mechanism in which the amount of current supplied by the source driver power supply device 10 changes according to an image (video) displayed on the liquid crystal panel 2 will be described with reference to FIGS. Here, as described above, it is assumed that the liquid crystal panel 2 is a normally black system and the source driver 3 applies a voltage by a dot inversion driving system. The output voltage AVDD of the source driver power supply apparatus 10 is assumed to be the initial setting value of 15.6V.

  The source driver 3 supplies charges to the pixel electrodes built in the liquid crystal panel 2 to charge them. An example of the correspondence relationship between the voltage Vlc applied to the pixel electrode by the source driver 3 and the gradation value output (displayed) by the liquid crystal panel 2 is shown in FIG. In FIG. 2, the vertical axis is a voltage value (V), and the horizontal axis is a gradation value. As shown in FIG. 2, the gradation value increases as the absolute value of the difference between the voltage Vlc applied to the pixel electrode by the source driver 3 and the intermediate voltage HVDD increases.

  Here, VH0 and VL0 shown in FIG. 2 are voltage values corresponding to the gradation value “0”, and VH255 and VL255 are voltage values corresponding to the gradation value “255”.

  The source driver 3 refers to each gradation value (digital value) of a video signal supplied from a control circuit (not shown) and responds to each gradation value within the range of voltage values output by the source driver power supply device 10. Set the voltage value (analog value).

  Specifically, the source driver 3 is a function having the reference voltage VREF as a variable, and the voltage values of VL255 to VH255 corresponding to the reference voltage VREF based on a function indicating the relationship between the gradation value and the voltage value. It functions as a DA converter that outputs. Further, the source driver 3 uses the table indicating the relationship between the gradation value and the voltage value, which is determined for each reference voltage VREF, instead of the above function, and the voltages of VL255 to VH255 corresponding to the reference voltage VREF. It may be expressed as having a function of specifying a value. For example, the source driver 3 outputs a value of 97% of the reference voltage VREF as VH255, outputs a value of 1% of the reference voltage VREF as VL255, and outputs the voltage values of VL255 to VH255 having a positive correlation with VREF. It can be set as the structure which outputs.

  Here, the reference voltage VREF of the gradation voltage is generated based on the output voltage AVDD of the power supply device 10 for source driver by a reference voltage generation circuit (not shown) such as an external DAC-IC or a resistance voltage dividing circuit. To do. The reference voltage generation circuit lowers the voltage value of the generated reference voltage VREF when the voltage value of the input AVDD decreases.

  That is, the output voltage AVDD of the source driver power supply device 10 and the output voltage Vlc (VL255 to VH255) of the source driver 3 are indirectly dependent, and the output voltage AVDD of the source driver power supply device 10 In synchronization with the voltage drop, the voltage value of the output voltage Vlc (VL255 to VH255) of the source driver 3 also drops.

  When the reference voltage VREF of the gradation voltage is generated from the power supply voltage of the source driver 3 (supply voltage of the source driver power supply device 10) using a step-down regulator, the step-down voltage is generated in the same manner as the source driver power supply device 10. It is preferable to provide a voltage switching control circuit in the regulator. As a result, the gradation voltage can be lowered in conjunction with a drop in the power supply voltage supplied to the source driver 3, and gradation abnormality can be suppressed.

  Further, the gradation value output from the liquid crystal panel 2 increases, and the luminance value output from the liquid crystal panel 2 also increases. An example of the correspondence between the two is shown in FIG. In FIG. 3, the vertical axis represents the luminance value and the horizontal axis represents the gradation value.

  Here, when displaying a solid white image on the liquid crystal panel 2, the source driver 3 alternately applies the voltage values VH255 and VL255 corresponding to the gradation value 255 to the capacitors of all the pixels (picture elements). An example of the waveform of the voltage value Vlc applied to the liquid crystal panel 2 by the source driver 3 at this time is shown in FIG.

