JP2000058289A - Discharge lamp luminance adjusting method and discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a luminance adjusting method for a discharge lamp which can reduce noise emission and make a wide range of brightness adjustment and provide a discharge lamp lighting device and also a liquid crystal display device and lighting system using the discharge lamp lighting device. SOLUTION: When the tube current in a fluorescent tube 54 (discharge lamp) is over the specified threshold to generate a dimmer condition of a high luminance, a continuous AC voltage is emitted from an inverter circuit 53 and the tube current is varied by changing the level of the output voltage to make a luminance adjustment, and when the tube current is below the threshold to generate a dimmer condition of low luminance a feedback voltage formed by superposing a triangular wave voltage on the tube current sensing voltage using an or circuit consisting of diodes D2 and D3 is prepared and fed back to a DC-DC converter circuit 52, and as luminance adjustment is made by lowering the level of the output voltage of the inverter circuit 53 in the periods to give a lower frequency than the frequency of the AC voltage emitted from the inverter circuit 53 and changing the tube current through changing of the proportion of the periods to generate lowering of the output voltage level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for adjusting the brightness of a discharge lamp used for backlighting a liquid crystal display panel used in a notebook personal computer or the like.

[0002]

2. Description of the Related Art Conventionally, in a discharge lamp lighting device (also called a backlight inverter device) for lighting a discharge lamp (for example, a cold cathode fluorescent tube), dimming of the brightness of the fluorescent tube is performed by changing a tube current. .

FIG. 1 is a configuration diagram showing a conventional discharge lamp lighting device. In the figure, reference numeral 11 denotes a DC power supply such as a battery;
Denotes a DC-DC converter circuit, 13 denotes a self-excited inverter circuit (hereinafter, referred to as an inverter circuit), 14 denotes a current detection circuit, and 15 denotes a cold cathode fluorescent tube.

In the above configuration, a cold cathode fluorescent tube (hereinafter, referred to as a cold cathode fluorescent tube)
The fluorescent tube current flowing through the fluorescent tube (referred to as a fluorescent tube) 15 is detected by the current detection circuit 14, and the detection result is fed back to the DC-DC converter circuit 12.

[0005] The DC-DC converter circuit 12 converts the voltage level supplied from the DC power supply 11 to another voltage level based on a feedback signal from the current detection circuit 14 and outputs the converted voltage level to the inverter circuit 13.

The inverter circuit 13 converts a DC voltage input from the DC-DC converter circuit 12 into an AC voltage having a predetermined frequency and applies the AC voltage to the fluorescent tube 15.

As described above, the tube current detected by the current detection circuit 14 is fed back to the DC-DC converter circuit 12 to change the supply voltage of the inverter circuit 13 so that the tube current is controlled at a constant current.

[0008] The tube current flowing through the fluorescent tube 15 is a continuous current, and is controlled to be a predetermined level set in advance. Further, dimming can be performed in a range of luminance MAX of about 100% to 50%, and this dimming method is generally called a current dimming method.

Further, in order to widen the range on the low luminance side in order to widen the dimming range, it is necessary to operate with a reduced tube current. However, when the tube current is reduced, the discharge becomes unstable due to the property of the fluorescent tube 15. Therefore, in the continuous constant current control method as described above, the lower limit on the low luminance side is about 50% of the luminance MAX. It is a limit.

On the other hand, recently, in order to extend the operation time of a battery drive in a notebook personal computer or the like, a method of operating a fluorescent tube with large power consumption at low luminance has been used. In this case, the luminance dimming range is required to have a luminance MAX of about 100% to 10%.

As a method for expanding the dimming range, there is a limit in the constant current control by the continuous current. For example, as disclosed in Japanese Patent Application Laid-Open No. Hei 5-198384, the tube current is intermittently controlled and the ratio is controlled. A variable burst dimming method is used. This dimming method is also called duty dimming or frequency dimming.

A discharge lamp lighting device using a burst dimming system converts an output voltage of a DC power supply 21 into a voltage of a predetermined level by a DC-DC converter circuit 22 as shown in FIG. Fill in 23,
DC-DC converter circuit 22 to inverter circuit 23
The power supply to the cold cathode fluorescent tube 25 is changed by intermittently supplying power to the cold cathode fluorescent tube 25 based on the burst signal generated by the burst signal oscillation circuit 24. At this time, dimming can be performed by adjusting the intermittent ratio of energization to the inverter circuit 23.

Next, a specific example of a conventional discharge lamp lighting device using a burst dimming method will be described.

FIG. 3 is a block diagram showing a conventional discharge lamp lighting device using a burst dimming system, and FIG. 4 is an operation waveform diagram thereof. In the figure, 31 is a DC power supply such as a battery, 32 is DC
-DC converter circuit, 33 is a dimming control circuit, 34 is a self-excited inverter circuit, 35 is a cold cathode fluorescent tube (hereinafter, referred to as
A fluorescent tube).

The DC-DC converter circuit 32 changes the voltage level supplied from the DC power supply 31 to a predetermined level and outputs the same to the inverter circuit 34.

The dimming control circuit 33 includes a triangular wave generation circuit 33.
a and a control signal generation circuit 33b, and outputs the triangular wave voltage Vtr and the threshold voltage Vth generated by the triangular wave generation circuit 33a to the comparator 331 of the control signal generation circuit 33b.
To generate a rectangular wave voltage Vreq (burst signal), and input this rectangular wave voltage Vreq to the inverter circuit 34.

The inverter circuit 34 includes a transformer 341, a choke coil 342, and transistors 343 to 345. Power is supplied from the DC-DC converter circuit 32 to the transformer 341 via the choke coil 342, and the transistor
By switching 343 with the rectangular wave voltage Vreq, the oscillation operation of the Loyer circuit constituted by the transistors 344, 345, etc. is turned on / off.

By the on / off operation, the power supply to the inverter circuit 23 is interrupted.

As a result, the voltage is applied to the fluorescent tube 35 only when the lower circuit is performing the oscillating operation.
Dimming can be performed by changing the on / off ratio in the switching operation of the transistor 343.

The on / off ratio in the switching operation of the transistor 343 can be changed by changing the level of the threshold voltage Vth by the variable resistor 332 in the control signal generation circuit 33b.

[0021]

However, the above-described conventional discharge lamp lighting device using the burst dimming method has the following problems.

That is, in the case of the burst dimming method, the frequency of the rectangular wave voltage Vreq (burst signal) (hereinafter, referred to as a burst frequency) is generally set to several hundred Hz to several KHz, and the inverter circuit 34 at this burst frequency. When the control signal generation circuit 33b and the transistor 343 are switched from off to on, the current supplied to the transformer 341 is interrupted. A hearing sound occurs. In this way, the growling sound generated from the transformer 341 and the choke coil 342 is very harsh,
It was a problem that had to be solved inherent in burst dimming.

