JP4576348B2 - Cold cathode tube drive - Google Patents

Description

  The present invention relates to a cold cathode tube driving device.

  For example, in a liquid crystal display or the like, a plurality of cold cathode tubes are arranged as a backlight on the back of the liquid crystal panel, and these cold cathode tubes are turned on to serve as a light source for illuminating the liquid crystal panel.

  When a cold cathode tube is used as a backlight, the brightness of each cold cathode tube needs to be constant. This is because, when the luminance is not constant, luminance unevenness occurs in the liquid crystal display, and the brightness does not become constant depending on the location of the display. Note that the main cause of luminance unevenness is considered to be a variation in parasitic capacitance generated between the cold cathode fluorescent lamp and the panel.

  Conventionally, as a technique for preventing the luminance unevenness of the backlight, for example, there is a technique shown in Patent Document 1.

JP 2006-41468 A (abstract, claims)

  By the way, in the technique shown in Patent Document 1, a transformer is used to balance the currents flowing through the plurality of cold cathode tubes. However, since the transformer is composed of a core and a coil and has a certain size, there is a problem that it is difficult to reduce the size and cost.

  In addition, in order to balance the current flowing in the cold cathode tube, it is necessary to make the element values (for example, the number of turns) of each winding the same. However, since the element values vary from transformer to transformer, they are balanced. There is also a problem that it is difficult to take.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a cold-cathode tube driving device capable of uniformizing the luminance of a plurality of cold-cathode tubes at a small size and low cost. With the goal.

In order to achieve the above object, a cold cathode tube driving device according to the present invention includes a power supply circuit for supplying AC power to a plurality of cold cathode tubes in a cold cathode tube driving device for driving a plurality of cold cathode tubes. An adjustment circuit that individually adjusts the current flowing through the plurality of cold cathode tubes, a sampling circuit that samples a predetermined physical quantity corresponding to the current flowing through each cold cathode tube at a predetermined period, and outputs corresponding digital data; The information about the phase of the output current output from the power supply circuit is compared with the digital data obtained by the sampling circuit, and the phase delay amount is calculated, and the peak of the amplitude of the digital data and the adjustment circuit are set. detecting the amplitude difference by comparing the target current, based on the delay amount and the amplitude difference of the phase, by controlling the adjusting circuit, control the current flowing through each cold cathode tube Having a control circuit for, the.

  Therefore, according to the present invention, it is possible to provide a cold-cathode tube driving device capable of making the luminance of a plurality of cold-cathode tubes uniform in a small size and at low cost.

  Further, in the cold cathode tube driving device of another invention, in addition to the above-described invention, the adjustment circuit is a current control current source or a voltage control voltage source connected to each of the plurality of cold cathode tubes, and the control circuit includes: The current flowing through each cold-cathode tube is controlled by controlling the current leading to the current-controlled current source or the voltage applied to the voltage-controlled current source. Therefore, based on the sampled digital data, the current flowing through each cold cathode tube can be accurately controlled with a simple configuration.

  In addition to the above-described invention, in the cold cathode tube driving device of another invention, the control circuit controls the adjustment circuit according to the amplitude and phase of the current flowing through each of the plurality of cold cathode tubes. Yes. Therefore, by adjusting the amplitude, it becomes possible to control the current flowing in each cold cathode tube to a desired value, and by adjusting the phase, appropriate control is performed to reduce the power loss. Occurrence can be prevented.

  The present invention can provide a cold-cathode tube drive device that is small and low-cost and that can uniformize the luminance of a plurality of cold-cathode tubes.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example of a liquid crystal display device having a cold cathode tube driving device according to an embodiment of the present invention. As shown in this figure, the liquid crystal display device includes a liquid crystal panel 1, a liquid crystal driving circuit 2, a cold cathode tube driving circuit 10, and a plurality of cold cathode tubes 14 as main components.

  Here, the liquid crystal panel 1 transmits or blocks light emitted from the cold cathode tube 14 by changing the arrangement state of some molecules of the liquid crystal according to the control of the liquid crystal driving circuit 2. Display text and images.

  The liquid crystal driving circuit 2 is a driving circuit that displays a desired character or image by driving a TFT (Thin Film Transistor) provided on the back surface of the liquid crystal panel 1, for example.

