JP2003100494A - Discharge lamp light control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp light control device setting a tube current frequency without being restricted by a critical fusion frequency, of which, the light control is enabled to accurately and minutely carry out by making a light control range bigger. SOLUTION: A plurality of current levels which are higher than the level of a prescribed value for lighting a discharge lamp, continued longer than a prescribed period, are continuously combined in a feed back circuit between an error voltage detecting circuit 3 and a driving circuit 4. As a light control signal generating means 5 outputs the light control signals generating a high frequency current at the plurality of combined current levels, abnormal generation of flicker or the like is prevented even when the frequency of the tube current flowing through the discharge lamp is less than a critical fusion frequency, and the light control is enabled to accurately and minutely carry out by making a light control range bigger.

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, it relates to a discharge tube dimming control device for adjusting and controlling the brightness of the discharge tube.

[0002]

2. Description of the Related Art Conventionally, there are a burst dimming system and a tube current dimming system as discharge tube dimming control devices of this type, which are shown in FIGS. FIG. 6 is a block diagram of a conventional discharge tube dimming control device using a burst dimming method, and FIG.
6 is a control voltage waveform diagram in the discharge tube dimming control device shown in FIG. 6, FIG. 8 is a block configuration diagram of a discharge tube dimming control device using a conventional tube current dimming method, and FIG. 9 is a discharge tube shown in FIG. The dimming characteristic figure of a dimming control apparatus is shown.

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 device, a switching circuit 2 for generating and outputting an AC driving voltage V1 to the piezoelectric transformer 1, and the cold cathode tube 100. The error voltage detection circuit 3 detects the tube current of the above as a detection voltage V0 by the tube current detection circuit 31, compares the detection voltage V0 with a preset reference voltage VREF, and outputs an error voltage V2.
Then, the error voltage V2 is inputted as a feedback signal, and the drive circuit 4 for generating the control voltage V3 for controlling the switching circuit 2 based on the error voltage V2 and the carrier pulse for the carrier wave on which the control voltage V3 is superimposed are generated. A pulse generator 61 that generates and adjusts the pulse width and outputs the adjusted pulse width to the drive circuit 4 is provided, and a burst signal generator 6 that generates a burst signal VB that adjusts and controls the pulse width of the pulse generator 61. .

Next, the dimming control operation of the conventional discharge tube dimming control device based on the above configuration will be described with reference to FIGS. 6 and 7. First, a switch (not shown) is turned on, the drive voltage V1 is output from the switching circuit 2 to the piezoelectric transformer 1, and the drive of the piezoelectric transformer 1 is started by this drive voltage V1. When the piezoelectric transformer 1 is driven, the supplied power is supplied to the cold cathode fluorescent lamp 100 to start light emission, and the tube current generated at the time of light emission is detected by the tube current detection circuit 31 of the error voltage detection circuit 3 as the detection voltage V0. The detection voltage V0 and a preset reference voltage VREF are used as a differential amplifier 3
An error voltage V2 is generated by performing a comparison operation in 2. This error voltage V2 is input to the drive circuit 4 as a feedback signal, and the drive circuit 4 adjusts the control voltage V3 in accordance with the value of the error voltage V2 so that the brightness (amount of light emission) corresponding to the reference voltage VREF becomes a cold cathode fluorescent lamp. The feedback control is performed to cause 100 to emit light.

By starting such feedback control, the cold cathode tube 1
00, the light emission amount is reduced in the light emission state (normal power mode) where a predetermined brightness (light emission amount) is obtained (power saving mode)
Alternatively, in the case of adjusting to increase (maximum power mode), the burst signal generator 6 outputs the burst signal VB to the pulse generator 61, and the pulse generator 61 determines the duty ratio based on the burst signal VB. The changed carrier pulse is generated. This carrier pulse is input to the drive circuit 4, and the drive circuit 4 controls the control voltage V3 in the power saving mode based on the carrier pulse having the duty ratio (30%) changed so as to decrease (shown in FIG. 7A). Is generated and is based on the carrier pulse of the duty ratio (100%) that is changed so as to increase.
(Shown in (C)).

