JP2575031Y2 - Dimming circuit of display device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dimming circuit for dimming a display device applied to a display unit of a vehicle instrument, and the like.
In particular, the present invention relates to a dimming circuit for dimming a display device having a fluorescent display tube.

[0002]

2. Description of the Related Art Hitherto, a dimming circuit of this type having a configuration shown in FIG. 9 has been known. In the figure, reference numeral 1 denotes a triangular wave generating circuit, which includes an operational amplifier OP1, a capacitor C1,
It is composed of resistors R1 to R4. The + input of the operational amplifier OP1 is connected to the power supply voltage + V _CC by the resistors R1 and R
2, the output voltage VO is fed back via a resistor R3, and is applied to the negative input of the capacitor C1 charged via the resistor R4 by the output voltage VO of the operational amplifier OP1. A voltage is applied.

[0003] The output voltage VO of the operational amplifier unit O P1 is + voltage input is - supply voltage Vc is higher period than the voltage of the input
c, and becomes 0 in a low period, and becomes a rectangular wave having a period determined by the time constant of the resistor R4 and the capacitor C1.
Therefore, the terminal voltage VC of the capacitor C1 becomes a triangular wave voltage by charging and discharging with the maximum value Vcc and the minimum value 0 of the output voltage.

[0004] VR1 is the reference variable resistance as a voltage regulator, the resistance R5 and R6 constitute a voltage divider circuit for dividing the supply voltage + V _CC, the capacitor C1 the voltage of the mover by moving the movable element Can be adjusted in the range between the maximum value and the minimum value of the terminal voltage.

[0005] CP1 is a comparison circuit comprising an operational amplifier.
Its - The input is applied terminal voltage VC of the capacitor C1, the + input, the variable resistor VR1 and the comparison reference voltage V _R which is adjusted is applied by comparing the two voltages with each other, as a result capacitor outputs an H level signal when C terminal voltage VC is less than the reference voltage V _R, and outputs the L level signal when large.

[0006] VFD is a fluorescent display tube, a constant voltage V is applied to its grit G, and anodes A1 to A8 are
The output of an anode driver 2 corresponding to each anode is connected. The anode driver 2 selectively applies a drive voltage to each anode according to display data supplied thereto, and a comparison circuit input to a blank input BLANK. While the output of CP1 is at the L level, the application of the drive voltage to the anode is interrupted.

[0007] With the above arrangement, by adjusting the magnitude of the reference voltage V _R by the variable resistor VR1, the comparator circuit C
Since the period of the L level of the signal output from P1 is adjusted and the suspension period of the driving voltage applied to the anode of the fluorescent display tube FVD is adjusted, dimming is performed.

[0008]

In the conventional example described above, the fluorescent display tube VFD is operated by static driving in which a constant voltage V is always applied to the grid G of the fluorescent display tube VFD. And the anodes A1 to A8 are connected one to one, and the number of output lines is required by the number of anodes.

Therefore, in order to reduce the number of output lines of the anode driver 2, the display segment of the display area is divided into a plurality of groups, and a dynamic (multiplex) drive for lighting each group in a time-division manner is performed. When the light control circuit described above is used, there is a problem that when the light control is performed in a wide range, the possibility of occurrence of flicker on the display increases, which is not preferable.

The flicker of this display is caused by the triangular wave generation circuit 1
Is a self-excited circuit which has a period completely unrelated to the signal for dynamic driving.

Therefore, in view of the above-mentioned conventional problems, the present invention divides a display area for performing display by light emission into a plurality of areas,
A simple and inexpensive display device capable of dimming a display device having a dynamic drive type display device in which the divided display areas are sequentially driven in a time division manner without causing flicker over a wide range . It is an object to provide a dimming circuit.

