JPH04105498U - dimmer circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To enable dimming of a display device having a dynamically driven display that displays by emitting light over a wide range using a simple and inexpensive circuit without flickering in a dimming circuit. The purpose is to [Structure] A triangular wave generation circuit 14 generates a triangular wave in synchronization with a signal for dynamic driving. Comparison circuit CP
11 generates a rectangular wave with a duty according to the magnitude of the reference voltage. This rectangular wave is used to dim the fluorescent display tube VFD.
Light dimming is achieved by switching the charging time constant of a capacitor that generates triangular waves when charging and discharging. Second comparison circuit car CP12
generates a second rectangular wave with a duty corresponding to the magnitude of the reference voltage, and when the light is dimmed (when the light switch is on), this second rectangular wave lights up the lamp LP for night illumination of the display device.
1 to LP3 are dimmed.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention is a light control circuit that controls the light of a display device that is applied to the display section of a vehicle instrument. In particular, displays using light emitted from the display area, such as fluorescent display tubes (VFD), etc. The present invention relates to a dimming circuit that performs dimming of a display device that performs.

0002

[Conventional technology]

Conventionally, as this type of dimming circuit, one having the configuration shown in FIG. 9 is known. In the figure, 1 is a triangular wave generation circuit, which is composed of an operational amplifier OP1, a capacitor C1, and resistors R1 to R4. The power supply voltage +V _CC is divided by resistors R1 and R2 and is applied to the + input of the operational amplifier OP1, and the output voltage VO is fed back and applied via the resistor R3, and the - input of the operational amplifier OP1 is applied. A charging voltage is applied to the capacitor C1 which is charged via the resistor R4 by the output voltage VO of the capacitor C1.

[0003] The output voltage VO of the operational amplifier OP1 becomes the power supply voltage V _CC during a period in which the voltage at the + input is higher than the voltage at the - input, and becomes 0 during a period when it is lower, and is determined by the time constant of the resistor R4 and the capacitor C1. It becomes a periodic square wave. Therefore, the terminal voltage VC of the capacitor C1 becomes a triangular wave voltage due to charging and discharging with the maximum value V _CC and the minimum value 0 of the output voltage.

VR1 is a variable resistor as a reference voltage adjustment section, and together with resistors R5 and R6 constitutes a voltage dividing circuit that divides the power supply voltage +V _CC , and by moving the movable element, the voltage of this movable element is transferred to the capacitor C1. The terminal voltage can be adjusted within the range of maximum and minimum values.

[0005] CP1 is a comparator circuit composed of an operational amplifier, the terminal voltage VC of the capacitor C1 is applied to its negative input, and the comparison reference voltage V _R adjusted by a variable resistor VR1 is applied to its positive input. The two voltages are compared with each other, and as a result, when the terminal voltage VC of the capacitor C is smaller than the reference voltage _VR , an H level signal is output, and when it is larger, an L level signal is output.

[0006] A VFD is a fluorescent display tube, and a constant voltage V is applied to its grid G, and the anode The outputs of the anode driver 2 corresponding to each anode are connected to A1 to A8. , this anode driver 2 controls each anode according to the display data supplied to it. While selectively applying the driving voltage, the input voltage is applied to the blank input BLANK. The application of the drive voltage to the anode is interrupted while the output of the comparator circuit CP1 is at L level. Ru.

With the above configuration, when the magnitude of the comparison reference voltage _VR is adjusted by the variable resistor VR1, the L level period of the signal output from the comparison circuit CP1 is adjusted, and the drive applied to the anode of the fluorescent display tube FVD is adjusted. The duration of the voltage interruption is adjusted so that dimming occurs.

[0008]

[Problem that the idea aims to solve]

In the conventional example explained above, a constant voltage V is always applied to the grid G of the fluorescent display tube VFD. Since the fluorescent display tube VFD is operated by the applied static drive, the The output of the node driver 2 and the anodes A1 to A8 are connected one-to-one, and the number of output lines is are required as many as the number of anodes.

[0009] Therefore, in order to reduce the number of output lines of anode driver 2, the display segment of the display area Dynamic mode that divides the components into multiple groups and lights up each group in a time-division manner. (multiplex) drive configuration, the above-mentioned dimming circuit can be used. On roads, there is a high possibility that flickering will occur on the display when dimming is performed over a wide range. There was a problem that this was not desirable.