As shown in FIG. 7, the power supplied from the piezoelectric transformer 1 to the cold cathode fluorescent lamp 100 is controlled on the basis of the generated control voltage V3, so that the maximum dimming range is adjusted in the maximum power mode. Light can be emitted, and in the power saving mode, dimming can be performed within the minimum dimming range. The discharge tube dimming control device according to the tube current dimming method shown in FIG. 8 is similar to the discharge tube dimming control device shown in FIG. 6, and includes the piezoelectric transformer 1, the switching circuit 2, the error voltage detection circuit 3, and the drive. A circuit 4 is provided to control the emission of the cold cathode fluorescent lamp 100. In addition to this configuration, the cold cathode fluorescent lamp 100 is connected in a feedback circuit from the error voltage detection circuit 3 to the drive circuit 4, and the error voltage V2 from the error voltage detection circuit 3 is connected. To the drive circuit 4 and add the adjustment control voltage V20 to
A configuration is provided that includes a dimming command signal generation unit 9 that generates a dimming command signal P13 for causing 0 to be output from the addition unit 7 as a current dimming signal.

This tube current dimming type discharge tube dimming control device is also similar to the burst dimming type discharge tube dimming control device in that the piezoelectric transformer 1, the cold cathode fluorescent lamp 100, the error voltage detection circuit 3,
A light emitting operation is performed by feedback control of a feedback loop formed by the adder 7, the drive circuit 4, and the switching circuit 2. When the brightness of the cold cathode fluorescent lamp 100 is adjusted by this tube current dimming method to perform dimming, the dimming command signal generation unit 9 outputs the dimming command signal P13 as an adjustment voltage, and this adjustment voltage is used as the error voltage V2. Is added by the adder 7 to output the added voltage V5 in the power saving mode, the normal power mode, and the maximum power mode to the drive circuit 4 according to the voltage value of the adjusted voltage. A control voltage V3 is generated from the drive circuit 4 according to each voltage value of the added voltage V5, and the switching circuit 2 generates the drive voltage V1 based on the control voltage V3 to drive and control the piezoelectric transformer 1. The cold cathode fluorescent lamp 100 is controlled to emit light by the electric power supplied from the piezoelectric transformer 1. The light emission control of the cold cathode fluorescent lamp 100 can perform the dimming operation in the extended wide range of the power saving mode, the normal power mode, and the maximum power mode as shown in FIG.

[0008]

Since each conventional discharge tube dimming control device is configured as described above, in the conventional discharge tube dimming control device by the burst dimming method, the maximum power consumption is increased. The dimming range in the mode can be relatively large, but when the duty ratio is small (for example, 30% or less) in the low power driving in the power saving mode, the fluctuation frequency of the emitted light is the critical fusion frequency (CFF). ; Critical F
(usion frequency), flicker occurs, display performance is degraded, and noise characteristics are poor. In particular, during low-luminance driving, it was necessary to set the driving frequency of the piezoelectric transformer to set the tube current of the cold-cathode tube 100 to be higher than the critical fusion frequency. On the other hand, the discharge tube dimming control device using the tube current dimming method has excellent noise characteristics, but has a problem that the dimming range in each power mode is extremely small.

The present invention has been made to solve the above-mentioned problems, and the frequency of the tube current is set without being limited by the critical fusion frequency, and the dimming adjustment is made more accurate and precise as a larger dimming range. It is an object of the present invention to provide a discharge tube dimming control device that can be implemented in the above.

