Automatic Backlight on/Off Control Apparatus for Liquid Crystal Display Television

1. Field of the Invention

The present invention relates to a backlight on/off control apparatus for use in a liquid crystal display television (hereinafter "LCD TV") and more particularly, to an automatic backlight on/off control apparatus for automatically turning a backlight on/off according to existing or non-existing of a composite video signal.

2. Description of the Prior Art

Various types of backlight on/off control apparatuses having a backlight which is turned on according to the pulse signals of a pulse generating member are well known in the art. One of such conventional backlight of/off control apparatuses for an LCD TV is illustrated in FIG. 1. As shown in FIG. 1, since a transistor TR.sub.1 is turned on or off according to pulse signals of a pulse generating member 1, the voltage of a backlight voltage terminal Vcc is induced in the second winding of a transformer T, which causes a first capacitor C1 to be charged. The charged voltage of the capacitor C1 is applied to a backlight 2 through a second capacitor C.sub.2 to turn on the backlight 2. However, such conventional backlight on/off circuit includes the backlight 2 turned on according to the pulse signals of the pulse generating member 1 regardless of existing or non-existing of a video signal. Therefore, such conventional backlight on/off circuit has a drawback so that unnecessary power consumption increases.

Accordingly, it is an object of the present invention to provide an automatic backlight on/off control apparatus for use in an LCD TV which prevents electric power from being unnecessarily consumed by turning a backlight off in case there is no input of any video signal while the backlight turns on according to the pulse signals of the pulse generating member only in case there is a video signal input.

Another object of the present invention is to provide an improved backlight on/off control apparatus for amplifying composite video signals, detecting a synchronizing signal out of the composite video signals, determining whether the video signal is inputted or not according to the synchronizing signal being detected or not, and supplying or cutting off the electric power to the backlight according to the determination of the existing or non-existing of the video signal input.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Briefly described, the present invention relates to an automatic backlight on/off control apparatus for use in a liquid crystal display television includes a buffer amplifier, a synchronizing signal detector, a switching controller, and a backlight power controller for preventing electric power consumed unnecessarily by turning the backlight off in case there is no input of any video signal and turning the backlight on according to the pulse signal of a pulse generating member only in case there is a video signal input.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a circuit diagram of a conventional backlight on/off control apparatus for an LCD TV; and

FIG. 2 is a circuit diagram of the automatic backlight on/off control apparatus for an LCD TV according to the present invention.

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, the automatic backlight on/off control apparatus as shown in FIG. 2 comprises a buffer amplifier member 3 for buffer-amplifying and integrating the composite video signals which enter a composite video signal input terminal Vi, a synchronizing signal detecting member 4 for detecting and outputting a synchronizing signal according to the signal output level of the buffer amplifier member 3, a switching control member 5 for outputting a switching control signal by integrating and differentially amplifying the output signal of the synchronizing signal detecting member 4, and a backlight voltage control member 6 for supplying or cutting off the voltage of a backlight voltage terminal Vcc to the backlight 2 with a switching operation in accordance with the switching control signal of the switching control member 5.

The buffer amplifier member 3 is constructed by connecting the composite video signal input terminal Vi to bias resistors R.sub.11 and R.sub.12 and a base of a transistor TR.sub.11 through a coupling capacitor C.sub.11, connecting a emitter of the transistor TR.sub.11 to a resistor R.sub.13, and connecting again the emitter of the transistor TR.sub.11 to a capacitor C.sub.12 through a resistor R.sub.14.

The synchronizing signal detecting member 4 is built by connecting the connection point of the resistor R.sub.14 and capacitor C.sub.12 through a resistor R.sub.15 and a capacitor C.sub.13 in a parallel connection to the emitter of a transistor TR.sub.12 which is supplied with a constant voltage through resistors R.sub.16 and R.sub.17, connecting the emitter of a transistor TR.sub.13 applied with a constant voltage through resistors R.sub.19 and R.sub.20 to the base of a transistor TR.sub.14 as well as to a collector of the transistor TR.sub.12 through a resistor R.sub.18, and connecting the collector of the transistor TR.sub.14 to the base of a transistor TR.sub.15 as well as to a resistor R.sub.24 and the emitter of the transistor TR.sub.15 through a resistor R.sub.23.