  The cold cathode tube driving circuit 10 is a circuit for driving and lighting a plurality of cold cathode tubes 14 as backlights provided on the back surface of the liquid crystal panel 1. The detailed configuration of the cold cathode tube driving circuit 10 will be described later.

  In the cold cathode tube 14, a phosphor is applied to the inner wall of the tube, electrodes are attached to both ends of the tube, and argon as a buffer gas and an appropriate amount of mercury are enclosed. When a high voltage is applied between the electrodes at both ends of the tube, electrons remaining in the tube are attracted by the anode and collide with argon molecules while moving at high speed, and the cations that have undergone impact ionization collide with the cathode. The next electron is knocked out and discharge starts. Electrons flowing through the discharge collide with mercury atoms, and the excited mercury emits ultraviolet rays. This ultraviolet light excites the phosphor and emits visible light unique to the phosphor. In the example of FIG. 1, the plurality of cold cathode tubes 14 are arranged in the vertical direction. However, this is an example, and the cold cathode tubes 14 may be arranged in the horizontal direction. Hereinafter, when the individual cold cathode tubes 14 are shown, they are referred to as cold cathode tubes 14-1 to 14-n. Each of the cold cathode fluorescent lamps 14-1 to 14-n has substantially the same current-luminance characteristics.

  FIG. 2 is a diagram showing a schematic configuration example of the cold cathode tube driving circuit 10 shown in FIG. As shown in this figure, the cold cathode tube drive circuit 10 includes a controller IC (Integrated Circuit) 11, a transformer 12, and capacitors 13-1 to 13-n as main components.

  Here, the controller IC 11 includes a driver 20, a control circuit 21, a current controlled current source (CCCS) 22-1 to 22-n, a multiplexer (MUX) 23, and an A / D (Analog to Digital). ) The converter 24 is a main component. The controller IC 11 is, for example, entirely or partially configured as a monolithic IC, and is housed in a plastic or ceramic case.

  Here, the driver 20 as a part of the power supply circuit switches a bipolar transistor (not shown) or a field effect transistor (FET) based on PWM (Pulse Width Modulation) control, and is supplied from a DC power source (not shown). DC power is converted into AC power and supplied to the primary winding of the transformer 12. Note that the frequency of the AC power is, for example, 50 kHz.

  The control circuit 21 serving as a control circuit controls the driver 20 and, according to digital data output from the A / D converter 24 (data corresponding to an alternating current flowing through each cold cathode tube), 22-n is controlled.

  The CCCSs 22-1 to 22-n as adjustment circuits are AC current sources that cause AC currents corresponding to the control currents ic1 to icn supplied from the control circuit 21 to flow through the cold cathode tubes 14-1 to 14-n. Specifically, for example, the CCCSs 22-1 to 22-n each have an alternating current (α · ic1 to α · icn) obtained by multiplying the control currents ic1 to icn supplied from the control circuit 21 by α (α> 1). Shed.

  The MUX 23 has a role of a switch that selects any one of the CCCSs 22-1 to 22-n and connects to the A / D converter 24.

  The A / D converter 24 as a sampling circuit has a physical quantity (for example, a voltage value corresponding to the current flowing through the cold cathode tube) corresponding to the current flowing through the CCCS selected by the MUX 23 (that is, the current flowing through the cold cathode tube). Are sampled, converted into corresponding digital data, and output.

  The transformer 12 as a part of the power supply circuit is a step-up transformer, and boosts and outputs the output voltage (AC voltage) supplied from the driver 20 according to the turn ratio of the primary winding and the secondary winding. One of the primary windings of the step-up transformer is connected to the output terminal of the driver 20, and the other is grounded. One of the secondary windings of the transformer 12 is grounded, and the other is connected to one terminal of each of the capacitors 13-1 to 13-n.

  The capacitors 13-1 to 13-n have one terminal connected to the high voltage side of the secondary winding of the transformer 12, and the other connected to one terminal of the cold cathode tubes 14-1 to 14-n. The capacitors 13-1 to 13-n have negative resistance characteristics when the cold cathode fluorescent lamps 14-1 to 14-n are turned on, and the system becomes unstable. Therefore, the negative resistance characteristics are canceled and the system is stabilized. For insertion.

