JP2007179920A - Method of adjusting brightness of discharge lamp, and power source device using piezoelectric transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of adjusting brightness of a discharge lamp of low power consumption restraining brightness deviation of the discharge lamp for a backlight of a liquid crystal display device, and a power source device using a piezoelectric transformer. <P>SOLUTION: During a period of lighting the discharge lamp, the piezoelectric transformer 7 is driven by a frequency at which boosting ratio of the piezoelectric transformer 7 is high, and during a period of darkly lighting a load 8 as the discharge lamp, the piezoelectric transformer 7 is driven by a frequency at which boosting ratio of the piezoelectric transformer is low. The ratio of the period driving the piezoelectric transformer with a frequency of high boosting ratio and that of low boosting ratio is adjusted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a brightness adjustment method for a discharge lamp and a power supply device using a piezoelectric transformer, and more particularly to a brightness adjustment method suitable for brightness adjustment of a discharge lamp for a backlight of a liquid crystal display device and a power supply device using a piezoelectric transformer.

  In the luminance adjustment (hereinafter referred to as dimming) of the backlight discharge lamp of the liquid crystal display device, the current value is decreased and the luminance is decreased by reducing the amplitude of the alternating current flowing through the discharge lamp. In this method, dimming can be performed only in the range of about 100% (at the maximum) to about 50%. If the current amplitude is further reduced, the discharge becomes unstable due to the nature of the discharge lamp.

  Recently, a notebook personal computer equipped with a liquid crystal display device with a dimming range of about 100% to 10% in which the low frequency range is widened in order to increase the battery operating time per charge has been strongly demanded. It was.

  Since the dimming range by continuous current operation cannot be expanded due to the need to lengthen the battery operating time per charge, time-division that performs dimming at the ratio of intermittent current operation by operating the current flowing in the discharge lamp intermittently Many dimming methods have been adopted.

  FIG. 8 shows a comparison of current waveforms between the dimming method using current amplitude and the dimming method using time division. The dimming method based on the current amplitude is a method of adjusting the luminance of the backlight discharge lamp of the liquid crystal display device by changing the amplitude by a continuous current operation and changing the current value. The dimming method based on time division is a method in which the current ON / OFF operation is repeated at a dimming frequency of about 100 Hz to 300 Hz, and the time ratio between the ON operation and the OFF operation is adjusted with a constant current amplitude. The dimming range of 100% to 10% can be realized by the dimming method by time division.

  FIG. 9 is a block diagram illustrating an example of a piezoelectric inverter that employs time-division dimming. As shown in FIG. 9, (1) a DC power supply 1 and (2) a switch Z2 with a protective element controlled by an output of an AND circuit 12 that inputs an output of a dimming circuit 10 and an output of a drive frequency generation circuit 11 ( 3) a flywheel diode 9 connected between the output terminal of the switch Z2 and the ground; and (4) a piezoelectric transformer 7 for inputting an AC voltage from the primary side electrode and outputting from the secondary side electrode using the piezoelectric effect. (8) The coil 3 connected between one primary electrode 14 of the piezoelectric transformer 7 and the output end of the switch Z2, and (9) between the other primary electrode 13 of the piezoelectric transformer 7 and the output end of the switch Z2. The connected coil 4, (10) the switch A 5 with a protective element connected between the primary electrode 14 of the piezoelectric transformer 7 and the ground, and (11) the protective element connected between the primary electrode 13 of the piezoelectric transformer 7 and the ground. With switch B6 and (12) Piezoelectric switch It comprises a secondary electrode 15 for supplying the output of the lance 7 to the load 8.

  The switches A5 and B6 are configured to be conductive when a high level signal is supplied from the drive frequency generation circuit 11. FIG. 10 is a diagram illustrating a switching operation of the push-pull piezoelectric transformer driving circuit. Further, since the signals supplied from the drive frequency generation circuit 11 to the switches A5 and B6 are signals whose phase inversion efficiency is less than 50% as shown in FIG. 10, the switches A5 and B6 are alternately turned on. To do. As a result, a resonance formed by the coil and the piezoelectric transformer input capacitance is generated every time the power is alternately conducted, and an equivalent alternating current is input between the primary side electrode 13 and the primary side electrode 14 of the piezoelectric transformer 7.

  The signal output from the drive frequency generation circuit 11 to the AND circuit 12 is a signal having a frequency about twice that of the signal sent to the switch A5 or the switch B6. The period during which the switch Z2 is to be conducted is at a high level. The signal output from the dimming circuit 10 to the AND circuit 12 is at a frequency of about 100 to 300 Hz, and becomes a low level during a period when the load 8 is desired to be extinguished during time-division dimming. The AND circuit 12 makes the switch Z2 non-conductive during a period in which it is desired to turn off during time-division dimming, and the frequency input from the drive frequency generation circuit 11 during periods other than the period in which it is desired to turn off during time-division dimming. By repeating the ON / OFF operation of the switch Z2, the power supplied to the block that performs the step operation after the switch Z2 is adjusted.

  The piezoelectric inverter shown in FIG. 9 creates the extinguishing period of the load 8 by setting the power supply to the block performing the step operation after the switch Z2 to zero by the switch Z2 at the time-division dimming.

  In addition, there is a simplified type of the piezoelectric inverter shown in FIG. 9 in which the switch Z2 and the diode 9 are omitted and the DC power source 1 is directly connected to the coils 3 and 4. Although the simplified type of the piezoelectric inverter shown in FIG. 9 does not have two components of the switch Z2 and the diode 9, its operation control circuit is also unnecessary, and there is a demerit that it cannot correspond to the wide voltage range of the DC power supply 1. There is a merit that the cost can be reduced. In the simplified type of the piezoelectric inverter shown in FIG. 9, the conduction of both the switch A5 and the switch B6 during time division dimming is stopped, and the AC input to the piezoelectric transformer 7 is stopped to turn off the load 8. Creating a period.

