Constant current driving circuit and constant current source circuit based on digital potentiometer

Abstract

The utility model belongs to the technical field of electronic circuits, and discloses a constant current drive circuit and a constant current source circuit based on a digital potentiometer, and the constant current drive circuit based on the digital potentiometer comprises a first operational amplifier, a second operational amplifier and a transistor, the non-inverting input end of the first operational amplifier serves as the input end of the constant-current driving circuit based on the digital potentiometer, the inverting input end of the first operational amplifier is connected with the output end of the second operational amplifier, and the output end of the first operational amplifier is connected with the base electrode of the transistor after being connected with the third resistor in series. The constant current drive circuit based on the digital potentiometer is simple in structure and low in cost, and is used for adjusting the brightness of the load light source according to the output voltage of the digital potentiometer. The utility model is suitable for accurately controlling the brightness of the light source.

Description

Technical Field

[0001] The utility model belongs to the technical field of electronic circuits, and relates to a constant-current drive circuit and a constant-current source circuit based on a digital potentiometer. Background Art

[0002] The tongue and face diagnosis in traditional Chinese medicine is to observe the tongue and face of the patient to obtain relevant information about the patient's tongue and face. The doctor analyzes according to this information combined with his own knowledge and experience to judge the patient's health status and provide diagnosis and treatment suggestions. With the progress of technology, the process of obtaining relevant information about the patient's tongue and face for comprehensive analysis and processing can be done by an image acquisition device with a camera function. By taking pictures of the tongue and face to collect the information in the pictures for intelligent traditional Chinese medicine diagnosis. However, when the image acquisition device takes pictures, it is easily interfered by the light source brightness in the current environment, and cannot objectively record the state of the patient's tongue and face, nor can it be used as an objective basis for other experts' consultations and remote diagnoses.

[0003] In order to ensure that the tongue and face information collected by the image acquisition device is consistent with the original tongue and face information in color and provide reliable data support for subsequent analysis, generally, the light source of the image acquisition device is driven by a drive circuit to adjust the light source brightness. However, the traditional drive circuit mainly uses a mechanical potentiometer or a digital-to-analog converter for driving, and the circuit structure is complex and the cost is relatively high.

[0004] For example, the Chinese invention patent with the authorization announcement number CN 101730353 B discloses a drive circuit for a light source, including a conversion circuit, a transformer, and a resonant capacitor. The conversion circuit includes a first N-type transistor and a second N-type transistor. The drive circuit has a complex structure, increases the hardware volume, and consumes a large amount of power. Therefore, it is of great significance to design a new constant-current drive circuit to provide a reliable light source for image acquisition. Summary of the Utility Model

[0005] The purpose of the utility model is to provide a constant-current drive circuit based on a digital potentiometer to solve the problem of light source control when collecting information through an image acquisition device in traditional Chinese medicine tongue inspection, and to achieve accurate control of the light source brightness.

[0006] Another purpose of the utility model is to provide a constant-current source circuit based on a digital potentiometer.

[0007] The technical solutions adopted by the utility model to achieve the above purposes are as follows:

[0008] A constant-current drive circuit based on a digital potentiometer, the constant-current drive circuit based on a digital potentiometer includes a first operational amplifier, a second operational amplifier, and a transistor;

[0009] The non-inverting input terminal of the first operational amplifier serves as the input terminal of the constant current drive circuit based on the digital potentiometer. The inverting input terminal of the first operational amplifier is connected to the output terminal of the second operational amplifier. The output terminal of the first operational amplifier is connected to the base of the transistor after being serially connected with a third resistor.

[0010] The output terminal of the second operational amplifier is also connected to its own inverting input terminal through a sixth resistor. The inverting input terminal of the second operational amplifier is also grounded after being serially connected with a fifth resistor. The non-inverting input terminal of the second operational amplifier is respectively connected to one end of a third capacitor, one end of a fourth resistor, and the emitter of the transistor. The other end of the third capacitor and the other end of the fourth resistor are both grounded. The collector of the transistor serves as the output terminal of the constant current drive circuit based on the digital potentiometer.

[0011] The negative power supply terminal of the first operational amplifier is grounded. The positive power supply terminal of the first operational amplifier is connected to the power supply, and the positive power supply terminal of the first operational amplifier is grounded after being serially connected with a second capacitor.

