JP3256008B2 - Automatic dimming circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic light control circuit,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic dimming circuit that can extend the duration of a battery in a device using a backlight that can operate on a battery.

[0002]

2. Description of the Related Art Generally, a liquid crystal display device is used as a display means of various devices, and there is a so-called liquid crystal television screen. That is, in a liquid crystal television, the screen is easily viewed by a backlight, and a battery (rechargeable battery,
Operation with a dry battery, etc.).

FIG. 4 is a circuit diagram showing an example of a conventional circuit for lighting such a backlight. In the backlight lighting circuit of FIG. 4, the transistor Q2 and the transistor Q3 are for oscillating a direct current (DC) / alternating current (AC) transformer T1, and the secondary winding T1 of the transformer T1 is used.
b oscillates at a predetermined frequency from the winding parallel capacitor C1, the resistors r2 and r3, the capacitor C2, the resistor r1, etc.
The direct current of the battery BT1 supplied via the reactor L is converted into an alternating current.

The transistor Q1 is for delaying the driving of the transistors Q2 and Q3, and performs a delay operation by the operation of the block 1 including the transistor Q4, the resistors r4, r5, and r6, the diode D1, and the capacitor C3. . That is, when the power supply from the battery BT1 is turned on, the capacitor C is connected via the resistors r4 and r5.
When the charging of the capacitor 3 starts and a predetermined time elapses and the terminal voltage of the capacitor is sufficiently increased, the transistor Q4 is turned on. When the transistor Q4 is turned on, the transistor Q1 is turned on, and the transistors Q2 and Q3 start oscillating. The backlight is turned on by this oscillation.

[0005] As the device using the backlight continues to turn on the backlight, the voltage of the battery BT1 decreases. In the conventional backlight lighting circuit, even if the battery voltage drops, the transistor Q1 remains in the ON state, the transistors Q2 and Q3 continue to oscillate normally, and thereafter the battery BT1 is consumed and the operation stops. . FIG. 5 is a graph showing the voltage of the battery BT1 and the operation characteristics of the backlight lighting circuit at that time. As shown in FIG. 5, the battery voltage gradually decreases, but the power consumption of the conventional backlight lighting circuit does not change. In this example, the operation stops in about 2 hours and 30 minutes.

[0006]

A battery-operated device is required to operate particularly for a long time. Currently, longevity of batteries and power saving of devices are being implemented, but in the case of LCD televisions, backlights, which account for the majority of power consumption, are not specifically addressed, and battery operation time is There was a problem that it was short. The present invention has been made in view of such a problem, and an object of the present invention is to provide an automatic dimming circuit that can extend the operation duration of a backlight lighting circuit. Still another object of the present invention is to provide an automatic dimming circuit capable of improving the contrast of a device illuminated by a backlight.

[0007]

According to the present invention, there is provided an automatic dimming circuit for a backlight which includes a battery in a power supply and is turned on by a driving circuit.
Means for detecting an output voltage of said battery is detected
Whether the output voltage falls below a predetermined reference voltage
A backlight drive control unit that adjusts the current consumption of the backlight based on the output of the comparator, and the backlight drive control unit reduces the detected output voltage to reduce the detected output voltage. Reference voltage
The adjustment is performed so as to reduce the current consumption of the backlight when the following occurs . Also, the present invention is an automatic dimming circuit for a backlight in which a battery is included in a power supply and is turned on by a drive circuit, wherein a means for detecting an output voltage of the battery, and an external light quantity of a device using the backlight are detected. And the detected output voltage is determined in advance.
To determine whether the voltage has become equal to or less than the first reference voltage.
The detected voltage from the parator and the means for detecting the external light quantity is
It is determined whether the voltage has fallen below a predetermined second reference voltage.
Different comparators and the output of each comparator,
The detected output voltage of the battery decreases and the
While decreasing the current consumption of the backlight when it is 1 less than the reference voltage, <br/> backlight when the output voltage from the means for detecting the external light quantity is equal to or less than the second reference voltage Backlight drive to reduce current consumption
Control means for controlling fluctuations in battery voltage and external light.
Adjust the backlight current consumption according to the amount of fluctuation
Things.