  The time-division dimming method is a method in which an operation of suddenly stopping the power supply to the piezoelectric transformer 7 and its driving unit (OFF operation) and an operation of suddenly starting (ON operation) are repeated. Since the frequency of the time division dimming method is an audible frequency, there is a problem that an audible sound is likely to be generated.

  A technique for reducing audible sound is disclosed in Patent Document 1. The current waveform at the time of light control in Patent Document 1 is shown in FIG. When the tube current is reduced from 5 mArms to 4 mArms, only the current amplitude is reduced. However, in continuous current operation, if the current amplitude is reduced from 4 mArms, the discharge becomes unstable due to restrictions on the characteristics of the discharge lamp. . When reducing the tube current to less than 4 mArms, the current amplitude is the same as the tube current of 4 mArms, and the output level of the piezoelectric transformer is continuously reduced at a period that is sufficiently lower than the AC frequency output from the piezoelectric transformer. This is a method of dimming by adjusting the time ratio of the period during which the output level of the piezoelectric transformer is continuously reduced. In this method, audible sound can be reduced by continuously changing the output level of the piezoelectric transformer.

JP 2000-58289 A

  The dimming method disclosed in Patent Document 1 described above has a problem that it is difficult to make the luminance of the backlight discharge lamp of the liquid crystal display device uniform.

  FIG. 12 shows a case where the current flowing through the low voltage side (grounding side) of the discharge lamp is reduced by changing the current amplitude by the dimming method (changing the driving frequency of the piezoelectric transformer) that changes the current amplitude. It is the data of the result of having actually measured the difference of the electric current which flows into the high voltage | pressure side (inverter side) of a discharge lamp, the electric current value of a high voltage | pressure side, and the electric current value of a low voltage | pressure side. FIG. 13 is a graph showing the relationship between the drive frequency of the piezoelectric transformer and the step-up ratio. As shown in FIG. 13, when the piezoelectric transformer 7 is driven at a frequency slightly higher than the frequency at which the step-up ratio of the piezoelectric transformer 7 is maximum, the low-voltage side current is 5 mArms, and the driving frequency of the piezoelectric transformer 7 is forcibly increased. As a result, the low-voltage side current decreases. The discharge became unstable when the low-voltage current was 3 mArms or less.

  According to FIG. 12, if the low-voltage side current is decreased, the high-voltage side current is also decreased. However, the high-voltage side current is less reduced than the low-voltage side current. As a result, the smaller the current amplitude, the greater the difference between the high-voltage side current and the low-voltage side current, and the ratio also increases. The brightness on the backlight tends to be high near the high-pressure side of the discharge lamp and low near the low-pressure side of the discharge lamp, and this tendency becomes more prominent by reducing the current amplitude.

  The current waveform shown in FIG. 11 will be described. When the current is reduced from 5 mArms to 4 mArms, the amplitude of the current is reduced, so that the luminance deviation on the backlight increases. Furthermore, when decreasing to less than 4 mArms, reducing the current gently for a predetermined period is effective in reducing sound, but since it is gentle (the current is further reduced over time), Since the period during which the difference between the low voltage side current and the low voltage side current is further increased, the luminance deviation on the backlight is further increased.

  The present invention has been made to solve the above-described problems, and its technical problem is to provide a method for adjusting the luminance of a discharge lamp with low power consumption and a piezoelectric transformer in which the luminance deviation of the backlight discharge lamp of the liquid crystal display device is suppressed. It is providing the power supply device which used the.

  According to a first aspect of the invention for achieving the above object, there is provided a discharge lamp for lighting a discharge lamp by applying an output voltage of a power supply device using a piezoelectric transformer that generates an AC voltage from a DC voltage to the discharge lamp. In the brightness adjustment method, the period during which the discharge lamp is lit is driven by driving the piezoelectric transformer at a frequency at which the step-up ratio of the piezoelectric transformer is high, and the period during which the discharge lamp is lit dark or the period during which the discharge lamp is extinguished The brightness of the discharge lamp that drives the piezoelectric transformer at a low frequency and adjusts the ratio of the time to drive the piezoelectric transformer at a high frequency of the boost ratio and the time to drive the piezoelectric transformer at a low frequency of the boost ratio It is an adjustment method.

  According to a second aspect of the present invention for achieving the above object, the brightness adjustment of the discharge lamp is performed by switching between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio in a period greater than 0 seconds and about 500 μsec or less. Is the method.

  According to a third aspect of the invention for achieving the above object, there is provided a discharge lamp luminance adjusting method for shortening a switching element conduction time per one cycle of the piezoelectric transformer driving frequency during a period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency. It is.

  According to a fourth aspect of the present invention for achieving the above object, there is provided a piezoelectric transformer for generating an AC voltage from a DC voltage having a function of adjusting the brightness of the discharge lamp when an output voltage is applied to the discharge lamp and the discharge lamp is turned on. In the power supply device using the above, the period during which the discharge lamp is lit is a period during which the piezoelectric transformer is driven at a frequency at which the step-up ratio of the piezoelectric transformer is high and the discharge lamp is lit darkly or the period during which the discharge lamp is extinguished is: A power source using a piezoelectric transformer having a function of adjusting the brightness of a discharge lamp that is driven at a frequency with a low step-up ratio and adjusts a ratio between a time for driving at a high frequency with the step-up ratio and a time for driving at a low frequency with the step-up ratio Device.

  According to a fifth aspect of the present invention for achieving the above object, the piezoelectric transformer has a function of switching between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio in a period greater than 0 seconds and less than about 500 μsec. This is a power supply device using a transformer.

  A sixth invention for achieving the above object is based on a function of detecting a current flowing through a discharge lamp, a function of comparing a detected current flowing through the discharge lamp with a comparator, and a result compared with the comparator. The power supply device includes a function of changing a reference voltage value and uses a piezoelectric transformer that switches between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio.