  As described above, when charging / discharging is repeated at VL255 and VH255 having the maximum voltage difference with respect to the intermediate voltage HVDD with respect to the pixel electrodes of all the pixels, the power consumption of the source driver 3 is maximized. The increase in power supplied from the source driver 3 to the liquid crystal panel 2 means that the current output from the power supply device 10 for source driver that supplies the power to the source driver 3 increases. In other words, the power consumption of the source driver 3 increases as the supply current of the source driver power supply device 10 increases.

  Therefore, the current value of the current supplied by the source driver power supply device 10 is detected, and if the supply current is equal to or greater than a predetermined value, the output voltage AVDD of the source driver power supply device 10 is lowered to reduce the source driver power. It is possible to lower the VH255 that is linked to the output voltage AVDD of the supply device 10. Therefore, the power consumption of the source driver 3 can be reduced.

[Configuration of power supply device for source driver]
Next, a detailed configuration and function of the source driver power supply apparatus will be described. As shown in FIG. 1, the source driver power supply apparatus 10 includes a source driver AVDD power supply circuit 7, a current detection circuit (current detection means) 8, and a voltage switching control circuit (voltage drop means) 9.

  The source driver AVDD power supply circuit 7 generates a predetermined voltage from the input voltage VIN input to the liquid crystal module 1 and supplies a current to the source driver 3 with the generated voltage. In this embodiment, the AVDD power supply circuit for source driver 7 generates a voltage with a voltage value of 15.6V.

  The current detection circuit 8 detects whether or not the output current of the source driver AVDD power supply circuit 7 is equal to or greater than a predetermined current value (detection threshold), and changes the level of the output signal based on the detection result. is there. The current detection circuit 8 is disposed on a path between the source driver AVDD power supply circuit 7 and the source driver 3. The output signal of the current detection circuit 8 is input to the voltage switching control circuit 9. Here, the output signal of the current detection circuit 8 is referred to as a detection circuit output signal (detection signal).

  The output waveform of the current detection circuit 8 will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of an output waveform of the current detection circuit 8. As shown in FIG. 5, when the output current of the source driver AVDD power supply circuit 7 exceeds the detection level (detection threshold), the output level of the current detection circuit 8 changes from the High level to the Low level. Further, when the output current of the source driver AVDD power supply circuit 7 falls below the detection level (detection threshold), the output level of the current detection circuit 8 changes from the Low level to the High level.

  In the example shown in FIG. 5, the current detection circuit 8 changes the output level from the high level to the low level when the output current of the source driver AVDD power supply circuit 7 exceeds the detection level (detection threshold). However, it is not limited to this. The current detection circuit 8 may transition the output level from the Low level to the High level when the output current of the source driver AVDD power supply circuit 7 exceeds the detection level (detection threshold).

  Further, the detection threshold may be appropriately set to a current value that does not damage the source driver 3 or the like due to heat generation based on the characteristics of the liquid crystal module 1 such as the liquid crystal panel 2 or the source driver 3.

  A specific configuration of the current detection circuit 8 will be described with reference to FIGS. 6 and 7 are diagrams showing an example of a specific configuration of the current detection circuit 8.

  First, in the example illustrated in FIG. 6, the current detection circuit 8 includes a resistor 21 and a comparator 22. The resistor 21 is disposed on the path between the source driver AVDD power supply circuit 7 and the source driver 3. Two input terminals of the comparator 22 are respectively connected to both ends of the resistor 21, and a potential difference between both ends of the resistor 21 becomes an input value of the comparator 22. The output terminal of the comparator 22 is connected to the voltage switching control circuit 9. When the input value exceeds a predetermined detection threshold, the comparator 22 transitions the output level to the active level and outputs it.

  Specifically, when the current flowing through the resistor 21 increases, the potential difference between both ends of the resistor 21 increases. When a certain current or more flows through the resistor 21, the input value to the comparator 22 exceeds the detection threshold, and the comparator 22 changes the output level to the active level and outputs it.