  Next, the operation of the above embodiment will be described.

  When the power of the liquid crystal display device shown in FIG. 1 is turned on, the liquid crystal driving circuit 2 applies a driving voltage to the TFT of the liquid crystal panel 1 based on the input video signal to display an image on the liquid crystal panel 1.

  At this time, the control circuit 21 of the controller IC 11 starts the operation of the driver 20. As a result, the driver 20 starts a switching operation, converts DC power supplied from a DC power source (not shown) into AC power, and outputs the AC power. The AC voltage output from the driver 20 is supplied to the transformer 12, where it is boosted according to the turns ratio.

  The AC power output from the transformer 12 is applied to the cold cathode tubes 14-1 to 14-n via the capacitors 13-1 to 13-n. When the applied voltage exceeds the discharge voltage, the cold cathode tubes 14-1 to 14-n start discharging. When the discharge starts, visible light (white light) is emitted from the cold cathode fluorescent lamps 14-1 to 14-n. The emitted visible light is transmitted or blocked according to the liquid crystal state of the liquid crystal panel 1. As a result, it is displayed as a predetermined character or visible image according to the driving of the liquid crystal driving circuit 2.

  By the way, the electric current which flows into the cold cathode tubes 14-1 to 14-n also flows to the CCCS 22-1 to 22-n. An alternating current corresponding to the control currents ic1 to icn supplied from the control circuit 21 flows through the CCCS 22-1 to 22-n. As a result, an alternating current corresponding to the control current flows through the cold cathode tubes 14-1 to 14-n. A method for determining the control currents ic1 to icn will be described below.

  At the start of lighting, the control circuit 21 supplies control currents ic1 to icn based on a preset current waveform to the CCCSs 22-1 to 22-n. That is, the control circuit 21 incorporates a memory (not shown), and data indicating a current waveform for starting lighting (data indicating a sine wave) is stored in advance in the memory. The control circuit 21 supplies the control currents ic1 to icn based on the data indicating the current waveform stored in the memory.

  As a result, CCCSs 22-1 to 22 -n are supplied with preset control currents ic1 to icn for starting lighting, and cold cathode tubes 14-1 to 14-n have currents corresponding thereto (for example, A current obtained by multiplying the control currents ic1 to icn by α) flows.

  By the way, the currents flowing through the cold cathode tubes 14-1 to 14-n are not constant due to the influence of stray capacitance or the characteristics of the cold cathode tubes 14-1 to 14-n. Therefore, the controller IC 11 adjusts these currents to be equal. Further, the current output from the driver 20 and the current detected by the control circuit 21 may not be in phase. That is, the current detected by the control circuit 21 may have a delay. In such a case, if the current is controlled based on the delayed current waveform, the control may not be performed accurately. Therefore, the control circuit 21 performs control so that the currents flowing through all the cold cathode fluorescent lamps 14-1 to 14-n become the target values and become equal to each other so that the luminance becomes equal. In addition, the control circuit 21 detects the delay amount of the detected current, and supplies the control currents ic1 to icn advanced to correct the delay amount to the CCCS 22-1 to 22-n, thereby controlling the current. To be done appropriately.

  Next, the operation of the controller IC 11 will be described in more detail. The MUX 23 sequentially selects the CCCSs 22-1 to 22-n in ascending order, for example, and connects them to the A / D converter 24. The A / D converter 24 samples the current flowing through the CCCS selected by the MUX 23 at a predetermined sampling rate, converts it into digital data, and supplies the digital data to the control circuit 21. The sampling rate of the A / D converter 24 is preferably a frequency higher than the frequency of the AC power output from the driver 20 in order to adjust the phase with high accuracy, for example. Further, it is not necessary to adjust the phase with high accuracy, and when only the amplitude of the current is adjusted, the frequency may be lower than this.