0010 The reason for this display flickering is that the triangular wave generator circuit 1 is a self-excited circuit and is dynamically driven. This occurs because the period is completely unrelated to the signal for motion.

[0011] Therefore, in view of the above-mentioned conventional problems, the present invention provides a display that displays by emitting light. The display area is divided into multiple areas, and the divided display areas are driven sequentially in a time-sharing manner. Flickering can be caused over a wide range of display devices with dynamically driven displays. The objective of the present invention is to provide a simple and inexpensive dimming circuit that can dim the light without any interference. This is an issue.

0012

[Means to solve the problem]

In order to solve the above problems, the dimmer circuit created by this invention provides an indication by emitting light. Divide the display area into multiple parts and drive the divided display areas sequentially in a time-sharing manner. A dimming circuit for dimming a display device having a dynamically driven display device as described above. a reference voltage generating means for generating a reference voltage, and a signal for performing the time division. and a triangular wave generating means for generating a triangular wave synchronized with the reference voltage and the triangular wave. and comparison means for generating a rectangular wave with a duty according to the magnitude of the reference voltage. Furthermore, the duty of the rectangular wave generated by the comparison means is changed by a change in the reference voltage. The present invention is characterized in that the dynamic drive type display device is dimmed by controlling the dynamic drive type display device.

[0013] The triangular wave generating means is charged and discharged in synchronization with the signal for performing the time division. A capacitor and a switching means for switching the charging time constant of the capacitor in two stages. and one step dimming is performed by switching the charging time constant by the switching means. It is characterized by

[0014] a second triangular wave that generates a second triangular wave synchronized with the signal for performing the time division; generating means, comparing the reference voltage and the second triangular wave and responding to the magnitude of the reference voltage; and second comparison means for generating a square wave with a duty similar to that of the first comparison means. The display device consists of a vehicle display device having a lamp for night illumination, and the switching the means comprises a light switch which turns on said lamp, said reference being turned on; The duty of the rectangular wave generated by the second comparing means is changed by a change in voltage. It is characterized in that the light of the night illumination lamp is also adjusted at the same time.

[0015]

[Effect]

In the above configuration, the display area that displays by emitting light is divided into multiple parts, and each of the divided parts is A triangular wave is generated that is synchronized with a signal to sequentially drive the displayed display area in time division. The triangular wave generated by the triangular wave generating circuit and the reference voltage generating means are The comparison means compares the generated reference voltage with the reference voltage, and this comparison determines the magnitude of the reference voltage. Generates a rectangular wave with a corresponding duty. Then, by changing the reference voltage, the comparison means The dimming of the dynamically driven display is controlled by changing the duty of the square wave generated by Is going.

[0016] The triangular wave generated by the triangular wave generating means sequentially drives the display area in a time-division manner. Since it is synchronized with the signal, the duty is proportional to the magnitude of the reference voltage generated by the comparison means. The square wave of the tee becomes synchronized with the time-division drive of the display area.

[0017] The triangular wave generation means generates a triangular wave by charging and discharging in synchronization with time-division driving. Since dimming is performed by switching the charging time constant of the capacitor, the dimming characteristics before and after dimming is approximated.

[0018] A second triangular wave generating means generates a second triangular wave synchronized with the signal for time division. The second triangular wave generated by the second triangular wave generating means and the reference voltage generating means The comparison means compares the generated reference voltage with the duty according to the magnitude of the reference voltage. generates a second rectangular wave of Since the brightness lamp is dimmed, dynamic driving is performed by changing one reference voltage. Both the dynamic display and the lighting lamp can be dimmed synchronously.

[0019]

【Example】

Hereinafter, embodiments of the present invention will be described based on the drawings. Figure 1 shows the display device according to the present invention. FIG. 2 is a circuit diagram showing an example of a dimming circuit for a dynamic drive type display device. In order to dynamically drive the fluorescent display tube VFD, the grid is divided into two groups G. 1 and G2. By this, the output of the anode driver 12 The line can be shared by both groups of anodes.

[0020] 13 is a grid G1 divided into two groups to divide the display area into two. and two outputs to output grid drive signals to drive G2 alternately. The two outputs are connected to grids G1 and G2, respectively. connected.