  According to a seventh aspect of the invention for achieving the above object, the piezoelectric device includes a function of lowering an output frequency when the input voltage of the voltage controlled oscillator is increased and increasing an output frequency when the input voltage of the voltage controlled oscillator is decreased. This power supply device uses a piezoelectric transformer that switches between a frequency with a high step-up ratio of the transformer and a frequency with a low step-up ratio.

  The eighth invention for achieving the above object uses a piezoelectric transformer having a function of shortening the switching element conduction time per cycle of the piezoelectric transformer driving frequency during the period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency. It is a power supply unit.

  The ninth invention for achieving the above object is as follows: (1) a piezoelectric transformer for inputting an AC voltage from the primary side electrode and outputting from the secondary side electrode using the piezoelectric effect; and (2) the piezoelectric from the input end. A current detection circuit for inputting the output of the transformer, outputting from the first output end, and outputting a current proportional to the current value output from the first output end from the second output end; and (3) the current detection A load for inputting an output from the first output terminal of the circuit; (4) a rectifier circuit for inputting an output from the second output terminal of the current detection circuit and outputting a rectified result; and (5) a dimming circuit. A switch that selects any one of a plurality of DC power supplies that are output to the comparator, and (6) inputs the output of the rectifier circuit and the output of the switch, and outputs the rectifier circuit and the The output of the rectifier circuit is compared with the output of the switch. And (7) an integrator circuit that inputs the output of the comparator and outputs an integration result having a specific time constant, and (8) the output of the integrator circuit is the input voltage, and the input voltage increases. Then, a voltage controlled oscillator that outputs a triangular wave that lowers the output frequency and raises the output frequency when the input voltage decreases, and (9) the voltage controlled oscillator output and the DC voltage are input, and the efficiency determined by the DC voltage is obtained. A second comparator that outputs the output signal at the output frequency of the voltage controlled oscillator, (10) a dimming circuit that outputs the efficiency for determining the lighting period at the frequency of time-division dimming, and (11) the second comparator. The output of the dimming circuit and the output of the dimming circuit are input, and the piezoelectric transformer is set so that both the output of the second comparator and the output of the dimming circuit output a high level only during a high level period. Generate a switching signal to drive AND circuit and (12) a drive signal generation circuit for inputting the output of the AND circuit and converting it into a signal for operating the drive circuit; and (13) a piezoelectric for driving the piezoelectric transformer by inputting the output of the drive signal generation circuit. A power supply device using a piezoelectric transformer including a transformer driving circuit.

  The tenth invention for achieving the above object is as follows: (1) a piezoelectric transformer that inputs an AC voltage from the primary side electrode and outputs from the secondary side electrode using the piezoelectric effect; A current detection circuit for inputting the output of the transformer, outputting from the first output terminal, and outputting a current proportional to the current value output from the first output terminal from the second output terminal; and (3) the current detection A load for inputting an output from the first output terminal of the circuit; and (4) a rectifier circuit for inputting an output from the second output terminal of the current detection circuit and outputting a rectified result; and (5) the rectifier circuit. And the output of the DC power supply, the output of the rectifier circuit and the output of the DC power supply are compared, and during a period when the output of the rectifier circuit is small, a comparator that outputs a high level; and (6) An integration circuit that inputs the output and outputs an integration result with a specific time constant and (7) dimming circuit A switch that is conductive during a low level instructing the extinguishing period; and (8) a discharge circuit that decreases the output level of the integration circuit during the period in which the switch is conductive; and (9) the output of the integration circuit is an input voltage, When the input voltage rises, the output frequency is lowered, and when the input voltage is lowered, the voltage controlled oscillator that outputs a triangular wave that raises the output frequency and (10) the output of the voltage controlled oscillator and the DC voltage are input, and the DC voltage A second comparator that outputs a signal having a defined efficiency at an output frequency of the voltage controlled oscillator; and (11) a dimming circuit that outputs an efficiency for determining a lighting period at a frequency of time-division dimming; and The second comparator output and the dimming circuit output are input, and the input of the second comparator output and the dimming circuit output both outputs a high level only during a high level period. Piezoelectric transformer An AND circuit for generating a switching signal to be moved, and (13) an input of the output of the AND circuit, a drive signal generating circuit for converting the signal to operate the driving circuit, and (14) an output of the drive signal generating circuit, A power supply apparatus using a piezoelectric transformer including a piezoelectric transformer driving circuit for driving the piezoelectric transformer.

  An eleventh invention for achieving the above object is a power supply device using a piezoelectric transformer in which a DC voltage value inputted to a second comparator is selected from a plurality of voltage values by a second switch.

  According to the present invention, the period during which the discharge lamp is turned on drives the piezoelectric transformer at a frequency at which the boost ratio of the piezoelectric transformer is high, and the period during which the discharge lamp is lit dark or is turned off at a frequency at which the boost ratio is low. The brightness of the discharge lamp can be adjusted by adjusting the ratio between the time for driving at a high boost ratio and the time for driving at a low boost ratio. Furthermore, the time constant is set so that the switching between the frequency with a high step-up ratio of the piezoelectric transformer and the frequency with a low step-up ratio is completed in a time greater than 0 seconds and about 500 μsec or less. Further, during the period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency, the input power to the piezoelectric transformer can be reduced by shortening the switching element conduction time per cycle of the piezoelectric transformer driving frequency.

  In addition, according to the present invention, while performing time-division dimming capable of setting a wide dimming range, the piezoelectric transformer is continuously vibrated without a period in which the AC input to the piezoelectric transformer is stopped. Generation of audible sounds due to changes in the vibration state can be suppressed. Furthermore, it is possible to prevent the luminance deviation from deteriorating by quickly switching between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio. Further, during the period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency, an increase in power consumption can be suppressed by limiting the input power of the piezoelectric transformer.