  FIG. 3 is a diagram showing waveforms at various parts of the block diagram shown in FIG. FIG. 3A shows the waveform of the output current of the driver 20. The output current of the driver 20 is a sine wave. FIG. 3B shows the waveform of the current flowing through the cold cathode tube 14-1 detected by the control circuit 21. In this example, the detected current is delayed in phase by τ compared to the output current of the driver 20, and the amplitude peak is smaller by β than the target current ip1. The target current ip1 is a target value of the current flowing through the CCCS 22-1.

  The control circuit 21 controls the driver 20 and has information regarding the phase of the output current output from the driver 20 (for example, the phase information or waveform information of the output current at that time is included as digital data) ing). Therefore, the control circuit 21 calculates the phase delay amount τ by comparing the phase of the output current output from the driver 20 with the digital data supplied from the A / D converter 24. The control circuit 21 detects the amplitude difference β by comparing the amplitude peak of the digital data supplied from the A / D converter 24 with the corresponding target current.

  Next, the control circuit 21 adjusts the phase of the waveform data for lighting start stored in a memory (not shown) so that the amplitude is the same while the phase is advanced by the above-described delay amount τ (for example, ic1). In this case, the amplitude is adjusted so that α · ic1 = ip1), and this is supplied to the CCCS 22-1 as the control current ic1 (see FIG. 3C). As a result, since a current having an amplitude value obtained by multiplying the control current ic1 by α flows through the CCCS 22-1, the phase of the output current of the driver 20 is equal to the CCCS 22-1, as shown in FIG. In addition, a current α · ic1 having the same amplitude as the target current ip1 flows. Note that the phase adjustment amount and the amplitude adjustment amount are stored in a memory (not shown) as control parameters for each CCCS, and can be continuously controlled by using the parameters.

  The processing as described above is performed for all the cold cathode fluorescent lamps 14-1 to 14-n. As a result, the currents flowing in the CCCS 22-1 to 22-n are in phase with the current output from the driver 20, and the amplitude is equal to the target currents ip1 to ipn. For example, since the target currents ip1 to ipn are set so that the brightness of each cold cathode tube is equal in the mounted state, the brightness of the cold cathode tubes 14-1 to 14-n is equal.

  As described above, according to the above embodiment, the current flowing through each cold cathode tube is detected and converted into digital data, and control is performed according to the digital data. It becomes possible to accurately detect the current flowing through the tube and to accurately control the current value accordingly. As a result, uneven brightness in the cold cathode tubes 14-1 to 14-n can be prevented. The image displayed on the liquid crystal panel 1 is a clean image with no luminance unevenness.

  The controller IC 11 can be configured as a monolithic IC. Therefore, according to the present embodiment, as described above, not only the current flowing through the cold cathode tubes 14-1 to 14-n is accurately controlled, but also the size of the apparatus is reduced by reducing the number of parts, and The device can be manufactured at a low cost. Therefore, the cost and size of the liquid crystal display device itself can be reduced.

  In the above embodiment, the control is performed by detecting the phase and amplitude at the start of lighting. For example, when a predetermined time (several minutes or several tens of minutes) has elapsed since the start of lighting, By performing such control, it is possible to adjust the characteristics in the steady state and obtain an image having no luminance unevenness in the steady state. In addition, if the above-mentioned processing is executed for the accumulated usage time (for example, several hundreds of hours) from the start of use and adjustments are made based on this, the difference in characteristics due to aging of each cold-cathode tube is absorbed. In addition, even when a secular change occurs, it is possible to obtain an image having no luminance unevenness.

  In the above embodiment, the CCCSs 22-1 to 22-n are used. However, for example, a VCCS (Voltage Controlled Current Source) as a voltage controlled current source can be used. In this case, these VCCCS are controlled by the control voltages vc1 to vcn instead of the control currents ic1 to icn. As a result, for example, the output voltage of the D / A converter can be directly supplied.

  In the above embodiment, the positive side (the side flowing from the cold cathode tubes 14-1 to 14-n to the ground) and the negative side (the cold from the ground) of the alternating current flowing through the cold cathode tubes 14-1 to 14-n. The current flowing in the CCCS 22-1 to 22-n is controlled on both of the cathode tubes 14-1 to 14-n), but may be one of the positive side and the negative side, for example. According to such a configuration, although the accuracy of controlling the current is somewhat lowered, since the one-side power source chip can be used as the controller IC 11, the cost of the apparatus can be further reduced.