[0021] The grid driver 13 crosses a positive voltage grid drive signal between its two outputs. Grids G1 and G2 are driven alternately by this grid drive signal. do. As a result, each segment corresponding to grids G1 and G2 points alternately. However, between the two lighting sections, the entire segment is lit to prevent lighting leakage. A blanking time is set to give a turn-off signal to all segments.

[0022] The grid drive signal output from the grid driver 13 is also input to the OR circuit OR. I feel empowered. The output of this OR circuit OR is either one of the outputs of the grid driver 13. When the grid drive signal is output to one side, it becomes H level, and both outputs have a positive voltage. It becomes L level only when no voltage is output. The output of this OR circuit OR is It is inverted by inverter I and taken out as an H level blanking signal. Ru.

The blanking signal taken out 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 this blanking signal is applied. Transistor T1 is connected to power supply voltage +V _CC via resistor R11 and in parallel with capacitor C11.

[0024] The capacitor C11 is connected to the capacitor C11 through the resistor R11 when the transistor T1 is off. When the transistor T1 is turned on, the electric charge is instantly discharged. Yo Therefore, the transistor T1, the resistor R11 and the capacitor C11 output the blanking signal. In other words, the triangular wave voltage VC synchronized with the grid drive signal is applied to the resistor R11 and the capacitor. It constitutes a triangular wave generating circuit 14 that is generated at the connection point with C11.

[0025] The triangular wave voltage generated by the triangular wave generation circuit 14 is generated by resistors R12 and R13 and Reference voltage V generated by reference voltage adjustment section 15 configured by variable resistor VR11 _R is applied to the - input of the comparator circuit CP11 consisting of an operational amplifier, which is applied to the + input. added. Comparison circuit CP11 mutually compares both voltages applied to the ± input, and The resulting triangular wave voltage VC is the reference voltage V_ROutputs an H level signal when the When the signal is large, an L level signal is output.

[0026] The output of the comparison circuit CP11 is the blank input BLANK of the anode driver 12. and the anode driver 12 is applied to the blank input BLANK. Application of drive voltage to the anode is interrupted while the output of comparator circuit CP11 is at L level. do.

[0027] The timing diagram in Figure 2 shows the operation of the circuit in the above configuration and the state of each part of the circuit. Explain with reference to the chart. The grid driver 13 is shown in FIGS. 2a and 2b. Its output is a grid drive signal with a certain blanking time between each occur alternately. The output of the OR circuit OR that takes the logical sum of this grid drive signal is The output of the inverting inverter I has a blanking time as shown in Fig. 2c. A blanking signal that goes high in synchronization is generated.

By turning on the transistor T1 in response to this blanking signal, a triangular wave voltage that changes as shown in d of FIG. 2 is generated at the terminal of the capacitor C11. This triangular wave voltage is compared with a reference voltage V _R adjusted by a variable resistor VR11 in a comparator circuit CP11, and as shown in e in _FIG . A rectangular wave that becomes L level in a small period is output.

The rectangular wave output from the comparator circuit CP11 is input to the blank input BLANK of the anode driver 12, so that the anode driver 12 drives the anode during the period when the rectangular wave is at L level, as shown in f in FIG. Interrupt and turn off the display for that period. When the display off period is long, the brightness emitted by the fluorescent display tube VFD is increased, and when it is short, the brightness is decreased to perform dimming. This is done by adjusting the magnitude of the reference voltage V _R using the variable resistor VR11 to change the H level period of the rectangular wave output from the comparator circuit CP11.

[0030] In the embodiment described above, the blanking signal corresponding to the blanking time is obtained. The OR circuit OR and the inverter I are composed of diodes and transistors. can be achieved. In addition, the grid driver 13 is connected to a microcomputer (C When configured to be controlled by a controller configured by , it is easy to cause the CPU to generate a blanking signal independently.

[0031] Figure 3 shows a version of the dimming circuit shown in Figure 1 that enables one-step dimming by operating a switch. In this figure, the same parts as in Fig. 1 are given the same reference numerals and explanations are omitted. are doing.

