JP2002124395A - Discharge tube illumination control device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge tube illumination control device that can make the illumination adjustment more frequently and finely by also making the illumination range large and equal range in each mode. SOLUTION: A piezoelectric transformer 1 is driven via a drive circuit 4 and a switching circuit 2 by feeding back, as a feedback current the tube current generated by the light emission of the discharge tube. From this piezoelectric transformer, supply power of the discharge tube is supplied, and a control voltage that has changed duty ratio from the pulse generator 5 is outputted to the drive circuit 4, and the current value of the feedback current that is fed back from the burst signal generating part 6 is made to be changed and outputted. Thereby, the illumination adjustment can be made sufficiently and nearly equal for each range, without narrowing the illumination range in each mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge tube dimming control device for driving and controlling a discharge tube using a piezoelectric transformer.
In particular, the present invention relates to a discharge tube dimming control device for adjusting and controlling the brightness of a discharge tube.

[0002]

2. Description of the Related Art Conventionally, there are a burst dimming system and a tube current dimming system as this type of discharge tube dimming control device, which are shown in FIGS. 5 is a block diagram of a conventional discharge tube dimming control device using a burst dimming method, FIG. 6 is a control voltage waveform diagram in the discharge tube dimming control device shown in FIG. 5, and FIG. FIG. 8 is a block diagram of a discharge tube dimming control device using an optical system, and FIG. 8 is a dimming characteristic diagram of the discharge tube dimming control device described in FIGS. 5 and 7.

The discharge tube dimming control device shown in FIG.
A piezoelectric transformer 1 for supplying a supply current to a cold-cathode tube 100 used as a backlight of a liquid crystal display, a switching circuit 2 for generating and outputting an AC driving voltage V1 to the piezoelectric transformer 1, And an error voltage detection circuit 3 for comparing the detected voltage V0 with a preset reference voltage VREF to output an error voltage V2, and using the error voltage V2 as a feedback signal. The driving circuit 4 generates a control voltage V3 for controlling the switching circuit 2 based on the error voltage V2, and generates a carrier pulse of a carrier wave on which the control voltage V3 is superimposed, and adjusts the pulse width. A pulse generator 5 for outputting to the drive circuit 4 and a burst signal generator 6 for generating a burst signal for adjusting and controlling the pulse width of the pulse generator 5 are provided. It is formed.

Next, a dimming control operation of the conventional discharge tube dimming control device based on the above configuration will be described with reference to FIGS. First, a switch (not shown) is turned on, and a driving voltage V1 is output from the switching circuit 2 to the piezoelectric transformer 1, and the driving of the piezoelectric transformer 1 is started with the driving voltage V1. When the driving of the piezoelectric transformer 1 is started, the supplied power is supplied to the cold-cathode tube 100 to start light emission, and a tube current generated at the time of this light emission is detected as a detection voltage V0 by the tube current detection circuit 31 of the error voltage detection circuit 3. This detection voltage V0 and a preset reference voltage VREF are connected to a differential amplifier 3
2 to generate an error voltage V2.

The error voltage V2 is supplied to the drive circuit 4 as a feedback signal. The drive circuit 4 adjusts the control voltage V3 according to the value of the error voltage V2, thereby obtaining the reference voltage VREF.
The feedback control for causing the cold-cathode tube 100 to emit a luminance (amount of light emission) corresponding to the above is performed. Such feedback control is started to change the light emission amount to a decrease (power saving mode) or increase (maximum power mode) in a light emission state (normal power mode) in which a predetermined luminance (light emission amount) can be obtained from the CCFL 100. When the adjustment is performed, the burst signal is output from the burst signal generator 6 to the pulse generator 5, and the pulse generator 5 generates a carrier pulse having a changed duty ratio based on the burst signal. The carrier pulse is input to the drive circuit 4, and the drive circuit 4 controls the power saving mode based on the carrier pulse having the duty ratio (30%) changed so as to decrease (see FIG. 6A). And the control voltage V3 in the maximum power mode (FIG. 3C) based on the carrier pulse having the duty ratio (100%) changed so as to increase.
Is generated).

By controlling the power supplied from the piezoelectric transformer 1 to the cold-cathode tube 100 as shown in FIG. 8 based on each of the generated control voltages V3, the maximum dimming range is achieved in the maximum power mode. Light can be controlled, and in the power saving mode, light can be controlled in the minimum light control range. The discharge tube dimming control device shown in FIG. 7 includes a piezoelectric transformer 1, a switching circuit 2, an error voltage detection circuit 3, and a driving circuit 4, similarly to the discharge tube dimming control device shown in FIG. The cathode tube 100 is configured to control light emission. In addition to this configuration, the error voltage detection circuit 3 is connected to a feedback circuit from the error voltage detection circuit 3 to the drive circuit 4 so that the error voltage V
An adder 7 that adds the adjustment voltage to 2 and outputs the result to the drive circuit 4
And a current dimming signal generation unit 9 that generates and outputs this adjustment voltage as a current dimming signal.