  As a result, it is possible to provide a method for adjusting the brightness of a low-power-consumption discharge lamp that suppresses the brightness deviation of the backlight discharge lamp of the liquid crystal display device and a power supply device using a piezoelectric transformer.

  A discharge lamp luminance adjusting method and a power supply apparatus using a piezoelectric transformer according to the best mode for carrying out the present invention will be described in detail below with reference to the drawings.

(Embodiment 1)
A discharge lamp luminance adjusting method and a power supply apparatus using a piezoelectric transformer in the first embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a method for adjusting the brightness of a discharge lamp and its power supply apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram showing a driving circuit for a piezoelectric transformer having a full bridge configuration. FIG. 3 is a block diagram illustrating a drive circuit for a piezoelectric transformer having a push-pull configuration. FIG. 4 is a block diagram showing a driving circuit for a piezoelectric transformer having a half-bridge configuration. FIG. 5 is a diagram illustrating the operation of the switch of the drive circuit.

  As shown in FIG. 1, (1) an AC voltage is input from the primary side electrode 13 and the primary side electrode 14 and output from the secondary side electrode 15 using the piezoelectric effect, and (2) from the input end. An output of the piezoelectric transformer 7 is input, output from the first output terminal, and a current detection circuit 16 that outputs a current proportional to the current value output from the first output terminal from the second output terminal, and (3) current A load 8 for inputting an output from the first output terminal of the detection circuit 16, and (4) a rectifier circuit 17 for inputting an output from the second output terminal of the current detection circuit 16 and outputting a rectified result (5) ) A switch W23 that receives the output signal of the dimming circuit 10 and selects either the DC power supply 26 or the DC power supply 27 and outputs it to the comparator 18. (6) The output of the rectifier circuit 17 and the output of the switch W23 And the output of the rectifier circuit and the output of the switch are compared, and the output of the rectifier circuit 17 During the shorter period, the comparator 18 that outputs a high level and (7) the output of the comparator 18 are input, and the integration circuit 19 that outputs an integration result having a specific time constant and (8) the integration circuit 19 The output is an input voltage, and when the input voltage increases, the output frequency decreases, and when the input voltage decreases, the voltage controlled oscillator 20 outputs a triangular wave that increases the output frequency, and (9) the output of the voltage controlled oscillator 20 and the DC power supply 30 By inputting a DC voltage, a comparator 31 that outputs a signal having an efficiency determined by the DC voltage of the DC power source 30 at the output frequency of the voltage controlled oscillator 20 and (10) time-sharing adjustment of the efficiency that determines the lighting period. The dimming circuit 10 that outputs at the frequency of light, (11) the comparator 31 output and the dimming circuit 10 output are input, and the comparator 31 output and the dimming circuit 10 output are both high only during a high level. Level output An AND circuit 12 for generating a switching signal for driving the piezoelectric transformer 7 so as to perform the above operation, and (12) a drive signal generation circuit 21 for inputting the output of the AND circuit 12 and converting it into a signal for operating the drive signal generation circuit 21 ( 13) A discharge lamp when the output of the drive signal generation circuit 21 is input and the output voltage of the configuration including the drive circuit 22 of the piezoelectric transformer for driving the piezoelectric transformer 7 is applied to the discharge lamp to light the discharge lamp. This is a power supply device using a piezoelectric transformer that generates an AC voltage from a DC voltage having a brightness adjustment function.

  Next, the operation of the power supply device using the discharge lamp luminance adjusting method and the piezoelectric transformer according to the first embodiment of the present invention will be described with reference to FIG. The output from the secondary electrode 15 of the piezoelectric transformer 7 is input to the current detection circuit 16. The current detection circuit 16 according to the first embodiment of the present invention preferably has a current transformer configuration. An input from the input terminal is output from the first output terminal, and a current corresponding to the current value output from the first output terminal is output from the second output terminal. Note that even if the current detection circuit 16 is inserted on the low voltage side, which is the opposite side of the load 8, the same effect can be obtained.

  Since the current change rate differs between the current on the low voltage side of the discharge lamp and the current on the high voltage side of the discharge lamp, whether you want to control the current on the low voltage side of the discharge lamp or the high voltage side of the discharge lamp Accordingly, the insertion location may be determined. Recently, both high-voltage drive systems in which a piezoelectric transformer is disposed at both ends of a discharge lamp are increasing. In this case, since the low voltage side does not exist, the method of inserting the high voltage side has versatility.

  The alternating current output from the second output terminal of the current detection circuit 16 is rectified by the rectifier circuit 17. The output of the rectifier circuit 17 becomes a pulse-like signal that is not completely smoothed. The switch W23 receives the output of the dimming circuit 10 and selects the DC power supply 26 having a high voltage value during a period in which it is desired to be turned on during time-division dimming, and lowers the period or luminance desired to be turned off during the time-division dimming. During the period, control is performed to select the DC power supply 27 having a low voltage value. The comparator 18 inputs the output signal of the rectifier circuit 17 and the DC power source 26 or the DC power source 27 selected by the switch W23. The comparator 18 is a step of outputting a high level during a period in which the pulse signal that is the output signal of the rectifier circuit 17 is lower than the DC voltage value selected by the switch W23. When the low DC power supply 27 is selected, the time ratio for outputting a high level is smaller than when the switch W23 selects the DC power supply 26 having a high voltage value. In other words, the time ratio during which high level output is performed is smaller in the period in which the light is to be turned off during the time-division dimming or the period in which the luminance is to be lowered. Since the integration circuit 19 is a step for receiving the output of the comparator 18 and outputting the result of integration, the output level is lower in the period in which the light is turned off or the brightness is lowered in the time division dimming than in the period in which the light is turned on. become.