[0010]

A high-frequency current detection residual discharge tube dimming controller according to the present invention detects a high-frequency current generating means for generating a high-frequency current and supplying it to the discharge tube, and a tube current flowing through the discharge tube. And a dimming signal generating means for generating a dimming signal for feedback-controlling the high-frequency current based on the detection signal, the high-frequency current generating means adjusting the current level of the high-frequency current based on the dimming signal. In the discharge tube dimming control device for dimming the light emission amount of the discharge tube, the high-frequency current generating means continuously sets a plurality of current levels that are equal to or more than a predetermined current value for causing the discharge tube to emit light and are equal to or more than a predetermined duration time. In addition, the high frequency current is generated at a plurality of combined current levels. Thus, in the present invention, a plurality of current levels that are equal to or greater than a predetermined current value for causing the discharge tube to emit light and that are equal to or greater than a predetermined duration are continuously combined, and the high-frequency current is generated at the plurality of combined current levels, Since this high-frequency current is supplied to the discharge tube, even if the frequency of the tube current flowing in the discharge tube is a frequency below the critical fusion frequency, it is possible to prevent flicker and other abnormalities from occurring, and to provide a larger dimming range. The dimming adjustment can be performed accurately and precisely.

Further, in the discharge tube dimming control device according to the present invention, the high frequency current generating means repeatedly generates the high frequency current by repeating a plurality of the combined current levels. As described above, in the present invention, a plurality of current levels that are equal to or higher than a predetermined current value for causing the discharge tube to emit light and that are equal to or longer than a predetermined time are continuously combined, and the combined current levels are repeated to generate a high-frequency current. Since the dimming signal controls the tube current flowing in the discharge tube, it is possible to prevent the occurrence of flicker and other abnormalities even when the frequency of the tube current flowing in the discharge tube is equal to or lower than the critical fusion frequency. The dimming adjustment can be performed accurately and precisely as a larger dimming range.

Further, in the discharge tube dimming control device according to the present invention, the dimming signal generating means continuously sets a plurality of current levels of a predetermined current value or more for causing the discharge tube to emit light and a predetermined duration or more. And outputs a dimming signal for generating the high-frequency current at a plurality of combined current levels. As described above, in the present invention, a plurality of current levels that are equal to or higher than the predetermined current value for causing the discharge tube to emit light and that are equal to or longer than the predetermined duration are continuously combined, and the high-frequency current is generated at the plurality of combined current levels. An optical signal is output and the dimming signal is used to control the tube current flowing in the discharge tube, so even if the frequency of the tube current flowing in the discharge tube is below the critical fusion frequency, flicker and other abnormalities occur. As a result, stable dimming control can be performed, and dimming adjustment can be performed accurately and precisely as a larger dimming range.

Further, in the discharge tube dimming control device according to the present invention, the current value of the current level of the high frequency current is set to 2 [mA] or more and 8 [mA] or less as necessary. As described above, in the present invention, when the current value of the high-frequency current is 2 [mA] or more, it is 8 [m].
A] Since it is set to be equal to or less than this, it is possible to continuously and surely perform the light emission of the discharge tube, and the dimming adjustment can be accurately and precisely performed as a larger dimming range. Further, the discharge tube dimming control device according to the present invention, if necessary,
Each predetermined duration of the current level of the high frequency current is adjusted so that it can expand and contract. As described above, according to the present invention, since the respective predetermined durations of the combined current levels are flexibly adjusted, the dimming adjustment can be accurately and precisely performed in a larger dimming range.

Further, in the discharge tube dimming control device according to the present invention, each predetermined duration of the current level in the high-frequency current is set to a constant total time of the predetermined durations of the combined current levels, if necessary. Then, the ratio is changed within the range of the constant total time. As described above, in the present invention, since the respective ratios of the combined current levels in the respective predetermined durations are changed, the dimming adjustment can be accurately and precisely performed in a larger dimming range.

Further, in the discharge tube dimming control device according to the present invention, the high frequency current generating means converts the voltage based on the detection signal into a frequency, as necessary, and a VF converter and the converted frequency. A switching circuit that outputs a drive voltage based on the drive voltage and a piezoelectric transformer that supplies a high-frequency current to the discharge tube based on the drive voltage are provided.

Further, in the discharge tube dimming control device according to the present invention, the dimming signal generating means generates one period of time for generating the dimming signal by the feedback control, if necessary, for each predetermined continuation of the current level. It should be sufficiently shorter than the time. As described above, in the present invention, since the cycle of the feedback control for generating the dimming signal is sufficiently shorter than the predetermined duration of each current level, even when the current level continuously changes, the dimming by the feedback control is performed. Can be performed accurately and reliably.

