LED brightness control circuit and method

Abstract

The embodiment of the invention provides an LED brightness control circuit and method. The circuit comprises a first operational amplifier, a divider resistor, a first adjusting resistor, a second adjusting resistor and a second operational amplifier. According to the LED brightness control circuit, the maximum current point required to be reached by an LED is calibrated, when the calibration of the maximum current point is completed, the reference voltage is determined, then the minimum current, namely the current zero point, is calibrated, and when the maximum current point and the minimum current point are determined, the two points are determined to be a line, and all current nodes in the middle are kept linearly increased or decreased. In this way, it can be guaranteed that the brightness of the LED changes stably, that is, the magnitude of the required current must cover all required change ranges and increase and decrease of high linearity need to be kept, and the absolute stability when the LED emits light is achieved. Therefore, the technical problems of low color saturation, incomplete picture information and low reduction degree of an imaging result obtained in a traditional photographing LED lighting mode are solved.

Description

Technical Field

[0001] The embodiments of the present application belong to the technical field of control circuits, and specifically, relate to an LED brightness control circuit and method. Background Art

[0002] Take the LED power supply lighting when taking a mobile phone video as an example. When shooting the same picture with different brightness, the traditional lighting method ignores the picture information and gives the same lighting brightness to each part of the picture, resulting in the overall shooting effect with low color vividness and inability to fully and accurately reflect the information of the photographed object. In this lighting method, the LED control circuit adjusts the current intensity each time the picture is taken. Once the current intensity is determined, the same current intensity, that is, the lighting brightness, is used for all partitions in the picture. This control method generally uses a fixed voltage power supply and only adjusts the resistance to adjust the LED current intensity each time. This method is low-cost and less difficult to adjust the current, and is easy to implement.

[0003] The biggest disadvantage of the existing technology is that when taking pictures, the LED light brightness remains the same regardless of how the picture information changes, resulting in unsaturated colors and a lack of picture information. For example, blocks with more picture information cannot be fully reflected, and blocks with too high brightness may be too bright and distorted. Therefore, if the technology can be improved, the picture can be divided into zones according to the collected picture information, and the corresponding current intensities can be matched in different zones, so that different areas and different picture information can be illuminated, thereby achieving the best effect of shooting and imaging, that is, color saturation, clear imaging, and high restoration. Summary of the invention

[0004] In order to solve or alleviate the problems in the prior art, in a first aspect, an embodiment of the present application provides an LED brightness control circuit, including: a first operational amplifier, a voltage divider resistor, a first adjustment resistor, a second adjustment resistor, and a second operational amplifier;

[0005] The positive input terminal of the first operational amplifier is connected to a reference voltage, the negative input terminal of the first operational amplifier is connected to a first end of a voltage divider resistor, the voltage of the positive input terminal and the negative input terminal of the first operational amplifier are the same, the second end of the voltage divider resistor is connected to a first end of a first adjustment resistor, and the second end of the first adjustment resistor is grounded;

[0006] The output end of the first operational amplifier is connected to the first end of the first switch, the second end of the first switch is connected to the power supply, and the third end of the first switch is connected to the first end of the voltage divider resistor;

[0007] The maximum resistance end or the minimum resistance end of the voltage divider resistor is connected to the positive input end of the second operational amplifier, the negative input end of the second budget amplifier is connected to the first end of the second adjustment resistor, the first end of the second adjustment resistor is also connected to the third end of the second switch, the output end of the second operational amplifier is connected to the first end of the second switch, and the second end of the second switch is connected to the LED input end;

[0008] The maximum reference current of the LED brightness is adjusted by adjusting the resistance of the second adjusting resistor; and the minimum reference current of the LED brightness is adjusted by adjusting the resistance of the first adjusting resistor.

[0009] As a preferred embodiment of the present application, a current amplification circuit is provided between the second end of the second switch and the LED to amplify the minimum reference current or the maximum reference current.

[0010] As a preferred embodiment of the present application, the voltage-dividing resistor includes a plurality of resistors connected in series.

[0011] An LED brightness control circuit provided by the embodiment of the present application calibrates the maximum current point that the LED needs to reach. When the maximum current point calibration is completed, the reference voltage is determined, and then the minimum current, that is, the current zero point, is calibrated. When the maximum current and minimum current points are determined, the two points determine a line, and all current nodes in the middle will maintain linear increase or decrease. In this way, it can be ensured that the LED brightness maintains a stable change, that is, the current size must cover all the required range of changes and the increase and decrease that need to maintain high linearity, so as to achieve absolute stability when the LED emits light. This solves the technical problems of low color saturation, incomplete picture information and low restoration of the imaging results obtained under the traditional LED lighting method for taking photos.