In the conventional burst dimming method, duty dimming is performed at a burst frequency over a wide range from a high luminance (high output power) state to a low luminance state. Therefore, during burst dimming,
The humming sound of an audible frequency generated from the coil 342 has a property that the sound becomes louder as the supply voltage to the inverter circuit 34 is higher and as the output power of the inverter circuit 34 is higher.

Therefore, the higher the voltage supplied to the inverter circuit 34, the steeper the voltage waveform when the inverter circuit 34 starts up, and the more the groaning sound is likely to occur. Similarly, the larger the power handled by the inverter circuit 34, the greater the current at the time of startup, so that a groaning sound is likely to occur.

FIG. 5 shows a transformer 34 during the conventional burst dimming.
FIG. 6 shows an example of an actually measured value of the noise level generated from 1; FIG. 6 shows an example of an actually measured value of the noise level generated from the choke coil 342 during the conventional burst dimming; FIGS. It is a figure which shows the collector voltage waveform and tube current waveform of a lower circuit.

5 and 6, the vertical axis represents the noise level (dB), and the horizontal axis represents the dimming state. Also,
Each of the three broken lines in the drawing represents a difference in the input voltage to the inverter circuit 34, and the input voltage in each is 7V, 12V, and 18V as described in the drawing.

The upper waveforms in FIGS. 7 to 10 show the collector voltage waveform (1) of the transistor in the lower circuit.
0V / div), lower waveform is tube current waveform (5mA / div)
7 shows a tube current of 5 mArms, and FIG. 8 shows a tube current of 4 mArms.
ms, Fig. 9 shows tube current of 3mArms, Fig. 10 shows tube current of 2.5m
It is a measurement result at the time of Arms.

Further, a conventional example shown in FIG.
In the discharge lamp lighting device using the burst dimming method of No. 98384), when the input voltage of the inverter circuit 34 fluctuates, the tube current (luminance) changes because the constant current control of the tube current is not performed. There was a disadvantage.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a method for adjusting the luminance of a discharge lamp, a discharge lamp lighting device, a liquid crystal display device and a lighting device using the same, which can reduce the generation of noise and perform a wide range of luminance adjustment. Is to provide.

[0030]

In order to achieve the above object, according to the present invention, an output voltage of an inverter circuit for generating an AC voltage from a DC voltage is applied to a discharge lamp to light the discharge lamp. A method of adjusting the brightness of a discharge lamp when the lamp current value flowing through the discharge lamp is equal to or greater than a predetermined threshold value, outputting a continuous AC voltage from the inverter circuit and changing the level of the output voltage. When the tube current value is smaller than the threshold value, the output voltage of the inverter circuit is changed at a cycle lower than the frequency of the AC voltage output from the inverter circuit. The present invention proposes a method of adjusting the brightness of a discharge lamp in which the level of the lamp is continuously reduced and the ratio of the period of the reduction and the cycle is changed to change the tube current to adjust the brightness. .

According to the method of adjusting the brightness of the discharge lamp, when the value of the tube current flowing through the discharge lamp is equal to or more than the predetermined threshold, that is, when the brightness of the discharge lamp is high, the continuous AC By outputting a voltage and changing the level of the output voltage, the tube current is changed to perform brightness adjustment. Further, when the tube current value is smaller than the threshold value, that is, when the brightness of the discharge lamp is in a low dimming state, the frequency of the inverter circuit is lower than the frequency of the AC voltage output from the inverter circuit. By lowering the level of the output voltage and changing the ratio of the period during which the output voltage is lowered, the tube current is changed to perform brightness adjustment.

According to a second aspect of the present invention, in the method for adjusting the brightness of a discharge lamp according to the first aspect, when the level of the output voltage of the inverter circuit is reduced in the cycle, the input voltage level to the inverter circuit is set to a predetermined value. We propose a method of adjusting the brightness of a discharge lamp that changes with the inclination of the lamp.

According to the method of adjusting the brightness of the discharge lamp, the input voltage level of the inverter circuit is changed so that the input voltage level of the inverter circuit has a predetermined slope.
Since the tube current of the discharge lamp is adjusted, the change in the input voltage level becomes gentle.

According to a third aspect of the present invention, there is provided a discharge lamp lighting device which includes an inverter circuit for generating an AC voltage from a DC voltage, and applies the output voltage of the inverter circuit to the discharge lamp to light the discharge lamp. A tube current detecting means for detecting a tube current flowing through the lamp, converting the voltage into a voltage, and outputting the voltage; and a frequency having a voltage level equal to or lower than a predetermined threshold voltage level and lower than the frequency of the AC voltage output from the inverter circuit. A burst signal generating means for generating and outputting a burst signal voltage whose voltage level changes with a predetermined slope in a cycle, and at least one of the supplied burst signal voltage and the output voltage of the tube current detecting means Feedback voltage generating means for generating a feedback voltage according to the following, and a DC full power and the feedback voltage are supplied to the inverter circuit according to the feedback voltage. Suggest discharge lamp lighting device and a control means for outputting to control the level of force to DC voltage.

According to the discharge lamp lighting device, the tube current flowing through the discharge lamp is detected by the tube current detecting means and converted into a voltage, and the burst signal generating means has a voltage level lower than a predetermined threshold voltage level. A burst signal voltage whose voltage level changes with a predetermined slope in a cycle having a frequency lower than the frequency of the AC voltage output from the inverter circuit is generated and output. It is output as a feedback voltage according to the burst signal voltage and the output voltage of the tube current detecting means. The level of the DC voltage input to the inverter circuit is controlled by the control means according to the feedback voltage.

Therefore, when the tube current is higher than the threshold voltage level, the AC voltage applied to the discharge lamp is continuous and the voltage level is changed to adjust the brightness. Further, when the tube current is lower than the threshold voltage level, the AC voltage applied to the discharge lamp has a wedge-shaped decreasing portion at a burst frequency from a continuous state, and as a result, it becomes intermittent and intermittent. The brightness is adjusted by changing the ratio.

According to a fourth aspect of the present invention, in the discharge lamp lighting device according to the third aspect, the feedback voltage generating means adds the burst signal voltage and the output voltage of the tube current detecting means by a logical OR connection of diodes. A discharge lamp lighting device is proposed.

According to the discharge lamp lighting device, since the burst signal voltage and the output voltage of the tube current detecting means are added or selected by the logical OR connection of the diodes, the adding circuit is extremely simplified.

According to a fifth aspect of the present invention, there is provided the discharge lamp lighting device according to the third or fourth aspect, wherein the inverter circuit has a piezoelectric transformer and generates an AC voltage from the piezoelectric transformer.

