JP4884994B2 - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device for improving light amount variation accompanying voltage fluctuation without generating noise influencing equipment. <P>SOLUTION: The display device has; a control circuit 13 for outputting a control signal of a power source voltage level for display control to a fluorescent indication tube 12 by supplying power source voltage to a power source terminal (VDD); a voltage lowering detection part 14 for detecting whether supplied power source voltage lowers down to a preset voltage value; a reference potential adjusting part 15 for holding a reference potential terminal (VSS) level at reference potential when indicating that it lowers down to a set voltage value by setting the reference potential terminal (VSS) level of the control circuit 13 to prescribed higher potential than reference potential when indicating that a detection signal DT14 of the voltage lowering detection part does not lower down to the set voltage value; and a voltage holding part 16 for holding filament voltage at rated voltage regardless of lowering down to the set voltage value or not lowering down to it. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a display device having a fluorescent display tube for performing time display, for example.

For example, an in-vehicle display device having a fluorescent display tube for displaying time is known (see, for example, Patent Document 1).
In a general display device, since the thermoelectrons emitted from the filament vary depending on the diameter and length of the filament used in the DC drive fluorescent display tube, the segment output time is individually set.

By the way, such an in-vehicle display device basically receives a vehicle battery (BAT) voltage and an accessory voltage (ACC) based on the vehicle battery and controls the light emission of the fluorescent display tube. The battery voltage is about 12V to 10V, for example. Fluctuates until.
Since the light quantity of the fluorescent display tube changes with this voltage fluctuation, the display device is generally provided with a booster circuit for compensating for the voltage drop in response to the voltage drop.

  FIG. 1 is a circuit diagram showing a configuration example of an in-vehicle display device having a booster circuit.

  The display device 1 includes an oscillation unit 2 having a crystal oscillator XTAL, a fluorescent display tube (VFD) 3, a control circuit 4 composed of a microcomputer, a booster circuit 5, a power supply terminal (TBAT1), a light Signal input terminal (TLIG2), accessory signal input terminal (TACC3), reference potential connection terminal (TGND4), resistance elements R1 to R10, capacitors C1 and C2, constant voltage diodes Z1 to Z3, inductor L1, npn transistor TR1, and n It has a channel MOS (NMOS) transistor TR2.

For example, as shown in FIG. 1, the fluorescent display tube 3 includes a filament 31, a grid electrode 32, and an anode electrode 33.
An accessory signal ACC is supplied to the filament 31 via the diode D2 and the resistance elements R3 and R4.

In the control circuit 4, the battery voltage VBAT is supplied to the power supply terminal (VDD) via the diode D1 and the resistance element R1, the write signal LIG is supplied to the I / O1 terminal via the resistance element R2, and the I / O2 terminal is supplied. The accessory signal ACC is supplied via the diode D2 and the resistance element R3. The control circuit 4 is supplied with a voltage-divided signal including voltage change information of the resistance elements R5 and R6 at the terminal (A / D). The reference potential terminal VSS of the control circuit 4 is connected to the ground potential GND.
The control circuit 4 measures time information based on, for example, an oscillation signal received from the oscillation unit 2 and outputs a display control grid control signal CTLG and an anode control signal CTLA to the fluorescent display tube 3 based on the time information. .
Further, the control circuit 4 supplies the boost signal BST to the boost circuit 5 via the capacitor C1 when the battery voltage VBAT drops from 12V and becomes lower than 10V, for example.

  When receiving the active boost signal BST from the control circuit 4, the booster circuit 5 supplies the boosted voltage to the connection node ND1 between the power supply terminal TBAT1 and the anode of the diode D1.

  As shown in FIG. 1, the booster circuit 5 includes an inductor L1, a capacitor C2, resistance elements R8 to R10, diodes D3 to D5, an npn transistor TR1, and an NMOS transistor TR2.