[0032] In the figure, 20 is a charger that charges the capacitor C11 in the triangular wave generation circuit 14. A time constant switching circuit connected in parallel with the electrical resistor R11 to switch the charging time constant. , a series circuit of transistor T2 and resistor R21 connected in parallel with resistor R11. , a transistor T3 connected to the base of the transistor T2, and a transistor It has a changeover switch SW1 connected to the base of T3.

With the above configuration, when switch SW1 is off, transistors T2 and T3 are both off, capacitor C11 is charged via resistor R11, and the terminal voltage of capacitor C11 is indicated by the solid line a in FIG. Increase as shown. The terminal voltage of this capacitor C11 is compared with the reference voltage V _R from the reference voltage generation circuit 15 in the comparator circuit CP11, and a rectangular wave as shown in FIG. 4B is generated at the output of the comparator circuit CP11. In FIG. 4B, the shaded area is a blanking period, and display is performed during the H level excluding this period.

On the other hand, when the switch SW1 is on, the voltage V _CC is applied to the base of the transistor T3 and the transistor T3 is turned on, thereby also turning on the transistor T2. When the transistor T2 is turned on, the resistor R21 is connected in parallel with the capacitor C11, and the capacitor C11 is charged through the parallel circuit of the resistors R11 and R21, and the terminal voltage of the capacitor C11 is indicated by the dotted line a in FIG. Increase as shown. When the switch SW1 is on, the charging voltage of the capacitor C11 rises faster than when it is off. Therefore, as shown in c in FIG. 4, the output of the comparator circuit CP11 has a shorter H level period excluding the blanking period indicated by diagonal lines, and the display brightness is lower than when the switch SW1 is off. .

[0035] When the charging characteristic of the capacitor C11 is switched to perform one-step dimming as described above, since the terminal voltage of the capacitor C11 only changes in a similar manner, the reference voltage is changed as shown in FIG. The effective duty characteristic with respect to a change in V _R does not change greatly depending on whether the switch SW1 is on or off, and it is easy to make it similar.

[0036] If the display device is for a vehicle, the dimming of the fluorescent display tube VFD can be done by turning off the night lights. It is common to do this in conjunction with turning on a light switch to turn on the light. Figure 6 is Night lighting lamps and 2-phase dynamic drive fluorescent display tubes, like automobile instruments. This figure shows an example applied to a vehicle display device having are given the same reference numerals and their explanations are omitted.

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 this grid drive signal is applied. Transistor T4 is connected to the power supply voltage +V _CC via resistor R31, and is also connected in parallel with capacitor C12.

[0038] The capacitor C12 is connected to the capacitor C12 through the resistor R31 when the transistor T4 is off. When the transistor T4 is turned on, the charge is instantly discharged. Yo The transistor T4, the resistor R31 and the capacitor C12 are connected to the grid drive signal. A triangular wave voltage VC2 synchronized with is generated at the connection point between resistor R31 and capacitor C12. A second triangular wave generating circuit 30 is configured.

The triangular wave voltage generated by the second triangular wave generation circuit 30 is calculated by applying the reference voltage V _R generated by the reference voltage adjustment section 15 composed of resistors R12 and R13 and variable resistor VR11 to the - input. It is applied to the +input of a comparator circuit CP12 consisting of an amplifier. Comparison circuit CP12 mutually compares both voltages applied to the ± inputs, and as a result outputs an H level signal when the triangular wave voltage VC2 is greater than the reference voltage _VR , and outputs an L level signal when it is smaller. .

[0040] The output of the comparison circuit CP12 is the output of the parallel-connected night lighting lamps LP1 to L. It is connected to one end of lamp P3, and the other end of lamp LP1 to LP3 is connected to light switch SW2. It is connected to battery B via. Light switch SW2 performs one step dimming. It is also used as a switch for It is connected in parallel with the charging resistor R11 that charges the capacitor C11, and cuts off the charging time constant. It is also connected to the base of the transistor T3 of the time constant switching circuit 20 for switching. Ru.

[0041] In the above configuration, the operation of the circuit shown in FIG. This will be explained with reference to the timing chart. The grid driver 13 is shown in FIG. As shown in , the grid drive signals with a certain blanking time between them are occurs alternately in the output. An OR circuit that takes the logical sum of this grid drive signal The output of the inverter I that inverts the output is blanked as shown by c in Figure 7. A blanking signal that goes to H level in synchronization with time is generated.