[0012] In a second aspect, an embodiment of the present application further provides an LED brightness control method, which is executed by an LED brightness control circuit as described in any one of the first aspects.

[0013] Compared with the prior art, the beneficial effects of the LED brightness control method provided by the second aspect are the same as those of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. Some specific embodiments of the present application will be described in detail in an illustrative and non-restrictive manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0015] Figure 1 This is a schematic diagram of the structure of an LED brightness control circuit provided in an embodiment of this specification. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0017] like Figure 1 As shown, in the first aspect, the embodiment of the present application provides an LED brightness control circuit, including: a first operational amplifier 01, a voltage-dividing resistor 02, a first adjustment resistor 03, a second adjustment resistor 06, and a second operational amplifier 05;

[0018] The positive input terminal of the first operational amplifier 01 is connected to a reference voltage, the negative input terminal of the first operational amplifier 01 is connected to a first terminal of a voltage-dividing resistor 02, the voltage of the positive input terminal and the negative input terminal of the first operational amplifier 01 are the same, the second terminal of the voltage-dividing resistor 02 is connected to a first terminal of a first regulating resistor 03, and the second terminal of the first regulating resistor 03 is grounded;

[0019] The output end of the first operational amplifier 01 is connected to the first end of the first switch 04, the second end of the first switch 04 is connected to the power supply, and the third end of the first switch 04 is connected to the first end of the voltage divider resistor 02;

[0020] The maximum resistance end or the minimum resistance end of the voltage-dividing resistor 02 is connected to the positive input end of the second operational amplifier 05, the negative input end of the second budget amplifier is connected to the first end of the second regulating resistor 06, the first end of the second regulating resistor 06 is also connected to the third end of the second switch 07, the output end of the second operational amplifier 05 is connected to the first end of the second switch 07, and the second end of the second switch 07 is connected to the input end of the LED 09;

[0021] The maximum reference current of the brightness of LED 09 is adjusted by adjusting the resistance of the second adjusting resistor 06 ; the minimum reference current of the brightness of LED 09 is adjusted by adjusting the resistance of the first adjusting resistor 03 .

[0022] In a preferred embodiment of the present application, a current amplifying circuit 08 is provided between the second end of the second switch 07 and the LED 09 to amplify the minimum reference current or the maximum reference current.

[0023] In a preferred embodiment of the present application, the voltage-dividing resistor 02 includes a plurality of resistors connected in series.

[0024] In specific applications, there is a specific brightness adjustment interval for each block in each shooting picture according to the needs, that is, the current size change interval of this block that the LED 09 control circuit needs to control. In this interval, all current increases or decreases must be completely linear and stable, otherwise it will cause the LED 09 to emit unstable light. Therefore, this application will make the current size adjustment according to the needs of the input protocol, and perform step-type linear changes. The current rise rate, the linear size change range of the current, and the accuracy when the current is stable can all be adjusted and guaranteed to the greatest extent in this application. Therefore, through the control circuit of the LED 09 brightness provided by this application, for a single-channel LED 09, first calibrate the maximum current point that needs to be reached. When the maximum current point calibration is completed, the reference voltage is determined, and then calibrate the minimum current, that is, the current zero point. When the maximum and minimum current points are determined, the two points determine a line, and all current nodes in the middle will maintain linear increase or decrease.

[0025] First, you need to select the reference voltage for inputting LED 09, such as Figure 1 As shown. The reference voltage generated by other circuits is used as the input of the positive input terminal of the first operational amplifier 01. The positive terminal of the first operational amplifier 01 is equal to the inverting terminal. A voltage divider resistor 02 is connected in series in this control circuit. According to the resistor voltage divider principle, Vref_max is the maximum reference voltage (the voltage corresponding to the maximum current point). The minimum current point selects the gear corresponding to the voltage divider resistor 02, and the corresponding voltage is Vref_min. When the maximum reference current and the minimum reference current corresponding to these two potentials are calibrated, the current points corresponding to all the intermediate voltage gears will change linearly, increasing or decreasing.

[0026] The Vref_max obtained by the output of the first operational amplifier 01 in the previous step is the reference voltage of this step as the positive input terminal of the second operational amplifier 05, according to the formula:

[0027] I max =V ref / R

[0028] It can be obtained that the maximum reference current Imax is calibrated. When Vref is determined, the maximum reference current Imax can be calibrated by adjusting the second adjusting resistor 06 so that the current is calibrated to the maximum current of the LED 09 .