The base of the npn transistor TR1 is connected to the supply line of the boost signal BST (one electrode of the capacitor C1), the cathode of the diode D3, one end of the resistor element R8, and the collector is connected to one end of the resistor element R9 and one end of the resistor element R10. Connected and the emitter is grounded.
The other end of the resistance element R8 and the other end of the resistance element R9 are connected, and the connection point is connected to the anode of the diode D4 and the connection node ND1 between the power supply terminal TBAT1 and the anode of the diode D1. The cathode of the diode D4 is connected to one end of the inductor L1.
The gate of the NMOS transistor TR2 is connected to the other end of the resistor element R10, the drain is connected to the other end of the inductor L1 and the anode of the diode D5, and the source is grounded.
One electrode of the capacitor C2 is connected to the cathode of the diode D5 and the power supply potential VDD, and the other electrode of the capacitor C2 is grounded.

When the battery voltage VBAT is maintained at 10 V or higher, the boost signal BST is held at a low level, so that the transistor TR1 is turned on and the transistor TR2 is turned off. Therefore, the node ND1 is not boosted.
On the other hand, when the battery voltage VBAT is lower than 10V, the boost signal BST is supplied, so that the boost operation is performed, and the energy stored in the inductor L1 is transmitted to the node ND1, and the node ND1 is boosted. The
Japanese Patent Laid-Open No. 9-240261

  In the above-described general apparatus, when the booster circuit 5 is operated by having the inductor L1, noise is generated because the switching current flowing through the inductor L1 is largely controlled, which has a great influence on the vehicle-side equipment. There was a disadvantage of giving.

  An object of the present invention is to provide a display device capable of improving light quantity fluctuations accompanying voltage fluctuations without generating noise that affects the device.

  In order to achieve the above object, a display device according to the present invention includes a filament that forms a cathode electrode, a grid electrode, and a phosphor that emits light by receiving thermoelectrons output from the filament through the grid electrode. A fluorescent display unit including an anode electrode, a control circuit for supplying a power supply voltage based on a battery to a power supply terminal, and outputting a control signal of the power supply voltage level to the fluorescent display unit for display control, and a supplied power supply A voltage drop detection unit for detecting whether or not the voltage has dropped to a preset voltage value; and when the detection signal of the voltage drop detection unit indicates that the voltage drop has not dropped to the set voltage value, the control circuit When the reference potential terminal level of the control circuit is set to a potential higher than the reference potential and indicates that the reference voltage has dropped to the set voltage value, the reference potential of the control circuit The reference potential adjustment unit that holds the child level at the reference potential, and the case where the detection result of the voltage drop detection unit indicates that it has not dropped to the set voltage value, it indicates that it has fallen to the set voltage value. However, it has a voltage holding unit for holding the filament voltage at the rated voltage.

  Preferably, the reference potential adjustment unit is connected between the reference potential terminal and a reference potential, holds a potential of the reference potential terminal higher than the reference potential by a predetermined level, the reference potential terminal and the reference potential A first switch connected in parallel with the level holding element between the potentials, and the first switch is turned on when the detection signal indicates that the voltage drops to the set voltage value, and the level holding element And the reference potential terminal and the reference potential are connected.

  Preferably, the voltage holding unit can bypass any of a plurality of resistance elements connected between the voltage supply line and the filament terminal and a plurality of resistance elements connected between the voltage supply line and the filament terminal. The second switch is turned on when the detection signal indicates that it has dropped to the set voltage value, and bypasses the resistance element.

  According to the present invention, it is possible to improve the light quantity fluctuation accompanying the voltage fluctuation without generating noise that affects the device.

  Hereinafter, for example, an in-vehicle display device having a fluorescent display tube that performs time display employing a display device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 2 is a circuit diagram showing a configuration example of the display device according to the embodiment of the present invention.

  As shown in FIG. 2, the display device 10 includes an oscillation unit 11 having a crystal oscillator XTAL, a fluorescent display tube (VFD) 12, a control circuit (IC) 13, a voltage drop detection unit 14, and a reference potential adjustment unit. 15, voltage holding unit 16, power supply terminal (TBAT11), write signal input terminal (TLIG12), accessory signal input terminal (TACC13), reference potential connection terminal (TGND14), resistance elements R11 to R21, constant voltage diode (Zener diode) Z11 to Z13, diodes D11 to D13, a pnp transistor TR11, and npn transistors TR12 and TR13.