The discharge tube dimming control device of the tube current dimming system also has a piezoelectric transformer 1, a cold cathode tube 100, an error voltage detecting circuit 3, an adding unit 7, A light emitting operation is performed by feedback control of a feedback loop formed by the drive circuit 4 and the switching circuit 2.
When adjusting the brightness of the cold-cathode tube 100 by using the tube current dimming method, the current dimming signal is output from the current dimming signal generation unit 9 as an adjustment voltage, and this adjustment voltage is converted to an error voltage V2. The addition by the adding unit 7 outputs the added voltage V5 in the power saving mode, the normal power mode, and the maximum power mode to the drive circuit 4 based on the voltage value of the adjusted voltage. A control voltage V3 is generated from the drive circuit 4 in accordance with each voltage value of the added voltage V5. Based on the control voltage V3, the switching circuit 2 generates a drive voltage V1 to drive and control the piezoelectric transformer 1. The light emission of the cold cathode tube 100 is controlled by the supply power output from the piezoelectric transformer 1. As shown in FIG. 8, the light emission control of the cold-cathode tube 100 can execute the dimming operation in the extended wide range of the power saving mode, the normal power mode, and the maximum power mode.

[0008]

Since each conventional discharge tube dimming control device is configured as described above, the dimming ranges are different in the power saving mode, the normal power mode, and the maximum power mode. In the power saving mode and the normal power mode, the dimming range becomes narrower than in the maximum power mode, and there is a problem that sufficient dimming adjustment cannot be performed.

The conventional discharge tube dimming control device using the burst dimming method can take a large dimming range in the maximum power mode, but has a problem of poor noise characteristics. On the other hand, the discharge tube dimming control device using the tube current dimming method has an excellent noise characteristic, but has a problem that the dimming range in the maximum power mode is small. The present invention has been made in order to solve the above-described problems, and has a discharge tube dimming control device capable of executing dimming adjustment more accurately and precisely as a dimming range that is large in each mode and equal to each other. The purpose is to provide.

[0010]

A discharge tube dimming control device according to the present invention supplies a current to a discharge tube used as a backlight of a liquid crystal display device via a piezoelectric transformer, and discharges the supplied current to the discharge tube. In a discharge tube dimming control device that performs feedback control based on a feedback current based on a tube current of a tube, and adjusts the amount of light emission of the discharge tube by changing the amount.
A switching unit that outputs an AC driving voltage to the piezoelectric transformer, a driving unit that converts a driving voltage supplied to the switching unit from a voltage value of a control voltage to a frequency and outputs the frequency, and changes a duty ratio of the driving voltage. And a tube current dimming unit that adjusts the light emission amount of the discharge tube by changing the current value of the feedback current. As described above, in the present invention, the tube current accompanying the light emission of the discharge tube is fed back as a feedback current to drive the piezoelectric transformer via the driving unit and the switching unit, and the power supplied to the discharge tube is supplied from the piezoelectric transformer. The driving voltage is output from the burst dimming means to the driving means with the duty ratio changed, and the current value of the feedback current fed back from the tube current dimming means is changed and output. Without diminishing the dimming range, sufficient dimming adjustment can be performed.

In the discharge tube dimming control device according to the present invention, if necessary, the burst dimming means or the tube current dimming means adjusts the light emission amount of the discharge tube in a plurality of stages. The current dimming means or the burst dimming means adjusts the light emission amount of the discharge tube. As described above, in the present invention, the light is adjusted in a plurality of stages by either the burst dimming means or the tube current dimming means, and the dimming operation is performed by controlling the light emission amount in each of these steps. A reliable dimming operation can be performed according to each dimming method.

Further, the discharge tube dimming control device according to the present invention can discharge the control voltage duty ratio change amount or the feedback current value change amount in at least any one of the plurality of adjusted stages as necessary. This is to change the adjustment ratio of the light emission amount of the tube. Thus, in the present invention,
Since the adjustment ratio of the light emission amount is changed at least at any one stage, various light control modes can be achieved while maintaining a wide light control range.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment of the Present Invention) Hereinafter, a discharge tube dimming control device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of a discharge tube dimming control device according to this embodiment.
FIG. 2 shows a characteristic diagram of dimming in the discharge tube dimming control device shown in FIG.