Further, in the discharge tube dimming control device according to the present invention, the dimming signal generating means interposes an impedance element in the feedback circuit of the feedback control, if necessary.
The impedance level of the impedance element is changed to adjust the current level at each of the predetermined durations. As described above, in the present invention, since the current level is adjusted by the impedance value of the impedance element, each current level can be adjusted in the feedback circuit, and dimming can be accurately and surely executed.

Further, in the discharge tube dimming control device according to the present invention, the dimming signal generating means outputs a high level high frequency current of a plurality of current levels from the high frequency current generating means as necessary. A high-level current dimming signal generating section for generating a level current dimming signal; and a low-level current dimming signal generating low-frequency current dimming signal for causing the high-frequency current generating means to output a low-level high-frequency current of the plurality of current levels. A level current dimming signal generation unit and a dimming signal that combines the generated high level current dimming signal and low level current dimming signal at an arbitrary ratio based on a dimming command signal input from the outside. And a signal adjusting unit for adjusting the.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment of the Invention) A discharge tube dimming control device according to a first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing the entire block circuit of the discharge tube dimming control device according to the present embodiment, and FIG. 2 is a detailed block circuit diagram showing the dimming signal generating means in the discharge tube dimming control device shown in FIG. Figure 1
FIG. 5 shows output waveform diagrams of the discharge tube dimming control device described in FIG.

In each of the above drawings, the discharge tube dimming control device according to the present embodiment is similar to the discharge current dimming control device of the tube current dimming system shown in FIG. 8 and has a piezoelectric transformer 1, a switching circuit 2 and an error. The cold cathode fluorescent lamp 100 is provided with a voltage detection circuit 3 and a driving circuit 4, and the cold cathode fluorescent lamp 100 is controlled to emit light. In addition to this structure, the cathode fluorescent lamp 100 emits light in a feedback circuit between the error voltage detecting circuit 3 and the driving circuit 4. A plurality of current levels that are equal to or greater than a predetermined current value and that are equal to or greater than a predetermined duration are continuously combined, and a current dimming signal that generates the high frequency current is output as the adjustment control voltage V20 at the plurality of combined current levels. This is a configuration including the optical signal generation means 5. The piezoelectric transformer 1, the switching circuit 2 and the drive circuit 4 constitute a high frequency current generating means 10.

The dimming signal generating means 5 has a switching element 51 interposed in the feedback circuit and an impedance element 52 connected in parallel with the switching element 51 and capable of changing the impedance value.
And a PWM control section 53 for generating a PWM signal P1 by controlling the pulse width for the timing of changing the current level in the current dimming signal based on a dimming command signal P10 input from the outside, and the PWM signal. The drive control unit 54 controls the switching operation of the switching element 51 based on P1 and the impedance control unit 55 controls the impedance value of the impedance element 52 based on the PWM signal P1.

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. As a premise, the display mode of the liquid crystal display device has a brightness of display capability of 10
A maximum power mode for dimming with 0% as a maximum, a normal power mode for dimming with a maximum of 80% for display capability, and a power saving mode for dimming with a maximum of 30% for display capability are set. It should be possible. Further, similarly to the conventional discharge tube dimming control device, a supply current is supplied to the cold cathode tube 100 by self-excited oscillation by the piezoelectric transformer 1, the switching circuit 2, the error voltage detection circuit 3 and the drive circuit 4.
With this supply current, the cold cathode fluorescent lamp 100 performs the light emitting operation of constant brightness set by the reference voltage VREF by the feedback control.

First, when the dimming operation is performed in the maximum current mode among the display modes, the PWM control unit 53 generates the PWM signal P1 having an on-duty of "100" (continuous ON state) to control the drive. Output to the unit 54 and the impedance control unit 55. The drive control unit 54 controls the switching element 51 so as to continuously maintain the closed state based on the input PWM signal P1 of the on-duty “100”. On the other hand, the impedance control unit 55
Controls the impedance value Z to be "0" based on the input PWM signal P1 of the on-duty "100".