First, the connection relationship between each component of the display apparatus 1 is demonstrated.
The power supply terminal (TBAT11) is connected to one end of a resistance element R11 for controlling VDD input current of the control circuit (IC) 13, and the other end of the resistance element R11 is a cathode of a constant voltage diode Z11 for power supply constant voltage, and The power supply input terminal (VDD) of the control circuit 13 is connected.
A node ND11 is formed by the connection point of the other end of the resistance element R11, the cathode of the constant voltage diode Z11 for power supply constant voltage, and the power supply terminal (VDD) of the control circuit 13.
The anode of the constant voltage diode Z11 is connected to a reference potential, for example, the ground potential GND.
The power supply terminal (TBAT11) and the node ND11 are connected to the voltage drop detection unit 14.

  The write signal input terminal (TLIG12) is connected to one end of the dimming input terminal input current control resistance element R12 of the control circuit (IC) 13, and the other end of the resistance element R12 is the dimming input terminal (DIM) of the control circuit 13. ) And the cathode of the constant voltage diode Z12, and the anode of the constant voltage diode Z12 is connected to the reference potential.

  The accessory signal input terminal (TACC13) is connected to one end of the input current control resistor element R13 for the fluorescent display tube lighting / extinguishing control input terminal (/ BLANK) of the control circuit (IC) 13. The other end of the resistance element R13 is connected to the cathode of the constant voltage diode Z13, the fluorescent display tube on / off control input terminal (/ BLANK) of the control circuit 13, and the input of the voltage holding unit 16. The anode of the constant voltage diode Z13 is connected to the reference potential.

  The reference potential connection terminal (TGND14) is connected to a reference potential, for example, the ground potential GND.

  For example, a power supply voltage (for example, 12V) from a battery built in the vehicle is applied to the power supply terminal (TBAT11).

For example, when a light provided in the vehicle is turned on, a high level light signal (LIG) is applied to the light signal input terminal (TLIG12), and a low level light signal (LIG) is applied when the light is turned off.
For example, when the vehicle engine key is turned to the “ACC” position, a high-level accessory signal (ACC) is applied to the accessory signal input terminal (TACC13), and the engine key is in a position before that (OFF). In the state), a low-level accessory signal (ACC) is applied.
That is, in a general vehicle, a high-level accessory signal is applied to the accessory signal input terminal (TACC 13) at least when the engine is driven.

  The oscillating unit 11 outputs an oscillation signal generated by, for example, the crystal oscillator XTAL to the control circuit 13. The control circuit 13 measures time information based on the oscillation signal received from the oscillating unit 11, and uses the grid control signal CTLG 13 and the anode control signal CTLA 13 which are control signals for time display based on the time information as the fluorescent display tube 12. Output to.

  The fluorescent display tube 12 is, for example, a flat-type display electron tube based on a dynamic drive system, and receives the control signals CTLG13 and CTLA13 from the control circuit 13, and performs time display, for example.

FIG. 3 is a view for explaining the fluorescent display tube 12 of the display device 10 shown in FIG.
For example, as shown in FIG. 3, the fluorescent display tube 12 includes a filament 121, a grid electrode 122, and an anode electrode 123.
The filament 121 corresponds to a cathode electrode, and is composed of, for example, a tungsten filament coated with an oxide such as strontium, barium, or calcium.
When a predetermined current flows through the filament 121, the filament 121 generates heat and emits thermoelectrons.

The general light emission principle of the fluorescent display tube 12 is that the thermoelectrons emitted by the filament 121 are accelerated in the direction of the grid electrode 122 to which a high voltage is applied by their own electron energy, and the thermoelectrons that have passed through the grid electrode 122 are anodes. By colliding with the electrode 123, kinetic energy is emitted as light.
A phosphor (light emitter) emits light when excited from a low energy state to a high energy state. Therefore, high light emission is possible by increasing the grid-anode voltage.

For example, when a predetermined voltage is applied between the filament 121 and the grid electrode 122 as described later, the grid electrode 122 selects and diffuses the thermoelectrons emitted from the filament 121 to reach the anode electrode 123. Let For example, as shown in FIG. 3, the grid electrode 122 is formed in a mesh shape.
The voltage applied to the grid electrode 122 and the anode electrode 123 is controlled by the control circuit 13.