By turning on the transistor T1 in response to this blanking signal, a triangular wave voltage that changes as shown by the solid line d in FIG. 7 is generated at the terminal of the capacitor C11 when the light switch SW2 is off. This triangular wave voltage is compared with a reference voltage V _R adjusted by a variable resistor VR11 in a comparator circuit CP11, and the output of the comparator circuit CP11 shows a period when the reference voltage V _R is large, as shown by the solid line in f of FIG. A rectangular wave is output that goes to H level in a short period and goes to L level in a short period.

The rectangular wave output from the comparator circuit CP11 is input to the blank input BLANK of the anode driver 12, whereby the anode driver 12 interrupts driving the anode during the period when the rectangular wave is at L level and turns off the display during that period. do. When the display off period is long, the brightness emitted by the fluorescent display tube VFD is increased, and when it is short, the brightness is decreased to perform dimming. This is done by adjusting the magnitude of the reference voltage V _R using the variable resistor VR11 and changing the H level period of the rectangular wave output from the comparator circuit CP11.

[0044] On the other hand, one grid drive signal from the grid driver 13 is input. The second triangular wave generation circuit 30 operates regardless of whether the light switch SW2 is on or off. Generate a triangular wave voltage that changes as shown in e in Figure 7 at the terminal of capacitor C12. . This triangular wave voltage is a reference voltage V adjusted by a variable resistor VR11._Rcompared with A comparison is made in circuit CP12. This comparison causes the output of the comparator circuit CP12 to be is the reference voltage V, as shown in Figure 7g._RL level in periods where is large and periods where is small A rectangular wave that becomes H level is output, and the L level time of this rectangular wave is equal to the reference voltage V. _R can be changed by adjusting.

[0045] The rectangular wave output from the comparator circuit CP12 is generated by the parallel-connected lamps LP1 to LP. However, when the light switch SW2 is off, the light is applied to one end of the light switch SW2. LP1 to LP3 are never lit.

On the other hand, when the light switch SW2 is on, a triangular wave voltage is generated at the terminal of the capacitor C11, which changes as shown by the dotted line in d of FIG. This triangular wave voltage is compared with a reference voltage _VR adjusted by a variable resistor VR11 in a comparison circuit CP11. As a result of this comparison, the output of the comparator circuit CP11 shows that the H level is shorter when the reference voltage V R is large, and the H level is shorter when the reference voltage V _R is smaller than when the light switch SW2 is off, as shown by the dotted line in f in FIG. A rectangular wave with a long L level is output, and dimming is performed.

At this time, since battery B is connected to the other ends of the parallel-connected lamps LP1 to LP3 via the light switch SW2, when the rectangular wave output from the comparator circuit CP12 becomes L level, , current flows from battery B to the output of comparator circuit CP2 via light switch SW2 and lamps LP1 to LP3, and lamps LP1 to LP3 are turned on. Then, the L level period is changed by adjusting the reference voltage _VR , and the dimming of the lamps LP1 to LP3 is performed simultaneously with the fluorescent display tube VFD.

[0048] By the way, in the case of a fluorescent display tube VFD, the brightness and lighting duty are in a proportional relationship. However, in the case of lamps LP1 to LP3, the brightness and lighting duty are in a proportional relationship. Rather, it is generally believed that brightness is proportional to the lighting duty to the 3.6th power. Therefore , the dimming range is set to 8 to 12 times, and the lighting duty at maximum brightness is set to 100%. Then, the minimum duty in the dimming range is 56% to 50%.

[0049] In this regard, in the embodiment described above with reference to FIG. synchronously with one of the grid drive signals from the grid driver 13 that drives the grid. Since the second triangular wave generation circuit 30 generates a triangular wave, the lamps LP1 to LP3 It is possible to compensate for a minimum lighting duty of about 50%.

In addition, the dimming range of the fluorescent display tube VFD is similarly set to 8 to 12 times, and the maximum brightness when the light switch SW2 is turned on to reduce the light by one step is the 100% lighting duty of the lamps LP1 to LP3. If the brightness is balanced with the brightness at the front, good dimming characteristics can be obtained over the entire variable range of the variable resistor VR1. FIG. 8 shows the brightness characteristics of the fluorescent display tube VFD and the lamps LP1 to LP3 with respect to the reference voltage V _R obtained by this example, and the characteristics of the fluorescent display tube VFD and the lamps LP1 to LP3 during dimming are similar. ing.