By controlling the switching element 51 and the impedance element 52, the error voltage V2 detected by the error voltage detecting circuit 3 is directly the adjustment control voltage V2 of the voltage V21.
It is output as 0 to the drive circuit 4. This adjustment control voltage V2
Based on 0, the drive circuit 4 converts the control voltage V3 into the maximum power mode of 100% luminance and executes the light emission control operation by the feedback control. Timing charts of the voltage values in the respective parts output based on the maximum power mode are shown from T0 to T1 in FIG.

Further, when the dimming operation is performed in the normal power mode among the display modes, the PWM control unit 53 causes the on-duty "50" (the ratio of the ON state and the OFF state is 1).
The drive control unit 5 generates the PWM signal P1 (in a ratio of 1)
4 and the impedance control unit 55. The drive control unit 54 receives the P of the input on-duty “50”.
A switch drive signal P2 is generated based on the WM signal P1,
The switching element 51 is turned on only when the PWM signal P1 is in the ON state, and the switching element 51 is controlled to be in the open state when the PWM signal P1 is in the OFF state.
On the other hand, the impedance control section 55 sets the impedance value Z to a predetermined value only when the PWM signal P1 is in the OFF state, based on the input PWM signal P1 of the on-duty "50", and the error voltage V2 is controlled to be attenuated.

The error voltage V2 detected by the error voltage detection circuit 3 under the control of the switching element 51 and the impedance element 52 is maintained as it is when the PWM signal P1 is in the ON state, and is output as the voltage V21.
When the signal P1 is in the OFF state, it becomes the value of the voltage V22 which is attenuated to a predetermined value, and these respective values continuously appear as the adjustment control voltage V2 as the current dimming signal shown between T1 and T2 in FIG.
0 will be generated. Based on the adjustment control voltage V20, the drive circuit 4 converts the control voltage V3 into the normal power mode with a brightness of 50% and executes the light emission control operation by the feedback control. Timing charts of the voltage values in the respective parts output based on the normal power mode are shown in T1 and T2 of FIG.

Further, when the dimming operation is performed in the power saving mode among the display modes, the PWM control unit 53 has the on-duty of "20" (the ratio of the ON state and the OFF state is 1 to 5). The drive control unit 54 is generated by generating the PWM signal P1.
And output to the impedance control unit 55. The drive control unit 54 receives the PW of the input on-duty “20”.
A switch drive signal P2 is generated based on the M signal P1, and the switching element 51 is turned on only when the PWM signal P1 is in the ON state, and the switching element 51 is opened when the PWM signal P1 is in the OFF state. . On the other hand, the impedance control unit 55 determines the P
Only when the WM signal P1 is in the OFF state, the impedance value Z is controlled to a predetermined value and the error voltage V2 is controlled to be attenuated.

The error voltage V2 detected by the error voltage detecting circuit 3 under the control of the switching element 51 and the impedance element 52 is maintained as it is when the PWM signal P1 is in the ON state and is output as the voltage V21.
When the signal P1 is in the OFF state, it becomes the value of the voltage V22 which is attenuated to a predetermined value, and these respective values are continuously set as the adjustment control voltage V2 as the current dimming signal shown between T2 and T3 in FIG.
0 will be generated.

Based on the adjustment control voltage V20, the drive circuit 4 converts the control voltage V3 into a power saving mode with a brightness of 20% and executes a light emission control operation by feedback control. Timing charts of the voltage values in the respective parts output based on the power saving mode are shown in T2 to T3 of FIG. The feedback control operation in each mode is executed in a band of hundreds to thousands of Hz which is sufficiently small with respect to the pulse width of the frequency band of tens of Hz.

(Second Embodiment of the Present Invention) Second Embodiment of the Present Invention
The discharge tube dimming control device according to the embodiment will be described based on FIGS. 4 and 5 with reference to FIG. FIG. 4 is a detailed block circuit configuration diagram of the dimming signal generating means of the discharge tube dimming control device according to the present embodiment, and FIG.