  In the above embodiment, the CCCSs 22-1 to 22-n are selected by the MUX 23, and the current flowing through the selected CCCS is detected by the A / D converter 24. The MUX 23 can be omitted by using a / D converter or by selecting a port internally using a multi-port A / D converter.

  In the above embodiment, the A / D converter 24 samples the waveform of the current flowing in the CCCS 22-1 to 22-n. For example, when the phase is not considered, the CCCS 22- The current flowing through 1 to 22-n may be smoothed by a low-pass filter, RMS (Root Mean Square) of the current may be detected, and only the amplitude may be controlled based on the value. According to such an embodiment, since the sampling frequency of the A / D converter 24 can be set low and an inexpensive A / D converter 24 can be used, the cost of the entire apparatus can be reduced.

  Next, an example of a more detailed embodiment of the present invention will be described with reference to FIG.

  FIG. 4 is a diagram showing a more detailed configuration example of the present invention. Note that, in the example of this figure, unlike the case of FIG. 2, a circuit that controls only the positive current is shown. In FIG. 4, the same reference numerals are given to portions common to FIG. 2, and description thereof is omitted.

  In the example of FIG. 4, the controller IC 11 is replaced with the controller IC 31 as compared with the case of FIG. 2. Further, diodes 15-1 to 15-n are inserted between the cold cathode tubes 14-1 to 14-n and the ground, and a diode is interposed between the cold cathode tubes 14-1 to 14-n and the controller IC 31. 16-1 to 16-n are inserted. Other configurations are the same as those in FIG.

  Here, the diodes 15-1 to 15-n have the anode terminals grounded and the cathode terminals connected to one terminals of the cold cathode tubes 14-1 to 14-n. These diodes 15-1 to 15-n have a function of blocking only the current on the negative side (side flowing from the ground to the cold cathode tubes 14-1 to 14-n) and blocking the positive side.

  The diodes 16-1 to 16-n have anodes connected to one terminal of the cold cathode tubes 14-1 to 14-n and are connected to the controller IC31. These diodes 16-1 to 16-n have a function of passing only the current on the positive side (the side flowing from the cold cathode fluorescent lamps 14-1 to 14-n to the ground) and blocking the negative side. That is, only the positive current flows into the controller IC 31.

  The controller IC 31 includes a driver 40, current mirror circuits 41-1 to 41-n, switches 42-1 to 42-n, resistors 43-1 to 43-n, a MUX 44, an A / D converter 45, and a phase difference calculator 46. The sequencer 47, the memory 48, the amplitude difference calculator 49, and the control circuit 50 are the main components.

  Here, the driver 40 as a part of the power supply circuit outputs AC power in accordance with the control of the sequencer 47 and supplies the current waveform of the output AC power to the phase difference calculator 46.

  The current mirror circuits 41-1 to 41-n as adjustment circuits are current control current sources configured by FET (Field Effect Transistor) or MOS (Metal-Oxide Semiconductor) -FET or the like, and are supplied from the control circuit 50. The same current as the control currents ic1 to icn. The current mirror circuits 41-1 to 41-n may be configured by bipolar transistors.

  The switches 42-1 to 42-n are composed of FETs or MOS-FETs, and are turned on or off according to the control of the sequencer 47. When these are turned on, the resistors 43-1 to 43-n are grounded, so that the current flowing through the cold cathode tubes 14-1 to 14-n goes to the ground via the resistors 43-1 to 43-n. Flowing. On the other hand, when these are turned off, currents flowing through the cold cathode fluorescent lamps 14-1 to 14-n flow to the current mirror circuits 41-1 to 41-n via the resistors 43-1 to 43-n.

  The resistors 43-1 to 43-n are detection resistors for detecting the current flowing through the cold cathode tubes 14-1 to 14-n. A voltage drop generated in the resistors 43-1 to 43-n is input to the MUX 44.

  The MUX 44 functions as a switch that selects any one of the resistors 43-1 to 43-n according to the control of the sequencer 47 and connects to the A / D converter 45.

  The A / D converter 45 samples the voltage drop generated in the resistor selected by the MUX 44, converts it into corresponding digital data, and supplies it to the phase difference calculator 46 and the memory 48.

