JP2565570Y2 - Fluorescent display tube drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] The present invention relates to a high-luminance fluorescent display tube driving circuit used for a head-up display device for a vehicle and the like.

[Conventional technology]

As a conventional fluorescent display tube driving circuit, for example, there is one as shown in FIG. This circuit is used for, for example, a head-up display device for a vehicle.

First, a description will be given of a head-up display device for a vehicle. In FIG.
Inside 21, two electronic meters 22A and 22B of the same structure, whose speed and the like are displayed on one side only by a fluorescent display tube, are installed back to back, and the display by one electronic meter 22A is:
While allowing the driver 27 to directly observe, the display by the other electronic meter 22B is projected on the windshield 24 via the reflecting mirror 23 provided inside the instrument panel 21, The driver 27 is configured to be able to visually recognize the display projected on the windshield 24. In addition, 25 is a steering wheel and 26 is a steering column.

On the other hand, in the driving circuit of the fluorescent display tube, in FIG. 4, 1 is a fluorescent display tube, 2 is a filament driving circuit of a filament electrode, and 3 is a segment electrode (anode).
(Pulse width modulation) circuit as a decoder driver having a blanking terminal (not shown), and a display circuit switch 4 which is turned on and off by the PWM signal from the PWM circuit 3. 5 is the display voltage
A voltage source for supplying V _DD , wherein 6 in the fluorescent display tube 1 is a filament electrode, 7 is a grid, 8 is a segment electrode, and 9 in the filament driving circuit 2 is a transformer,
10 is a pulse generation source.

Next, the operation will be described. The In Figure 4, the fluorescent display tube 1 is applied a voltage E _f by a filament driving circuit 2 supplies electrons from the filament electrode 6, the display voltage to the grid 7 from the center tap of the transformer 9 for supplying power to the filament electrode 6 Apply _Vf . as a result,
The electrons are accelerated and sent to the segment electrode 8.

On the other hand, for the segment electrode 8, the blanking terminal (not shown) in the PWM circuit 3 is set to "1"
Outputs the PWM signal of the level or “0” level,
On or off. That is, the light is turned on when the switch 4 is turned on, and turned off when the switch 4 is turned off. The dimming of the segment electrodes 8, that is, the dimming of the fluorescent display tube 1 is controlled by changing the frequency and duty ratio of the PWM signal for turning on and off the switch 4 in the PWM circuit 3. Is being done.

[Problems to be solved by the invention]

However, a head-up type display overlaps with the outside scene, so high brightness is required during the daytime, and a dimming brightness ratio of about 1000: 1 is required between day and night. In the dimming circuit in the display tube driving circuit, the response of turning on and off the display of the fluorescent display tube is limited (several tens of microseconds), and the flickering state of the display and the dimming frequency are also limited. Therefore, the control of the duty ratio of the PWM signal is also limited, and the improvement of the dimming rate is limited.Therefore, during nighttime dimming of a head-up type display device using a fluorescent display tube for high brightness, There has been a problem that a sufficiently satisfactory light control cannot be performed.

This invention focuses on these conventional problems, and adds a center tap voltage control circuit that controls the center tap display voltage V _DD of the transformer connected to the filament electrode to the conventional dimming circuit. However, for a high-luminance fluorescent display tube, the above-described problem is caused by reducing the dimming rate by using both the voltage dimming by the center tap voltage control and the duty dimming for the segment electrodes or the grid by the PWM circuit. It is intended to solve.

〔Example〕

The present invention will be described with reference to the drawings. 1 is an overall circuit diagram of a fluorescent display tube driving circuit, FIG. 2 is a detailed circuit diagram mainly showing a power supply circuit section 31 in FIG. 1, and FIG. 3 is an equivalent circuit diagram of a main part of FIG. It is. The circuit shown in FIG. 1 is also used in the vehicle head-up display device shown in FIG. 5 described as a conventional example.

In FIG. 1, a power supply circuit section 31 is an ignition signal.
IGN is supplied and details are shown in Fig. 2 and Fig. 3.
A circuit for receiving a center tap control signal from the microcomputer 32 and controlling the center tap voltage of the filament electrode is included. Then, a filament voltage and a display voltage V _DD are supplied to the fluorescent display tube 1. The structure of the fluorescent display tube 1 is the same as that of the conventional example described with reference to FIG.

On the other hand, the microcomputer 32 has an interface
33, a signal 34 from a sensor such as a speedometer, a dimming characteristic curve for changing the brightness of the display device according to the brightness of the surroundings of the display device (for example, in a memory (not shown) (A stored two types) are supplied from a lighting switch (L / SW) 35 as a brightness signal generating means for switching between them, and a dimming rate signal 36 for center tap voltage control. The PWM circuit 3 is built in the microcomputer 3, and the microcomputer 32 outputs the center tap control signal, the PWM signal, and the display control signal.

Reference numeral 37 denotes a latch driver which supplies a segment signal to the fluorescent display tube 1. The voltage applied to the grid 7 may be turned on and off like a display control signal which changes according to a PWM signal. Latch driver for ON / OFF signal
It is necessary to supply the grid 7 from 37.