In each of the above drawings, the discharge tube dimming control device according to the present embodiment is similar to the discharge tube dimming control device according to the first embodiment shown in FIG. The cathode ray tube 100 is provided with an error voltage detection circuit 3 and a drive circuit 4 to control light emission. In addition to this configuration, a discharge tube is caused to emit light in a feedback circuit between the error voltage detection circuit 3 and the drive circuit 4. A dimming signal generating means 50 for outputting a dimming signal for generating the high-frequency current at a plurality of current levels which are equal to or more than a predetermined current value and are equal to or more than a predetermined duration in succession and which generate a high frequency current at the plurality of combined current levels (FIG. 1 corresponds to the number 5).

The dimming signal generating means 50 supplies a high frequency current of about 6 [mA] among the plurality of current levels to the cathode tube 1.
A high-level dimming signal generation unit 501 for generating a high-level dimming signal P11 for outputting to H.00, and a low voltage for outputting a high frequency current of about 3 [mA] among the plurality of current levels to the cathode tube 100. A low-level dimming signal generation unit 502 that generates a level dimming signal P12, and the generated high-level dimming signal P11 and low-level dimming signal P12 are combined at an arbitrary ratio based on a dimming command signal P10. In addition, the signal adjusting unit 504 that adjusts the current dimming signal and outputs it to the drive circuit 4
And a dimming command signal input unit 503 for inputting the dimming command signal P10.

Next, the dimming operation of the discharge tube dimming control device according to the present embodiment based on the above configuration will be described. Similar to the dimming operation of the first embodiment, control is performed in each mode of maximum power / normal power / power saving. First, when the dimming command signal P10 for performing the dimming control operation in the maximum power mode is input from the dimming command signal input unit 503, the signal adjusting unit 504 causes the error voltage V2 and the high level dimming signal P11. Based on and, the brightness 1 shown at T0 to T1 in FIG.
A current dimming signal of 00% is generated and output to the drive circuit 4.

Further, when the dimming command signal P10 for performing the dimming control operation in the normal power mode is input from the dimming command signal input unit 503, the signal adjusting unit 504 determines that the error voltage V2 and the high level. Based on the dimming signal P11 and the low level dimming signal P12, a current dimming signal having a luminance of 50% is generated and output to the drive circuit 4. The signal adjusting unit 504 sets the ratio of the high level dimming signal P11 and the low level dimming signal P12 to 1
The pulse width is adjusted to 1 and T1 to T in FIG. 5 are adjusted based on the adjusted pulse width signal and the error voltage V2.
The current dimming signal shown in 2 is generated.

Further, when the dimming command signal P10 for performing the dimming control operation in the power saving mode is input from the dimming command signal input unit 503, the signal adjusting unit 504 causes the error voltage V2 and the high level. Based on the dimming signal P11 and the low level dimming signal P12, a current dimming signal having a brightness of 20% is generated and output to the drive circuit 4. The signal adjusting unit 504 sets the ratio of the high level dimming signal P11 and the low level dimming signal P12 to 1
The pulse width is adjusted to be 5, and T2 to T in FIG. 5 are adjusted based on the adjusted pulse width signal and the error voltage V2.
The current dimming signal shown in 3 will be generated.

(Other Embodiments of the Present Invention) In the discharge tube dimming control device according to the first embodiment, whether the value of the impedance element 52 is "0" (the impedance element 52 is separated from the feedback circuit). "Predetermined value"
The impedance element 52 may be switched to a state in which it is connected to a feedback circuit.
In the discharge tube dimming control device according to each of the first and second embodiments, the high frequency current is generated by continuously combining two kinds of current levels that continue for a predetermined time. It is also possible to generate a high frequency current by continuously combining three or more current levels that continue for a time.

In the discharge tube dimming control device according to each of the first and second embodiments, the maximum power / normal power /
Although the dimming control is performed in three steps in each power saving mode, the PWM control unit 53 arbitrarily changes the pulse width, or the signal adjusting unit 504 sets the high level dimming signal P11 and the low level dimming signal. It is also possible to arbitrarily change the ratio of P12 to generate a current dimming signal and change it steplessly or in multiple steps to perform dimming control.