  Next, in the example illustrated in FIG. 7, the current detection circuit 8 includes a resistor 23, a comparator 24, a resistor 25, and a resistor 26. The resistor 23 is disposed on a path between the source driver AVDD power supply circuit 7 and the source driver 3. One end of the resistor 25 is connected to a power source (not shown) that outputs a reference voltage that is higher than AVDD, and the other end is connected to the resistor 26. One end of the resistor 26 is connected to the resistor 25 and the other end is grounded. One end of the input terminal of the comparator 24 is connected to a terminal on the source driver 3 side of the resistor 23. The other end of the input terminal of the comparator 24 is connected between the resistor 25 and the resistor 26, and a voltage value obtained by dividing the reference voltage by resistance is input. When the potential on the source driver 3 side of the resistor 23 is lower than the potential between the resistor 25 and the resistor 26, the comparator 24 changes the output level to the active level and outputs it.

  Here, the voltage value of the reference voltage and the resistance values of the resistors 25 and 26 so that the voltage value obtained by dividing the reference voltage by resistance (the potential between the resistor 25 and the resistor 26) becomes a value lower than AVDD. Is set as appropriate.

  At this time, when the current flowing through the resistor 23 is small, the potential on the source driver 3 side of the resistor 23 is higher than the potential between the resistor 25 and the resistor 26, so the comparator 24 outputs the output level. Is output at the inactive level. On the other hand, when the current flowing through the resistor 23 increases and a current exceeding a certain level flows, the potential on the source driver 3 side of the resistor 23 is lower than the potential between the resistor 25 and the resistor 26, and the comparison is made. The device 24 changes the output level to the active level and outputs it.

  The voltage switching control circuit 9 controls the voltage value of the output voltage of the source driver AVDD power circuit 7 based on the detection circuit output signal (switching signal) input from the current detection circuit 8. Specifically, when receiving the active level detection circuit output signal from the current detection circuit 8, the voltage switching control circuit 9 reduces the output voltage of the source driver AVDD power supply circuit 7. When the voltage switching control circuit 9 receives the detection circuit output signal of the inactive level from the current detection circuit 8, the voltage switching control circuit 9 increases the output voltage of the source driver AVDD power supply circuit 7 (returns to the original voltage value).

  A signal input to the voltage switching control circuit 9 is referred to as a switching signal. That is, in the first embodiment, the detection circuit output signal is a switching signal.

  A specific configuration of the voltage switching control circuit 9 will be described with reference to FIGS. FIG. 8 and FIG. 9 are diagrams showing an example of a specific configuration of the voltage switching control circuit 9. 8 and 9 show a method of changing the feedback voltage for the source driver AVDD power supply circuit 7 as a voltage switching method.

  First, in the example illustrated in FIG. 8, the voltage switching control circuit 9 includes resistors 31, 32, and 33 and a changeover switch 34. One end of the resistor 31 is connected to the output terminal of the source driver AVDD power supply circuit 7, and the other end is connected to the resistor 32 and the resistor 33. One end of the resistor 32 is connected to the resistor 31 and the resistor 33, and the other end is grounded. One end of the resistor 33 is connected to the resistor 31 and the resistor 32, and the other end is connected to the changeover switch 34. Note that the resistance values of the resistors 31, 32, and 33 are R1, R2, and R3, respectively.

  The changeover switch 34 has one end connected to the resistor 33 and the other end grounded to the ground. Further, a feedback input terminal of the source driver AVDD power supply circuit 7 is connected between the resistor 31, the resistor 32, and the resistor 33. Here, it is assumed that the changeover switch 34 is disconnected when the switch signal is at the active level (turns the switch OFF) and is conductive when the switch signal is at the inactive level (turns the switch ON).