The grid electrode 122 according to the present embodiment includes a first grid electrode 1221 and a second grid electrode 1222 as shown in FIG. 3, for example.
In addition, the anode electrode 123 includes a first anode electrode 1231 and a second anode electrode 1232.
For example, as shown in FIG. 3, the first and second anode electrodes 1231 and 1232 are formed in parallel, and the first and second grid electrodes 1221 and 1222 are formed in parallel. For example, the anode electrodes 1231 and 1232 are formed on the same plane, and the grid electrodes 1221 and 1222 are formed on the same plane. The first grid electrode 1221 is disposed between the first anode electrode 1231 and the filament 121, and the second grid electrode 1222 is disposed between the second anode electrode 1232 and the filament 121.

  The first grid electrode 1221 is connected to the grid signal line LGR1. The second grid electrode 1222 is connected to the grid signal line LGR2.

For example, as shown in FIG. 3, the anode electrode 123 (1231, 1232) has a plurality of segments for displaying time. In the anode electrode 123 (1231, 1232), each segment is connected to each of the segment terminals SG1, SG2,.
For the sake of brevity, for example, as shown in FIG. 3, each segment of the anode electrode 123 (1231, 1232) is connected in common to the segment terminals SG1, SG2,. That is, in the fluorescent display tube 12, the segments of the anode electrode 123 (1231, 1232), which are controlled by the grid electrodes 122 (1221, 1222), are connected by a common wiring.
The control circuit 13 applies a high-level or low-level voltage corresponding to the time information to the anode electrode 123 corresponding to each segment of the fluorescent display tube 12.
A phosphor (FLU) is formed near the surface of the anode electrode 123, and when the thermoelectrons emitted from the filament 121 reach the phosphor (FLU), the phosphor (FLU) emits light. By doing this, the time is displayed.

  Further, the control circuit 13 controls the voltage applied to the grid signal, thereby controlling the number and speed of the thermoelectrons reaching the anode electrode 123 from the filament 121 corresponding to the cathode. As a result, the phosphor (FLU) Controls the brightness of light emission and the on or off state of light emission. That is, the control circuit 13 controls the brightness of the fluorescent display tube 12 and the on or off state of light emission.

In the control circuit 13, a power supply voltage is supplied to the power supply terminal (VDD), a light signal (LIG) is supplied to the dimming control input terminal (DIN), and an accessory signal ACC of the on / off control input terminal (/ BLANK) is supplied. Is done.
In addition, the control circuit 13 has a reference potential terminal (VSS) connected to the reference potential adjustment unit 15, and when the supplied power supply voltage VDD is higher than 10 V (˜12 V), the ground potential 0 V, which is the reference potential. Is maintained at a potential higher than 0.7V.
On the other hand, the reference potential terminal (VSS) of the control circuit 13 is held at the ground potential 0 V by the reference potential adjusting unit 15 when the supplied power supply voltage VDD becomes 10 V or less (or a voltage lower than that).
That is, when the supplied power supply voltage VDD is higher than 10V (˜12V), the control circuit 13 operates with a magnitude of 11.3V of 12V−0.7V, and sets the high level of the control signals CTLG13 and CTLA13. Output at 11.3V.
When the supplied power supply voltage VDD is 10V or less (or lower voltage), the control circuit 13 operates with a magnitude of 10V-0V and outputs the high level of the control signals CTLG13 and CTLA13 at 10V. To do.

The voltage drop detection unit 14 detects whether or not the supplied power supply voltage VDD is a preset voltage (set voltage) of, for example, 10 V or less (or a lower voltage), and a detection signal DT14 indicating the detection result. Is output to the reference potential adjusting unit 15 and the voltage holding unit 16.
The voltage drop detection unit 14 outputs the detection signal DT14 at a low level when the power supply voltage VDD does not drop to the set voltage value, and sets the detection signal DT14 high when the power supply voltage VDD drops to the set voltage value. Output by level.

  As shown in FIG. 2, the voltage drop detection unit 14 of the present embodiment includes a pnp transistor TR11, battery voltage drop detection resistance elements R14 and R15, accessory voltage drop detection resistance elements R16 and R17, and a stabilization resistor for the transistor TR11. An element R18 and diodes D11 and D12 are included.

