CN101197115A - Display brightness automatic adjustment circuit - Google Patents

Abstract

An automatic brightness adjustment circuit for a display, used for automatically adjusting the brightness of a display, which includes a voltage adjustment circuit with a light source detection element, which detects the brightness of the external environment through the light source detection element and outputs a brightness corresponding to the external environment A variable voltage signal; and a pulse width modulation signal generating circuit for receiving the voltage signal and outputting a pulse width modulation signal varying with the voltage signal to the brightness control circuit of the display to control the brightness of the display . The display brightness automatic adjustment circuit can automatically adjust the brightness of the display itself according to the change of the ambient brightness.

Description

Display brightness automatic adjustment circuit

technical field

The invention relates to a circuit for adjusting the brightness of a display.

Background technique

With the increasing popularity of liquid crystal displays, the application of liquid crystal displays becomes more and more extensive. When using a liquid crystal display, the human eye is more sensitive to the brightness of the surrounding environment of the display, especially a sudden change in brightness will have a negative impact on human vision, which is especially prominent for notebook computer users. In order to achieve the most comfortable visual effect, users need to adjust the brightness of the display to adapt to changes in the environment.

The existing liquid crystal display brightness adjustment circuit is arranged in the liquid crystal display and is provided with a number of adjustment buttons on its shell, and the user needs to manually operate the buttons to adjust the brightness of the display, which is not very convenient, especially for using notebooks on the road. For computer users, adjusting the brightness is even more troublesome due to the constant changes in the ambient brightness.

Contents of the invention

In view of the above, it is necessary to provide a display brightness automatic adjustment circuit to automatically adjust the brightness of the display.

A display brightness automatic adjustment circuit, used to automatically adjust the brightness of a display, which includes a voltage adjustment circuit with a light source detection element, which detects the brightness of the external environment through the light source detection element and outputs a brightness corresponding to the external environment A variable voltage signal; and a pulse width modulation signal generating circuit for receiving the voltage signal and outputting a pulse width modulation signal varying with the voltage signal to the brightness control circuit of the display to control the brightness of the display .

Compared with the prior art, the automatic brightness adjustment circuit of the display uses the light source detection element to detect the external light source, and converts the signal of the external light source into a voltage signal, and then converts the voltage signal into a device that can control the display The pulse width modulation signal of the brightness is sent to the brightness control circuit of the display, so that the display can automatically adjust the brightness with the change of the ambient brightness, which is very convenient.

Description of drawings

The present invention will be further described below in combination with specific embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram of a preferred embodiment of an automatic brightness adjustment circuit for a display in the present invention.

FIG. 2 is a circuit diagram of the voltage regulation circuit and the PWM signal generation circuit in FIG. 1 .

FIG. 3 is a waveform diagram of the voltage signal at the output terminal of the integrating circuit in FIG. 2 .

FIG. 4 is a waveform diagram of the voltage signal at the output terminal of the comparator circuit in FIG. 2 .

Detailed ways

Please refer to FIG. 1 and FIG. 2 together. The automatic display brightness adjustment circuit of the present invention is used to automatically adjust the brightness of a display. Its preferred embodiment includes a voltage adjustment circuit 10 and a PWM (Pulse Width Modulation, pulse width modulation) signal generation Circuit 20. The PWM signal generating circuit 20 includes an integrating circuit 22 , a comparing circuit 24 and a switching circuit 26 .

The voltage regulating circuit 10 includes a light source detection element (such as a photoresistor 11), a first resistor 12, a second resistor 13, a third resistor 14, a first capacitor 15 and a first DC power supply terminal Vcc. The first DC power supply terminal Vcc is sequentially connected to the photoresistor 11 and the first resistor 12 and then grounded, the first capacitor 15 is connected in parallel to the first resistor 12, and the photoresistor 11 is connected to the first resistor 12 in parallel. The node of the first resistor 12 is sequentially connected to the second resistor 13 and the third resistor 14 and then grounded. The photoresistor 11 is arranged on the outer frame of the display to collect the external light source signal and change its own resistance value according to the change of the brightness of the external light source, that is, when the external light source becomes brighter, the resistance value of the photoresistor 11 becomes smaller; when the external light source becomes darker, the resistance value of the photoresistor 11 becomes larger. Other components are all set on the internal circuit board of the display.