[0029] The Vref_min obtained in the previous step is used as the positive input of the second operational amplifier 05, and the minimum reference current Iref corresponding to Vref_min should be the current corresponding to Vref_min. Assuming that the voltage divider resistor 02 has 0-255 gears for selection, and the maximum reference current is 1020mA, the current corresponding to 01H is 4mA. After the calibration of the maximum current point, the resistance of the second adjustment resistor 06 is fixed, and the calibration of the minimum current uses the first adjustment resistor 03 between the minimum reference voltage Vref_min and the ground terminal in the previous step. The size of the first adjustment resistor 03 can make the minimum reference current point upward or downward until it is calibrated to the minimum unit current. After the minimum and maximum reference currents are determined, the current size of LED 09 at each gear of the voltage divider resistor 02 will maintain absolute linear regulation, thereby ensuring the stable increase and decrease of the light emission of LED 09.

[0030] In specific applications, the captured image is divided into zones, and the current is controlled according to the information of each zone. The areas with concentrated image information need to be set to high brightness. The areas with high brightness of the object itself need to appropriately reduce the LED light-sensitive brightness. The completely black areas in the image need to be set to the lowest brightness to increase the color contrast. That is, after the information of the photographed object is extracted, the image information is cut to obtain the current required for each zone. After the LED control circuit receives the information, it controls the current of each zone, so that different zones have different display brightness, making the overall information richer and fuller.

[0031] When the screen is partitioned and the block information is extracted, the maximum current information required for each block can be known. The screen can be divided into nine areas and the brightness is controlled and adjusted by 9 LEDs respectively. The middle area or the area with richer information needs to achieve the highest brightness, that is, the maximum control current of the LED is the largest, and the maximum current required for some areas will be lower.

[0032] That is, for a fixed block, the required brightness, i.e., the current size, is acquired through image information collection, and the I2C communication protocol is written, which includes: 1) the maximum current required 2) the rate of increase from 0A to the maximum current 3) the duration required to maintain the maximum current. When this information is set through the protocol, for a single LED, within the set time, all gears of the voltage divider resistor correspond to different LED current sizes, and follow a strict linear increase or decrease, and the rate of increase remains unchanged after being set, thereby maintaining a high degree of stability.

[0033] The current calibration method used in the present invention first calibrates the maximum current point, and then calibrates the minimum current based on the accuracy of the maximum current point, so that the two points determine a line. After all brightness codes are input, the current size changes remain highly linear, thereby achieving a stable change in the LED display brightness. The figure below is the test result, and the results show that the current remains absolutely linear under all brightness code changes.

[0034] In a second aspect, an embodiment of the present application further provides an LED brightness control method, which is executed by an LED brightness control circuit as described in any one of the first aspects.

[0035] Compared with the prior art, the beneficial effects of the LED brightness control method provided by the second aspect are the same as those of the first aspect.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An LED brightness control circuit, characterized in that: include: A first operational amplifier, a voltage-dividing resistor, a first adjusting resistor, a second adjusting resistor, and a second operational amplifier; The positive input terminal of the first operational amplifier is connected to a reference voltage, the negative input terminal of the first operational amplifier is connected to a first end of a voltage divider resistor, the voltage of the positive input terminal and the negative input terminal of the first operational amplifier are the same, the second end of the voltage divider resistor is connected to a first end of a first adjustment resistor, and the second end of the first adjustment resistor is grounded; The output end of the first operational amplifier is connected to the first end of the first switch, the second end of the first switch is connected to the power supply, and the third end of the first switch is connected to the first end of the voltage divider resistor; The maximum resistance end or the minimum resistance end of the voltage divider resistor is connected to the positive input end of the second operational amplifier, the negative input end of the second budget amplifier is connected to the first end of the second adjustment resistor, the first end of the second adjustment resistor is also connected to the third end of the second switch, the output end of the second operational amplifier is connected to the first end of the second switch, and the second end of the second switch is connected to the LED input end; The maximum reference current of the LED brightness is adjusted by adjusting the resistance of the second adjusting resistor; and the minimum reference current of the LED brightness is adjusted by adjusting the resistance of the first adjusting resistor.

2. The LED brightness control circuit according to claim 1, characterized in that: A current amplifying circuit is provided between the second end of the second switch and the LED to amplify the minimum reference current or the maximum reference current.

3. The LED brightness control circuit according to claim 1, characterized in that: The voltage-dividing resistor includes a plurality of resistors connected in series.

4. A method for controlling LED brightness, characterized in that: The method is implemented by an LED brightness control circuit as claimed in any one of claims 1 to 3.

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