  The voltage controlled oscillator 20 that receives the output of the integrating circuit 19 is configured to output a triangular wave having a lower frequency as the input voltage is higher, and to output a triangular wave having a higher frequency as the input voltage is lower. During the period in which the light is sometimes turned on, a triangular wave having a lower frequency than the period in which the light is to be turned off or the period in which the luminance is to be lowered is output.

  The output signal frequency of the voltage controlled oscillator 20 is twice the frequency for driving the piezoelectric transformer 7. A half frequency of the output frequency in the voltage controlled oscillator 20 is a frequency for actually driving the piezoelectric transformer 7. As shown in FIG. 13, the lowest frequency is a frequency slightly lower than the frequency at which the step-up ratio of the piezoelectric transformer is maximized, and the highest frequency is a sweep range where there is no or almost no output from the piezoelectric transformer. If the voltage value of the DC power supply is set to a value lower than any value of the pulse signal output from the rectifier circuit, the input voltage of the voltage controlled oscillator 20 becomes the lowest potential. The output frequency is the highest frequency in the sweep range, and becomes a point B where the output of the piezoelectric transformer 7 does not appear or hardly appears at a half frequency (point B in FIG. 13). Note that the voltage value of the DC power supply is set to a piezoelectric transformer driving frequency at which a desired current is obtained during lighting.

  Switching between the frequency of the lighting period and the frequency of the period for turning off the light or the period for reducing the luminance is performed by reducing the time constant of the integrating circuit and switching instantaneously so as not to pass the frequency between them. The value switches instantly to the none state. As a result, since the frequency at which the difference between the high-voltage side current and the low-voltage side current becomes very large is not passed, the luminance deviation on the backlight can be prevented from increasing.

  However, when the frequency is switched instantaneously so as not to pass the frequency in between, the vibration state of the piezoelectric transformer 7 is also switched suddenly, but not so much that the vibration is suddenly switched from a state without vibration to a large vibration. Will occur. Furthermore, overshoot may occur in the output voltage waveform or output current waveform of the piezoelectric transformer 7 at the moment when the lighting period starts. In order to suppress the luminance deviation while avoiding these problems, the time constant of the integrating circuit 19 is adjusted, and the switching between the frequency of the lighting period and the frequency of the period in which the luminance is to be turned off or the period in which the luminance is to be lowered is from 0 second. It is desirable to switch in a large time of 500 μsec or less.

  The comparator 31 inputs the output triangular wave of the voltage controlled oscillator 20 and the DC voltage of the DC power supply 30 and outputs a high level during a period when the output of the voltage controlled oscillator 20 is higher. The time ratio output from the comparator 31 is the time ratio of conduction per cycle of driving the piezoelectric transformer 7 in the switching element built in the drive circuit 22. The power supply to the piezoelectric transformer 7 is reduced by reducing the ratio of conduction of the switching element within a possible range, and the reduced power operates at a frequency with a high step-up ratio of the piezoelectric transformer 7 and a high conversion efficiency. By doing so, the power consumption of the entire power supply device is reduced.

  The dimming circuit 10 outputs a high level only during a period in which the piezoelectric transformer 7 outputs at a predetermined dimming frequency during time division dimming. The output of the dimming circuit 10 controls the switching state of the switch W23 and is output to the AND circuit 12.

  The AND circuit 12 inputs the output of the comparator 31 and the output of the dimming circuit 10, and both outputs a high level only when both inputs are at a high level. Therefore, the output signal of the AND circuit 12 is turned off during time-division dimming. It is low level for the period you want to let. In other periods, the signal repeats a high level and a low level with an efficiency determined by the voltage value of the DC power supply 30 at the frequency output by the voltage controlled oscillator 20.

  The drive signal generation circuit 21 is a circuit that converts a high-level signal input from the AND circuit 12 into a signal that controls the switching element of the drive circuit 22.

  Typical examples of combinations of the drive circuit 22 and the piezoelectric transformer 7 are shown in FIGS. In either case, a switch A5 and a switch B6 are provided so that an equivalent alternating current is input between the primary side electrode 13 and the primary side electrode 14 of the piezoelectric transformer 7. Further, in the case of a full bridge configuration, the switches C32 and D33 need to be controlled as indicated by the solid lines in FIG. In FIG. 5, ON indicates a conductive state, and OFF indicates a non-conductive state.

  The drive signal generation circuit 21 has means for alternately allocating a high-level signal that is twice the drive frequency of the piezoelectric transformer 7 input from the AND circuit 12 to the conduction signal of the switch A5 and the conduction signal of the switch B6. . When the full bridge circuit of FIG. 2 is used, the same signal as the conduction signal of the switch A5 is supplied as the conduction signal of the switch D33, and the same signal as the conduction signal of the switch B6 is supplied as the conduction signal of the switch C32. As a result, the drive signal generation circuit 21 and the drive circuit 22 drive the piezoelectric transformer 7 by dividing the output frequency of the voltage controlled oscillator 20 by half. Further, by increasing the voltage value of the DC power supply 30, the signal indicated by the solid line in FIG. 5 changes to the signal indicated by the broken line, and the supply of power to the piezoelectric transformer 7 can be reduced.

  By the operation described above, the piezoelectric transformer is driven at a frequency where the boosting ratio of the piezoelectric transformer is high during the period when the discharge lamp is turned on, and is driven at a frequency where the boosting ratio is low during the period where the discharge lamp is darkened or turned off. By adjusting the ratio between the time for driving at a high frequency and the time for driving at a low boosting ratio, a power supply device using a piezoelectric transformer for adjusting the brightness of the discharge lamp can be realized. Further, the means for switching between the frequency with a high step-up ratio of the piezoelectric transformer and the frequency with a low step-up ratio can change the reference voltage value by comparing the result of detecting the current flowing through the discharge lamp with a comparator.