[0012] The present invention also provides a constant current source circuit based on a digital potentiometer, which includes an MCU controller, a digital potentiometer having a number of sliding positions and controlling the resistance value digitally, a power supply, and the above-mentioned constant current drive circuit based on the digital potentiometer. The output terminal of the power supply is respectively connected to the MCU controller, the digital potentiometer, and the power supply terminal of the constant current drive circuit based on the digital potentiometer.

[0013] The MCU controller is communicatively connected to the communication interface of an external control host to receive a mediation instruction. The resistance value adjustment signal output terminal of the MCU controller is connected to the digital potentiometer through an SPI interface. After the digital potentiometer receives the resistance value adjustment instruction and adjusts to the corresponding resistance, the adjustment signal output terminal outputs a voltage. After the signal input terminal of the constant current drive circuit based on the digital potentiometer receives the output voltage of the digital potentiometer, it outputs a drive current to drive the load light source.

[0014] As a limitation, the digital potentiometer uses a TPL0202 digital potentiometer. The digital potentiometer includes two linearly tapered digital potentiometers. The sliding terminal of any linearly tapered digital potentiometer serves as the signal output terminal and is connected to the signal input terminal of the constant current drive circuit based on the digital potentiometer. Each linearly tapered digital potentiometer has 256 sliding positions, and each linearly tapered digital potentiometer is configured to be a three-terminal voltage divider or a two-terminal resistor.

[0015] As a second limitation, the MCU controller is connected to the communication interface of the external control host through its own UART interface.

[0016] As a further limitation, the MCU controller uses a circuit with the STM32F302CBT6TR chip as the core.

[0017] As the utility model adopts the above technical solution, compared with the prior art, the technical progress achieved is:

[0018] (1) The constant current driving circuit based on the digital potentiometer of the utility model comprises a first operational amplifier, a second operational amplifier and a transistor, and is a low-cost constant current driving circuit. By connecting the reverse input terminal of the first operational amplifier with the output terminal of the second operational amplifier, in-phase amplification is achieved, the resistance value of the fourth resistor is reduced, and the power consumption of the current sampling of the fourth resistor is reduced; compared with the existing driving circuit, the constant current driving circuit based on the digital potentiometer of the utility model has a simple structure, can achieve the same effect as a complex driving circuit, and has a low cost; in addition, the driving current output by the constant current driving circuit based on the digital potentiometer of the utility model can be adjusted from zero, the adjustment range of the output driving current is large, and more applicable scenarios are available;

[0019] (2) The utility model includes an MCU controller, a digital potentiometer, a constant current drive circuit based on the digital potentiometer, and a power supply. The power supply is used to provide power output for the entire circuit. After receiving the control command from the external host, the MCU controller controls the resistance value of the digital potentiometer. After the digital potentiometer is adjusted to the corresponding resistance value, it can output the corresponding voltage to the constant current drive circuit based on the digital potentiometer. The constant current drive circuit based on the digital potentiometer outputs the corresponding drive current to drive the load light source to emit light. Since the resistance value of the digital potentiometer can be adjusted under the mediation of the MCU controller, the value of the output voltage of the digital potentiometer can be adjusted, and finally the drive current output by the constant current drive circuit based on the digital potentiometer can be controlled and adjusted. The brightness of the load light source can be adjusted under the drive of different drive currents. Therefore, the utility model can realize accurate control of the brightness of the light source when the image acquisition device collects facial and tongue information;

[0020] (3) The utility model adopts a digital potentiometer. The digital potentiometer is set with a number of sliding positions, which solves the problem of mechanical potentiometers causing resistance drift due to mechanical wear. The digital potentiometer is controlled by an MCU controller, which solves the problem that mechanical potentiometers cannot be programmed. In addition, the technologies of the MCU controller and the digital potentiometer are relatively mature, which reduces the cost. The digital potentiometer can connect the high end to the highest voltage and the low end to the lowest voltage to form a voltage divider, thereby controlling the resistance value and dividing the voltage. There is no need to add an external reference source, which reduces the complexity.

[0021] (4) The digital potentiometer in the utility model has the advantages of good stability, convenient operation, low noise, long service life, etc., which further ensures the reliability of the constant current drive circuit based on the digital potentiometer;

[0022] (5) The utility model has a simple structure, low cost and mature technology, and has the possibility of extensive development and application.