According to the discharge lamp lighting device, an AC voltage is generated by the piezoelectric transformer of the inverter circuit.

According to a sixth aspect of the present invention, there is provided a discharge lamp lighting device which includes an inverter circuit for generating an AC voltage from a DC voltage and applies the output voltage of the inverter circuit to the discharge lamp to light the discharge lamp. Current control means for controlling the direction of current flow and the current flow to the transformer primary winding of the inverter circuit based on the voltage and a predetermined voltage level in a cycle having a frequency lower than the frequency of the AC voltage output from the inverter circuit. A control voltage generation unit that generates a burst signal voltage that changes with a slope, and supplies a control voltage corresponding to the burst signal voltage to the current control unit; and a control voltage generation unit that is connected to the control voltage generation unit and controls a DC level of the control voltage. The present invention proposes a discharge lamp lighting device including a DC level changing means for changing the DC level.

According to the discharge lamp lighting device, the control voltage generating means generates the burst signal voltage whose voltage level changes in a cycle having a frequency lower than the frequency of the AC voltage output from the inverter circuit. Is output as Further, the current control means controls the direction of current and the current supplied to the primary winding of the transformer of the inverter circuit based on the control voltage. Further, the DC level of the control voltage is changed by the DC level varying means, whereby the direction of current and the current supplied to the primary winding of the transformer of the inverter circuit by the current control means are changed to adjust the brightness of the discharge lamp. Is performed.

According to a seventh aspect of the present invention, there is provided the discharge lamp lighting device according to the third, fourth, fifth or sixth aspect, wherein the burst signal voltage is a triangular wave voltage.

According to the discharge lamp lighting device, since the burst signal voltage is a triangular wave voltage, the input voltage of the inverter circuit can be easily and smoothly changed with a predetermined slope.

In the eighth aspect, the third to seventh aspects are described.
A liquid crystal display device using the discharge lamp lighting device according to any of the above items is proposed.

According to the liquid crystal display device, a discharge lamp for a backlight is turned on by the discharge lamp lighting device.

In the ninth aspect, the third to seventh aspects are described.
A lighting device using the discharge lamp lighting device according to any one of the above is proposed.

According to the lighting device, the discharge lamp lighting device turns on the discharge lamp for lighting.

According to a tenth aspect of the present invention, an inverter circuit for generating an AC voltage from the supplied DC voltage and applying the AC voltage to a discharge lamp to turn on the discharge lamp; Supplying the DC voltage to a circuit, detecting a tube current flowing through the discharge lamp, and when the value of the tube current is equal to or greater than a predetermined threshold value, outputting a continuous AC voltage from the inverter circuit according to the DC voltage. The brightness is adjusted by changing the tube current by outputting and changing the level of the output voltage.If the value of the tube current is smaller than the threshold value, the value is output from the inverter circuit according to the DC voltage. By lowering the level of the output voltage of the inverter circuit in a cycle in which the frequency is lower than the frequency of the AC voltage, and changing the ratio of the period in which the output voltage is reduced to the cycle Changing the serial tube current Suggest brightness adjusting circuit of a discharge lamp and a voltage supply circuit which performs brightness adjustments.

According to the discharge lamp luminance adjusting circuit, when the value of the tube current flowing through the discharge lamp is equal to or higher than a predetermined threshold value, that is, when the luminance of the discharge lamp is high, the voltage is adjusted according to the DC voltage. By continuously outputting an AC voltage from the inverter circuit and changing the level of the output voltage, the tube current is changed and the brightness is adjusted. Further, when the tube current is smaller than the threshold value, that is, when the brightness of the discharge lamp is low, the frequency is lower than the frequency of the AC voltage output from the inverter circuit according to the DC voltage. The tube current is changed by changing the ratio between the feedback and the cycle for lowering and lowering the output voltage level of the inverter circuit in a certain cycle, and the brightness is adjusted.

[0051]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 11 is a block diagram showing a discharge lamp lighting device according to the first embodiment of the present invention. In the figure, 41
Is a DC power supply, 42 is a DC-DC converter circuit as control means, 43 is a self-excited inverter circuit, 44 is a cold cathode fluorescent tube (hereinafter simply referred to as a fluorescent tube) as a discharge lamp,
Reference numeral 45 denotes a current detection circuit serving as tube current detection means and feedback voltage generation means, and reference numeral 46 denotes a burst signal generation circuit serving as burst signal generation means. Further, the DC-DC converter circuit 42, the current detection circuit 45, and the burst signal generation circuit 46 correspond to a voltage supply circuit.

The DC-DC converter circuit 42 converts the DC voltage output from the DC power supply 41 to a predetermined level based on the feedback voltage output from the current detection circuit 45 so that the feedback voltage maintains a substantially constant value. Convert to DC voltage,
By continuously or intermittently applying this voltage, the inverter circuit 43
To supply.

The inverter circuit 43 is composed of, for example, a transistor and a transformer in the same manner as in the above-described conventional example. I do.

The current detection circuit 45 detects a tube current flowing through the fluorescent tube 44 and converts it into a voltage corresponding to, for example, a tube current value.
After adding the burst signal voltage output from 6, this voltage level is level-converted by a variable resistor or the like, and this is output to the DC-DC converter circuit 42 as a feedback voltage. By adjusting the resistance value of the variable resistor, the fluorescent tube 4
4 can be performed.

The burst signal generation circuit 46 has a voltage level equal to or lower than a predetermined threshold voltage level, and has a voltage level having a predetermined slope (horizontal axis) at a frequency that is lower than the frequency of the AC voltage output from the inverter circuit 43. And a burst signal voltage that varies with the time and the vertical axis as a voltage value). In addition, here, the burst signal voltage is a triangular wave voltage, and the threshold voltage level is a detection voltage level corresponding to a tube current when the luminance of the fluorescent tube 44 is approximately halfway between the maximum value and the minimum value.

According to the above configuration, as shown in the waveform diagram of FIG. 12, from the state where the luminance of the fluorescent tube 44 is high (the state where the tube current is large) to the normal luminance level (the luminance level corresponding to the threshold voltage). Since the level of the detection voltage is higher than the burst signal voltage, the level of the feedback voltage is almost always constant, and the dimming is performed by the current dimming method of the constant current control.

In a low-luminance state in which dimming is reduced (a state in which the tube current is small), the level of the burst signal voltage becomes higher than the level of the detection voltage. , And the output voltage level of the converter circuit is pulse width modulated by the triangular wave voltage component in the feedback voltage, and the dimming is performed by the burst dimming method in which the output voltage level of the DC-DC converter circuit is reduced or interrupted.