The switching control member 5 is constituted by connecting the resistors R.sub.23 and R.sub.24 and the emitter of the transistor TR.sub.15 to a capacitor C.sub.14 and the base of a transistor TR.sub.16 of forming a darlington connection with a transistor TR.sub.17, connecting the collectors of transistors TR.sub.20 and TR.sub.21 in a darlington configuration supplied with a constant voltage through resistors R.sub.26, R.sub.27, and R.sub.28 to the bases of transistors TR.sub.18 and TR.sub.19 as a constant current source and the collector of the transistor T.sub.18, connecting the emitters of the transistors TR.sub.17 and TR.sub.21 to the collector of a transistor TR.sub.22 supplied with a constant bias voltage through the resistors R.sub.26, R.sub.27, and R.sub.28, and connecting the collector of the transistor TR.sub.19 to a resistor R.sub.25.

The backlight voltage control member 6 is formed by connecting a connection point of the resistor R.sub.25 and the collector of the transistor TR.sub.19 to the base of a transistor TR.sub.23, connecting the emitter of the transistor TR.sub.23 to the base of a transistor TR.sub.24 and a resistor R.sub.29 through a resistor R.sub.30, and connecting the emitter of the transistor TR.sub.24 to the backlight voltage terminal Vcc while connecting the collector of the transistor TR.sub.24 to the primary winding of a transformer T and the collector of the transistor TR.sub.1 being controlled by the pulse generating member 1.

And, reference numeral 7 in FIG. 2 denotes a video signal display member indicative of the video signal entering the composite video signal input terminal Vi.

The operation and the effect of the configuration mentioned above according to the present invention will be described below in detail.

When a voltage is applied to a voltage terminal B.sup.+ and the backlight voltage terminal Vcc, and the composite video signal is inputted to the composite video signal input terminal Vi, the composite video signal is applied to and displayed on a video signal display member 7 through a resistor R.sub.10 and a capacitor C.sub.10. Also, the composite video signal is buffer-amplified through the transistor TR.sub.11 after the direct current component of the signal is removed when the signal crosses the coupling capacitor C.sub.11, the emitter output signal is charged in the capacitor C.sub.12 through the resistor R.sub.14, the charged voltage in the capacitor C.sub.12 is applied to the emitter of the transistor TR.sub.12 through the resistor R.sub.15 and the capacitor in a parallel connection in order for the transistor TR.sub.12 to be controlled.

That is, the transistor TR.sub.12 is turned on in case there is a lower voltage at the emitter of the transistor TR.sub.12 than a bias voltage applied to the base of the transistor TR.sub.12 because of a constant bias voltage application to the base of the transistor TR.sub.12 through resistors R.sub.16 and R.sub.17.

Accordingly, when a negative synchronizing signal is inputted to the composite synchronizing signal input terminal Vi, a low level signal is applied to the base of the transistor TR.sub.11 so that the transistor TR.sub.11 is turned off, which causes the charged voltage in the capacitor C.sub.12 to be discharged through resistors R.sub.13 and R.sub.14.