FIG. 2 shows the details of the power supply circuit section 31 including the center tap voltage control circuit. In the figure, 41 is a diode for receiving the ignition signal, 42 is a noise removing element, 43 and 44 are capacitors, and 45 is an external constant voltage source. Three-terminal regulator,
46 is a capacitor, 47 is a transistor, 48 and 49 are resistors, 50
Is a capacitor, 51 is a Zener diode, 9 is the transformer, and a first output winding 9a with a center tap connected to both ends of the filament electrode 6 of the fluorescent display tube 1 and one end of the grid 7 of the fluorescent display tube. Is connected to the second output winding 9b. Reference numeral 52 denotes a diode, reference numeral 53 denotes a capacitor, and transistors TR1 and TR2, and bias means 55 constituting a center tap voltage control circuit in which the resistors of R1 and R2 constitute the gist of the invention. 56 is a diode, and 57 is a capacitor.

Next, the operation will be described. When the surroundings of the fluorescent display tube 1 are bright as in the daytime and it is desired to increase the brightness of the display, a microcomputer according to the output of the dimming rate signal 36
A signal for controlling the center tap voltage of “1” level is output from the gate 32 to the gate of the transistor TR2. Therefore the transistor TR2 is turned off, the emitter potential of the transistor TR1 and the voltage V _D shown in the figure, the base - the sum of the emitter voltage V _BE V
_D + V _BE . In this case, V _D = V _D ′.

Therefore, the display voltage for the fluorescent display tube 1 is V _DD + V _D + V _BE
, The dimming is prohibited, and the display is performed at a high luminance.

On the other hand, when the surroundings of the fluorescent display tube 1 are dark such as at night and the brightness thereof is desired to be reduced, the output of the dimming rate signal 36 is inverted to that of daytime, and the microcomputer 32 responds to this by setting the center of "0" level. A signal for tap voltage control is output, and the transistor TR2 is turned on. Therefore, a resistor R between the voltages V _CC and V _D
1 and R2 to generate a divided voltage V _D ′. Therefore the emitter potential of the transistor TR1 is V _D '+ V _BE, and the
The display voltage for the fluorescent display tube 1 is V _DD + V _D '+ V _BE , and the display luminance is reduced.

In any of the above cases, the fluorescent display tube 1 is, of course, subjected to ordinary dimming control by the PWM signal. In this case, the PWM signal is synchronized with the center tap voltage control signal. This enables continuous light control from high luminance to low luminance.

Although the center tap voltage control for the grid electrode is performed in the above embodiment, the control may be performed for the segment electrode or may be performed simultaneously for both.

As described above, according to the present invention, the configuration is used as a dimming circuit of a high-luminance fluorescent display tube driving circuit.
By controlling the center tap voltage, the grid voltage can be switched between night and daytime, and dimming (display control signal is changed by PWM) in the switched voltage state, so high brightness over a wide range Dimming between the fluorescent lights becomes possible, and the effect that the optimal display quality at each time can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is an overall circuit diagram of a fluorescent display tube driving circuit according to an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of main parts, and FIG.
FIG. 4 is a circuit diagram of a conventional fluorescent display driving circuit, and FIG. 5 is a block diagram of a head-up display device for a vehicle. 3. PWM circuit (decoder driver), 6 filament electrode, 7 grid, 8 segment electrode, 9 transformer, 31 power supply (circuit section), 32 microcomputer (center tap voltage control means), 35 lighting Switch (brightness signal generating means), 55 ... bias means.

Claims (1)

(57) [Scope of request for utility model registration] A fluorescent display device for a high brightness used in a head-up type display device for a vehicle, comprising a filament electrode (6), a grid electrode (7), and a segment electrode (8). A fluorescent display tube (1),
A first output winding with a center tap (9a) having both ends connected to the filament electrode (6) and one end connected to a latch driver (37) for supplying a segment signal to the segment electrode (8); A transformer (9) having a second output winding (9b) connected to the grid electrode (7), a signal (34) from a sensor, an output signal (35) from a lighting switch, and a dimming rate signal (36) A display control signal for creating the segment signal and a PWM signal for duty-dimming the segment signal to a latch driver (37), and based on a dimming rate signal (36) A microcomputer (32) for outputting a center tap control signal, and a microcomputer (32) interposed between a center tap of a first output winding (9a) of the transformer (9) and an external constant voltage source; A center tap voltage control circuit (55) for switching the potential of the tap to a low level or a high level based on a center tap control signal from the microcomputer (32), wherein the center tap voltage control circuit (55) The emitter of the first transistor (TR1) is at the center tap of the first output winding (9a), and the collector is the second output winding (9) of the transformer (9).
b) connected to the other end of the first transistor (TR1), a first resistor (R1) is connected between the base and the collector of the first transistor (TR1), and a base of the first transistor (TR1) is connected to the second transistor (TR2). A second resistor (R2) is connected between the collectors and a second transistor (TR
2) the emitter is connected to the external constant voltage power supply, a bias resistor is connected between the base and the emitter of the second transistor (TR2), and the base of the second transistor (TR2) is connected to the microcomputer (32). The center tap voltage control circuit is connected to a terminal for outputting the center tap control signal. When a signal indicating ambient lightness / darkness from the dimming rate signal (36) is supplied to the microcomputer (32), the center tap voltage control is performed. A center tap control signal for switching the potential of the center tap of the circuit (55) to a high level or a low level in accordance with the signal indicating the lightness / darkness is outputted, and the voltage control by the voltage control of the high-luminance fluorescent display tube is performed. A high-intensity fluorescent display tube driving circuit for a head-up display device for a vehicle, which performs duty dimming.