Here, when the feedback voltage input from the voltage switching control circuit 9 to the source driver AVDD power supply circuit 7 is VFB, when an active level switching signal is input to the voltage switching control circuit 9, the source driver AVDD power supply circuit. The voltage AVDD (on) output by 7 is
AVDD = VFB * (R1 + R2) / R2 = AVDD (on) (Formula 1)
The above (Formula 1) is obtained.

On the other hand, when an inactive level switching signal is input to the voltage switching control circuit 9, the combined resistance value Rp of the resistors 32 and 33 is
Rp = R2 * R3 / (R2 + R3) (Formula 2)
The above (Formula 2) is obtained. At this time, the voltage AVDD (off) output from the source driver AVDD power supply circuit 7 is:
AVDD = VFB * (R1 + Rp) / Rp = AVDD (off) (Formula 3)
(Equation 3) above.

  At this time, AVDD (on) <AVDD (off). Therefore, when the feedback voltage VFB generated by the voltage switching control circuit 9 is input to the AVDD power source circuit 7 for source driver, the voltage switching control circuit 9 receives the active level switching signal, and then the AVDD power source circuit 7 for source driver. Can be lowered from the initial value (AVDD (off)) to AVDD (on).

  Next, an example in which an N-channel FET (Field-Effect Transistor) 35 is used as a switch instead of the changeover switch 34 is shown in FIG. In this case, when a voltage exceeding the threshold is applied to the gate terminal of the FET 35, the switch is turned on, and when a GND level voltage is applied, the switch is turned off. That is, like the changeover switch 34, the FET 35 is disconnected when the switch signal is at the active level (turns the switch OFF), and conducts when the switch signal is at the inactive level (turns the switch ON).

[Processing of power supply device for source driver]
Next, processing executed by the source driver power supply apparatus 10 will be described with reference to FIG. FIG. 10 is a flowchart illustrating an example of processing executed by the source driver power supply apparatus 10.

  As shown in FIG. 10, the current detection circuit 8 detects whether or not the current value of the current supplied from the source driver AVDD power supply circuit 7 to the source driver 3 exceeds the detection threshold (S1). If the output current of the source driver AVDD power supply circuit 7 exceeds the detection threshold (YES in S1), the current detection circuit 8 outputs the detection circuit output signal to the voltage switching control circuit 9 with the output level set to the active level. To do.

  When receiving the active level detection circuit output signal from the current detection circuit 8, the voltage switching control circuit 9 decreases the voltage value of the output voltage of the source driver AVDD power supply circuit 7 (S2). Thereby, the power supply apparatus 10 for source drivers supplies electric power to the source driver 3 by using the voltage value lower than the initial value by a predetermined value as the output voltage.

  On the other hand, when the output current of the source driver AVDD power supply circuit 7 does not exceed the detection threshold (NO in S1), the current detection circuit 8 sets the output level to the inactive level and outputs the detection circuit output signal to the voltage switching control circuit 9. To do.

  Here, when the voltage switching control circuit 9 decreases the voltage value of the output voltage of the source driver AVDD power supply circuit 7 (YES in S3), the voltage switching control circuit 9 receives the inactivity received from the current detection circuit 8. Based on the level detection circuit output signal, the output voltage of the source driver AVDD power supply circuit 7 is raised, that is, returned to the original voltage value. Accordingly, the source driver power supply apparatus 10 supplies power to the source driver 3 using the initially set voltage value as the output voltage.

  The output current of the source driver AVDD power supply circuit 7 does not exceed the detection threshold (NO in S1), and the voltage switching control circuit 9 does not reduce the voltage value of the output voltage of the source driver AVDD power supply circuit 7. In this case (NO in S3), the voltage switching control circuit 9 receives the inactive level detection circuit output signal from the current detection circuit 8, and keeps the voltage value of the output voltage of the source driver AVDD power supply circuit 7 as the initial value. maintain.

<Second Embodiment>
The following describes the second embodiment of the present invention with reference to FIGS. For convenience of explanation, members having the same functions as those shown in the first embodiment are given the same reference numerals, and explanation thereof is omitted.