In the vicinity of a normal luminance level (a luminance level corresponding to the above-mentioned threshold value), as shown in FIG. After reaching a smaller value (hereinafter referred to as a minimum value), it gradually increases. At the time of transition from the increasing state to the state having the constant value, a sudden increase or decrease in current as an excessive response corresponding to the overshoot does not occur, and the current gradually and gradually converges to the constant value. . The waveform in FIG. 16 is wedge-shaped for the tube current in this portion. The ratio of the minimum value to the fixed value is a value larger than 0 and smaller than 1.

Further, the burst signal voltage is changed to a triangular wave voltage such that the waveform of the input voltage to the inverter unit at the time of the burst dimming is changed from a conventional rectangular waveform steep waveform to a waveform having a gentle rising and falling slope. Thus, magnetostriction generated in a transformer or the like used in the inverter circuit 43 is reduced.

Therefore, when the brightness of the fluorescent tube 44 is high and the load is in a dimming state, a continuous AC voltage is output from the inverter circuit 43 and the level of the output voltage of the converter circuit is changed to change the level of the tube flowing through the fluorescent tube 44. The brightness is adjusted by changing the current, and when the brightness of the fluorescent tube 44 is low and the load is dimmed, the frequency of the inverter circuit 43 is lower than the frequency of the AC voltage output from the inverter circuit 43. A period during which the level of the output voltage is reduced and reduced (including a period of at least two states in which the level of the output voltage of the inverter circuit 43 decreases and becomes constant at the reduced value. In addition to the period of the two states, It may be defined to include a period in which the level of the output voltage of the inverter circuit 43 rises.), The tube current is changed. The luminance adjustment is performed, it is possible to reduce the magnetostriction occurring in the transformer or the coil or the like at the time of high load, a beat sound generated from the transformer and the coil by said magnetostrictive can be greatly reduced as compared with the prior art.

Next, a first example showing a specific circuit configuration in this embodiment will be described.

FIG. 13 is a block diagram showing a discharge lamp lighting device according to the first embodiment. In the figure, 51 is a DC power supply,
52 is a DC-DC converter circuit, 53 is a self-excited inverter circuit, 54 is a cold cathode fluorescent tube (hereinafter simply referred to as a fluorescent tube), 55 is a detection / feedback circuit, 56 is an impedance conversion / DC level setting circuit, 57 is a triangular wave generation circuit.

The DC-DC converter circuit 52 includes an error amplifier 521, a comparator 522, a triangular wave generation circuit 523, an NP
It comprises an N-type transistor 524, a field effect transistor (hereinafter referred to as FET) 525, a diode 526, a choke coil 527, and a capacitor 528.

The error amplifier 521 receives the feedback voltage output from the detection / feedback circuit 55 and outputs an error voltage corresponding to the difference between the two so that the feedback voltage becomes substantially the same as the reference voltage Vref. I do.

The comparator 522 compares the triangular wave voltage output from the triangular wave generation circuit 523 with the error voltage,
When the error voltage is larger than the triangular wave voltage, a high-level signal is output, and when the triangular wave voltage is larger than the error voltage, a low-level signal is output. This output voltage is input to the base of the transistor 524, and the transistor 524 performs a switching operation.
525 also performs a switching operation.

Thus, when the FET 525 is on, the diode 526 and the choke coil are connected via the FET 525.
DC power supply 51 to the smoothing circuit composed of 527 and capacitor 528
Is supplied. Therefore, the choke coil 527
And from the output terminal of the capacitor 528, a continuous substantially constant level DC voltage based on the switching operation of the FET 525,
Alternatively, a DC voltage whose level changes based on the switching operation of the FET 525 or an intermittent DC voltage is output.

The inverter circuit 53 comprises a transformer 531, a choke coil 532, NPN transistors 533 and 534, a resistor 535 and capacitors 536 and 537, and has a well-known lower circuit.

The output voltage of the DC-DC converter circuit 52 is applied to an intermediate tap of the primary winding of the transformer 531 via a choke coil 532 and a fuse (which may be omitted), and the tertiary winding is connected via a resistor 535. Of the transistor 533 and the base of the transistor 533. The other end of the tertiary winding of the transformer 531 is connected to the base of the transistor 534, and the collector of each of the transistors 533 and 534 is connected to the transformer 531.
Are connected to both ends of the primary winding, and the emitter is grounded. A capacitor 536 is connected between both ends of the primary winding. One end of a secondary winding of the transformer 531 is connected to one end of the fluorescent tube 54 via a capacitor 537, and the other end of the secondary winding is grounded.

The detection / feedback circuit 55 includes resistors R1 to R
3, composed of diodes D1 to D3, a capacitor C1, and a variable resistor VR1. The other end of the fluorescent tube 54 is grounded via a resistor R1, and connected to the anode of the diode D2 and the cathode of the diode D1. I have.

The cathode of the diode D2 is connected to the cathode of the diode D3 and one end of the resistor R2 and grounded via the capacitor C1, and the other end of the resistor R2 is connected to the resistor R3 and the variable resistor connected in series. It is grounded via the device VR1.

A triangular wave voltage output from a triangular wave generating circuit 57 via an impedance conversion / DC level setting circuit 56 is applied to the anode of the diode D3.

Here, the value of the capacitor C1 is set so that the impedance becomes sufficiently high with respect to the frequency (burst frequency) of the triangular wave voltage.

As a result, the tube current flowing through the fluorescent tube 54 is converted into a voltage by the resistor R1, and the detected voltage is combined with the triangular wave voltage by a combining circuit (OR circuit) which is a connection between the anodes of the diodes D2 and D3. After that, the voltage is divided by the resistors R2 and R3 and the variable resistor VR1, and output as a feedback voltage. The level of this feedback voltage can be changed by the variable resistor VR1.

The triangular wave generating circuit 57 has, for example, a frequency 22
A triangular wave voltage having a frequency of 0 Hz and an amplitude of 1.5 Vp-p is generated. The triangular wave voltage is set to a DC level by an impedance conversion / DC level setting circuit 56, converted to a low impedance by an emitter follower, and applied to the anode of the diode D3. Is done.

Next, the operation of this embodiment having the above-described configuration will be described with reference to the waveform diagrams shown in FIG. 12 and FIGS. 14 to 17, the upper waveform is the collector voltage of the lower circuit in the inverter circuit 53, and the lower waveform is the tube current waveform. The collector voltage is represented by 10 V per scale, the tube current waveform is represented by 5 mA per scale, and the time axis (horizontal axis) is 1
1 ms per scale.

The waveforms shown in FIGS. 14 to 17 depict waveforms actually measured using an oscilloscope.

The AC signal (detection voltage) at the inverter frequency rectified by the diode D2 is smoothed by the capacitor C1 to become a DC voltage.

The voltage of the capacitor C1 is connected to the resistors R2 and R
3 and the variable resistor VR1 to divide the voltage.
It is applied to the feedback input of the C-DC converter circuit 52.