The resistance elements R14 and R15 are connected in series between the power supply terminal (TBAT11) and a reference potential (in this embodiment, the ground potential GND), and the connection point of the resistance elements R14 and R15 is connected to the cathode of the diode D11. The anode of the diode D11 is connected to the base of the transistor TR11. A resistance element R18 is connected between the node ND11 and the base of the transistor TR11.
The emitter of the transistor TR11 is connected to the node ND11, and the collector is connected to one end of the resistor element R21, the input of the reference potential adjusting unit 15, and the input of the voltage holding unit 16. An output node ND12 of the detection signal DT14 is formed by the collector side of the transistor TR11.
The resistance elements R16 and R17 are connected in series between the accessory signal input terminal (TACC13) and the reference potential (the ground potential GND in this embodiment), and the connection point of the resistance elements R16 and R17 is connected to the cathode of the diode D12. The anode of the diode D12 is connected to the base of the transistor TR11.
A node ND13 is formed by a connection point of the base of the transistor TR11, one end of the resistance element R18, the anode of the diode D11, and the anode of the diode D12.

In such a voltage drop detection unit 14, the resistance values (divided values) of the resistance elements R 14 and R 15 and the resistance elements R 16 and R 17 are transistors when the battery voltage VBAT and the accessory voltage VACC are 10% or less from the normal 12V. It is set so that TR11 is turned on.
In the present embodiment, the transistor TR11 is configured to be turned on when the base voltage of the transistor TR11 becomes 9.3V.
In the voltage drop detection unit 14 of the present embodiment, the anode side of the diodes D11 and D12 is connected to the base of the transistor TR11, the cathode side is connected to the connection point of the voltage dividing resistance elements R14 and R15, and the connection of the resistance elements R16 and R17. Since it is configured to be connected to a point, the transistor TR11 is turned on when both the battery voltage VBAT and the accessory voltage VACC are 10 V or less.
Thus, accurate voltage drop detection can be performed.

The reference potential adjustment unit 15 indicates that the detection signal DT14 of the voltage drop detection unit 14 has not dropped to the set voltage value (10 V in the present embodiment) (the detection signal ST14 is at a low level). The reference potential terminal (VSS) level is set to a potential (0.7 V in this embodiment) that is a predetermined potential higher than the reference potential (ground potential GND in this embodiment).
The reference potential adjustment unit 15 indicates that the detection signal DT14 of the voltage drop detection unit 14 has dropped to the set voltage value (10 V in the present embodiment) (the detection signal ST14 is high level). The potential terminal (VSS) level is set to the reference potential (in this embodiment, the ground potential GND).

As shown in FIG. 2, the reference potential adjustment unit 15 of the present embodiment includes an npn transistor TR12 as a first switch and a diode D13 as a level holding element.
The anode of the diode D13 and the collector of the transistor TR12 are connected to the reference potential terminal (VSS) of the control circuit 13, and a node ND14 is formed by these connection points.
The cathode of the diode D13 and the emitter of the transistor TR12 are connected to a reference potential (in this embodiment, the ground potential GND).
The base of the transistor TR12 is connected to the collector of the transistor TR11 of the voltage drop detection unit 14 (the output terminal of the detection signal DT14).

In the reference potential adjustment unit 15 of FIG. 2, when the detection signal DT14 of the voltage drop detection unit 14 indicates that it has not dropped to the set voltage value (10 V in the present embodiment) (the detection signal ST14 is low level). The transistor TR12 is turned off, and the reference potential terminal (VSS) is set higher than the reference potential GND by 0.7V which is the forward voltage VF of the diode D13.
Further, in the reference potential adjustment unit 15, when the detection signal DT14 of the voltage drop detection unit 14 indicates that it has dropped to the set voltage value (10 V in this embodiment) (the detection signal ST14 is high level), the transistor TR12 Is turned on, the diode D13 is bypassed, the reference potential terminal (VSS) is directly connected to the reference potential GND, and is set to 0V.

  When the detection signal DT14 of the voltage drop detection unit indicates that the voltage drop detection unit has not dropped to the set voltage value, the voltage holding unit 16 sets the voltage of the filament 121 to the rated voltage ( For example, 1.3V ± 10%).

