JPH054187U - Brightness control circuit for backlight - Google Patents

Abstract

(57) [Abstract] [Purpose] The brightness of the backlight light source is gradually decreased without making the user feel the brightness decrease, and the power consumed by the backlight light source is decreased. [Structure] The lighting control unit controls the backlight source while maintaining the average voltage applied to the backlight source constant.
A drive signal for applying a high effective value voltage for a short time when the voltage of the secondary battery is high and for a long time when the voltage of the secondary battery is low is supplied to the lighting drive unit. By controlling the lighting of the backlight light source in this manner, the brightness of the backlight light source is gradually decreased with the voltage drop of the secondary battery without causing the user to feel a decrease in brightness,
In addition, the power consumed by the backlight light source is reduced.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a brightness control circuit for a backlight light source such as an ELD (Electro Luminescent Display) used for a backlight of a personal computer or a Japanese word processor.

[0002]

[Prior Art]

 In recent years, a so-called backlight type display device has been realized in which a liquid crystal display device used as a display device such as a battery-powered personal computer or a Japanese word processor is illuminated by a light source such as an ELD from the back or side.

An ELD or the like used as a light source of a backlight in such a backlight type display device is usually brightness-controlled so as to emit light with a constant brightness from the start of lighting.

[0004]

[Problems to be solved by the device]

 However, as described above, in battery-operated personal computers and Japanese word processors, the power consumed by the backlight source for lighting accounts for a large proportion of the total power consumption, and personal computers and Japanese word processors are used. There was a problem that the operating time of was shortened.

The present invention has been made in view of the above circumstances, and the backlight for gradually reducing the brightness of the backlight light source without making the user feel the brightness decrease and reducing the power consumed by the backlight light source. It is an object to provide a brightness control circuit for a light source.

[0006]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention provides a rechargeable secondary battery, a backlight light source that illuminates a display device from the back or side, a lighting drive unit that drives the backlight light source, and the backlight. A voltage detector that detects the average voltage applied to the light source, a reference device that outputs the reference voltage, the reference voltage output from the reference device, and the average voltage detected by the voltage detector described above. While maintaining the average voltage applied to the backlight source constant, a high effective voltage is applied for a short time when the secondary battery voltage is high, and a low effective voltage is long when the secondary battery voltage is low. A lighting control unit that supplies a driving signal to be applied to the lighting driving unit to the lighting driving unit is provided.

[0007]

[Action]

 Since the present invention is configured as described above, the lighting control unit keeps the average voltage applied to the backlight light source constant and provides a high effective value voltage to the backlight light source when the voltage of the secondary battery is high. By supplying a drive signal to the lighting drive unit that applies a low effective value voltage for a long time when the voltage of the secondary battery is low for a short time, the brightness of the backlight light source can be reduced without making the user feel the brightness decrease. As the voltage of the secondary battery drops, the voltage is gradually reduced and the power consumed by the backlight light source is reduced, so that the usage time of the secondary battery can be extended.

[0008]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a brightness control circuit of a backlight light source according to an embodiment of the present invention. In FIG. 1, 1 is a secondary battery 2 that can be charged by a separate AC adapter (not shown). This is a resistor that stabilizes the charging current when charging the battery. The power of the secondary battery 2 charged through this resistor 1 is supplied to the main body of the personal computer (not shown) as drive power and the personal computer. The liquid crystal display device (not shown), which is the display device, is supplied to a lighting power source unit 4 for illuminating and driving a backlight light source for illuminating the liquid crystal display device (not shown) from the back surface or the side surface, for example, an AC electroluminescence type ELD3. The lighting power supply unit 4 is a lighting power supply circuit for an electric luminescence lamp as disclosed in, for example, Japanese Utility Model Laid-Open No. 62-7197, and has an inductance that resonates with the electrostatic capacitances of the transistor 5 and ELD3 and the ELD3 and the resonance circuit. ELD3 is driven to be lit by an AC voltage output from the lighting power supply section 4. The transistor 5 has an emitter connected to the transformer 6, a collector connected to the secondary battery 2, and a base to which a drive signal described later is applied.

