JPH0132059Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a switching device for back lighting in various displays.

(Prior Art) Incandescent light bulbs, cold cathode discharge tubes (hereinafter referred to as discharge lamps), and the like are used as back lighting for various displays, that is, as light sources provided at the back of the display surface and illuminating the display surface from the back. In addition, some devices use discharge lamps during the day and switch to incandescent lamps at night when there is no outside light. in this case,
During the daytime, the brightness can be as bright as outside light, and at night, the brightness can be switched to an appropriate brightness, so the display effect can be improved.

However, when conventional incandescent lamps or discharge lamps are used alone, the display surface becomes dark during the day and becomes too bright at night, or vice versa, making it difficult to obtain a clear display both day and night. In addition, a relatively bright discharge lamp is used as a light source during the day,
At night, switching to incandescent light bulbs provides adequate illumination, but immediately after switching from discharge lamps to incandescent light bulbs, it quickly becomes dark, making it difficult to see even temporarily until your eyes can adjust. For example, in the case of various displays provided on automobile dashboards, it is extremely dangerous if the above-mentioned switching occurs while the vehicle is in motion.

(Problem to be solved by the invention) As mentioned above, when switching from discharge lamps to incandescent lamps for various displays, in which discharge lamps are used for daytime illumination and incandescent lamps are used at night, the brightness of the display surface decreases. The disadvantage is that visibility deteriorates significantly until the eyes become accustomed to the light because the light suddenly becomes dark.

(Means for solving the problem) A backlight that is equipped with a discharge lamp and an incandescent bulb as backlighting for a liquid crystal display, etc., and a changeover switch turns on the discharge lamp during the day and switches to the incandescent bulb at night. The switching device includes an inverter circuit that drives the discharge lamp, a switching circuit connected in series to the inverter circuit, and a circuit that discharges when the changeover switch is switched to the incandescent light bulb side and keeps the switching circuit in an on state for a certain period of time. After the discharge lamp is maintained, the switching circuit is turned off, the driving of the inverter circuit is stopped, and the discharge lamp is turned off.

(Function) When switching from discharge lamps to incandescent lamps, the output of the inverter circuit gradually decreases due to the action of the charging circuit, and as a result, the discharge lamps also gradually dim and switch to incandescent lamp-only lighting. The discomfort of time can be resolved.

(Example) Fig. 1 shows a power supply circuit for backlighting various displays such as liquid crystal meters installed on the dashboard of an automobile. 1 is a discharge lamp such as a cold cathode discharge tube used for daytime illumination; 2 is a discharge lamp such as a cold cathode discharge tube; Discharge lamp 1 at night
The incandescent bulb that lights up instead of the lighting, 3 is the discharge lamp 1
This is a switch for switching between a light bulb and an incandescent light bulb 2, and is generally linked to a light switch in a car. 4 is an inverter circuit for starting the discharge lamp 1.

A switching circuit 5 consisting of Darlington-connected transistors Q ₁ and Q ₂ is connected in series to the inverter circuit 4, and when the changeover switch 3 is turned on, it is turned off and the switching circuit 5 is turned off after a certain period of time has elapsed. Charging circuit 6
It is equipped with This charging circuit 6 is a transistor
The main component is a timer consisting of Q ₃ , Q ₄ , a resistor R ₁ , and a capacitor C ₁ . When the changeover switch 3 is open, the transistors Q ₃ and Q ₄ are on, and the capacitor C ₁ is connected to the transistor Q ₃
collector current is charged through the resistor _R1 , and when the changeover switch 3 is turned on, the switching circuit 5
It has the function of discharging through the base of the transistor _Q2 and keeping the switching circuit 5 in an on state for a certain period of time.

Therefore, during the daytime when the changeover switch 3 is open, the charging circuit 6 and the switching circuit 5 are both on, and the inverter circuit 4 is driven, so the discharge lamp 1 is in the lighting state. At this time, the capacitor _C1 of the charging circuit 6 is in a charging state, and the incandescent light bulb 2 is off.

Next, when the light switch 3 of the vehicle is turned on at dusk or the like, the incandescent light bulb 2 lights up if the changeover switch 3 is linked to this. At this time, the transistor Q ₄ of the charging circuit 6 is turned off because its base terminal is grounded, and thereby the transistor Q ₃ is also turned off. On the other hand, switching circuit 5
uses capacitor _C1 as a power source and remains on for a certain period of time and then turns off. That is, from the time when the changeover switch 3 is turned on and the incandescent light bulb 2 is turned on, the discharge lamp 1 remains lit for a certain period of time while gradually dimming, and then is turned off. Therefore, even when the changeover switch 3 is turned on, the light does not dim instantly, and the illuminance gradually decreases, so there is no discomfort.

FIG. 2 is a characteristic diagram of illuminance when the changeover switch 3 is turned on, where A shows discharge lamp illumination, B shows incandescent lamp illumination, and S shows the time when the changeover switch 3 is turned on.

From the time when the changeover switch 3 is turned on, the light from the discharge lamp 1 gradually decreases, and after a certain period of time has elapsed, it becomes the illumination light from the incandescent bulb 2. The time it takes for the discharge lamp 1 to start dimming and turn off is determined by the values of the resistor R ₁ and capacitor C ₁ of the charging circuit 6, and is usually about 10 to 15 seconds.

(Effects) As described above, when switching backlights such as liquid crystal meters, the illuminance is gradually reduced to a predetermined brightness, which has the effect of eliminating the sense of discomfort when switching. In particular, when the brightness of the backlight of a liquid crystal meter in an automobile or the like changes rapidly, the visibility is significantly reduced, but this inconvenience can be overcome.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of this invented device, and FIG. 2 is an illuminance characteristic diagram when switching back illumination. 1: discharge lamp, 2: incandescent light bulb, 3: changeover switch, 4: inverter circuit, 5: switching circuit, 6: charging circuit.

Claims (1)

[Scope of utility model registration request] In a switching device for backlighting, which is equipped with a discharge lamp and an incandescent bulb as backlighting for a liquid crystal display, etc., and uses a changeover switch to turn on the discharge lamp during the daytime and switch to the incandescent bulb at night, the discharge lamp is driven. an inverter circuit connected in series to the inverter circuit, and a switching circuit connected in series to the inverter circuit, which discharges when the changeover switch is switched to the incandescent light bulb side, keeps the switching circuit in the on state for a certain period of time, and then turns off the inverter circuit. A switching device for backlighting equipped with a charging circuit that stops driving the circuit and turns off the discharge lamp.