Therefore, the voltage applied to the emitter of the transistor TR.sub.12 becomes so lower than the bias voltage applied to the base of the transistor TR.sub.12 that the transistor TR.sub.12 is turned on. When the transistor TR.sub.12 is turned on, the transistor TR.sub.13 is also turned on causing electric current flow to the collector of the transistor TR.sub.12 through the resistor R.sub.18. Therefore, the transistor TR.sub.14 is turned on so that the collector of the transistor TR.sub.14 has a high potential output. The voltage of the voltage terminal B.sup.+ is rapidly charged in the capacitor C.sub.14 through the resistor R.sub.22 and the transistor TR.sub.15 because the transistor TR.sub.15 is turned on by the high potential. Thereafter, when the transistor TR.sub.15 is turned off, the charged voltage of the capacitor C.sub.14 is discharged slowly through the resistor R.sub.24. Accordingly, in the situation for the composite synchronizing signal to be applied to the composite synchronizing signal input terminal Vi, the transistors TR.sub.16 and TR.sub. 17 are turned on and the transistors TR.sub.20 and TR.sub.21 are turned off because the charged voltage of capacitor C.sub.14 keeps above the determined voltage level higher than that divided by resistors R.sub.26, R.sub.27, and R.sub.28. At this time, the transistor TR.sub.22 is turned on because of the bias voltage application to the base of the transistor TR.sub.22 through resistors R.sub.26, R.sub.27, and R.sub.28. When the transistors TR.sub.20 and TR.sub.21 keep the off-stage, the transistors TR.sub.18 and TR.sub.19 are also turned off so that the base of the transistor TR.sub.23 is applied with low potential. Therefore, the transistor TR.sub.23 is turned on to output a low potential at the emitter thereof so that the transistor TR.sub.24 is turned on. And then the backlight voltage of the backlight voltage terminal Vcc is applied to the collector of the transistor TR.sub.1 and the primary winding of the transformer T through the transistor TR.sub.24.

Accordingly, as shown in FIG. 1, when the transistor TR.sub.1 is turned on or off according to the pulse signals of the pulse generating member 1, the voltage of the backlight voltage terminal Vcc is induced in the second winding of the transformer T, which causes a capacitor C.sub.1 to be charged. The charged voltage of the capacitor C.sub.1 is applied to the backlight 2 through a capacitor C.sub.2 to turn the backlight 2 on. On the other hand, in case the composite video signal is not inputted to the composite video signal input terminal Vi, the transistor TR.sub.11 is turned on by the bias voltage through resistors R.sub.11 and R.sub.12 so that the emitter of the transistor TR.sub.11 keeps a high potential. This high potential is charged in the capacitor C.sub.12 through the resistor R.sub.14. The charged voltage of the capacitor C.sub.12 makes the voltage applied to the emitter of the transistor TR.sub.12 higher than that applied to the base of the transistor TR.sub.12. Therefore, the transistor TR.sub.12 is turned off.

As a result, the transistor TR.sub.13 is also turned off, the base of the transistor TR.sub.14 is applied with a high potential and the transistor TR.sub.14 is turned off, causing the transistor TR.sub.15 to be kept off. Therefore, the base of the transistor TR.sub.16 is applied with a low potential.

At this time, the transistors TR.sub.16 and TR.sub.17 are turned off since the voltage applied to the base of the transistor TR.sub.20 through the resistors R.sub.26, R.sub.27, and R.sub.28 becomes higher than that applied to the base of the transistor TR.sub.16 causing the transistors TR.sub.20 and TR.sub.21 to be kept on. And the transistor TR.sub.22 is turned on by the bias voltage through the resistors R.sub.26, R.sub.27, and R.sub.28, which causes the transistors TR.sub.18 and TR.sub.19 as a constant current source to be turned on. When the transistor TR.sub.18 is turned on, the collector of the transistor TR.sub.19 has a high potential causing the transistor TR.sub.23 to be turned off. Therefore, the transistor TR.sub.24 is turned off by the high potential at the emitter of the transistor TR.sub.19.

When the transistor TR.sub.24 is turned off, the backlight 2 is kept off because the backlight voltage of the backlight voltage terminal Vcc applied to the collector of the transistor TR.sub.1 and the primary winding of the transformer T is cut off.

As mentioned above in detail, the present invention has the effect that prevents the unnecessary electric power consumption by turning the backlight 2 off in case there is no input of any video signal and turning the backlight 2 on according to the pulse signals of the pulse generating member 1 only in case there is a video signal input.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included in the scope of the following claims.