[0012]

In order to solve the above-mentioned problems, a dimming circuit of a display device according to the present invention comprises an anode.
Is divided into a plurality of groups, and each of the divided groups is
Die with grit corresponding to anode
Compatible with the above-mentioned groups, with a fluorescent display tube of the Namic drive type
Drive voltage based on the display data
Anode driver to apply each time-sequentially
And each of the groups to which the drive voltage is applied.
A grid driver for applying a constant voltage to the corresponding grid
And a grit to which the constant voltage is applied.
The drive voltage in each group corresponding to
The anode is illuminated to display, and the grid driver is displayed.
Iva blanks during application period to different grit
Display that generates the constant voltage for a set time
An OR device for ORing the constant voltage;
A source voltage, and the charged electric charges are added to the logical sum means.
Having a capacitor discharged by the output of the
A triangular wave synchronized with the time division is generated by the charging voltage of the sensor.
The generated triangular wave generation means and the dimming operation
A reference voltage generating means for generating a reference voltage that can be saved;
The reference voltage is compared with the triangular wave to respond to the magnitude of the reference voltage.
And a comparing means for generating a square wave having the same duty.
The anode driver according to the duty of the rectangular wave.
Iva outputs the drive voltage to each of the groups
It is characterized in that dimming is performed with a reduced time .

[0013] The triangular wave generating means, a charging time constant before Kiko capacitor and a switching means for switching in two stages,
One step of dimming is performed by switching the charging time constant by the switching means.

A second triangular wave generating means for generating a second triangular wave synchronized with the signal for performing the time division, and comparing the reference voltage with the second triangular wave and according to the magnitude of the reference voltage And a second comparing means for generating a rectangular wave of duty, wherein the display device comprises a vehicular display device having a lamp for night lighting, and the switching means turns on the lamp by turning on the lamp. The duty of the rectangular wave generated by the second comparing means is changed by the change of the reference voltage, and the dimming of the night illumination lamp is performed at the same time.

[0015]

According to the above configuration, a group to which a constant voltage is applied is provided.
Drive voltage in each group corresponding to the lit
The anode to emit light to drive the fluorescent display
Perform dynamic display and use different grit driver
A blank is applied during the application period of applying a constant voltage to the grid.
Display that sets the running time to prevent leakage lighting
Device.

In addition, a grit having a different grit driver is used.
Means for generating a triangular wave by the logical sum of constant voltages applied to
Is constantly charged by the power supply voltage.
Discharge the received charge of the sensor and generate a triangular wave synchronized with time division.
Occurs and the comparison means is adjusted by this triangular wave and dimming operation
The reference voltage is compared and the data according to the magnitude of the reference voltage is
And generate a square wave of
Depending on the anode driver, the drive voltage for each group
Dimming is performed by reducing the output time of
As a result, the constant applied to the grit synchronized with the time division
Has the same effect as increasing the time of the voltage blanking period
Therefore, dimming is performed.

Since the triangular wave generating means performs dimming by switching the charging time constant of a capacitor that generates a triangular wave by charging and discharging in synchronization with time-division driving, the dimming characteristics before and after dimming are approximated. .

A second triangular wave generating means generates a second triangular wave synchronized with a signal for performing time division, and a second triangular wave generated by the second triangular wave generating means and a reference voltage generating means generate. The comparison means generates a second rectangular wave having a duty corresponding to the magnitude of the reference voltage by comparing the reference voltage with the reference voltage,
Since the lamp for night illumination of the display device is dimmed by the second rectangular wave at the time of dimming, both the dynamic drive type display and the illumination lamp are synchronously dimmed by one reference voltage change. be able to.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of a dimming circuit of a display device according to the present invention. In order to dynamically drive a fluorescent display tube VFD which is a dynamically driven display, grids are divided into two groups G1 and G2. Has been split. Thus, the output line of the anode driver 12 can be shared by the anodes of both groups.

Reference numeral 13 denotes a grid driver having two outputs for outputting grid drive signals for alternately driving the grids G1 and G2 divided into two groups to divide the display area into two. Two outputs are connected to grids G1 and G2, respectively.

The grid driver 13 alternately outputs a positive voltage grid drive signal to its two outputs, and alternately drives the grids G1 and G2 according to the grid drive signal. As a result, the segments corresponding to the grids G1 and G2 are turned on alternately. However, a blanking time for giving a light-off signal to all segments is provided between both lighting sections in order to prevent leakage lighting of the segments. Is set.

The grid drive signal output from the grid driver 13 is also input to an OR circuit OR as a logical sum means . The output of the OR circuit OR goes high when a grid drive signal is output to one of the outputs of the grid driver 13, and goes low only when a positive voltage is not output to both outputs. . This OR
The output of the circuit OR is inverted by the inverter I and taken out as an H level blanking signal.