[0023] In summary, the utility model is applicable to realizing the accurate control of the light source brightness, ensuring that the tongue surface information collected by the image acquisition device during traditional Chinese medicine tongue inspection is consistent with the original tongue surface information in terms of color. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The following shows the circuit schematic diagram of the constant current drive circuit based on a digital potentiometer in Embodiment 1 of the utility model;

[0025] Figure 2 The following shows the structural block diagram of the constant current source circuit based on a digital potentiometer in Embodiment 2 of the utility model;

[0026] Figure 3 The following shows the circuit schematic diagram of the digital potentiometer and the constant current drive circuit based on the digital potentiometer in Embodiment 2 of the utility model;

[0027] Figure 4 The following shows the circuit principle block diagram of the digital potentiometer in Embodiment 2 of the utility model;

[0028] Figure 5 The following shows the circuit schematic diagram of the voltage divider formed in the digital potentiometer in Embodiment 2 of the utility model;

[0029] Figure 6 The following shows the circuit schematic diagram of the digital potentiometer and the constant current drive circuit based on the digital potentiometer in Embodiment 3 of the utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to better explain the utility model for easy understanding, the following will describe the utility model in detail with reference to the drawings through specific embodiments.

[0031] Embodiment 1

[0032] As Figure 1 shown, this embodiment is a constant current drive circuit based on a digital potentiometer. The constant current drive circuit based on the digital potentiometer includes a first operational amplifier U1, a second operational amplifier U2, and a transistor Q1.

[0033] The non-inverting input terminal of the first operational amplifier U1 serves as the input terminal of the constant current drive circuit based on the digital potentiometer. The inverting input terminal of the first operational amplifier U1 is connected to the output terminal of the second operational amplifier U2. The output terminal of the first operational amplifier U1 is connected to the base of the transistor Q1 after being connected in series with a third resistor R3.

[0034] The output terminal of the second operational amplifier U2 is also connected to its own inverting input terminal through the sixth resistor R6. The inverting input terminal of the second operational amplifier U2 is grounded through the fifth resistor R5 connected in series. The non-inverting input terminal of the second operational amplifier U2 is connected to one end of the third capacitor C3, one end of the fourth resistor R4, and the emitter of the transistor Q1 respectively. The other end of the third capacitor C3 and the other end of the fourth resistor R4 are both grounded. The collector of the transistor Q1 serves as the output terminal of the constant current drive circuit based on the digital potentiometer.

[0035] The negative power supply terminal of the first operational amplifier U1 is grounded. The positive power supply terminal of the first operational amplifier U1 is connected to the power supply, and the positive power supply terminal of the first operational amplifier U1 is grounded through the second capacitor C2 connected in series.

[0036] Among them, the fourth resistor R4 is a current sampling resistor, and the fifth resistor R5 is an amplification feedback resistor.

[0037] Embodiment 2

[0038] As Figure 2 shown, this embodiment is a constant current source circuit based on a digital potentiometer, including an MCU controller, a digital potentiometer with several sliding positions and digitally controlled resistance values, the constant current drive circuit based on the digital potentiometer in Embodiment 1, and a power supply. The output terminal of the power supply is connected to the power supply terminals of the MCU controller, the digital potentiometer, and the constant current drive circuit based on the digital potentiometer respectively.

[0039] In this embodiment, the MCU controller is communicatively connected to an external control host through a communication interface to receive the adjustment instruction of the control host. At the same time, the resistance value adjustment signal output terminal of the MCU controller is connected to the digital potentiometer through an SPI interface. The output terminal of the digital potentiometer is connected to the input terminal of the constant current drive circuit based on the digital potentiometer. The output terminal of the constant current drive circuit based on the digital potentiometer is connected to a load light source. Among them, after the digital potentiometer receives the resistance value adjustment instruction and adjusts to the corresponding resistance, the adjustment signal output terminal outputs a voltage. After the signal input terminal of the constant current drive circuit based on the digital potentiometer receives the output voltage of the digital potentiometer, it outputs a drive current to drive the load light source.

[0040] In this embodiment, the MCU controller adopts a circuit with the STM32F302CBT6TR chip as the core. The MCU controller is connected to the communication interface through its own UART interface, and the communication interface is the interface of the control host.