The voltage holding unit 16 includes filament current control resistance elements R19 and R20, and an npn transistor TR13 as a second switch.
One end of the resistor element R19 is connected to the other end of the resistor element R13, and the other end of the resistor element R19 is connected to one end of the resistor element R20 and the collector of the transistor TR13.
The other end of the resistor element R20 is connected to the filament terminal and the emitter of the transistor TR13, and the base of the transistor TR13 is connected to the output line of the detection signal DT14 of the voltage drop detector 14 and one end of the resistor element R21. The other end of the resistance element R21 is connected to a reference potential, for example, a ground potential GND.
A node ND15 is formed by a connection point between the filament terminal, the other end of the resistance element R20, and the emitter of the transistor TR13. The other end of the filament 121 is connected to a reference potential, for example, a ground potential GND.

In the voltage holding unit 16, when the detection signal DT14 of the voltage drop detection unit 14 indicates that it has not dropped to the set voltage value (10 V in the present embodiment) (the detection signal ST14 is low level), the transistor TR13 The terminal voltage of the filament 121 is maintained at 1.3 V ± 10% through the resistance elements R13, R19, R20.
In the voltage holding unit 16, when the detection signal DT14 of the voltage drop detection unit 14 indicates that it has dropped to the set voltage value (10 V in this embodiment) (the detection signal ST14 is high level), the transistor TR13 is turned on. The resistance element R20 is bypassed, and the terminal voltage of the filament 121 is maintained at 1.3 V ± 10% through the resistance elements R13 and R19.

FIG. 4 is a diagram for explaining a specific example of a vehicle-mounted display device that employs the display device 10 shown in FIG. 2.
For example, as shown in FIG. 4, the display device 10 has a fluorescent display tube 12 that displays time on the upper front portion. As shown in the figure, the hour information correction switch SW1 is formed at the right part of the fluorescent display tube 12, the minute information correction switch SW2 is formed at the lower part thereof, and the hour setting switch SW3 is further formed at the lower part thereof.

  For example, as shown in FIG. 4, the fluorescent display tube 12 includes four anode electrodes 123, a segment common line a and a segment common line d are connected, and a segment common line b and a segment common line c are connected. .

  For example, as shown in FIG. 4, an operation input device for operating a device provided in the vehicle and a device display unit for displaying the state of the device provided in the vehicle are provided below the fluorescent display tube 12. A display unit 17 is formed.

  For example, as shown in FIG. 4 in detail, the operation display unit 17 includes a temperature adjustment switch 171, an air volume adjustment switch 172, an air conditioning (A / C) switch 173, a temperature display unit 174, and an air bag status display unit 175. And a seat belt wearing state display unit 176.

  The temperature adjustment switch 171 is operated, for example, when setting a set temperature inside the vehicle by an air conditioner provided in the vehicle. The control circuit 13 controls the set temperature of the air conditioner according to the operation by the temperature adjustment switch 171.

  The air volume adjustment switch 172 is operated, for example, when setting the air volume by an air conditioner provided in the vehicle. The control circuit 13 controls the air volume of the air conditioner according to the operation by the air volume adjustment switch 172.

The air conditioner (A / C) switch 173 is operated, for example, when switching an on state or an off state of a cooling device included in an air conditioner provided in a vehicle. The control circuit 13 switches the air conditioner (A / C) switch 173 between the on state and the off state according to the operation of the air conditioner (A / C) switch 173.
The temperature display unit 174 displays the indoor temperature based on, for example, a signal from a temperature sensor that detects the indoor temperature of the vehicle.
The airbag state display unit 175 is a display unit that lights up when an airbag, which is an occupant safety device provided in a vehicle, is provided.
The seat belt wearing state display unit 176 is a display unit that is lit when, for example, a seed belt that is an occupant safety device provided in the vehicle is properly worn.

  In the vicinity of the fluorescent display tube 12, the operation display unit 17, and the switch group 18, a light emitting element 19 for illuminating various components is provided.