Reference numeral 7 is an error amplifier which receives the outputs of a voltage detector 8 which detects the average voltage applied to the ELD 3 and a reference device 9 which outputs a reference voltage. The output of this error amplifier 7 is the base of the transistor 5. The transistor 5 is turned on by a pulse having a constant cycle so that the average voltage applied to the ELD3 as a drive signal becomes constant. The pulse output from the error amplifier 7 has a constant cycle, but when the output voltage of the transformer 6 is high, that is, when the terminal voltage of the secondary battery 2 is high, the pulse width for turning on the transistor 5 is short, and the terminal When the voltage is low, the pulse width is long and the transistor 5 is driven and controlled so that the average voltage applied to the ELD3 becomes constant.

Next, the operation of the embodiment of the present invention having the above-described structure will be described with reference to the charge / discharge characteristics of the secondary battery 2 shown in FIG. 2 and the applied voltage characteristics to the ELD 3 shown in FIG.

The terminal voltage of the secondary battery 2 fluctuates during charging and discharging as shown in FIG. 2, but is output from the error amplifier 7 that operates so that the average voltage applied to the ELD3 becomes constant. The transistor 5 which uses a pulse of a constant cycle as a drive signal operates so that the on-time is short when the terminal voltage of the secondary battery 2 is high, and the on-time is long when the terminal voltage is low. The effective voltage applied to ELD3 at this time fluctuates as shown in FIG. That is, when the terminal voltage of the secondary battery 2 is high, the effective value voltage of the waveform 10 shown by the solid line is low, when the terminal voltage is low, the effective value voltage of the waveform 11 shown by the alternate long and short dash line, and when the terminal voltage is an intermediate value. The RMS voltage of waveform 12 shown by the dotted line is applied to ELD3, respectively. When the terminal voltage of the secondary battery 2 is high, the effective value of the voltage applied to the ELD3 is high, and when the terminal voltage is low, the effective value is low, but the drive time of the transistor 5 is different. The average voltage applied is constant.

On the other hand, regarding the brightness of the ELD3, the brightness is bright when the effective value voltage applied to the ELD3 is high, and the brightness is dark when the effective value voltage applied to the ELD3 is low, although the average voltage applied to the ELD3 is constant. Fluctuates. Moreover, since the driving time of the transistor 5 is shorter when the rms voltage is high than when the rms voltage is low, the power consumed by the ELD3 lighting drive is reduced as a whole compared to the conventional case. It becomes electric power. Also, the brightness of the ELD3 gradually decreases with the voltage drop of the secondary battery 2 because the fluctuation of the terminal voltage of the secondary battery 2 is gradual, and the user may notice the brightness fluctuation. There is no.

In the above embodiment, an example in which the ELD3 is applied as the backlight light source has been described, but the invention is not limited to this, and other light sources such as an FL (Fluorescent) tube may be applied. Good.

Further, the present invention is not limited to the above embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0016]

[Effect of the device]

 As described in detail above, according to the brightness control circuit of the backlight light source of the present invention, the backlight light source is driven brightly for a short time when the voltage of the secondary battery is high, and dark for a long time when the voltage of the secondary battery is low. By doing so, it is possible to gradually reduce the brightness of the backlight light source along with the voltage drop of the secondary battery without causing the user to feel a decrease in brightness and reduce the power consumed by the backlight light source. Therefore, the secondary battery can be used for a long time.

Further, since it is possible to drive the backlight light source brightly for a short time, it is possible to extend the life of the backlight light source.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a brightness control circuit of a backlight light source according to an embodiment of the present invention.

FIG. 2 is a diagram showing charge / discharge characteristics of a secondary battery.

FIG. 3 is a diagram showing a voltage characteristic applied to an ELD.

[Explanation of symbols]

 2 ... Secondary battery 3 ... ELD (backlight light source) 4 ... Lighting power supply section (lighting drive section) 7 ... Error amplifier (lighting control section) 8 ... Voltage detection section 9 ... Standard unit

Claims (1)

[Claims for utility model registration] 1. A rechargeable secondary battery, a backlight light source for illuminating the display device from the back or side, a lighting drive unit for lighting and driving the backlight light source, and the backlight described above. A voltage detector for detecting an average voltage applied to the light source, a reference device for outputting a reference voltage, the reference voltage output from the reference device and the back voltage based on the average voltage detected by the voltage detector. While maintaining the average voltage applied to the light source constant, a high RMS voltage is applied for a short time when the secondary battery voltage is high, and a low RMS voltage is applied for a long time when the secondary battery voltage is low. A brightness control circuit for a backlight light source, comprising: a lighting control unit that supplies a drive signal to the lighting drive unit.