(Embodiment 2)
FIG. 6 is a block diagram showing a discharge lamp luminance adjustment method and its power supply apparatus according to the second embodiment of the present invention. As shown in FIG. 6, (1) a piezoelectric transformer 7 that inputs an AC voltage from the primary side electrode 13 and the primary side electrode 14 and outputs it from the secondary side electrode 15 using the piezoelectric effect, and (2) a piezoelectric transformer 7. Are output from the input terminal, output from the first output terminal, and output a current proportional to the current value from the second output terminal, and (3) the first of the current detection circuit 16 A load 8 for inputting an output from the output terminal, (4) a rectifier circuit 17 for inputting an output from the second output terminal of the current detection circuit 16 and outputting a rectification result, and (5) an output of the rectifier circuit 17 Comparing the output of the DC power supply 26 and comparing it, the comparator 18 that outputs a high level during the period when the output of the rectifier circuit 17 is smaller, and (6) the output of the comparator 18 are input and have a specific time constant. The integration circuit 19 that outputs the integration result and (7) dimming circuit 10 output indicate the extinguishing period. The switch X24 that conducts during the -level period, (8) the discharge circuit 28 that lowers the output level of the integrating circuit 19 while the switch X24 is conducting, and (9) the output of the integrating circuit 19 is the input voltage, and the input voltage increases Then, the output frequency is lowered, and the voltage-controlled oscillator 20 that outputs a triangular wave whose output frequency is increased when the input voltage is lowered, and (10) the output of the voltage-controlled oscillator 20 and the DC power supply 30 are input, whereby the voltage-controlled oscillator 20 A comparator 31 for outputting a signal having an efficiency determined by the DC power source 30 at an output frequency; and (11) a dimming circuit 10 for outputting an efficiency for determining a lighting period at a frequency of time-division dimming; and (12) a comparator 31. AN that generates the switching signal for driving the piezoelectric transformer 7 by inputting the output and the output of the dimming circuit 10 and outputting a high level only when both inputs are at a high level. The D circuit 12 and (13) the output of the AND circuit 12 is input and converted into a signal for operating the drive signal generation circuit 21; and (14) the output of the drive signal generation circuit 21 is input and the piezoelectric transformer 7 is a method for adjusting the luminance of a discharge lamp including a drive circuit 22 of a piezoelectric transformer for driving the power supply 7, and a power supply device for the method.

  The difference between the configuration of FIG. 1 and the configuration of FIG. 6 is that the DC power supply 27 of the switch W23 is present in FIG. 1 but not in FIG. 6, and the DC power supply 26 is directly input to the comparator 18, and FIG. The switch discharge circuit 28 exists but does not exist in FIG. In FIG. 6, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. Since the DC power supply 27 of the switch W23 in FIG. 1 is deleted, there is no frequency shifting means for changing the reference voltage value for comparing the result of detecting the current flowing through the discharge lamp with the comparator. The alternative frequency shifting means can reduce the input voltage to the voltage controlled oscillator 20 because the switch X24 is conductive during the extinguishing period and the output of the integrating circuit 19 is lowered by the discharging circuit 28. Since the output frequency of the voltage controlled oscillator 20 increases as the input voltage decreases, as shown in FIG. 13, the driving frequency of the piezoelectric transformer 7 is a frequency with a low step-up ratio at the time of lighting, for example, the point A when the light is turned off. Moving to point B, the extinguishing period is realized. When the discharge capacity of the discharge circuit 28 is large, switching from the point A to the point B is performed in a time almost close to 0 seconds, so that an increase in luminance deviation on the backlight can be prevented. In this state, when an overshoot occurs in a small sound or the output voltage or output current of the piezoelectric transformer 7, it is desirable to adjust the discharge capacity so that the switching is performed in a time of 500 μsec or less greater than 0 seconds.

  By the operation described above, the piezoelectric transformer is driven at a frequency where the boosting ratio of the piezoelectric transformer is high during the period when the discharge lamp is turned on, and is driven at a frequency where the boosting ratio is low during the period where the discharge lamp is darkened or turned off. By adjusting the ratio between the time for driving at a high frequency and the time for driving at a low step-up ratio, a power supply device using a brightness adjusting piezoelectric transformer for the discharge lamp can be realized. The means for switching between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio is characterized by forcibly changing the input voltage of the voltage controlled oscillator.

(Embodiment 3)
FIG. 7 is a block diagram showing a discharge lamp luminance adjustment method and its power supply apparatus according to the third embodiment of the present invention. FIG. 8 is a diagram illustrating current waveforms of a dimming method using current amplitude and a dimming method using time division. FIG. 12 is a graph showing the correlation between the low-voltage side current and the high-voltage side current when the current amplitude is changed. FIG. 13 is a graph showing the relationship between the drive frequency of the piezoelectric transformer and the step-up ratio.

  The configuration of FIG. 7 will be described again. (1) The piezoelectric transformer 7 that receives an AC voltage from the primary side electrode 13 and the primary side electrode 14 and outputs it from the secondary side electrode 15 using the piezoelectric effect, and (2) the piezoelectric element. An output of the transformer 7 is input from the input end, output from the first output end, and a current detection circuit 16 that outputs a current proportional to the current value from the second output end; and (3) a first of the current detection circuit 16 A load 8 for inputting an output from one output terminal, (4) a rectifier circuit 17 for inputting an output from a second output terminal of the current detection circuit 16 and outputting the rectification result, and (5) a dimming circuit 10 The switch W23 that selects one of the outputs of the DC power supply 26 and the DC power supply 27 in response to the output signal and outputs to the comparator 18 and (6) the output of the rectifier circuit 17 and the output of the switch W23 are input and compared. Therefore, when the output of the rectifier circuit 17 is smaller, the high level output is reduced. The comparator 18 and (7) the output of the comparator 18 are input, the integration circuit 19 that outputs an integration result having a specific time constant, and (8) the output of the integration circuit 19 is the input voltage. The voltage controlled oscillator 20 that outputs a triangular wave that lowers the output frequency when the input voltage increases and the output frequency increases when the input voltage decreases, and (9) either the DC power supply 29 or the DC power supply 30 depending on the output of the voltage controlled oscillator 20 and the switch Y25. A comparator 31 that outputs a signal having an efficiency determined by the DC power source 30 at the output frequency of the voltage controlled oscillator 20 by inputting the selected DC voltage, and (10) the lighting period is determined by the time-division dimming frequency. The dimming circuit 10 that outputs the efficiency, (11) the comparator 31 output and the dimming circuit 10 output are input, and the piezoelectric transformer 7 is driven by outputting a high level only when both inputs are at a high level. The AND circuit 12 for generating the switching signal and (12) the output of the AND circuit 12 are input and converted to a signal for operating the driving signal generating circuit 21 and (13) the output of the driving signal generating circuit 21 And a piezoelectric transformer drive circuit 22 for driving the piezoelectric transformer 7.