The blanking signal obtained by the OR circuit OR and the inverter I is applied to the base of the switching transistor T1, and the transistor T1 is turned on while the blanking signal is applied. Transistor T1 is connected to the supply voltage + V _CC through a resistor R11, is connected in parallel with the capacitor C11.

The capacitor C11 is a transistor T1
When the transistor T1 is off, it is charged via the resistor R11, and when the transistor T1 is turned on, the charge is discharged instantaneously. Therefore, the transistor T1, the resistor R11, and the capacitor C11 constitute a triangular wave generating circuit 14 that generates a triangular wave voltage VC synchronized with a blanking signal, that is, a grid drive signal, at a connection point between the resistor R11 and the capacitor C11.

The triangular wave voltage triangular wave generating circuit 14 is generated, consisting of operational amplifier reference voltage V _R to the reference voltage adjusting unit 15 constituted by resistors R12 and R13 and variable resistor VR11 is generated is applied to the + input This is applied to the-input of the comparison circuit CP11. Comparison circuit CP1
1 compares the two voltages applied to ± inputted to each other, it outputs an H level signal when the result triangular wave voltage VC is less than the reference voltage V _R, and outputs the L level signal when large.

The output of the comparison circuit CP11 is applied to a blank input BLANK of the anode driver 12, and the anode driver 12 outputs the drive voltage to the anode while the output of the comparison circuit CP11 applied to the blank input BLANK is at the L level. Interrupt the application.

The operation of the circuit in the above configuration will be described with reference to the timing chart of FIG. 2 showing the state of each part of the circuit. As shown in FIGS. 2A and 2B, the grid driver 13 alternately generates a grid drive signal having a fixed blanking time therebetween at its output. At the output of the inverter I which inverts the output of the OR circuit OR which takes the logical sum of the grid drive signal, a blanking signal which becomes H level in synchronization with the blanking time is generated as shown in FIG. 2C. You.

When the transistor T1 is turned on by the blanking signal, a triangular wave voltage that changes as shown in FIG. 2D is generated at the terminal of the capacitor C11. The triangular wave voltage is compared at the reference voltage V _R and comparator circuit CP11 which is regulated by the variable resistor VR11, the output of the comparator circuit CP11, as shown in e of FIG. 2, the reference voltage V _R is a large period H A rectangular wave that becomes L level in a small period is output.

The rectangular wave output from the comparison circuit CP11 is input to the blank input BLANK of the anode driver 12, whereby the anode driver 12 drives the anode while the rectangular wave is at the L level as shown in FIG. Suspend and turn off the display for that period. When the display extinguishing period is long, the luminance emitted from the fluorescent display tube VFD is increased, and when it is short, the luminance is reduced and the dimming is performed. this is,
Variable resistor VR11 by adjusting the magnitude of the reference voltage V _R by carried out by changing the period of H level of the rectangular wave of the output of the comparator circuit CP11.

In the above-described embodiment, an OR circuit O for obtaining a blanking signal corresponding to a blanking time is provided.
R and the inverter I can be constituted by a diode and a transistor. Also, the grid driver 13
Is controlled by a controller configured by a microcomputer (CPU),
A blanking signal can be easily generated independently by the CPU.

FIG. 3 shows another embodiment of the dimming circuit of FIG. 1 in which one-step dimming is enabled by a switch operation. In FIG. 3, the same parts as those of FIG. doing.

In the figure, reference numeral 20 denotes a triangular wave generating circuit 14.
A time constant switching circuit for switching the charging time constant, which is connected in parallel with a charging resistor R11 for charging the capacitor C11 in the middle, and a transistor T connected in parallel with the resistor R11.
2 and a series circuit of a resistor R21, a transistor T3 connected to the base of the transistor T2, and a transistor T3.
And a changeover switch SW1 connected to the base of the third switch.

With the above configuration, when the switch SW1 is off, the transistors T2 and T3 are both off, and the capacitor C11 is charged via the resistor R11.
The terminal voltage of the capacitor C11 increases as shown by the solid line in FIG. Terminal voltage of the capacitor C11 is compared with a reference voltage V _R from the reference voltage generating circuit 15 in the comparison circuit CP11, a rectangular wave as shown in b of FIG. 4 is generated at the output of the comparator circuit CP11. In FIG. 4B, a hatched portion is a blanking period, and H is excluded during this period.
The display is made during the level.