[0051] In the embodiments described above, the dimming of the fluorescent display tube was explained. It is equally applicable to the dimming of dynamically driven LED displays, for example, instead of display tubes. can be done. In addition, the light is dimmed by manual adjustment of the variable resistor, but the light receiving element The present invention can also be applied to automatically adjust the light by detecting the surrounding brightness. I can do that.

[0052]

[Effect of the idea]

As explained above, according to the present invention, the rectangular wave for dimming can be used to time-divide the display area. Since it is synchronized with the signal for sequentially driving the Display devices with drive-type displays can be used over a wide range without flickering. It can be dimmed, and the circuit is simple and inexpensive.

[0053] In addition, the triangular wave generation means generates a triangular wave by charging and discharging in synchronization with time-division driving. Since the light is dimmed by switching the charging time constant of the capacitor, the adjustment before and after dimming is possible. The optical characteristics are similar.

[0054] Furthermore, the same reference voltage as the second triangular wave generated in synchronization with the signal for time division is used. generate a second rectangular wave with a duty according to the magnitude of the reference voltage by comparing the voltage with the reference voltage, When the light is dimmed, this second square wave is used to dim the lamp for night illumination, so 1 Synchronizes both dynamically driven indicators and lighting lamps by changing two reference voltages. The light can be dimmed depending on the period.

[Brief explanation of drawings]

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

FIG. 2 is a timing chart diagram showing the states of each part 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 diagram showing the states of each part in FIG. 3;

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

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 diagram showing the states of each part in FIG. 6;

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

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

[Explanation of symbols]

VFD Fluorescent display tube (dynamically driven display) G1, G2 Grid 13 Grid driver 14 Triangular wave generation circuit (triangular wave generation means) 15 Reference voltage generation circuit (reference voltage generation means) 20 Switching circuit (switching means) 30 Second triangular wave Generation circuit (second triangular wave generation means) C11 Capacitor CP11 Comparison circuit (comparison means) CP12 Second comparison circuit (second comparison means) SW2 Light switches LP1 to LP3 Night lighting lamp

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[Procedural amendment]

[Submission date] October 14, 1991

[Procedural amendment 1]

[Name of document to be corrected] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction details]

[Figure 3]

[Procedural amendment 2]

[Name of document to be corrected] Drawing

[Correction target item name] Figure 6

[Correction method] Change

[Correction details]

[Figure 6]

Claims (3)

[Scope of utility model registration request] 1. Light control of a display device having a dynamic drive type display device in which a display area that displays by emitting light is divided into a plurality of parts, and the divided display areas are sequentially driven in a time-sharing manner. In the dimming circuit, a reference voltage generating means for generating a reference voltage, a triangular wave generating means for generating a triangular wave synchronized with the signal for performing time division, and a comparison between the reference voltage and the triangular wave to determine the magnitude of the reference voltage. and a comparison means for generating a rectangular wave with a duty according to a change in the reference voltage, and the duty of the rectangular wave generated by the comparison means is changed in accordance with a change in the reference voltage to perform dimming of the dynamic drive type display. Features a dimming circuit. 2. The triangular wave generating means includes a capacitor that is charged and discharged in synchronization with the signal for performing the time division, and a switching means that switches a charging time constant of the capacitor in two stages, the switching 2. The dimming circuit according to claim 1, wherein one stage of dimming is performed by switching the charging time constant by the means. 3. Second triangular wave generating means for generating a second triangular wave synchronized with the signal for performing time division, and comparing the reference voltage and the second triangular wave to determine the magnitude of the reference voltage. and a second comparing means for generating a rectangular wave with a corresponding duty, and the display device is a vehicle display device having a lamp for night illumination, and when the switching means is turned on, the light turns on the lamp. 3. The light control device according to claim 2, further comprising a switch, wherein the duty of the rectangular wave generated by the second comparing means is changed in response to a change in the reference voltage, and the light control device also simultaneously controls the light intensity of the night illumination lamp. circuit.