Specifically, a light emitting element 19 for illuminating the fluorescent display tube 12 and the switch group 18 is provided on the left side of the fluorescent display tube 12 and the right side of the switch group 12. A light emitting element 19 is provided in the vicinity of the seat belt wearing state display unit 176 from the temperature adjustment switch 171 of the operation display unit 17.
The control circuit 13 according to the present embodiment controls the switch group 18, the fluorescent display tube 12, and the operation by controlling the luminance due to the light emission of the light emitting element 19 based on the grid signal to the fluorescent display tube 12 when the light is turned on, for example. The brightness of illumination on the display unit 17 and the like is controlled.

Next, the operation of the display device 10 will be described with reference to FIGS.
5A shows the battery voltage VBAT (for example, 12V), FIG. 5B shows the accessory signal ACC, FIG. 5C shows the potential of the node ND15 of the filament 121, and FIG. 5D shows the node. FIG. 5E shows the detection signal DT14 (node ND12), FIG. 5F shows the potential of the node ND14, FIG. 5G shows the potential of the node ND11, and FIG. FIG. 5I shows the grid control signal CTLG13, and FIG. 5I shows the anode control signal CTLA13.

For example, as shown in FIG. 5A, a power supply voltage BAT (12 V) is applied to the power supply terminal (TBAT11) at time t1, and a constant voltage is supplied to the power supply input terminal of the control circuit 13 by the function of the constant voltage diode Z1. (VCC) is applied. At this time, as shown in FIG. 5B, the accessory signal ACC is also at the 12V level.
When the power supply voltage VDD is 12V, the transistors TR11 to TR13 are off.
As shown in FIG. 5C, the node ND15 which is a terminal of the filament 121 is held at the rated voltage 1.3V. This is maintained at the rated voltage of 1.3 V even if the power supply voltage varies by the voltage holding unit 16.
The reference electronic terminal (VSS) of the control circuit 13 is held at 0.7V.
Therefore, the potential difference between VDD and VSS (including the grid and anode control signal) of the control circuit 13 is maintained at 12V−0.7V = 11.3V.
In the control circuit 13, display control of the fluorescent display tube 12 is performed at this level.

On the other hand, as shown in FIGS. 5A, 5B, and 5G, when the voltage drops below 10V, the node ND13 drops from 12V to 9.3V and the transistor TR11 is turned on. As a result, as shown in FIG. 5E, a high level detection signal DT14 is output from the voltage drop detection unit 14 to the reference potential adjustment unit 15 and the voltage holding unit 16.
As a result, the transistor TR12 of the reference potential adjustment unit 15 is turned on, and the node ND14 is held at 0V as shown in FIG. In the voltage holding unit 16, the transistor TR13 is turned on, and the node ND15 that is the terminal of the filament 121 is held at the rated voltage 1.3V.
Therefore, the potential difference between VDD and VSS (including the grid and anode control signals) of the control circuit 13 is held at 10V-0V = 10V.
In the control circuit 13, display control of the fluorescent display tube 12 is performed at this level.

Depending on the characteristics of the fluorescent display tube 12, the amount of light varies with the 2.7th power of the grid and anode voltage.
In this case, the light amount change in this apparatus when the power supply voltage VDD is 12V and 10V is 72% at 10V with respect to 12V.
When the power supply voltage VDD is 10 V, the filament voltage is 1.1 V below the rating when the voltage holding unit 16 is not provided, and the light quantity at this time is 85% (of the filament rating) × 72% = 61.2%. .
In contrast, in the present embodiment, when the transistor TR13 of the voltage holding unit 16 is turned on, the filament voltage becomes 73% at a filament power of 140 mW when the filament voltage is increased by 73%, for example, 1.4V.
In the present embodiment, since the filament changes in the rated range of 1.3V ± 10% and the light amount also changes in the range of ± 10%, the display device 10 uses the fluorescent display tube 12 when the power supply voltage VDD is 12V. (72% + 10% (filament rating + 10%)) = 82% (−18% at 12 V). That is, the display device 10 of the present embodiment can improve the change in the light amount of the fluorescent display tube 12.