[0038]

According to the present invention, a plurality of current levels that are equal to or higher than a predetermined current value for causing the discharge tube to emit light and have a predetermined duration or longer are continuously combined, and the high-frequency current is generated at the plurality of combined current levels. However, since this high-frequency current is supplied to the discharge tube, even if the frequency of the tube current flowing in the discharge tube is below the critical fusion frequency, it is possible to prevent flicker and other abnormalities from occurring, and to achieve greater dimming. As a range, there is an effect that the dimming adjustment can be accurately and precisely executed.

Further, in the present invention, a plurality of current levels which are equal to or higher than a predetermined current value for causing the discharge tube to emit light and which are equal to or longer than a predetermined time are continuously combined, and the combined current levels are repeated to generate a high frequency current. Since the dimming signal is generated and the tube current flowing in the discharge tube is controlled by the dimming signal, even if the frequency of the tube current flowing in the discharge tube is equal to or lower than the critical fusion frequency, the occurrence of flicker and other abnormalities can be prevented. Therefore, there is an effect that the dimming adjustment can be accurately and precisely performed as a larger dimming range.

Further, in the present invention, a plurality of current levels that are equal to or higher than a predetermined current value for causing the discharge tube to emit light and that are equal to or longer than a predetermined duration are continuously combined, and the high frequency current is generated at the plurality of combined current levels. Output the dimming signal to
Since the tube current flowing in the discharge tube is controlled by this dimming signal, it is possible to prevent the occurrence of flicker and other abnormalities even if the frequency of the tube current flowing in the discharge tube is a frequency below the critical fusion frequency. The dimming control described above can be performed, and the dimming adjustment can be performed accurately and precisely as a larger dimming range.

Further, in the present invention, when the current value of the current level in the high frequency current is 2 [mA] or more, it is 8 [m].
A] Since it is set to be equal to or less than this, it becomes possible to continuously and surely perform the light emission of the discharge tube, and there is an effect that the dimming adjustment can be accurately and precisely performed in a larger dimming range.

Further, in the present invention, since the cycle of the feedback control for generating the dimming signal is sufficiently shorter than the predetermined duration of each current level, the feedback control is performed even when the current level continuously changes. There is an effect that dimming can be accurately and surely executed.

Further, in the present invention, since the current level is adjusted by the impedance value of the impedance element, each current level can be adjusted in the feedback circuit, and the effect that dimming can be accurately and surely executed. Have.

[Brief description of drawings]

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

FIG. 2 is a detailed block circuit configuration diagram of a dimming signal generating means in the discharge tube dimming control device shown in FIG.

FIG. 3 is each output waveform diagram of the discharge tube dimming control device shown in FIG.

FIG. 4 is a detailed block circuit configuration diagram of a dimming signal generation unit of a discharge tube dimming control device according to a second embodiment of the present invention.

5 is a waveform diagram of the output signal of each part in FIG.

FIG. 6 is a block diagram of a conventional discharge tube dimming control device using a burst dimming method.

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

FIG. 8 is a block configuration diagram of a discharge tube dimming control device according to a conventional tube current dimming method.

9 is a dimming characteristic diagram of the discharge tube dimming control device described in each of FIGS. 6 and 8. FIG.

[Explanation of symbols]

1 Piezoelectric transformer 2 switching circuits 3 Error voltage detection circuit 4 drive circuit 5, 50 Dimming signal generating means 7 adder 9 Dimming command signal generator 10 High-frequency current generating means 31 Tube current detection circuit 32 differential amplifier 51 switching element 52 Impedance element 53 PWM control unit 54 Drive control unit 55 Impedance controller 61 pulse generator 100 cathode tube 501 High-level dimming signal generator 502 Low-level dimming signal generator 503 Dimming command signal input section P1 PWM signal P2 switch drive signal P10, P13 dimming command signal P11 High level dimming signal P12 Low level dimming signal V0 detection voltage V1 drive voltage V2 error voltage V3 control voltage V5 addition voltage V20 adjustment control voltage V21, V22 voltage VB burst signal VREF reference voltage