  In the liquid crystal module 1 according to the first embodiment, since the output voltage is increased or decreased depending on whether or not the current value exceeds the detection threshold, the current value fluctuates in the vicinity of the detection threshold, or the current value When the voltage changes periodically, the output voltage may drop or rise frequently. In this case, the screen flickers, so-called flicker display, which causes discomfort to the user.

  Therefore, in order to avoid such a situation, the liquid crystal module according to the second embodiment maintains that state for a certain period when the output voltage is once lowered. Specifically, the liquid crystal module 1a according to the second embodiment includes a source driver power supply device 10a instead of the source driver power supply device 10 of the liquid crystal module 1 according to the first embodiment. The liquid crystal module according to the second embodiment is otherwise the same as the liquid crystal module 1 according to the first embodiment.

  By providing the source driver power supply device 10a, flicker can be prevented from being generated. Hereinafter, the configuration and function of the source driver power supply apparatus 10a will be described in detail.

[Configuration of power supply device for source driver]
As shown in FIG. 11, the source driver power supply device 10 a includes a source driver AVDD power supply circuit 7, a current detection circuit 8 a, a voltage switching control circuit 9 a, and a timer circuit (output maintaining means) 11.

  The current detection circuit 8a is different from the current detection circuit 8 of the first embodiment only in that a detection circuit output signal is output to the timer circuit 11, and other functions and processes are the same as those of the current detection circuit of the first embodiment. Same as 8.

  The voltage switching control circuit 9a is different from the voltage switching control circuit 9 of the first embodiment only in that it receives a timer circuit output signal (switching signal) from the timer circuit 11, and other functions and processes are the same as those in the first embodiment. This is the same as the voltage switching control circuit 9 of the embodiment. In the second embodiment, the timer circuit output signal is a switching signal.

  When the output level of the counter output signal generated by the timer circuit 11 at this time is the inactive level, the timer circuit 11 receives a detection circuit output signal that transitions from the inactive level to the active level from the current detection circuit 8a. The counter output signal whose output level becomes the active level during the output maintaining time T is generated. The timer circuit 11 generates a timer circuit output signal (output maintaining signal) by taking the logical product of the detection circuit output signal received from the current detection circuit 8a and the generated counter output signal, and outputs the generated timer circuit output. The signal is output to the voltage switching control circuit 9a.

  A specific configuration of the timer circuit 11 will be described with reference to FIG. FIG. 12 is a diagram illustrating an example of a specific configuration of the timer circuit 11. As shown in FIG. 12, the timer circuit 11 includes an oscillator 41, a counter 42, and an AND circuit 43.

  The oscillator 41 generates an output signal having a predetermined frequency and outputs it to the counter 42.

  When the output level of the counter output signal output from the counter 42 is a non-active level at the present time, the counter 42 receives the detection circuit output signal that transitions from the non-active level to the active level from the current detection circuit 8a. The counter output signal is output. Further, the counter 42 outputs an active level counter output signal based on an input from the oscillator 41, then measures an output maintaining time T, and maintains an active level output for the duration of the output maintaining time T. When the output maintaining time T elapses, the output level is changed and a counter output signal having an inactive level is output. Further, the counter 42 outputs the generated counter output signal to the AND circuit 43.

  The AND circuit 43 generates a timer circuit output signal by taking the logical product of the detection circuit output signal received from the current detection circuit 8a and the counter output signal generated by the counter 42, and switches the voltage of the generated timer circuit output signal. Output to the control circuit 9a. That is, when the output level of either the detection circuit output signal or the counter output signal is an active level, the AND circuit 43 outputs an active level timer circuit output signal, and the output levels of the detection circuit output signal and the counter output signal are In the case of an inactive level, an inactive level timer circuit output signal is output.