Adjustment of the tube current flowing through the fluorescent tube 54 is performed by changing the variable resistor VR1 and changing the DC-DC converter circuit 5
2 by adjusting the level of the feedback voltage applied to the feedback input. As a result, when the value of the variable resistor VR1 is small, the tube current increases to increase the luminance, and when the value is large, the tube current decreases to decrease the luminance.

That is, when the luminance of the fluorescent tube 54 is increased to the maximum value and the tube current is set to 5 mArms, the level of the detected voltage of the tube current of the fluorescent tube 54 is changed to the level of the triangular wave voltage injected through the diode D3. DC-D
As the feedback voltage fed back to the C converter circuit 52, the detection voltage of the tube current has priority. At this time, normal constant current control is performed, and the tube current becomes continuous. (See FIGS. 12 and 14)

When the brightness of the fluorescent tube 54 is slightly lowered from the maximum value by adjusting the variable resistor VR1 and the tube current is set to 4 mArms, the level of the detected voltage of the tube current is lower than the burst frequency in the same manner as described above. Since the voltage is higher than the level of the triangular wave voltage, the device operates under normal constant current control, and the level of the tube current waveform is lower than that of the tube current of 5 mArms. (See FIGS. 12 and 15)

When the tube current is set to 3 mArms by adjusting the variable resistor VR1, the level of the tube current waveform further decreases, the tube current detection voltage decreases, and the triangular wave voltage connected by the diode OR is reduced. Appears gradually in the feedback voltage, the triangular wave voltage is superimposed on the tube current detection voltage, and DC-
It is fed back to the DC converter circuit 52.

In the portion where the triangular wave voltage jumps out of the feedback voltage, the DC-DC converter circuit 52 operates in the direction of suppressing the output voltage. Therefore, the collector voltage of the lower circuit in the inverter circuit 53 is the portion where the triangular wave appears. descend. As a result, the tube current decreases in a wedge-like manner at the portion where the triangular wave appears. When the tube current is further reduced by adjusting the variable resistor VR1, the wedge-shaped portion of the tube current waveform expands to be in a burst dimming state. (FIGS. 12 and 1
6)

When the tube current is further reduced by adjusting the variable resistor VR1, the triangular wave is almost dominant in the feedback voltage to the DC-DC converter circuit 52, and the collector voltage of the lower circuit in the inverter circuit 53 is inactive. This is an operation of burst dimming in which (the off-state period in which the tube current does not completely flow) is widened. (See FIGS. 12 and 17)

The transformer 531 and the choke coil 532
As shown in FIGS. 18 and 19, noise generated from the conventional example is significantly reduced as compared with the conventional example.

FIG. 18 is a diagram showing measured values of the noise level generated from the transformer 531, and FIG. 19 is a diagram showing measured values of the noise level generated from the choke coil 532.

In FIGS. 18 and 19, the vertical axis represents the noise level (dB), and the horizontal axis represents the dimming state. Also, each of the three broken lines in the figure represents a difference in the input voltage to the inverter circuit 53, and the input voltage in each of them is 7V, 12V, 18
V.

As described above, according to the first embodiment, the conventional constant current dimming system and the burst dimming system are used together in a very simple circuit configuration to cover a wide range from the maximum luminance to the minimum luminance. The brightness of the fluorescent tube 54 can be continuously adjusted. When the brightness of the fluorescent tube 54 is high and the load is dimmed, the lamp current is changed by the constant current dimming method to adjust the brightness. When the luminance of the tube 54 is low and the load is dimmed at a low load, the tube current is changed and the luminance is adjusted by using both the constant current dimming method and the burst dimming method. Therefore, the growling noise generated from the transformer or the coil due to the magnetostriction can be significantly reduced as compared with the related art.

Further, since the feedback voltage is obtained by superimposing a triangular wave voltage, the change in the input voltage level of the inverter circuit 53 can be made smooth, and the transformer 531 and the choke coil 532 used in the inverter circuit 53 can be changed.
Is not applied to the transformer 53, the transformer 53
1 and the magnetostriction generated in the choke coil 532 can be reduced, and the occurrence of growling noise can be further reduced.

Next, a second example of the present embodiment will be described.

FIG. 20 is a configuration diagram showing a discharge lamp lighting device according to the second embodiment. In the figure, the same components as those in the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. Further, the difference between the first embodiment and the second embodiment is that the operation of the inverter circuit is controlled on the ground side of the lower circuit of the inverter circuit 53.

That is, in the second embodiment, the output voltage of the DC power supply 51 is directly applied to the input terminal of the inverter circuit 53, and the control unit 6 replaces the DC-DC converter 52 of the first embodiment.
1 (control means) was provided.

The control unit 61 includes an error amplifier 611, a triangular wave generation circuit 612, a comparator 613, a diode 614, an NPN
The transistor 615 includes a transistor 615 and a choke coil 616.

The error amplifier 611 receives the feedback voltage output from the detection / feedback circuit 55, and outputs an error voltage corresponding to the difference between the two so that the feedback voltage becomes substantially equal to the reference voltage Vref. I do.

The comparator 613 compares the triangular wave voltage output from the triangular wave generation circuit 612 with the error voltage,
When the error voltage is larger than the triangular wave voltage, a high-level signal is output, and when the triangular wave voltage is larger than the error voltage, a low-level signal is output. This output voltage is input to the base of the transistor 615, and the transistor 615 performs a switching operation.

The emitter of the transistor 615 is grounded,
The collector is connected to the anode of the diode 614 and to the emitters of the transistors 533 and 534 of the inverter circuit 53 via the choke coil 616. The cathode of the diode 614 is connected to the input terminal of the inverter circuit 53.

As a result, when the transistor 615 is on, the inverter circuit 5
3 is grounded, and the inverter circuit 53 receives a DC voltage of a continuous substantially constant level based on the switching operation of the transistor 615, or a DC voltage whose level changes based on the switching operation of the transistor 615 or an intermittent DC voltage. Applied.

Therefore, the same effects as those of the first embodiment can be obtained in the second embodiment.

Next, a third example of this embodiment will be described.

FIG. 21 is a configuration diagram showing a discharge lamp lighting device according to the third embodiment. In the figure, the same components as those in the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. The difference between the first embodiment and the third embodiment lies in that a separately-excited inverter circuit 62 is used.

Thus, the separately excited inverter circuit 62
The same effect as that of the first embodiment can be obtained by using.

Next, a fourth example of this embodiment will be described.

FIG. 22 is a configuration diagram showing a discharge lamp lighting device according to a fourth embodiment. In the figure, the same components as those in the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. The difference between the first embodiment and the fourth embodiment resides in that a self-excited piezoelectric inverter circuit 63 for generating an AC high voltage by using a piezoelectric transformer is used.

