JPH0747759Y2 - Automotive fluorescent display clock - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-vehicle fluorescent display timepiece, and more particularly to an improvement of one having display brightness adjustment.

[0002]

2. Description of the Related Art A fluorescent display type clock mounted on an automobile is configured to display the time by increasing the brightness during the daytime and decreasing the brightness at night, and displaying the time according to the brightness of the surroundings. It was made easier to see by changing the brightness. In this type of timepiece, the brightness is switched by changing the pulse ratio of the voltage applied to the grid or anode of the display section in response to the on / off of the light switch, and the brightness of the instruments is further adjusted. The brightness was adjusted in conjunction with the illumination control signal.

[0003]

However, in the conventional timepiece described above, the display of the timepiece may disappear when the brightness of the instruments is adjusted by the illumination control signal. There was a problem that the red light emission of the filament was conspicuous as it was being applied, hindering the visual recognition of other instruments. SUMMARY OF THE INVENTION An object of the present invention is to solve the above problem by preventing voltage from being applied to the filament when the time display of the watch is off to prevent unnecessary light emission.

[0004]

In order to achieve the above object, the present invention provides a vehicle-mounted fluorescent display in which the brightness can be adjusted by an illumination control signal in response to an operation of a light switch for turning on an instrument, a vehicle width or the like. The timepiece is characterized in that a control circuit for controlling the interruption of the filament current when the duty of the illumination control signal is equal to or less than a constant value is provided.

[0005]

The brightness of the timepiece and instruments is adjusted by the illumination control signal when the light switch is turned on during nighttime driving, and when the timepiece display disappears, the filament is turned off to prevent red light emission.

[0006]

1 is a circuit diagram of an embodiment according to the present invention, and its time chart is shown in FIG. The present invention will be described below with reference to the drawings. In FIG. 1, 2 is a watch I
C is for dividing the reference signal to perform a timekeeping operation, outputting a display drive signal via the driver, and changing the duty ratio of the display drive signal when the light switch is turned on to reduce the brightness. Reference numeral 4 is a time display section, which is composed of a fluorescent display tube, and has an anode 4a,
It is composed of a grid 4b and a filament 4c.

Reference numeral 22 denotes a dimming circuit, which is an AND gate 6 for inputting a signal from the light switch to the inverting terminal and an H level at the other end, and an AND gate for inputting a signal from the light switch and an illumination control signal. 8 and an OR gate 1 that inputs the outputs of both AND gates 6 and 8
0, this output and an AND gate 12 for inputting the display drive signal from the timepiece IC, this output is connected to the base via a resistor 14, the collector is connected to the power supply via a resistor 16, and the emitter is The transistor 18 is connected to the grid 4b of the time display unit 4 and is grounded via a resistor 20. The transistor 18 is connected to the grid 4b of the time display unit 4. When the light switch is off, the display drive signal is displayed, and when the light switch is on, the display is displayed. The luminance is adjusted by controlling the voltage supplied to the grid 4b in response to the drive signal and the illumination control signal.

Reference numeral 40 denotes a control circuit, which is the dimming circuit 22.
The output from the AND gate 12 is connected to the base via the resistor 24, the collector is connected to the power source via the resistor 26, and the emitter is grounded via the capacitor 30. It is connected to the base via 32 and the collector is a resistor 3
A transistor 34 connected to the power supply via 8 and an emitter connected to the filament of the time display unit 4, and a resistor 34 connected between the base of the transistor 36 and the ground.
When the duty of the dimming signal output from the AND gate 12 becomes a certain value or less, the capacitor 30 starts discharging, and after a predetermined time, the transistor 3
When 6 is turned off, the filament current is cut off.

Next, the operation will be described. IC for clock 2
The display drive signal is output from the display unit, and the segment of the time display unit 4 is turned on with a constant periodic signal to display the time. At this time, the constant period signal is also applied to the grid 4b. Here, when the light switch is turned on due to dark surroundings, the timepiece IC 2 changes the frequency or duty of the constant cycle signal to lower the display brightness. At this time, the AND signal of the illumination control signal and the display drive signal is output to the grid 4b,
If the duty ratio of the illumination control signal is reduced in order to reduce the brightness of the instruments, the voltage applied to the grid 4b also decreases, and the display brightness also becomes dark and disappears. On the other hand, the filament current causes the transistor 36 to turn on due to the discharge of the capacitor 30, but the base voltage gradually decreases and turns off after a predetermined time, and the supply of the filament current is cut off.

FIG. 3 shows a second embodiment of the control circuit 40,
The inverter 42, the AND gate 44, and the counter 46
, Delay circuit 48, and three flip-flops (hereinafter,
FF) 50, 54 and 56, a one-shot circuit (hereinafter referred to as OSM) 70, resistors 58 and 38, and a transistor 36. The same parts as those in FIG. 1 are designated by the same reference numerals.

The operation will be described below.
The output from the AND gate 12 of No. 2 is input to the AND gate 44 together with the reference signal Φ1 via the inverter 42, and this output is input to the counter 46. The signal from the AND gate 12 is input to the reset terminal of the counter 46, and the time during which the dimming signal is not output is measured. If it is not output for a certain time or more, a carry signal is output and this signal is sequentially latched by the FFs 50 and 54. The inverted Q output of the FF 54 becomes L level, the transistor 36 is turned off, and the filament current is cut off. The FF 56 sets the inverted Q output to the L level at the rising edge of the dimming signal. Also, F
F50 is delayed from the rising edge of the dimming signal, the Q output is set to L level, and the latch is released. When the duty ratio of the dimming signal becomes high and the L level time becomes short, the carry signal is not output from the counter 46, the Q output of the FF 50 becomes the L level, and the FF 56 outputs the inverted Q output at the rising edge of the dimming signal. OSM7 by setting to H level
With a single pulse generated from 0, the FF 54 sets the Q output to the H level. Therefore, since the transistor 36 is turned on, the filament current is supplied.

[0012]

As described above, according to the present invention, since the control circuit for cutting off the filament current by the duty ratio of the dimming signal synthesized by the illumination control signal is provided, the filament remains active even if the time display disappears. It does not emit light, and it is possible to prevent unnecessary light from being emitted to the eyes of the driver, to prevent distraction, and to reduce current consumption.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a time chart diagram in FIG.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

[Explanation of symbols]

 2 Clock IC 4 Time display section 22 Light control circuit 40 Control circuit

Claims (1)

[Scope of utility model registration request] 1. A vehicle-mounted fluorescent display timepiece in which the brightness can be adjusted by an illumination control signal in response to an operation of a light switch for turning on an instrument, a vehicle width, etc., when the duty of the illumination control signal is below a certain value. An in-vehicle fluorescent display timepiece having a control circuit for controlling the cutoff of filament current.