The switch SW1 contrast is on, the transistor T3 is a voltage V _CC is applied to turn on its base, whereby the transistor T2 is also turned on. When the transistor T2 is turned on, the capacitor C11
The capacitor C11 is charged through the parallel circuit of the resistors R11 and R21, and the terminal voltage of the capacitor C11 increases as shown by a dotted line in FIG. 4A. When the switch SW1 is on, the rise of the charging voltage of the capacitor C11 is faster than when it is off. Therefore, the output of the comparison circuit CP11 includes
As shown in FIG. 4C, the period of the H level excluding the blanking period indicated by oblique lines is shortened, and the display luminance is reduced as compared with the case where the switch SW1 is turned off.

As described above, when one-step dimming is performed by switching the charging characteristic of the capacitor C11,
11 only changes in a similar manner, the terminal voltage of FIG.
As shown in, run the duty characteristics with respect to the change of the reference voltage V _R does not change significantly between on of the switch SW1 and off, it is easy to similarity.

When the display device is for a vehicle, dimming of the fluorescent display tube VFD is generally performed in conjunction with turning on a light switch for turning on a night light. FIG. 6 shows an embodiment in which the present invention is applied to a vehicle display device having a night illumination lamp and a two-phase dynamic drive fluorescent display tube, such as an automotive instrument. In FIG. 6, the same parts as those in FIG. The description is omitted here.

In FIG. 6, one grid drive signal output from the grid driver 13 is applied to the base of the switching transistor T4, and the transistor T4 is turned on while the grid drive signal is applied.
The transistor T4 is connected to the power supply voltage + V _CC via the resistor R31.
And connected in parallel with the capacitor C12.

The capacitor C12 is connected to a transistor T4
When the transistor T4 is turned off, the charge is performed via the resistor R31, and when the transistor T4 is turned on, the charge is discharged instantaneously. Therefore, the transistor T4, the resistor R31, and the capacitor C12 output the triangular wave voltage V
A second triangular wave generation circuit 30 that generates C2 at a connection point between the resistor R31 and the capacitor C12 is configured.

The triangular wave voltage generated by the second triangular wave generating circuit 30 is connected to the resistors R12 and R13 and the variable resistor VR1.
The reference voltage V _R generated by the reference voltage adjusting unit 15 constituted by 1 is applied to the + input of a comparison circuit CP12 composed of an operational amplifier applied to the − input. Comparator circuit CP12 compares the two voltages applied to ± inputted to each other, so that outputs an H level signal when the triangular wave voltage VC2 is higher than the reference voltage V _R, and outputs the L level signal when a small .

The output of the comparison circuit CP12 is connected to one end of night lighting lamps LP1 to LP3 connected in parallel, and the other end of the lamps LP1 to LP3 is connected to a light switch S.
It is connected to battery B via W2. The light switch SW2 is also used as a switch for performing one-step dimming. For this purpose, the light switch SW2 is connected in parallel with the charging resistor R11 for charging the capacitor C11 in the first triangular wave generation circuit 14, and switches the charging time constant. Time constant switching circuit 20
Is also connected to the base of the transistor T3.

In the above configuration, the operation of the circuit of FIG.
This will be described with reference to the timing chart of FIG. 7 showing the state of each part of the circuit. As shown by a and b in FIG. 7, the grid driver 13 alternately generates a grid drive signal having a fixed blanking time therebetween at its output.
At the output of the inverter I which inverts the output of the OR circuit OR which takes the logical sum of the grid drive signal, a blanking signal which becomes H level in synchronization with the blanking time is generated as shown by c in FIG. You.

When the transistor T1 is turned on by the blanking signal, the light switch SW
2 is off, the terminal of the capacitor C11 is
A triangular wave voltage is generated as shown by a solid line in FIG.
The triangular wave voltage is compared at the reference voltage V _R and comparator circuit CP11 which is regulated by the variable resistor VR11,
The output of the comparator circuit CP11, as shown by the solid line in f in FIG. 7, H-level reference voltage V _R is greater period, square waves at the L level in a small period is outputted.

The rectangular wave output from the comparison circuit CP11 is input to a blank input BLANK of the anode driver 12, whereby the anode driver 12 outputs
The drive of the anode is suspended during the level period, and the display is turned off during that period. When the display extinguishing period is long, the luminance emitted from the fluorescent display tube VFD is increased, and when it is short, the luminance is reduced and the dimming is performed. This variable resistor VR11 by adjusting the magnitude of the reference voltage V _R by comparison circuit CP11
By changing the period of the H level of the rectangular wave output.