  Next, the output waveform of the timer circuit 11 will be described with reference to FIGS. FIG. 13 is a diagram illustrating an example of an output waveform of the current detection circuit 8 of the liquid crystal module 1 according to the first embodiment. 14 and 15 are diagrams showing examples of output waveforms of the timer circuit 11. FIG.

  As shown in FIG. 13, in the liquid crystal module 1 according to the first embodiment, every time the output current of the source driver AVDD power supply circuit 7 exceeds the detection level (detection threshold), the output level of the current detection circuit 8 becomes High. The output level of the current detection circuit 8 changes from the Low level to the High level every time the output current of the source driver AVDD power supply circuit 7 falls below the detection level (detection threshold).

  As described above, when the output current of the source driver AVDD power supply circuit 7 frequently fluctuates the detection level, the output of the current detection circuit 8 also frequently changes, so the output voltage of the source driver power supply device 10 is frequently changed. Change. Since the output voltage supplied to the source driver 3 frequently changes, the luminance output from the liquid crystal panel 2 also changes frequently, so that the user appears to flicker.

  On the other hand, as shown in FIG. 14, in the liquid crystal module 1 a according to the second embodiment, the counter 42 outputs an active level counter output signal for the period of the output maintaining time T from the first rise of the output of the current detection circuit 8. In order to output, the timer circuit 11 outputs to the voltage switching control circuit 9a a timer circuit output signal that becomes an active level during the output maintaining time T from the first rise of the output of the current detection circuit 8.

  Therefore, in the liquid crystal module 1a according to the second embodiment, the output of the current detection circuit 8 frequently transitions because the output current of the source driver AVDD power supply circuit 7 frequently increases and decreases the detection level. However, since the voltage drop of the output voltage of the AVDD power source circuit 7 for the source driver is maintained at least for the period of the output maintaining time T from the first rise of the output of the current detection circuit 8, the occurrence of flicker display is suppressed. Can do.

  Since AND circuit 43 uses the logical product of the detection circuit output signal and the counter output signal as the timer circuit output signal, as shown in FIG. 15, the output of current detection circuit 8 should be at the active level when output maintaining time T has elapsed. For example, the output level of the timer circuit output signal is maintained at the active level until the output of the current detection circuit 8 falls after the output maintaining time T has elapsed.

[Processing of power supply device for source driver]
Next, processing executed by the source driver power supply apparatus 10a will be described with reference to FIG. FIG. 16 is a flowchart illustrating an example of processing executed by the source driver power supply apparatus 10a.

  As shown in FIG. 16, the current detection circuit 8 detects whether or not the current value of the current supplied from the source driver AVDD power supply circuit 7 to the source driver 3 exceeds the detection threshold (S11). Here, when the output current of the source driver AVDD power supply circuit 7 exceeds the detection threshold (YES in S11), the current detection circuit 8 sets the output level to the active level during the period when the output current exceeds the detection threshold. A detection circuit output signal is generated in the timer circuit 11 (S12). On the other hand, when the output current of the source driver AVDD power supply circuit 7 does not exceed the detection threshold (NO in S11), the current detection circuit 8 sets the output level to the inactive level during the period when the output current does not exceed the detection threshold. A detection circuit output signal is generated in the timer circuit 11 (S13). The current detection circuit 8 outputs the generated detection circuit output signal to the counter 42 of the timer circuit 11.

  When the counter 42 receives an active level detection circuit output signal from the current detection circuit 8, the output level of the counter output signal output by the counter 42 is an inactive level, and the received detection circuit output signal is inactive at the present time. It is determined whether or not the transition is from a level to an active level (S14). When the counter output signal is at an inactive level and the detection circuit output signal transitions from the inactive level to the active level at this time (YES in S14), the counter 42 is a period of the output maintaining time T from the current time. Then, a counter output signal for setting the active level is generated (S15). The counter 42 outputs the generated counter output signal to the AND circuit 43.