In each of the drawings, the discharge tube dimming control device according to the present embodiment includes a piezoelectric transformer 1 for supplying a supply current to a cold cathode tube 100 used as a backlight of a liquid crystal display device, and an alternating current to the piezoelectric transformer 1. A switching circuit 2 for generating and outputting the driving voltage V1 of the cold cathode fluorescent lamp 100, and detecting the tube current of the cold cathode fluorescent lamp 100 as a detection voltage V0, comparing the detection voltage V0 with a preset reference voltage VREF, and detecting an error. An error voltage detection circuit 3 that outputs a voltage V2, and the error voltage V2 is input as a feedback signal.
A driving circuit 4 for generating a control voltage V3 for controlling the switching circuit 2 based on the control signal, a pulse for generating a carrier pulse of a carrier wave on which the control voltage V3 is superimposed, adjusting the pulse width and outputting the pulse to the driving circuit 4 A generator 5, a burst signal generator 6 for generating a burst signal for adjusting and controlling the pulse width of the pulse generator 5, and a feedback circuit from the error voltage detection circuit 3 to the drive circuit 4; An adder 7 for adding an adjustment voltage to the error voltage V2 from the detection circuit 3 and outputting the same to the drive circuit 4; a current dimming signal generator 9 for generating and outputting the adjustment voltage as a tube current dimming control signal; There is provided a matching circuit 8 for matching the impedance of the tube current dimming control signal output from the current dimming signal generating unit 9 and outputting the control signal to the adding unit 7.

Next, the dimming control operation of the discharge tube dimming control device according to the present embodiment based on the above configuration will be described with reference to FIGS. As a premise, the display mode of the liquid crystal display device includes a maximum power mode in which the brightness of the display capability is set to 100% as the maximum, a normal power mode in which the brightness of the display capability is set to 80%, and a brightness of the display capability. Can be set to a power saving mode in which dimming is performed up to 40%. Further, similarly to the conventional discharge tube dimming control device, the cold cathode fluorescent lamp 100 is self-oscillated by the piezoelectric transformer 1, the switching circuit 2, the error voltage detection circuit 3, and the drive circuit 4.
Supply current to the cold cathode fluorescent lamp 10 by the supply current.
0 executes the light emission operation of the constant luminance set by the reference voltage VREF.

First, when performing the dimming operation in the normal power mode, the burst signal generator 6 outputs a burst signal VBM in the normal power mode to the pulse generator 5, and the pulse generator 5 outputs the burst signal VBM. , A transport pulse VBM having a duty ratio (80%) corresponding to. The carrier pulse VBM is input to the drive circuit 4, and the drive circuit 4 generates a control voltage V3 in the normal power mode shown in FIG. The switching circuit 2 generates a control voltage V3 in the normal power mode and outputs the control voltage V3 to the switching circuit 2. The switching circuit 2 operates based on the control voltage V3 in the normal power mode.
Is driven to supply the supplied power to the cold cathode tube 100 to emit light at a luminance of 80%.

When the dimming operation is to be performed with the luminance of 80% being the maximum value in the normal power mode, the tube current dimming control signal is supplied from the current dimming signal generator 9 to the adjusting voltage VA by the tube current dimming method. Output to the adder 7 via the matching circuit 8. The adder 7 adds the adjustment voltage VA to the error signal V2 that is fed back, generates an adjustment control voltage V20, and outputs the adjustment control voltage V20 to the drive circuit 4. The adjustment voltage VA (tube current dimming control signal) causes a linear change from the maximum H to the minimum L as shown in the normal power mode in FIG. It can be dimmed between% and 40%.

When switching from the normal power mode to the power saving mode, a burst signal VBL in the power saving mode is output from the burst signal generator 6 to the pulse generator 5 by a burst dimming method, and the normal power mode is switched. Similarly to the above, the dimming operation by the tube current dimming method is executed in the power saving mode as shown in FIG. Further, when switching from the normal power mode (or the power saving mode) to the maximum power mode, the burst signal generation unit 6 is also operated by the burst dimming method.
And outputs the burst signal VBH in the maximum power mode to the pulse generator 5, and executes the dimming operation by the tube current dimming method in the maximum power mode as shown in FIG.

In the above embodiment, the burst signal VB from the burst signal generator 6 and the tube current dimming control signal from the current dimming signal generator 9 are input to combine the burst dimming and the tube current dimming. Although the dimming operation is performed by using the configuration, the dimming operation is performed only by one of the burst dimming and the tube current dimming. I can do it.

(Second Embodiment of the Present Invention) FIG. 3 is a block circuit configuration diagram of a discharge tube dimming control device according to a second embodiment of the present invention. In the figure, the discharge tube dimming control device according to the present embodiment includes a burst signal generation unit 6 and a pulse generator 5 in addition to the configuration of the discharge tube dimming control device according to the first embodiment shown in FIG. And a power dimming control unit 90 comprising a matching circuit 8 and a current dimming signal generating unit 9 by switching between the maximum power, normal power and power saving modes. This is a configuration including a mode control unit 10 that changes the dimming ratio.