As described above, the self-excited piezoelectric inverter circuit 6
3, the same effect as in the first embodiment can be obtained.

Next, a fifth example of the present embodiment will be described.

FIG. 23 is a configuration diagram showing a discharge lamp lighting device according to a fifth embodiment. In the figure, the same components as those in the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. The difference between the first embodiment and the fifth embodiment lies in that the secondary winding of the transformer 531 in the inverter circuit 53 is floated and connected to the fluorescent tube 54.

In this case, the voltage applied to the primary winding of the transformer 531 is applied to the input terminal of the detection / feedback circuit 55 via the resistor 64 instead of the tube current. Since the tube current changes in accordance with the voltage of the primary winding of the transformer 531, this configuration can perform constant current control,
The same effect as that of the embodiment can be obtained.

Next, a second embodiment of the present invention will be described.

FIG. 24 is a configuration diagram showing a discharge lamp lighting device according to the second embodiment. In the figure, the same components as those in the first example of the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. The difference between the first embodiment of the first embodiment and the second embodiment is that a separately-excited piezoelectric inverter circuit 66 using a piezoelectric transformer is provided, and the inverter circuit is controlled by a frequency control circuit 65 as control means. 66
Is controlled to adjust the tube current (brightness adjustment).

The frequency control circuit 65 includes an error amplifier 651,
It comprises a voltage-controlled oscillator (hereinafter referred to as VCO) 652, a waveform shaping circuit 653, and a buffer circuit 654.

The error amplifier 651 receives the feedback voltage output from the detection / feedback circuit 55, and outputs an error voltage corresponding to the difference between the two so that the feedback voltage becomes substantially equal to the reference voltage Vref. I do.

The VCO 652 outputs a control signal of a frequency set based on the error voltage output from the error amplifier 651. This control signal is supplied to the inverter circuit 66 via the buffer circuit 654 after the waveform is shaped by the waveform shaping circuit 653.

The inverter circuit 66 is directly supplied with a DC voltage from the DC power supply 51, and changes the AC output voltage based on a control signal input from the frequency control circuit 65.

As described above, even when the separately excited inverter circuit 66 using the piezoelectric transformer is used, the same effect as that of the first example of the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described.

FIG. 25 is a configuration diagram showing a discharge lamp lighting device according to the third embodiment. In the figure, the same components as those in the first example of the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted. Further, the difference between the first embodiment of the first embodiment and the third embodiment is that the DC-DC converter circuit 52 and the detection / feedback circuit 55 are eliminated, and the drive control circuit 67 serving as a current control means is provided. And the operation of the drive control circuit 67 is controlled by the triangular wave voltage, which is a burst signal voltage supplied from the triangular wave generation circuit 57 and the impedance conversion / DC level setting circuit 68 as control means.

That is, the drive control circuit 67 comprises a PNP transistor 671 and two resistors 672 and 673. The base of the transistor 671 is connected to the DC power supply 5 via the resistor 672.
A resistor connected to the positive electrode and its own emitter
It is connected to the output terminal of the impedance conversion / DC level setting circuit 68 via 673. In addition, transistors
The collector of 671 is connected to the secondary winding via the resistor 535 of the inverter circuit 53. The primary winding intermediate tap of the transformer 531 of the inverter circuit 53 is connected to the positive electrode of the DC power supply 51 via the choke coil 532 and a fuse (may be omitted). A variable resistor 69 as a DC level varying means is connected between the ground and the impedance conversion / DC level setting circuit 68.

According to the above configuration, impedance conversion and
D of the triangular wave voltage output from the DC level setting circuit 68
By changing the C level, the inverter circuit 53
The input power to the primary winding of the transformer 531 to control the brightness of the fluorescent tube 54 over a wide range,
It is possible to reduce the generation of a growling sound as in the related art.

That is, the transistor 67 of the drive control circuit 67
The base voltage level of 1 is changed according to the level of the triangular wave voltage output from the impedance conversion / DC level setting circuit 68.

As a result, the collector current of transistor 671 changes in accordance with the base voltage level, so that the base voltages of transistors 533 and 534 forming the lower circuit of inverter circuit 53 change in accordance with the increase and decrease in the collector current of transistor 671. However, the collector currents of transistors 533 and 534 change correspondingly.

Therefore, the voltage applied to the primary winding of the burst dimming operation transformer 531 smoothly changes in accordance with the slope of the triangular wave voltage.

As a result, no sharply changing voltage is applied to the transformer 531 or the choke coil 532 used in the inverter circuit 53. Magnetostriction generated in the transformer 531 and the choke coil 532 can be reduced, and generation of a growling sound can be reduced.

On the other hand, when adjusting the luminance of the fluorescent tube 54, as shown in FIG. 26, by changing the resistance value of the variable resistor 69 of the impedance conversion / DC level setting circuit 68, the DC level of the triangular wave voltage is changed. Alternatively, the DC offset level is changed.

Thus, the base-emitter voltage Vbe of the transistor 671 changes according to the difference between the voltage Vdc of the DC power supply 51 and the triangular wave voltage Vtr. That is, when the luminance is high, the base-emitter voltage Vbe is saturated at about 0.7V. When the luminance is low, the base-emitter voltage Vbe
Becomes a triangular wave and enters a burst dimming state.

Accordingly, the operation of the lower circuit of the inverter circuit 53 can be made continuous or intermittent, the intermittent ratio can be changed, and a wide range of luminance adjustment can be performed.

As described above, according to the above embodiments,
The range of the burst dimming operation in the dimming range of the fluorescent tube (discharge lamp) 54 is set to a relatively light load range, and the rising and falling of the voltage waveform applied to the transformer or the choke coil during the burst dimming operation is made gentle. ing. Furthermore, even in the case of burst dimming, when the tube current detection voltage is in a state (on state) higher than the burst signal voltage, constant current control of the tube current is effective.

Therefore, according to the present embodiment, in the dimming state where the luminance of the fluorescent tube having a large load power is high, the detection / feedback circuit 55 gives priority to the level of the tube current waveform and returns to the control section, Constant current control for flowing a continuous tube current is performed.

When the dimming level is reduced and the load power becomes small, the feedback voltage is fed back in a form in which the burst signal voltage (triangular wave voltage) is superimposed on the tube current detection voltage, and the voltage of the burst signal is reduced. In a portion where is large, the tube current is suppressed, and the tube current switches to burst dimming. Switching to the burst dimming can be set arbitrarily, and is gradually switched according to the set tube current.

At the time of burst dimming, since a waveform having a gentle slope such as a triangular wave is injected into the feedback loop, the rise and fall of the voltage waveform applied to the transformer at the time of on / off switching is gentle. Become.

Therefore, when compared with a discharge lamp lighting device in which the entire dimming range is performed by the burst dimming method, the humming sound of the audible frequency generated from the transformers and coils is greatly improved.