  The difference between the configuration of FIG. 1 and the configuration of FIG. 7 (the third embodiment) is that the DC power supply 29 of the switch Y25 exists in FIG. 7 and the input to the comparator 31 is switched by the switch Y25. Since the DC power supply 29 of the switch Y25 does not exist, the DC voltage input to the comparator 31 is constant. In FIG. 7, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The switch Y25 receives the output signal of the dimming circuit 10, and is configured to conduct to the DC power supply 30 during the lighting period and to conduct the DC power supply 29 during the extinguishing period. The voltage value of the DC power supply 29 is set higher than the voltage value of the DC power supply 30. Therefore, the DC voltage input to the comparator 31 during the extinguishing period is higher than the DC voltage value input during the lighting period. As described in the operation description of FIG. 1, the DC voltage input to the comparator 31 is increased, whereby the signal indicated by the solid line in FIG. 5 is changed to the signal indicated by the broken line and supplied to the piezoelectric transformer 7. Electric power can be reduced. As a result, it is possible to reduce the input power to the piezoelectric transformer 7 during a period in which it is desired to turn off the light (a period in which the output of the piezoelectric transformer 7 is unnecessary). As a result, power saving of the power supply device can be achieved.

(Embodiment 4)
The switch Y25 and the DC power supply 29 added to the first embodiment in the third embodiment are also effective for power saving of the power supply device even if added to the second embodiment.

  As described above, according to the present invention, it is possible to provide a method for adjusting the luminance of a discharge lamp with low power consumption, which suppresses the luminance deviation of a backlight discharge lamp of a liquid crystal display device, and a power supply device using a piezoelectric transformer. .

The block diagram which shows the brightness | luminance adjustment method of the discharge lamp in the 1st Embodiment of this invention, and its power supply device. The block diagram which shows the drive circuit of the piezoelectric transformer of a full bridge structure. The block diagram which shows the drive circuit of the piezoelectric transformer of a push pull structure. The block diagram which shows the drive circuit of the piezoelectric transformer of a half bridge structure. The figure which showed operation | movement of the switch of a drive circuit. The block diagram which shows the brightness | luminance adjustment method of the discharge lamp in 2nd embodiment of this invention, and its power supply device. The block diagram which shows the brightness | luminance adjustment method of the discharge lamp in 3rd embodiment of this invention, and its power supply device. The figure which shows the current waveform of the light control method by an electric current amplitude, and the light control method by a time division. The block diagram which shows an example of the piezoelectric inverter which employ | adopts time division dimming. The figure which shows the drive circuit of the piezoelectric transformer of a push pull structure. The figure which shows the electric current waveform at the time of the light control in patent document 1. FIG. The graph which shows the correlation of the low voltage side current at the time of current amplitude change, and the high voltage side current. The graph which shows the relationship between the drive frequency of a piezoelectric transformer, and a step-up ratio.

Explanation of symbols

1 DC power supply 2 Switch Z
3 Coil 4 Coil 5 Switch A
6 Switch B
7 Piezoelectric transformer 8 Load 9 Diode 10 Dimming circuit 11 Drive frequency generation circuit 12 AND circuit 13 Piezoelectric transformer primary electrode 14 Piezoelectric transformer primary electrode 15 Piezoelectric transformer secondary electrode 16 Current detection circuit 17 Rectifier circuit 18 Comparator 19 Integration Circuit 20 Voltage controlled oscillator 21 Drive signal generation circuit 22 Drive circuit 23 Switch W
24 Switch X
25 Switch Y
26 DC power supply 27 DC power supply 28 discharge circuit 29 DC power supply 30 DC power supply 31 comparator 32 switch C
33 Switch D

Claims (11)