In the first embodiment, each mode is switched by the burst dimming method. However, each mode is switched by the tube current dimming method, and the burst dimming is performed in each of the switched modes. Cold cathode ray tube 10
The mode control unit 10 can also execute dimming control for adjusting the light emission amount of 0. Further, in each of the above embodiments, the light emission amount is changed linearly during each mode. However, as shown in FIG. 4, the change rate of the light emission amount can be controlled to be different from an arbitrary luminance state.

Further, in each of the above embodiments, the configuration is switched to the three modes of maximum power, normal power, and power saving. However, the configuration may be changed to any number of steps or stepless. Further, in each of the embodiments, the configuration was set by the burst dimming method in each mode of the maximum power, the normal power, and the power saving, but each of the modes was set by the tube current dimming method, and the setting was performed. In each mode, a dimming operation by the burst dimming method can be executed.

[0023]

According to the present invention, the tube current accompanying the light emission of the discharge tube is fed back as a feedback current to drive the piezoelectric transformer via the driving means and the switching means, and the power supplied to the discharge tube is supplied from the piezoelectric transformer. Since a control voltage with a changed duty ratio is output from the burst dimming means to the driving means, and a current value of the feedback current fed back from the tube current dimming means is changed and output, There is an effect that sufficient dimming adjustment can be performed by making the dimming ranges in each mode substantially equal without narrowing.

Further, in the present invention, either the burst dimming means or the tube current dimming means adjusts to a plurality of stages, and the dimming operation is performed by controlling the amount of light emission at each stage. Therefore, there is an effect that a reliable dimming operation can be performed according to each dimming method. Furthermore, in the present invention, since the adjustment ratio of the light emission amount is changed at least in any one step, there is an effect that various light control modes can be achieved while maintaining a wide light control range.

[Brief description of the drawings]

FIG. 1 is a block circuit configuration diagram of a discharge tube dimming control device according to a first embodiment of the present invention.

FIG. 2 is a dimming characteristic diagram in the discharge tube dimming control device shown in FIG.

FIG. 3 is a block circuit configuration diagram of a discharge tube dimming control device according to a second embodiment of the present invention.

FIG. 4 is a dimming characteristic diagram in the discharge tube dimming control device shown in FIG. 3;

FIG. 5 is a block diagram of a conventional discharge lamp dimming control device using a burst dimming method.

FIG. 6 is a control voltage waveform diagram in the discharge tube dimming control device shown in FIG.

FIG. 7 is a block diagram of a conventional discharge tube dimming control device using a tube current dimming method.

8 is a dimming characteristic diagram of the discharge tube dimming control device described in each of FIGS. 5 and 7. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric transformer 2 Switching circuit 3 Error voltage detection circuit 4 Drive circuit 5 Pulse generator 6 Burst signal generation part 7 Addition part 8 Matching circuit 9 Current dimming signal generation part 10 Mode control part 31 Tube current detection circuit 32 Differential amplifier 60 Burst dimming control unit 90 Power dimming control unit V0 Detection voltage V1 Drive voltage V3 Control voltage V2 Error voltage V5 Addition voltage V20 Adjustment control voltage VA Adjustment voltage VREF Reference voltage

Claims (3)

[Claims] 1. A current is supplied to a discharge tube used as a backlight of a liquid crystal display device via a piezoelectric transformer, and the supplied current is feedback-controlled by a feedback current based on the tube current of the discharge tube and is varied. A discharge tube dimming control device that adjusts the amount of light emitted from the discharge tube by: switching means for outputting an AC drive voltage to the piezoelectric transformer; and A driving means for converting and outputting; a burst dimming means for adjusting a light emission amount of the discharge tube by changing a duty ratio of the drive voltage; and a light emission amount of the discharge tube by changing a current value of the feedback current. And a tube current dimming means for adjusting the discharge current. 2. The discharge tube dimming control device according to claim 1, wherein the burst dimming unit or the tube current dimming unit adjusts the light emission amount of the discharge tube in a plurality of stages, and the tube is adjusted for each of the stages. A discharge tube dimming control device, wherein a current dimming unit or a burst dimming unit adjusts a light emission amount of a discharge tube. 3. The discharge tube dimming control device according to claim 2, wherein at least one of the adjusted plurality of stages discharges with respect to a variation in a control voltage duty ratio or a variation in a feedback current value. A discharge tube dimming control device characterized by changing an adjustment ratio of a light emission amount of a tube.