  The AND circuit 43 determines whether the output level of either the detection circuit output signal or the counter output signal is an active level (S16). When the output level of either the detection circuit output signal or the counter output signal is an active level (YES in S16), the AND circuit 43 outputs an active level timer circuit output signal to the voltage switching control circuit 9a.

  Upon receiving the active level timer circuit output signal (switching signal) from the AND circuit 43, the voltage switching control circuit 9a enters a voltage drop state in which the voltage value of the output voltage of the source driver AVDD power supply circuit 7 is reduced (S17). ). That is, in the initial state in which the voltage value of the output voltage of the source driver AVDD power supply circuit 7 is the initial value, the voltage switching control circuit 9a reduces the voltage value of the output voltage of the source driver AVDD power supply circuit 7. If the output voltage of the source driver AVDD power supply circuit 7 is in a voltage drop state, the voltage drop state is maintained.

  By setting the output voltage of the source driver AVDD power supply circuit 7 to a voltage drop state, the source driver power supply apparatus 10 supplies power to the source driver 3 using a voltage value that is a predetermined value lower than the initial value as an output voltage. To do.

  On the other hand, when the output levels of the detection circuit output signal and the counter output signal are inactive levels (NO in S16), the AND circuit 43 outputs an inactive level timer circuit output signal to the voltage switching control circuit 9a.

  When the voltage switching control circuit 9a receives the inactive level timer circuit output signal (switching signal) from the AND circuit 43, the voltage switching control circuit 9a sets the output voltage of the source driver AVDD power supply circuit 7 to the initial state (S18). That is, when the output voltage of the source driver AVDD power supply circuit 7 is in the initial state, the voltage switching control circuit 9a maintains the output voltage of the source driver AVDD power supply circuit 7 in the initial state. If the output voltage of the source driver AVDD power supply circuit 7 is in the voltage drop state, the voltage value of the output voltage is raised and returned to the initial value.

  Accordingly, the source driver power supply apparatus 10 supplies power to the source driver 3 using the initially set voltage value as the output voltage.

<Supplement>
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be used in a power supply device that supplies power to a source driver in a liquid crystal module.

DESCRIPTION OF SYMBOLS 1, 1a Liquid crystal module 2 Liquid crystal panel 3 Source driver 4 Gate driver 5 VGon power supply circuit for gate drivers 6 VGoff power supply circuit for gate drivers 7 AVDD power supply circuit for source drivers 8, 8a Current detection circuit (current detection means)
9, 9a Voltage switching control circuit (voltage drop means)
10, 10a Source driver power supply device 11 Timer circuit (output maintaining means)

Claims (5)

A power supply device for supplying power to a source driver in a liquid crystal module,
It detects whether the current value of the current supplied to the source driver exceeds a predetermined detection threshold, and generates an active level detection signal while the current value exceeds the detection threshold, Current detection means for generating a detection signal of an inactive level while the current value is below the detection threshold;
A power supply device comprising: voltage drop means for dropping a voltage value of an output voltage supplied to the source driver during a period when the detection signal generated by the current detection means is at an active level. At a certain point in time, when the output level of the output maintenance signal generated by itself is an inactive level and the detection signal transitions from an inactive level to an active level, a period of a predetermined output maintaining time from the certain point in time, It further comprises output maintaining means for generating an output maintaining signal whose output level is an active level,
2. The power supply according to claim 1, wherein the voltage drop means drops a voltage value of an output voltage supplied to the source driver during a period when either the detection signal or the output maintenance signal is at an active level. apparatus. The power supply device according to claim 1 or 2,
A liquid crystal module comprising: a source driver that receives power from the power supply device.   A television receiver comprising the liquid crystal module according to claim 3. A control method of a power supply device that supplies power to a source driver in a liquid crystal module,
A current value determination step for determining whether or not the current value of the current supplied to the source driver exceeds a predetermined detection threshold;
And a voltage drop step of dropping the voltage value of the output voltage supplied to the source driver when the current value is determined to exceed the detection threshold in the current value determination step. Control method of the device.

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