  In the method for adjusting the brightness of the discharge lamp when the output voltage of the power supply device using a piezoelectric transformer that generates an AC voltage from the DC voltage is applied to the discharge lamp and the discharge lamp is turned on, the period during which the discharge lamp is turned on is The piezoelectric transformer is driven at a frequency with a high step-up ratio of the piezoelectric transformer, and the piezoelectric transformer is driven at a frequency with a low step-up ratio during a period in which the discharge lamp is lit dark or a period in which the discharge lamp is turned off. A method for adjusting a luminance of a discharge lamp, comprising adjusting a ratio of a time for driving the piezoelectric transformer at a frequency having a high step-up ratio and a time for driving the piezoelectric transformer at a frequency having a low step-up ratio.   2. The method for adjusting the brightness of a discharge lamp according to claim 1, wherein switching between a frequency with a high step-up ratio of the piezoelectric transformer and a frequency with a low step-up ratio is performed in a period greater than 0 seconds and about 500 μsec or less.   The method for adjusting the luminance of a discharge lamp according to claim 1 or 2, wherein, in a period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency, a switching element conduction time per cycle of the piezoelectric transformer driving frequency is shortened.   Applying an output voltage to a discharge lamp to light the discharge lamp in a power supply device using a piezoelectric transformer that generates an AC voltage from a DC voltage having a function of adjusting the brightness of the discharge lamp when the discharge lamp is turned on During the period, the piezoelectric transformer is driven at a frequency where the boost ratio of the piezoelectric transformer is high, and the period during which the discharge lamp is lit darkly or during the period when the discharge lamp is extinguished is driven at a frequency where the boost ratio is low. A power supply device using a piezoelectric transformer, comprising a brightness adjusting function of a discharge lamp that adjusts a ratio between a time for driving at a high frequency and a time for driving at a low frequency of the step-up ratio.   5. The piezoelectric transformer according to claim 4, wherein the piezoelectric transformer has a function of switching between a frequency having a high step-up ratio and a frequency having a low step-up ratio in a period of greater than 0 seconds and about 500 μsec or less. Power supply.   A function of detecting a current flowing through a discharge lamp, a function of comparing a detected current flowing through the discharge lamp with a comparator, and a function of changing a reference voltage value based on a result of comparison with the comparator; 6. The power supply device using a piezoelectric transformer according to claim 4, wherein a frequency with a high step-up ratio of the transformer is switched between a frequency with a low step-up ratio.   When the input voltage of the voltage controlled oscillator is increased, the output frequency is decreased, and when the input voltage of the voltage controlled oscillator is decreased, the output frequency is increased, and the piezoelectric transformer has a high boost ratio and a low boost ratio. The power supply device using the piezoelectric transformer according to claim 4, wherein:   8. The piezoelectric device according to claim 4, wherein the piezoelectric transformer has a function of shortening a switching element conduction time per cycle of the piezoelectric transformer driving frequency during a period in which the step-up ratio of the piezoelectric transformer is driven at a low frequency. A power supply using a transformer.   (1) An AC voltage is input from the primary side electrode and a piezoelectric transformer is used to output from the secondary side electrode using the piezoelectric effect. (2) The output of the piezoelectric transformer is input from the input end, and from the first output end. A current detection circuit that outputs and outputs a current proportional to a current value output from the first output terminal from the second output terminal; and (3) inputs an output from the first output terminal of the current detection circuit. A load and (4) a rectifier circuit that outputs an output from the second output terminal of the current detection circuit and outputs a rectified result; and (5) a plurality of DC power supplies that receive an output signal of the dimming circuit. A switch that selects one of them and outputs it to the comparator; and (6) inputs the output of the rectifier circuit and the output of the switch, compares the output of the rectifier circuit and the output of the switch, and outputs the output of the rectifier circuit A comparator that outputs a high level during a period when (7) the comparator is An integration circuit that inputs an output and outputs an integration result with a specific time constant. (8) The output of the integration circuit is an input voltage. When the input voltage increases, the output frequency decreases, and when the input voltage decreases, the output (9) a voltage-controlled oscillator that outputs a triangular wave that increases the frequency; and (9) the voltage-controlled oscillator output and a DC voltage are input, and a signal having an efficiency determined by the DC voltage is output at an output frequency of the voltage-controlled oscillator. Two comparators and (10) a dimming circuit that outputs the efficiency for determining the lighting period at a frequency of time-division dimming, and (11) input the output of the second comparator and the output of the dimming circuit, An AND circuit for generating a switching signal for driving the piezoelectric transformer so that both the output of the second comparator and the output of the dimming circuit output a high level only during a high level period; AND circuit A drive signal generation circuit for inputting an output and converting the signal into a signal for operating the drive circuit; and (13) a piezoelectric transformer drive circuit for inputting the output of the drive signal generation circuit and driving the piezoelectric transformer. A power supply device using the piezoelectric transformer according to claim 4, 5 or 6.   (1) An AC voltage is input from the primary side electrode and a piezoelectric transformer is used to output from the secondary side electrode using the piezoelectric effect. (2) The output of the piezoelectric transformer is input from the input end, and from the first output end. A current detection circuit that outputs and outputs a current proportional to a current value output from the first output terminal from the second output terminal; and (3) inputs an output from the first output terminal of the current detection circuit. A load and (4) a rectifier circuit that inputs an output from the second output terminal of the current detection circuit and outputs a rectified result; and (5) an output of the rectifier circuit and an output of a DC power source and the rectifier Comparing the output of the circuit and the output of the DC power source, and when the output of the rectifier circuit is small, a comparator that outputs a high level and (6) the output of the comparator is input and integration with a specific time constant The integration circuit that outputs the result and (7) dimming circuit output is low level indicating the extinguishing period. A switch that conducts for a period; and (8) a discharge circuit that lowers the output level of the integration circuit during the period in which the switch is conducted; and (9) the output of the integration circuit is used as an input voltage, and when the input voltage increases, the output frequency is lowered. A voltage-controlled oscillator that outputs a triangular wave that increases the output frequency when the input voltage decreases, and (10) an output of the voltage-controlled oscillator and a DC voltage are input, and a signal having an efficiency determined by the DC voltage is input to the voltage A second comparator that outputs at the output frequency of the controlled oscillator, and (11) a dimming circuit that outputs the efficiency for determining the lighting period at a frequency of time-division dimming, and (12) the second comparator output and the dimming A circuit output is input, and a switching signal is generated to drive the piezoelectric transformer so that the second comparator output and the dimming circuit output both output a high level only during a high level period. And an AND circuit that inputs the output of the AND circuit and converts it into a signal for operating the drive circuit, and (14) inputs the output of the drive signal generation circuit and drives the piezoelectric transformer. 8. A power supply device using a piezoelectric transformer according to claim 4, further comprising a piezoelectric transformer drive circuit.   11. The power supply device using a piezoelectric transformer according to claim 9, wherein a DC voltage value input to the second comparator is selected from a plurality of voltage values by a second switch.

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