The integration circuit 22 includes a first operational amplifier A1, a fourth resistor 222 and a second capacitor 224, and the comparison circuit 24 includes a second operational amplifier A2, a fifth resistor 242, a sixth resistor 244, A third capacitor 246 and a second DC power supply terminal Vdd. The switch circuit 26 includes a seventh resistor 262 , an eighth resistor 264 and a transistor Q. The cathode input terminal of the first operational amplifier A1 is connected to the node of the photoresistor 11 and the first resistor 12 through the fourth resistor 222, and the second capacitor 224 is connected to the first operational amplifier Between the cathode input terminal and the output terminal of A1, the anode input terminal of the first operational amplifier A1 is connected to the node between the second resistor 13 and the third resistor 14 . The output terminal of the first operational amplifier A1 is connected to the cathode input terminal of the second operational amplifier A2, the second DC power supply terminal Vdd is connected to the third capacitor 246 and then grounded, and the second DC power supply terminal Vdd It is also connected to the anode input terminal of the second operational amplifier A2 through the sixth resistor 244, and the anode input terminal of the second operational amplifier A2 is connected to the anode input terminal of the second operational amplifier A2 through the fifth resistor 242. output terminal, the output terminal of the second operational amplifier A2 is connected to the base of the transistor Q through the seventh resistor 262, the emitter of the transistor Q is grounded, and the collector of the transistor Q is connected to the base of the transistor Q through the seventh resistor 262. Eight resistors 264 are connected to the cathode input terminal of the first operational amplifier A1. The first DC power supply terminal Vcc and the second DC power supply terminal Vdd can be directly connected to the DC power supply inside the display.

The PWM signal generating circuit 20 is also arranged on the internal circuit board of the display, and is connected to the PWM signal input terminal of the inverter in the internal brightness control circuit of the display through the output terminal of the second operational amplifier A2, The inverter can change the change of its output current according to the change of the PWM signal input to its PWM signal input terminal, and the change of the output current of the inverter corresponds to the change of the brightness of the display.

Assuming that the resistance value of the photosensitive resistor 11 is R0, the resistance value between the node between the photosensitive resistor 11 and the first resistor 12 and the ground is R1, and the resistance value of the second resistor 13 is R2, The resistance value of the third resistor 14 is R3, the node voltage between the first resistor 12 and the photosensitive resistor 11 is Vi, and the node voltage between the second resistor 13 and the third resistor 14 is Vp , the DC voltage connected to the first DC power supply terminal Vcc is V, and the following relational expression is given:

Vi=V*R1/(R0+R1); Vp=Vi*R3/(R2+R3);

It can be deduced that: Vp=[V*R1/(R0+R1)]*R3/(R2+R3)

Here R1, R2, R3, and V are fixed values, and the resistance value R0 of the photosensitive resistor 11 is inversely proportional to the brightness of the external environment, then when the external environment becomes brighter, the resistance value R0 of the photosensitive resistor 11 changes. When the external environment becomes darker, the resistance value R0 of the photoresistor 11 becomes larger, resulting in a smaller value of the node voltage Vp.

The integration circuit 22 generates a triangular wave voltage signal to the comparison circuit 24 to output a PWM voltage signal, and the switch circuit 26 is used to feed back the PWM voltage signal to the integration circuit 22, and through the PWM The voltage signal is used to control the turn-on and turn-off of the transistor Q, so that the second capacitor 224 can be charged and discharged cyclically, so that the integrating circuit 22 can continuously generate the triangular wave voltage signal.

Please continue to refer to Fig. 3, which is a waveform diagram of the triangular wave voltage signal generated by the integrating circuit 22, the initial voltage of the triangular wave voltage signal is the node voltage Vp, as can be seen from the above: when the external environment becomes bright, the triangular wave The initial voltage of the voltage signal becomes larger; when the external environment becomes darker, the initial voltage of the triangular wave voltage signal becomes smaller.

Please continue to refer to FIG. 4 , which is a waveform diagram of the corresponding PWM voltage signal generated by the comparison circuit 24 when the voltage of the node voltage Vp is equal to the voltage of the anode input terminal of the first operational amplifier A1 . It is easy to know that when the voltage of the node voltage Vp is greater than the voltage of the anode input terminal of the first operational amplifier A1, the duty ratio of the PWM voltage signal will be correspondingly increased; otherwise, when the voltage of the node voltage Vp is less than When the voltage at the anode input terminal of the first operational amplifier A1 is high, the duty cycle of the PWM voltage signal will be correspondingly smaller, that is, the duty cycle of the PWM voltage signal is proportional to the node voltage Vp, according to the aforementioned The content can be deduced: when the external environment becomes brighter, the duty cycle of the PWM voltage signal becomes larger; when the external environment becomes darker, the duty cycle of the PWM voltage signal becomes smaller.