  The phase difference calculator 46 compares the information indicating the AC power output from the driver 40 with the phase of the data supplied from the A / D converter 45, and compares the data supplied from the A / D converter 45. The phase difference (delay amount (see τ in FIG. 3B)) is calculated and notified to the control circuit 50.

  A sequencer 47 as a part of the control circuit controls each part of the controller IC 31 according to a program stored in a built-in memory. Specifically, the sequencer 47 controls the driver 40 to generate AC power. The sequencer 47 turns on the switches 42-1 to 42-n when measuring the currents flowing through the cold cathode fluorescent lamps 14-1 to 14-n, and turns them off otherwise. To do. Further, the sequencer 47 controls the MUX 44 to select a resistance to be measured. Further, the sequencer 47 controls the control circuit 50 so that a predetermined current flows through the cold cathode tubes 14-1 to 14-n.

  The memory 48 is constituted by, for example, a semiconductor memory, and stores digital data corresponding to currents flowing through the cold cathode tubes 14-1 to 14-n supplied from the A / D converter 45.

  The amplitude difference calculator 49 compares the digital data indicating the currents flowing in the cold cathode tubes 14-1 to 14-n stored in the memory 48 with the target currents ip1 to ipn, and compares these differences (amplitudes). Difference) is calculated and notified to the control circuit 50.

  The control circuit 50 as a part of the control circuit controls the amplitude difference supplied from the amplitude difference calculator 49 and the control current ic1 corresponding to the phase difference supplied from the phase difference calculator 46 under the control of the sequencer 47. ... Icn are output and supplied to the current mirror circuits 41-1 to 41-n to control the current flowing through the cold cathode tubes 14-1 to 14-n.

  Other configurations are the same as those in FIG.

  Next, the operation of the embodiment shown in FIG. 4 will be described with reference to the flowchart shown in FIG. FIG. 5 is a flowchart for explaining the flow of processing executed when, for example, a cold cathode tube is turned on. When this flowchart is started, the following steps are executed.

  Step S10: The sequencer 47 assigns an initial value 1 to a variable i for counting the number of processes.

  Step S11: The sequencer 47 turns on the switch corresponding to the value of the variable i, and turns off the others. For example, when i = 1, the switch 42-1 is turned on, and otherwise it is turned off.

  Step S12: The sequencer 47 controls the MUX 44 to select a resistor corresponding to the switch turned on in step S11. As a result, the A / D converter 45 samples the voltage generated in the resistor selected by the MUX 44, converts it into digital data, and supplies it to the memory 48. For example, when i = 1, the A / D converter 45 generates digital data corresponding to the voltage generated in the resistor 43-1 (voltage corresponding to the current flowing through the cold cathode tube 14-1).

  Step S13: The memory 48 stores the digital data sampled in step S12. For example, when i = 1, digital data corresponding to the current flowing through the cold cathode tube 14-1 is stored in a predetermined area of the memory 48.

  Step S14: The control circuit 50 compares the amplitude difference supplied from the amplitude difference calculator 49 with the target current to calculate an amplitude correction amount. Specifically, the amplitude difference calculator 49 obtains an amplitude difference by comparing the digital data stored in the memory 48 with the corresponding one of the target currents ip1 to ipn and supplies it to the control circuit 50. . The control circuit 50 calculates the correction amount of the current flowing in the corresponding cold cathode tube with reference to the supplied amplitude difference. For example, when i = 1, the control circuit 50 determines ic1 so that ic1 = ip1 when the target current is ip1.

  Step S15: The phase difference calculator 46 compares the information regarding the current output from the driver 40 with the digital data supplied from the A / D converter 45, and calculates the delay amount as the phase difference.

  Step S16: The control circuit 50 stores the phase correction amount based on the delay amount supplied from the phase difference calculator 46 and the amplitude correction amount calculated in step S14 in the internal memory as correction parameters. Such correction parameters are stored separately for each current mirror circuit.

  Step S17: The sequencer 47 turns off the switch that was turned on in step S11. Then, the current flowing through the cold cathode tube flows into the current mirror circuit. Since the control circuit 50 controls each current mirror circuit on the basis of the stored correction parameter, a current having a desired amplitude and a desired phase flows for the cold-cathode tube in which the processing in step S17 has been completed. It will be.