[0041] The digital potentiometer uses the TPL0202 digital potentiometer. The TPL0202 digital potentiometer has two linearly tapered digital potentiometers (DPOTs), each linearly tapered digital potentiometer has 256 sliding positions, and each linearly tapered digital potentiometer can be configured as a three-terminal potentiometer or a two-terminal resistor. The TPL0202 digital potentiometer allows users or software to digitally control and adjust the resistance value. The TPL0202 digital potentiometer has an internal non-volatile memory (EEPROM) that can store the sliding position for automatic restoration when powered on. The internal registers of the TPL0202 digital potentiometer can be accessed through a digital interface compatible with SPI.

[0042] As Figure 3 shown, the pins of the digital potentiometer are respectively connected to the NSS pin of the SPI interface of the MCU controller and one end of the first resistor R1. The other end of the first resistor R1 is connected to the power supply. The DIN pin of the digital potentiometer is connected to the MOSI pin of the SPI interface of the MCU controller. The SCLK pin of the digital potentiometer is connected to the SCK pin of the SPI interface of the MCU controller; the VDD pin of the digital potentiometer is respectively connected to the power supply and one end of the first capacitor C1. The other end of the first capacitor C1 is grounded and connected to the GND pin of the digital potentiometer; the LA pin of the digital potentiometer is grounded. The WA pin of the digital potentiometer serves as the output end of the digital potentiometer and is connected to the input end of the constant current drive circuit based on the digital potentiometer. The output end of the digital potentiometer outputs the voltage LED1_CTR to the input end of the constant current drive circuit based on the digital potentiometer. The HA pin of the digital potentiometer is connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the power supply.

[0043] In the constant current drive circuit based on the digital potentiometer, the non-inverting input terminal of the first operational amplifier U1 is connected to the output end of the digital potentiometer. The collector of the transistor Q1 is used to connect to the load light source. The output end of the constant current drive circuit based on the digital potentiometer outputs the drive current I_OUT to adjust the brightness of the load light source.

[0044] The working principle of this embodiment is as follows:

[0045] As Figure 4 shown is the circuit principle block diagram of the TPL0202 digital potentiometer. Among them, the high end, namely the HA pin, the low end, namely the LA pin, and the sliding end, namely the WA pin, form a linearly tapered digital potentiometer. The high end, namely the HB pin, the low end, namely the LB pin, and the sliding end, namely the WB pin, form another linearly tapered digital potentiometer. In this embodiment, the digital potentiometer uses a linearly tapered digital potentiometer to control the constant current drive circuit based on the digital potentiometer to adjust the drive current output by the constant current drive circuit based on the digital potentiometer to drive the load light source to emit light.

[0046] When the TPL0202 digital potentiometer uses the three terminals of the HA pin, LA pin, and WA pin, a voltage divider will be generated, as Figure 5 shown. In the figure, V HW is the voltage from the sliding end to the high end, V WL is the voltage from the sliding end to the low end, and V H -V L is the voltage from the high end to the low end. Among them, the voltage V WL from the sliding end to the low end is proportional to D A , and the voltage V WL from the sliding end to the low end is:

[0047]

[0048] Among them, D A ∈[0, 256], D A is an integer and is the position of the sliding tap of the sliding end of the linear gradient digital potentiometer.

[0049] Therefore, when Figure 3 the resistance from the high end to the low end of the TPL0202 digital potentiometer in is 10 KΩ, the output voltage LED1_CTR of the digital potentiometer is:

[0050]

[0051]

[0052] Among them, VCC is the power supply voltage.

[0053] After the output voltage LED1_CTR of the digital potentiometer is output to the input end of the constant current drive circuit based on the digital potentiometer, the output drive current I_OUT of the constant current drive circuit based on the digital potentiometer is:

[0054]

[0055] Among them, the amplification factor N is:

[0056]

[0057] According to the above formula, the relationship between the digital potentiometer and the output drive current I_OUT is:

[0058]

[0059] Therefore, according to the above formula, the user can first determine the resistance values of the second resistor R2, the fifth resistor R5, the sixth resistor R6, and the fourth resistor R4 according to the brightness requirement of the load light source. Then, when in use, the MCU controller receives a control instruction to control the resistance of the digital potentiometer, so that the digital potentiometer adjusts the output voltage to the constant current drive circuit based on the digital potentiometer, realizing the control of the drive current output by the constant current drive circuit based on the digital potentiometer, and adjusting the brightness of the load light source to the required brightness.