The generation of a growling sound in burst dimming generally increases as the load power increases, and the generated sound also decreases as the load power decreases, so that the maximum sound pressure level of the generated growling sound is greatly reduced. I do.

Also, the steeper the voltage waveform at the time of switching between off and on, the greater the sound generation due to the magnetostriction of the core. For this reason, in the conventional burst dimming, on / off switching is performed by a rectangular pulse signal, and a steep voltage is applied to the transformer to generate a growling sound. However, in this embodiment, the on / off switching is performed by comparing the triangular wave voltage to be injected into the feedback voltage with the detection level of the tube current and gradually switching to the burst dimming.
The growling noise generated from the transformer cores is reduced.

Further, in each of the above embodiments, a complicated circuit is not required to realize the above operation.

A similar effect can be obtained in a liquid crystal display device or a lighting device using the discharge lamp lighting device of each of the above embodiments and examples.

In each of the above embodiments, the burst signal is a triangular wave. However, the present invention is not limited to this. If the signal has a waveform having a gentle slope, a sawtooth signal, a sine wave signal, a trapezoidal wave The same effect can be obtained even with a signal or a composite wave signal thereof.

Further, each of the above embodiments and examples will be described with reference to FIG.
Needless to say, the same effect can be obtained by controlling on the ground side as in the second example of the first embodiment shown in FIG.

[0138]

As described above, according to the method for adjusting the brightness of a discharge lamp according to the first aspect of the present invention, when the brightness of the discharge lamp is high and the load is dimmed, a continuous AC voltage is supplied from the inverter circuit. And by changing the level of the output voltage, the tube current flowing through the discharge lamp is changed to adjust the brightness. When the brightness of the discharge lamp is low and the load is dimmed, the output is output from the inverter circuit. Since the level of the output voltage of the inverter circuit is reduced in a cycle in which the frequency is lower than the frequency of the AC voltage, and the ratio between the period in which the output voltage is reduced and the cycle is changed, the tube current is changed and the brightness is adjusted. Since it is possible to reduce a sudden change in waveform due to magnetostriction generated in a transformer or a coil at a high load, the growling sound generated from the transformer or the coil due to the magnetostriction can be reduced. It can be significantly reduced as compared to come.

According to the method for adjusting the brightness of a discharge lamp according to the second aspect, in addition to the above-described effects, the change in the input voltage level of the inverter circuit can be made gentle, so that the inverter circuit Because a voltage that changes rapidly is not applied to the transformers and coils used in the above, the waveform sharply changes due to magnetostriction generated in these transformers and coils due to the sharp change in the voltage. The change can be reduced, and the generation of a growling sound can be further reduced.

Further, according to the discharge lamp lighting device of the present invention, when the tube current flowing through the discharge lamp is higher than the threshold voltage level, the AC voltage applied to the discharge lamp becomes continuous, and The voltage level is changed to perform brightness adjustment. When the tube current is lower than the threshold voltage level, the AC voltage applied to the discharge lamp is intermittent and the intermittent ratio is changed to perform brightness adjustment. Therefore, since the magnetostriction generated in the transformer, the coil, and the like of the inverter circuit at the time of a high load can be reduced, the growling sound generated from the transformer and the coil due to the magnetostriction can be significantly reduced as compared with the related art.

According to the discharge lamp lighting device of the fourth aspect, in addition to the above effects, the burst signal voltage and the output voltage of the tube current detecting means are combined by the diode coupling of the combining circuit. The circuit is extremely simplified, and the circuit configuration can be simplified.

According to the discharge lamp lighting device of the sixth aspect, the current control means is controlled based on the control voltage whose voltage level changes in a cycle having a frequency lower than the frequency of the AC voltage output from the inverter circuit. As a result, the direction of current and the current flowing to the primary winding of the transformer of the inverter circuit are changed to adjust the brightness of the discharge lamp, so that a rapidly changing voltage is not applied to the transformer.
Abrupt changes in waveform due to magnetostriction generated in these transformers and coils with the steep change in the voltage can be reduced,
Generation of a growling sound can be reduced.

According to the discharge lamp lighting device of claim 7, in addition to the above effects, the burst signal voltage is a triangular wave voltage, so that the input voltage of the inverter circuit has a predetermined slope and is gentle. Can be easily changed.

Further, according to the liquid crystal display device of the present invention, since the discharge lamp for backlight is turned on by the discharge lamp lighting device, it is possible to reduce the occurrence of growling noise as compared with the related art.

Further, according to the lighting device of the ninth aspect,
Since the discharge lamp for lighting is turned on by the discharge lamp lighting device, it is possible to reduce the occurrence of a growling sound as compared with the related art.

According to the luminance adjusting circuit for a discharge lamp according to the tenth aspect, when the luminance of the discharge lamp is high and the load is in a dimming state, a continuous AC voltage is output from the inverter circuit and the output voltage is controlled. By changing the level of the lamp, the tube current flowing through the discharge lamp is changed and the brightness is adjusted.If the brightness of the discharge lamp is low and the load is dimmed, the frequency is lower than the frequency of the AC voltage output from the inverter circuit. The tube current is changed by lowering the output voltage level of the inverter circuit in a cycle in which the frequency becomes low and changing the ratio of the period in which the output voltage is reduced to the cycle, and the brightness is adjusted. Since it is possible to reduce a sudden change in waveform due to magnetostriction generated in a transformer or a coil, a growling sound generated from the transformer or the coil due to the magnetostriction can be reduced as compared with the related art. It can be reduced in width.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a conventional discharge lamp lighting device.

FIG. 2 is a configuration diagram showing a conventional discharge lamp lighting device using a burst dimming method.

FIG. 3 is a configuration diagram showing a conventional discharge lamp lighting device using a burst dimming method.

FIG. 4 is a diagram showing operation waveforms of a conventional discharge lamp lighting device using a burst dimming method.

FIG. 5 is a diagram illustrating an example of a measured value of a noise level generated from a transformer during burst dimming in a conventional example.

FIG. 6 is a diagram illustrating an example of a measured value of a noise level generated from a choke coil during burst dimming in a conventional example.

FIG. 7 is a diagram showing a collector voltage waveform and a tube current waveform of a lower circuit in a conventional inverter circuit.

FIG. 8 is a diagram showing a collector voltage waveform and a tube current waveform of a lower circuit in a conventional inverter circuit.

FIG. 9 is a diagram showing a collector voltage waveform and a tube current waveform of a lower circuit in a conventional inverter circuit.

FIG. 10 is a diagram showing a collector voltage waveform and a tube current waveform of a lower circuit in a conventional inverter circuit.

FIG. 11 is a configuration diagram showing a discharge lamp lighting device according to the first embodiment of the present invention.