  Step S18: The sequencer 47 increments the value of the variable i for counting the number of processes by one.

  Step S19: The sequencer 47 determines whether or not the value of the variable i is larger than the value of n indicating the number of cold cathode fluorescent lamps. If it is larger, the process is terminated. Otherwise, the process returns to step S11. Then, the same processing as described above is repeated.

  As a result of the above processing, the current flowing through the current mirror circuits 41-1 to 41-n has the same phase as the alternating current output from the driver 40. Further, the amplitude of the current flowing through the current mirror circuits 41-1 to 41-n is equal to a preset target current value. Thereby, since the brightness | luminance of the cold cathode tubes 14-1 to 14-n becomes fixed, generation | occurrence | production of a brightness nonuniformity can be prevented.

  As described above, according to the embodiment of the present invention, the current flowing through each cold-cathode tube is converted into digital data and detected, and control is performed accordingly. It is possible to detect the current flowing through the current accurately and control the current value accurately according to the current. Thereby, the uneven brightness of the cold cathode fluorescent lamps 14-1 to 14-n can be prevented. The image displayed on the liquid crystal panel 1 is a clean image with no luminance unevenness.

  The controller IC 31 can be configured as a monolithic IC. Therefore, according to the present embodiment, as described above, not only the current flowing through the cold cathode tubes 14-1 to 14-n is accurately controlled, but also the size of the apparatus is reduced by reducing the number of parts, and The device can be manufactured at a low cost. Therefore, it is possible to contribute to reducing the cost and size of the liquid crystal display device itself.

  Further, in the embodiment of the present invention, control is performed by detecting the phase and amplitude at the start of lighting. For example, when a predetermined time (several minutes or several tens of minutes) has elapsed from the start of lighting, By performing such control, it is possible to adjust the characteristics in the steady state and obtain an image having no luminance unevenness in the steady state. In addition, if the above-mentioned processing is executed for the accumulated usage time (for example, several hundreds of hours) from the start of use and adjustments are made based on this, the difference in characteristics due to aging of each cold-cathode tube is absorbed. In addition, even when a secular change occurs, it is possible to obtain an image having no luminance unevenness.

  In the above embodiment, the current mirror circuits 41-1 to 41-n are inserted into the low-voltage side of the cold cathode tubes 14-1 to 14-n. Since a transistor having a low withstand voltage can be used as the transistor constituting n, the cost can be reduced. In addition, a transistor with a low breakdown voltage has better high-frequency characteristics than a transistor with a high breakdown voltage, and thus it is possible to maintain a current balance up to a high frequency.

  Further, by making the controller IC 31 a monolithic IC, the relative characteristics of the transistors constituting the current mirror circuits 41-1 to 41-n can be made uniform. Can be further enhanced. Further, by making a monolithic IC, these transistors can be thermally coupled, so that it is possible to prevent a current balance from being lost due to a change in temperature.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the embodiment shown in FIG. 4, FETs or MOS-FETs are used as the transistors constituting the current mirror circuits 41-1 to 41-n. However, for example, bipolar transistors may be used.

  In the embodiment shown in FIG. 4, only the positive-side current mirror circuit is provided, but both positive-side and negative-side current mirror circuits may be provided. Only the negative side current mirror circuit may be provided. When both positive and negative current mirror circuits are provided, the accuracy of current control can be improved. In addition, when only one of the positive side and the negative side is provided, the accuracy of controlling the current is reduced, but the manufacturing cost of the device can be reduced by simplifying the circuit.

  In the embodiment shown in FIG. 4, the switches 42-1 to 42-n are provided, and the current flowing through the cold cathode tubes 14-1 to 14-n is directly passed through the resistors 43-1 to 43-n. It was made to flow into the ground and the current was measured. However, for example, it is also possible to directly measure the current flowing into the current mirror circuits 41-1 to 41-n via the resistors 43-1 to 43-n without providing these switches. In the case where the switches 42-1 to 42-n are provided, the current flowing through the cold cathode tubes 14-1 to 14-n can be obtained without being affected by the control of the control circuit 50. Thereby, the precision which controls an electric current can be improved.