[0060] This embodiment can not only be used to accurately control the light source brightness when collecting facial and tongue information through an image acquisition device, but also be used in other scenarios where the light source brightness needs to be adjusted.

[0061] Embodiment 3

[0062] As Figure 6 shown, this embodiment is a constant current source circuit based on a digital potentiometer. The difference from Embodiment 2 is that in this embodiment, two linear gradient digital potentiometers in the TPL0202 digital potentiometer are respectively connected to a constant current drive circuit based on the digital potentiometer, and are used to adjust the brightness of a load light source through two constant current drive circuits based on the digital potentiometer, such as the load light source being a cold light source and a warm light source.

[0063] When only the brightness of one of the load light sources needs to be adjusted, the position of the sliding tap of the sliding end corresponding to the other load light source can be controlled to be zero; when the brightness of both load light sources needs to be adjusted simultaneously, according to the received control instruction, the MCU controller controls the position of the sliding taps of the sliding ends of the two linear gradient digital potentiometers in the digital potentiometer, controls the resistance of the two linear gradient digital potentiometers, and then the digital potentiometer outputs the corresponding voltage to the two constant current drive circuits based on the digital potentiometer. The constant current drive circuits based on the digital potentiometer then output the corresponding drive current to drive the connected load light sources to emit different brightnesses.

[0064] It should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, for those skilled in the art, they can still modify the technical solutions described in the above embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A constant current drive circuit based on a digital potentiometer, characterized in that, The constant current driving circuit based on a digital potentiometer includes a first operational amplifier, a second operational amplifier, and a transistor; The non-inverting input terminal of the first operational amplifier serves as the input terminal of the constant current driving circuit based on the digital potentiometer. The inverting input terminal of the first operational amplifier is connected to the output terminal of the second operational amplifier. The output terminal of the first operational amplifier is connected to the base of the transistor after being serially connected with a third resistor; The output terminal of the second operational amplifier is also connected to its own inverting input terminal through a sixth resistor. The inverting input terminal of the second operational amplifier is also grounded after being serially connected with a fifth resistor. The non-inverting input terminal of the second operational amplifier is respectively connected to one end of a third capacitor, one end of a fourth resistor, and the emitter of the transistor. The other end of the third capacitor and the other end of the fourth resistor are both grounded. The collector of the transistor serves as the output terminal of the constant current driving circuit based on the digital potentiometer; The negative power supply terminal of the first operational amplifier is grounded. The positive power supply terminal of the first operational amplifier is connected to the power supply, and the positive power supply terminal of the first operational amplifier is grounded after being serially connected with a second capacitor.

2. A constant current source circuit based on a digital potentiometer, characterized in that, It includes an MCU controller, a digital potentiometer having a number of sliding positions and digitally controlling the resistance value, a power supply, and the constant current driving circuit based on the digital potentiometer as described in claim 1. The output terminal of the power supply is respectively connected to the power supply terminals of the MCU controller, the digital potentiometer, and the constant current driving circuit based on the digital potentiometer; The MCU controller is communicatively connected to the communication interface of an external control host to receive adjustment instructions. The resistance value adjustment signal output terminal of the MCU controller is connected to the digital potentiometer through an SPI interface. After the digital potentiometer receives the resistance value adjustment instruction and adjusts to the corresponding resistance, the adjustment signal output terminal outputs a voltage. After the signal input terminal of the constant current driving circuit based on the digital potentiometer receives the output voltage of the digital potentiometer, it outputs a driving current to drive the load light source.

3. The constant current source circuit based on a digital potentiometer according to claim 2, wherein The digital potentiometer uses a TPL0202 digital potentiometer. The digital potentiometer includes two linearly tapered digital potentiometers. The sliding terminal of any linearly tapered digital potentiometer serves as the signal output terminal and is connected to the signal input terminal of the constant current driving circuit based on the digital potentiometer. Each linearly tapered digital potentiometer has 256 sliding positions, and each linearly tapered digital potentiometer can be configured as a three-terminal voltage divider or a two-terminal resistor.

4. The constant current source circuit based on a digital potentiometer according to claim 2, wherein The MCU controller is connected to the communication interface of the external control host through its own UART interface.

5. The constant current source circuit based on a digital potentiometer according to claim 4, characterized in that, The MCU controller uses a circuit with the STM32F302CBT6TR chip as the core.

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