Since the output terminal of the second operational amplifier A2 is connected to the PWM signal input terminal of the inverter in the internal brightness control circuit of the display, that is, the output current of the inverter is proportional to the duty ratio of the PWM voltage signal. It can be seen that the brightness of the display can change with the brightness of the external environment. The specific changes are as follows: when the external environment becomes brighter, the resistance value of the photosensitive resistor 11 becomes smaller, and the node voltage Vp becomes larger, so that the duty cycle of the PWM voltage signal becomes larger, and then the inverter The output current of the device becomes larger, so the display becomes brighter. Conversely, when the external environment becomes dark, the display will dim. The degree of brightness change of the display can be adjusted by selecting an appropriate resistance value for the photoresistor 11 and parameters of other components.

When the display is working, through the control of the automatic brightness adjustment circuit of the display, the display can be automatically adjusted as the brightness of the external environment changes, so that the user can adapt to the light of the display, thereby protecting the eyes well . The display is generally a liquid crystal display, and may also be a liquid crystal TV or a liquid crystal DVD player.

Claims (10)

1. automatic brightness regulation circuit of display equipment, be used for regulating automatically the brightness of a display, it comprises that one has the voltage regulator circuit of light source detecing element, and it is by described light source detecing element detecting external environment brightness and export a voltage signal with external environment brightness variation; And a pulse width modulating signal produces circuit, is used to receive described voltage signal and exports a pulse width modulating signal that changes with described voltage signal and give the intednsity circuit of described display to control the brightness of described display.

2. automatic brightness regulation circuit of display equipment as claimed in claim 1, it is characterized in that: described voltage regulator circuit also comprises one first resistance, one second resistance, one the 3rd resistance and one first dc power supply terminal, described first dc power supply terminal connects ground connection behind described light source detecing element and described first resistance successively, described light source detecing element and ground connection after the node of described first resistance is connected described second resistance and the 3rd resistance successively.

3. automatic brightness regulation circuit of display equipment as claimed in claim 2 is characterized in that: described first resistance one first electric capacity also in parallel.

4. automatic brightness regulation circuit of display equipment as claimed in claim 1 is characterized in that: described pulse width modulating signal produces circuit and comprises an integrating circuit, is used to receive the voltage signal of described voltage regulator circuit output and produce a triangle wave voltage signal; One comparator circuit is used to receive described triangle wave voltage signal and produces described pulse width modulating signal; And an on-off circuit, be used for described pulse width modulating signal being fed back to described integrating circuit and making it continue to produce described triangle wave voltage signal.

5. automatic brightness regulation circuit of display equipment as claimed in claim 4, it is characterized in that: described integrating circuit comprises one first operational amplifier, one the 4th resistance and one second electric capacity, the anode of described first operational amplifier and negative electrode input end are used to receive the voltage signal of described voltage regulator circuit output, described second electric capacity is connected between the negative electrode input end and output terminal of described first operational amplifier, and the output terminal of described first operational amplifier is connected in the input end of described comparator circuit.

6. automatic brightness regulation circuit of display equipment as claimed in claim 4, it is characterized in that: described comparator circuit comprises one second operational amplifier, one the 5th resistance, one the 6th resistance and one second dc power supply terminal, the negative electrode input end of described second operational amplifier is used to receive the triangle wave voltage signal of described integrating circuit output, the anode input end of described second operational amplifier is connected in the output terminal of described second operational amplifier by described the 5th resistance, described second dc power supply terminal is connected in the anode input end of described second operational amplifier by described the 6th resistance, and the output terminal of described second operational amplifier connects the intednsity circuit of described on-off circuit and described display.

7. automatic brightness regulation circuit of display equipment as claimed in claim 6 is characterized in that: described comparator circuit also comprises one the 3rd electric capacity, and described second dc power supply terminal connects ground connection behind described the 3rd electric capacity.

8. automatic brightness regulation circuit of display equipment as claimed in claim 5, it is characterized in that: described on-off circuit comprises one the 7th resistance, one the 8th resistance and a transistor, the described pulse width modulating signal that described comparator circuit produces exports described transistorized base stage to by described the 7th resistance, described transistorized grounded emitter, described transistorized collector are connected in the negative electrode input end of first operational amplifier of described integrating circuit by described the 8th resistance.

9. automatic brightness regulation circuit of display equipment as claimed in claim 1 is characterized in that: described light source detecing element is a photoresistance.

10. automatic brightness regulation circuit of display equipment as claimed in claim 1 is characterized in that: described display is a LCD.

Images