  Further, in the embodiment shown in FIG. 4, the switches 42-1 to 42-n are sequentially turned on, and the voltage appearing in the resistor connected to the switch in the on state is detected. All of these may be turned on, and the resistors may be selected by the MUX 44.

  In the embodiment shown in FIGS. 2 and 4, the current flowing through the cold cathode tubes 14-1 to 14-n is controlled. However, the current flowing through other types of loads is controlled. Also good.

  Further, the target currents ip1 to ipn may be the same value or different values. When the target currents ip1 to ipn are equal, they can be integrated together and the amount of data can be reduced, thereby reducing the manufacturing cost of the device. In the case of using different values, since the optimum current can be set for each cold cathode tube in consideration of the current-luminance characteristics of each cold cathode tube, the luminance unevenness can be further reduced.

  Further, the target currents ip1 to ipn may be set manually by the user. According to such an embodiment, the brightness can be adjusted while visually confirmed by the user, so that finer adjustment can be performed, and even if an aging change occurs, the brightness can be confirmed while visually confirming. Settings can be made.

  Further, the target currents ip1 to ipn may be set in consideration of the secular change and the like. Specifically, when the current-luminance characteristics change over time, the total use time from the start of use is stored in the memory, and the target currents ip1 to ipn are set according to the total use time. It may be. According to such an embodiment, it becomes possible to suppress a change in luminance due to the influence of secular change.

  Further, the block diagrams shown in FIGS. 2 and 4 are examples, and it goes without saying that the present invention is not limited to such a circuit.

  The present invention can be used for a liquid crystal display, for example.

It is a block diagram which shows the structural example of the liquid crystal display which concerns on embodiment of this invention. FIG. 2 is a block diagram showing a schematic configuration example of a cold cathode tube driving circuit shown in FIG. 1. FIGS. 3A and 3B are diagrams showing current waveforms of respective parts of the circuit shown in FIG. 2, wherein FIG. 3A shows an output current waveform of a driver, FIG. 3B shows a current waveform detected by the control circuit 21, and FIG. And the current flowing in the current mirror circuit. FIG. 2 is a block diagram showing a detailed configuration example of a cold cathode tube driving circuit shown in FIG. 1. 5 is a flowchart for explaining a flow of processing executed in the embodiment shown in FIG. 4.

Explanation of symbols

  12 transformer (part of power supply circuit), 20 driver (part of power supply circuit), 21 control circuit (control circuit), 22-1 to 22-n CCCS (regulation circuit), 24 A / D converter ( Sampling circuit), 41-1 to 41-n current mirror circuit (regulation circuit), 45 A / D converter (sampling circuit), 47 sequencer (part of control circuit), 50 control circuit (part of control circuit)

Claims (3)

In a cold cathode tube driving device for driving a plurality of cold cathode tubes,
A power supply circuit for supplying AC power to the plurality of cold cathode tubes;
An adjustment circuit for individually adjusting the currents flowing through the plurality of cold cathode tubes;
A predetermined physical quantity corresponding to the current flowing through each of the cold cathode tubes is sampled at a predetermined period,
A sampling circuit for outputting corresponding digital data;
The information on the phase of the output current output from the power supply circuit is compared with the digital data obtained by the sampling circuit to calculate the phase delay amount and to adjust the amplitude peak of the digital data and the adjustment Control that detects an amplitude difference by comparing with a target current set in the circuit, controls the adjustment circuit based on the delay amount of the phase and the amplitude difference , and controls the current flowing through each cold cathode tube Circuit,
A cold-cathode tube driving device comprising: The adjustment circuit is a current control current source or a voltage control voltage source respectively connected to the plurality of cold cathode tubes,
The control circuit controls a current flowing to each cold cathode tube by controlling a current leading to the current controlled current source or a voltage applied to the voltage controlled current source;
The cold-cathode tube driving device according to claim 1.   3. The cold cathode tube driving device according to claim 1, wherein the control circuit controls the adjustment circuit according to an amplitude and a phase of a current flowing through each of the plurality of cold cathode tubes. 4.

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