[0008]

According to the present invention, when the voltage of the battery becomes lower than a predetermined reference voltage, the current consumption of the backlight is reduced to adjust the current consumption of the backlight. In some cases, the power consumption of the backlight can be reduced, and the operating time of the battery is extended. According to the present invention, when the voltage of the battery becomes lower than a predetermined first reference voltage, the current consumption of the backlight is reduced, and the detection voltage of the external light amount is set to the second reference voltage. When the voltage is lower than the voltage, the current consumption of the backlight is reduced to adjust the current consumption of the backlight.Therefore, not only the voltage of the battery is reduced as described above, but also when the external light is weakened, the power consumption of the backlight is reduced. Can be reduced and the operating time of the battery is extended. Further, since the light can be adjusted by the intensity of the external light, the light can be adjusted in consideration of the improvement of the contrast. Further, according to the present invention, since the means for detecting the voltage and the means for detecting the external light quantity are provided together, the current consumption of the backlight is adjusted in both cases of the voltage drop and the external light quantity drop, The current consumption can be reduced, and the operation duration of the battery can be extended.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an automatic dimming circuit according to a first embodiment of the present invention. In FIG. 1, the same parts as those of the backlight drive circuit of FIG. 4 are denoted by the same reference numerals. As shown in FIG. 1, this automatic dimming circuit is provided with a block 2 instead of the block 1 in FIG. Block 2
It mainly comprises a counter ic1 and a comparator ic2.

The counter ic1 switches on / off the transistor Q1 to turn on / off the transistors Q2 and Q3.
Is to perform duty control of the oscillation circuit. That is, the counter ic1 outputs from the QE terminal by input to the clock CLK terminal, and stops output from the QE terminal by input to the inverted clear * CLR terminal. The clock pulse is input to the clock CLK terminal, and the output of the comparator ic2 is input to the inverted clear * CLR terminal. The output of the QE terminal is the transistor Q1.
Is input via a resistor r7. In the comparator ic2, a reference voltage is input to a non-inverting input, and a voltage of the battery BT1 is input to an inverting input. The output voltage of the comparator ic2 becomes low potential ("L") when the battery voltage exceeds the reference voltage, and becomes high potential ("H") when the battery voltage is lower than the reference voltage. Note that r8 to r11 are characteristic resistances.

Next, the operation of the first embodiment will be described. The switch SW is turned on to turn on the battery BT1. The voltage of the battery BT1 immediately after being turned on is high, and the output of the comparator ic2 becomes “L”. Therefore, since the input of the counter * CLR terminal of the counter ic1 (counter) is "L", the counter clear operation is performed, and the output of the QE terminal is fixed at "L". Therefore, during a certain period immediately after turning on, the transistor Q1
Is always ON, the driving transistor Q2 and the transistor Q3 oscillate in a normal state, and the output of the DC / AC transformer T1 also becomes a normal output.

As the operation time elapses, the output voltage of the battery BT1 gradually decreases. When the output voltage falls below the reference voltage of the comparator ic2, the output of the comparator ic2 changes to “H”. So the counter ic
Inversion clear of 1 * The CLR terminal becomes "H" and the clock input of the counter ic1 is divided, so that the output of the QE terminal is output with a certain period. Then, since the transistor Q1 repeats ON / OFF in its output cycle, the oscillation of the transistor Q2 and the transistor Q3 is
A duty change having an ON / OFF cycle occurs.

Accordingly, dimming of the backlight (connected to the output side of the DC / AC transformer T1) (decrease in light quantity)
As a result, the overall current consumption including the backlight and the backlight drive circuit is reduced. As a result, the backlight is slightly darkened, but the operation duration of the battery BT1 is extended. If the conditions of the comparator ic2 and the like of the block 2 in FIG. 1 are devised, it is possible to perform dimming control according to each voltage of various batteries. As for the counter ic1, according to the inventor's investigation, when the input frequency is approximately 42KH _Z clock CLK pin QE pin in the circumferential 128 minutes, QE pin output 42kH _Z / 128
= 328H _Z, and the duty became 50%.
The operation under these conditions was the best from the viewpoint of the flicker efficiency.

FIG. 2 shows a graph when dimming is controlled by the automatic dimming device of the first embodiment. In this case, control was performed under the same conditions as in FIG. As shown in FIG. 2, dimming is performed when the battery voltage becomes approximately 9 volts, and the voltage curve becomes gentle to reduce current consumption. In this case,
The duration of the operation was about 3 hours and 40 minutes. In the example of FIG. 5, the operation duration is greatly extended as compared with the time of 2 hours and 30 minutes, from which the usefulness of the present invention can be understood.