FIG. 12 is a diagram showing operation waveforms of the discharge lamp lighting device according to the first embodiment of the present invention.

FIG. 13 is a configuration diagram showing a discharge lamp lighting device in a first example of the first embodiment of the present invention.

FIG. 14 is a diagram showing a collector voltage waveform and a tube current waveform of the lower circuit in the inverter circuit according to the first embodiment of the present invention.

FIG. 15 is a diagram showing a collector voltage waveform and a tube current waveform of the lower circuit in the inverter circuit according to the first embodiment of the present invention.

FIG. 16 is a diagram showing a collector voltage waveform and a tube current waveform of the lower circuit in the inverter circuit according to the first embodiment of the present invention.

FIG. 17 is a diagram showing a collector voltage waveform and a tube current waveform of the lower circuit in the inverter circuit according to the first embodiment of the present invention.

FIG. 18 is a diagram showing actually measured values of a noise level generated from a transformer at the time of dimming in the first embodiment of the present invention.

FIG. 19 is a diagram showing measured values of a noise level generated from a choke coil during dimming in the first embodiment of the present invention.

FIG. 20 is a configuration diagram showing a discharge lamp lighting device according to a second example of the first embodiment of the present invention.

FIG. 21 is a configuration diagram illustrating a discharge lamp lighting device according to a third example of the first embodiment of the present invention.

FIG. 22 is a configuration diagram showing a discharge lamp lighting device according to a fourth example of the first embodiment of the present invention.

FIG. 23 is a configuration diagram illustrating a discharge lamp lighting device according to a fifth example of the first embodiment of the present invention.

FIG. 24 is a configuration diagram showing a discharge lamp lighting device according to a second embodiment of the present invention.

FIG. 25 is a configuration diagram showing a discharge lamp lighting device according to a third embodiment of the present invention.

FIG. 26 is a signal waveform diagram illustrating a luminance adjustment operation according to the third embodiment of the present invention.

[Explanation of symbols]

41 DC power supply, 42 DC-DC converter circuit, 4
3: self-excited inverter circuit, 44: cold cathode fluorescent lamp, 4
5 ... current detection circuit, 46 ... burst signal generation circuit, 51
... DC power supply, 52 ... DC-DC converter circuit, 53 ...
Self-excited inverter circuit, 531 transformer, 532 choke coil, 54 cold cathode fluorescent tube, 55 detection / feedback circuit, 56 impedance conversion / DC level setting circuit,
56a: Variable resistor, 57: Triangular wave generation circuit, 61: Control unit, 62: Inverter type inverter circuit, 63: Self-excitation type piezoelectric inverter circuit, 64: Resistor, 65: Frequency control circuit, 66: Piezoelectric inverter circuit , 67: drive control circuit, D1 to D3: diode, R1 to R3: resistor, C
1 ... condenser, VR1 ... variable resistor.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) DC02 EA13

Claims (10)

[Claims] 1. A method of adjusting the brightness of a discharge lamp when the discharge lamp is turned on by applying an output voltage of an inverter circuit for generating an AC voltage from a DC voltage to the discharge lamp, comprising: a tube current flowing through the discharge lamp. When the value is equal to or greater than a predetermined threshold, a continuous AC voltage is output from the inverter circuit, and the level of the output voltage is changed to change the tube current to perform brightness adjustment. When it is smaller, the level of the output voltage of the inverter circuit is continuously reduced at a cycle that is lower than the frequency of the AC voltage output from the inverter circuit, and the ratio of the period during which the level is reduced and the cycle is changed. The brightness of the discharge lamp is adjusted by changing the tube current. 2. The discharge lamp according to claim 1, wherein when the output voltage level of the inverter circuit is reduced in the cycle, the input voltage level to the inverter circuit is changed with a predetermined slope. Brightness adjustment method. 3. A discharge lamp lighting device which comprises an inverter circuit for generating an AC voltage from a DC voltage and applies an output voltage of the inverter circuit to the discharge lamp to light the discharge lamp, wherein a tube current flowing through the discharge lamp is provided. And a tube current detecting means for detecting and converting the voltage into a voltage, and having a voltage level equal to or lower than a predetermined threshold voltage level and having a frequency lower than the frequency of the AC voltage output from the inverter circuit. A burst signal generating means for generating and outputting a burst signal voltage whose level changes with a predetermined slope; and a feedback according to either the supplied burst signal voltage or the output voltage of the tube current detecting means. Feedback voltage generating means for generating and outputting a voltage; DC power and the feedback voltage being supplied, and inputting directly to the inverter circuit according to the feedback voltage. The discharge lamp lighting device is characterized in that a control means for outputting to control the level of voltage. 4. The discharge lamp lighting device according to claim 3, wherein said feedback voltage generating means adds said burst signal voltage and an output voltage of said tube current detecting means by a logical OR connection of diodes. 5. The discharge lamp lighting device according to claim 3, wherein the inverter circuit has a piezoelectric transformer and generates an AC voltage from the piezoelectric transformer. 6. A discharge lamp lighting device which includes an inverter circuit for generating an AC voltage from a DC voltage and applies an output voltage of the inverter circuit to the discharge lamp to light the discharge lamp, wherein the inverter is controlled based on a control voltage. Current control means for controlling the direction of current flow and the current flow to the primary winding of the transformer of the circuit; and a burst whose voltage level changes with a predetermined slope in a cycle having a frequency lower than the frequency of the AC voltage output from the inverter circuit. A control voltage generating means for generating a signal voltage and supplying a control voltage corresponding to the burst signal voltage to the current control means; a DC level variable connected to the control voltage generating means for changing a DC level of the control voltage And a discharge lamp lighting device. 7. The discharge lamp lighting device according to claim 3, wherein the burst signal voltage is a triangular wave voltage. 8. A liquid crystal display device using the discharge lamp lighting device according to claim 3. 9. An illumination device using the discharge lamp lighting device according to claim 3. 10. An inverter circuit for generating an AC voltage from the supplied DC voltage and applying the AC voltage to a discharge lamp to turn on the discharge lamp, DC power is supplied, and the DC voltage is supplied to the inverter circuit. Detecting a tube current flowing through the discharge lamp, and when the value of the tube current is equal to or greater than a predetermined threshold, outputting a continuous AC voltage from the inverter circuit in accordance with the DC voltage; The brightness is adjusted by changing the tube current by changing the voltage level. When the value of the tube current is smaller than the threshold value, the frequency of the AC voltage output from the inverter circuit according to the DC voltage is adjusted. The tube current is changed by lowering the level of the output voltage of the inverter circuit in a cycle having a frequency lower than that of the inverter circuit and changing the ratio of the period in which the output voltage is reduced and the cycle. And a voltage supply circuit for adjusting the brightness of the discharge lamp.