On the other hand, the second triangular wave generating circuit 30 to which one grid drive signal from the grid driver 13 is input is connected to the terminal of the capacitor C12 as shown in FIG. Generates a triangular wave voltage that varies as shown. The triangular wave voltage is compared in the comparator circuit CP12 with a reference voltage V _R which is regulated by the variable resistor VR11. The output of the comparator circuit CP12 This comparison, as shown in g of FIG. 7, L-level by the reference voltage V _R is greater period, output rectangular waves to the H level at a small period, L level of the rectangular wave the time is changed by adjusting the reference voltage V _R.

The rectangular wave output from the comparison circuit CP12 is applied to one end of the lamps LP1 to LP3 connected in parallel, but when the light switch SW2 is off,
The lamps LP1 to LP3 are not turned on.

On the other hand, when the light switch SW2 is turned on, a triangular wave voltage which changes as shown by a dotted line in FIG. 7D is generated at the terminal of the capacitor C11. The triangular wave voltage is compared in the comparator circuit CP11 with a reference voltage V _R which is regulated by the variable resistor VR11. The output of the comparator circuit CP11 This comparison, as shown by the dotted line in f in FIG. 2, compared to the case light switch SW2 is off, H level of the reference voltage V _R is greater period is short, a small period Is output by outputting a rectangular wave having a long L level.

At this time, the lamps LP connected in parallel
Since the battery B is connected to the other ends of the first to LP3 via the light switch SW2, the comparison circuit CP
When the square wave output from the battery 12 goes low, the battery B
To light switch SW2 and lamps LP1 to LP3
, A current flows into the output of the comparison circuit CP2, and the lamps LP1 to LP3 are turned on. And the reference voltage V
_By adjusting _R , the period of the L level is changed, and the lamp L
Light control for P1 to LP3 is performed simultaneously with the fluorescent display tube VFD.

By the way, in the case of the fluorescent display tube VFD, the brightness and the lighting duty are in a proportional relationship, but in the case of the lamps LP1 to LP3, the brightness and the lighting duty are not in a proportional relationship. It is considered to be proportional to the .6 power. Therefore, assuming that the light control range is 8 to 12 times and the lighting duty at the maximum luminance is 100%, the minimum duty of the light control range is 56% to 50%.

In this regard, in the embodiment described above with reference to FIG. 6, the second triangular wave generating circuit 30 generates a triangular wave in synchronization with one of the grid driving signals from the grid driver 13 for dynamically driving the fluorescent display tube VFD in two phases. Therefore, the minimum lighting duty of about 50% of the lamps LP1 to LP3 can be compensated.

The dimming range of the fluorescent display tube VFD is similarly set to 8 to 12 times, and the light switch SW2
If the maximum luminance at the time of one-step dimming by turning on the LED is balanced with the luminance at the 100% lighting duty of the lamps LP1 to LP3, good dimming characteristics can be obtained over the entire variable range of the variable resistor VR1. . Figure 8 fluorescent display tube with respect to the reference voltage V _R obtained according to this example is VFD and the lamp L
The luminance characteristics of P1 to LP3 are shown, and the characteristics of the fluorescent display tube VFD and the lamps LP1 to LP3 at the time of dimming are similar.

In the embodiment described above, the dimming of the fluorescent display tube has been described. However, the present invention can be equally applied to the dimming of a dynamic drive type LED display instead of the fluorescent display tube. In addition, although the dimming is performed by manual adjustment of the variable resistor, the present invention can be applied to a case where the light is automatically adjusted by detecting the surrounding brightness by a light receiving element.

[0052]

According to the present invention as described above, according to the invention], different
Synchronized with the logical division of a constant voltage applied to the grit
Generates a triangle wave and adjusts it with this triangle wave and dimming operation.
Compare the reference voltage to
Generates a square wave of
Output drive voltage to anodes of each group
Since dimming is performed with decreasing time, as a result,
A constant voltage brass applied to the grit synchronized with time division
Dimming due to the same effect as increasing the duration of the printing period
The display device having a dynamically driven fluorescent display tube can be dimmed without causing flicker on the display, and synchronization to time division can be marked on different grids.
The capacitor is discharged by the OR of the applied constant voltage.
And reduce the time required to output the drive voltage to the anode.
The circuit is simple and inexpensive because the light is reduced by reducing the light .