Continued front page    (72) Inventor Tomofumi Yamashita             Saga Prefecture Kubo Izumi-machi, Saga Oita Shimozumi Ippon chestnut             3144-1 Ricoh Keiki Co., Ltd. F term (reference) 3K098 CC24 CC41 CC44 DD21 DD22                       DD37 EE31 EE32 EE33 FF04                       FF14

Claims (10)

[Claims] 1. A high-frequency current generating means for generating a high-frequency current and supplying it to a discharge tube, and a dimming signal for detecting a tube current flowing in the discharge tube as a detection signal and performing feedback control of the high-frequency current based on the detection signal. In the discharge tube dimming control device, which comprises a dimming signal generating means for generating, wherein the high-frequency current generating means adjusts the current level of the high-frequency current based on the dimming signal to dimming the light emission amount of the discharge tube. The high-frequency current generating means continuously combines a plurality of current levels equal to or more than a predetermined current value for causing the discharge tube to emit light and has a predetermined duration or more, and generates the high-frequency current at the plurality of combined current levels. Discharge tube dimming control device featuring. 2. The discharge tube dimming control device according to claim 1, wherein the high frequency current generation means repeats the combined plurality of current levels to generate the high frequency current. Tube dimming control device. 3. The discharge tube dimming control device according to claim 1 or 2, wherein the dimming signal generation means has a plurality of current levels equal to or higher than a predetermined current value for causing the discharge tube to emit light and equal to or higher than a predetermined duration time. A discharge tube dimming control device, characterized in that the dimming signals are continuously combined and a dimming signal for generating the high-frequency current is output at a plurality of combined current levels. 4. The discharge tube dimming control device according to claim 1, wherein a current value of a current level of the high frequency current is 2 [m
A discharge tube dimming control device characterized by being set to not less than A] and not more than 8 [mA]. 5. The discharge tube dimming control device according to any one of claims 1 to 4, wherein each predetermined duration of the current level of the high frequency current is flexibly adjusted. Tube dimming control device. 6. The discharge tube dimming control device according to claim 1, wherein the predetermined durations of the current levels of the high frequency current are the sum of the predetermined durations of the combined current levels. The discharge tube dimming control device is characterized in that the total time is kept constant and the ratio is changed within the range of the constant total time. 7. The discharge tube dimming control device according to any one of claims 1 to 6, wherein the high-frequency current generation means converts a voltage based on the detection signal into a frequency, and a VF converter, A discharge tube dimming control device comprising: a switching circuit that outputs a drive voltage based on the converted frequency; and a piezoelectric transformer that supplies a high frequency current to the discharge tube based on the drive voltage. 8. The discharge tube dimming control device according to claim 1, wherein the dimming signal generation means generates a dimming signal by the feedback control for one cycle of the current. A discharge tube dimming control device characterized in that it is sufficiently shorter than each predetermined duration of level. 9. The discharge tube dimming control device according to claim 1, wherein the dimming signal generation means interposes an impedance element in a feedback circuit of the feedback control, and the impedance element. The discharge tube dimming control device is characterized in that the current level is adjusted for each of the predetermined durations by changing the impedance value of the. 10. The discharge tube dimming control device according to claim 1, wherein the dimming signal generation unit outputs a high-level high-frequency current from a plurality of current levels from the high-frequency current generation unit. A high-level current dimming signal generator for generating a high-level current dimming signal for outputting, and a low-level current dimming device for outputting a low-level high-frequency current of the plurality of current levels from the high-frequency current generating means. A low-level current dimming signal generation unit that generates a signal, and the high-level current dimming signal and the low-level current dimming signal that are respectively generated are combined at an arbitrary ratio based on a dimming command signal input from the outside. A discharge tube dimming control device, further comprising: a signal adjusting unit that adjusts a dimming signal.