Next, a second embodiment will be described. FIG. 3 shows an automatic light control device according to the second embodiment. As shown in FIG. 3, this automatic light control device is provided with a block 3 instead of the block 2 of the automatic light control device of the first embodiment of FIG. Block 3 is a block in which the external light amount detection element OPC is maintained on the inverting input side of the comparator ic2, and the rest is the same as block 2.

A reference voltage is set to the non-inverting input of the comparator ic2. The output of the external light amount detection element OPC changes according to the change of the external light amount. Therefore,
When the external light amount is large and the output voltage is equal to or higher than the reference voltage, the output of the comparator ic2 becomes “L”, so that the transistor Q1 is always turned on, and the current consumption of the backlight remains unchanged. On the other hand, when the amount of external light is small and the output voltage is equal to or lower than the reference voltage, the output of the comparator ic2 becomes “H”, so that the transistor Q1 is turned on at a constant cycle.
/ OFF, and the current consumption of the backlight decreases.

Therefore, the backlight driving circuit is provided with a dimming function depending on the amount of external light, and can perform dimming of the backlight in consideration of the improvement of the contrast. In such a case, further power saving is possible. Therefore, the operation duration of the battery BTI can be extended while improving the contrast.

In the embodiment described above, the means for detecting the voltage of the battery and the means for detecting the amount of external light are provided.
Although an automatic dimming circuit provided separately is shown, it is configured to include these means in combination, and the current consumption of the backlight is adjusted according to the fluctuation of the battery voltage and the fluctuation of the external light amount. Is also good. In this case,
For example, the output of the means for detecting the voltage of the battery and the output of the means for detecting the external light amount may be connected to the inverted clear * CLR terminal of the counter of the block 2 via an OR circuit. Note that the present invention is not limited to the embodiments. That is, the number of reference voltages set in the comparator ic2 is not limited to one, and two or more reference voltages can be set to change the rate of decrease in current consumption for each of the reference voltages. For example, the duty ratio of the output of the counter ic1 is changed for each of a plurality of reference voltages to change the current reduction ratio. In this way, the decrease in the current consumption can be gradually increased, so that there is no unnatural change in the amount of light.

[0019]

As described above, according to the present invention, since the current consumption of the backlight is reduced based on the decrease in the battery voltage, the duration of the battery operation can be extended. In addition, since the current consumption of the backlight is reduced based on the decrease in the amount of external light, the duration of the battery is extended, and dimming can be performed according to the intensity of external light. Excellent effects such as being able to be obtained. In addition, the current consumption of the backlight can be reduced in response to both a decrease in the battery voltage and a decrease in the amount of external light, so that the backlight can be adjusted more finely according to the usage conditions. An extended duration of operation can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an automatic dimming circuit according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a battery operation of the first embodiment.

FIG. 3 is a circuit diagram of an automatic dimming circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional backlight drive circuit.

FIG. 5 is an explanatory diagram of a conventional battery operation.

[Explanation of symbols]

 Q1 Transistor for switch Q2, Q3 Transistor for oscillation ic1 Counter ic2 Comparator OPC External light intensity detection element

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/66

Claims (2)

(57) [Claims] An automatic dimming circuit for a backlight which includes a battery in a power supply and is turned on by a drive circuit, wherein a means for detecting an output voltage of the battery, and the detected output voltage is predetermined. Below the reference voltage
A comparator for determining whether Tsu, based on the output of the comparator, and a backlight drive control means for adjusting the current consumption of the backlight, the backlight drive control unit, the detected output
An automatic dimming circuit, which adjusts so that current consumption of a backlight is reduced when a voltage drops and becomes lower than the reference voltage . 2. An automatic light control circuit for a backlight, which includes a battery in a power supply and is turned on by a drive circuit, comprising: means for detecting an output voltage of the battery; and detecting an external light amount of a device using the backlight. Means for detecting that the detected output voltage is equal to or lower than a predetermined first reference voltage.
The detection voltage from the comparator for determining whether the temperature has fallen below and the means for detecting the external light amount is predetermined.
To determine whether the voltage has fallen below the second reference voltage.
And the detected battery by the output of each comparator.
Output voltage drops below the first reference voltage.
While decreasing the current consumption of the backlight when the,
The output voltage from the means for detecting the external light amount is the second voltage.
Backlight drive control means for reducing the current consumption of the backlight when the voltage becomes equal to or lower than the reference voltage of, and according to the fluctuation of the battery voltage and the fluctuation of the external light amount,
An automatic dimming circuit, wherein a current consumption of a backlight is adjusted .