As described above, according to the present embodiment, the filament 121 that forms the cathode electrode, the grid electrode 122, and the phosphor that receives the thermoelectrons output from the filament through the grid electrode 123 and emits light are formed. And a control circuit for supplying power supply voltage level control signals CTLG13 and CTLA13 for display control to the fluorescent display tube 12 by supplying a power supply voltage based on the battery to the power supply terminal (VDD). 13, the voltage drop detection unit 14 for detecting whether or not the supplied power supply voltage has dropped to a preset voltage value, and the detection signal DT14 of the voltage drop detection unit has not dropped to the set voltage value. In this case, the reference potential terminal (VSS) level of the control circuit 13 is set to a potential higher than the reference potential by a predetermined potential. When indicating that the voltage has dropped to the pressure value, the reference potential adjusting unit 15 that holds the reference potential terminal (VSS) level of the control circuit 13 at the reference potential, and the detection signal DT14 of the voltage drop detecting unit drops to the set voltage value. In the case of indicating that the voltage has not been reduced, the voltage holding unit 16 that holds the filament voltage at the rated voltage is provided even if it indicates that the voltage has dropped to the set voltage value, so that the following effects can be obtained.
Increasing the amount of light in the fluorescent display tube at the time of voltage drop can improve the amount of change in light amount without using an inductor booster circuit, and there is no generation of noise due to the switching current flowing through the inductor, affecting each device in the vehicle There is an advantage that can be prevented.

Note that the present invention is not limited to the present embodiment, and various suitable modifications can be made.
Although the on-vehicle display device has been described in the above-described form, it is not limited to this form.

It is a circuit diagram which shows the structural example of the vehicle-mounted display apparatus which has a booster circuit. It is a circuit diagram which shows the structural example of the display apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the fluorescent display tube of the display apparatus shown in FIG. It is a figure for demonstrating one specific example of the vehicle-mounted display apparatus which employ | adopted the display apparatus shown in FIG. 5 is a timing chart for explaining the operation of the display device of the present embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Display apparatus, 11 ... Oscillation part, 12 ... Fluorescent display tube, 13 ... Control circuit (IC), 14 ... Voltage drop detection part, 15 ... Reference potential adjustment part, 16 ... Voltage holding unit, TBAT11 ... Power supply terminal, TLIG12 ... Write signal input terminal, TACC13 ... Accessory signal input terminal, TGND14 ... Reference potential connection terminal, R11-R21 ... Resistance element , Z11 to Z13 ... constant voltage diodes (Zener diodes), D11 to D13 ... diodes, TR11 ... pnp transistors, TR12, TR13 ... npn transistors.

Claims (3)

A fluorescent display unit including a filament that forms a cathode electrode, a grid electrode, and an anode electrode that is formed with a phosphor that emits light by receiving thermoelectrons output from the filament through the grid electrode;
A power supply voltage based on the battery is supplied to the power supply terminal, and a control circuit that outputs a control signal of the power supply voltage level to the fluorescent display unit for display control,
A voltage drop detection unit for detecting whether or not the supplied power supply voltage has dropped to a preset voltage value;
When the detection signal of the voltage drop detection unit indicates that the voltage has not dropped to the set voltage value, the reference potential terminal level of the control circuit is set to a potential higher than the reference potential and dropped to the set voltage value. A reference potential adjustment unit that holds the reference potential terminal level of the control circuit at a reference potential;
A voltage holding unit that holds the filament voltage at the rated voltage even when the detection result of the voltage drop detection unit indicates that the voltage has not dropped to the set voltage value, even if it indicates that the voltage drop has fallen to the set voltage value. And a display device. The reference potential adjustment unit is
A level holding element connected between the reference potential terminal and a reference potential and holding the potential of the reference potential terminal at a predetermined level higher than the reference potential;
A first switch connected in parallel with the level holding element between the reference potential terminal and a reference potential;
The first switch is turned on when the detection signal indicates that it has dropped to the set voltage value, and bypasses the level holding element to connect between the reference potential terminal and the reference potential. Display device. The voltage holding unit is
A plurality of resistance elements connected between the voltage supply line and the filament terminal;
A second switch disposed so as to be able to bypass any of a plurality of resistance elements connected between the voltage supply line and the filament terminal,
The display device according to claim 1, wherein the second switch is turned on when the detection signal indicates that the voltage falls to the set voltage value, and bypasses the resistance element.

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