Also, since the triangular wave generating means performs dimming by switching the charging time constant of a capacitor that generates a triangular wave by charging and discharging in synchronization with time-division driving, the dimming characteristics before and after dimming are approximated. It has become.

Further, the second triangular wave generated in synchronization with the signal for performing the time division is compared with the same reference voltage to generate a second rectangular wave having a duty corresponding to the magnitude of the reference voltage, Since the lamp for nighttime illumination is dimmed by the second rectangular wave at the time of dimming, both the dynamic drive display and the illumination lamp can be synchronously dimmed by one change of the reference voltage. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a dimming circuit according to the present invention.

FIG. 2 is a timing chart illustrating a state of each unit in FIG. 1;

FIG. 3 is a circuit diagram showing another embodiment of the dimming circuit according to the present invention.

FIG. 4 is a timing chart showing a state of each unit in FIG. 3;

FIG. 5 is a diagram showing a reference voltage-duty characteristic before and after dimming in the circuit of FIG. 3;

FIG. 6 is a circuit diagram showing still another embodiment of the dimming circuit according to the present invention.

FIG. 7 is a timing chart showing a state of each unit in FIG. 6;

8 is a diagram showing reference voltage-luminance characteristics before and after dimming in the circuit of FIG. 6;

FIG. 9 is a circuit diagram showing an example of a conventional dimming circuit.

[Explanation of symbols]

VFD Fluorescent display tubes G1 , G2 Grids A1 to A8 Anode OR OR circuit (logical sum means) 12 Anode driver 13 Grid driver 14 Triangular wave generating circuit (triangular wave generating means) 15 Reference voltage generating circuit (reference voltage generating means) 20 Switching circuit (Switching means) 30 Second triangular wave generating circuit (Second triangular wave generating means) C11 Capacitor CP11 Comparison circuit (Comparison means) CP12 Second comparison circuit (Second comparison means) SW2 Light switches LP1 to LP3 For night illumination lamp

Claims (3)

(57) [Scope of request for utility model registration] 1. The method according to claim 1 , wherein the anode is divided into a plurality of groups.
Grit corresponding to each divided anode
Dynamically driven fluorescent display tubes provided separately
And driving based on display data corresponding to each group.
The voltage is applied to each group in time-division order.
An anode driver to be applied and the drive voltage being applied
A constant voltage on the grit corresponding to each group
And a grid driver for applying the constant voltage.
In each of the groups corresponding to the applied grit
The display is displayed by causing the anode to which the drive voltage is applied to emit light.
The grit driver applies to different grit
The constant voltage that sets the blanking time during the period
A display device configured to generate, a logical sum unit for calculating a logical sum of the constant voltage, and charged by the voltage;
Having a capacitor discharged by the output;
Generates a triangular wave synchronized with the time division by the charging voltage
A triangular wave generating means for generating a reference voltage whose magnitude can be adjusted by dimming operation.
Reference voltage generating means, and comparing the reference voltage with the triangular wave to determine the magnitude of the reference voltage.
And a comparing means for generating a square wave having a duty corresponding to
The anode driver according to the duty of the square wave
For outputting the drive voltage for each group
Dimming the display device by dimming the light.
Optical circuit. Wherein said triangular wave generating means, before and a switching means for switching in two stages the charge time constant of Kiko capacitor, and to perform one-stage dimming by switching the charging time constant by said switching means 2. The table according to claim 1, wherein :
Dimming circuit of display device . 3. A second triangular wave generating means for generating a second triangular wave synchronized with a signal for performing the time division, comparing the reference voltage with the second triangular wave to reduce the magnitude of the reference voltage. A second comparing means for generating a rectangular wave having a duty corresponding to the light, wherein the display device comprises a vehicular display device having a lamp for night illumination, and the switching means turns on the lamp when turned on. 3. The night illumination lamp according to claim 2, further comprising a switch, wherein the duty of the rectangular wave generated by the second comparing means is changed by the change of the reference voltage, and the dimming of the night illumination lamp is performed at the same time.
Dimming circuit for display device .