Adjustable semiconductor laser constant current driving circuit

Abstract

The invention relates to the technical field of semiconductor laser driving circuits. The invention provides an adjustable semiconductor laser constant current driving circuit which comprises a microcontroller, a DC / DC voltage reduction module, a semiconductor laser and a current regulation and control module. The microcontroller is connected with an enabling end of the DC / DC voltage reduction module, an input end of the DC / DC voltage reduction module is connected with an external power supply, an output end is connected with a positive electrode of the semiconductor laser, a negative electrode of the semiconductor laser is connected with the current regulation and control module, and the current regulation and control module is connected with an ADC sampling interface of the microcontroller. The microcontroller is connected with a digital-analog conversion module, and the output end of the digital-analog conversion module is connected to the feedback end of the DC / DC voltage reduction module through a current regulation and control module; and the microcontroller is also connected with a communication module for exchanging data with external equipment. Through the integrated communication and closed-loop control architecture, the controllability and system integration capability of the driving circuit are improved, and high-precision adjustable output of the driving current of the semiconductor laser is realized.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor laser drive circuits, and in particular to an adjustable semiconductor laser constant current drive circuit. Background Art

[0002] Semiconductor lasers, characterized by high efficiency, miniaturization, and excellent modulation capabilities, are widely used in optical communications, lidar, medical diagnosis, and industrial processing. The luminous intensity of semiconductor lasers is highly sensitive to changes in the driving current. Current fluctuations can lead to unstable output power, center wavelength drift, and even device damage. Therefore, their operating current must be precisely controlled through a constant current method. Achieving stable constant current output depends on the structural design and regulation capabilities of the driving circuit, particularly in terms of control accuracy and dynamic response, which directly determine the effectiveness of current regulation.

[0003] Existing constant current drive circuits mostly use an open-loop structure composed of current-limiting resistors or linear current stabilization devices. Although they have the advantages of simple circuit structure and low implementation cost, the adjustment method relies on static parameter configuration, and the adjustment accuracy and dynamic response capability are limited, making it difficult to adapt to complex working conditions such as load changes or power supply fluctuations. Some improved constant current circuits have introduced current sampling and feedback adjustment functions, but their target currents are usually statically set by means of resistors, transistors, etc., and lack a programmable setting mechanism. The feedback adjustment process cannot be flexibly adjusted according to the operating status, making it difficult to achieve a high-resolution, closed-loop updateable control mechanism. At the system integration level, most existing drive circuits are not equipped with communication interfaces and cannot exchange data and transmit parameters with external control units. This limitation is particularly prominent in complex application environments such as multi-laser arrays, automated maintenance systems, or modular intelligent devices.

[0004] In summary, the existing semiconductor laser constant current drive circuit lacks a programmable control mechanism based on dynamic adjustment of the operating status, which makes it difficult to meet the needs of flexible adjustment and integrated control of the output current in complex application scenarios. It is urgent to propose a constant current drive circuit with programmable target current adjustment function and data interaction capability. Summary of the Invention

[0005] The object of the present invention is to provide an adjustable constant current drive circuit for a semiconductor laser in view of the above-mentioned deficiencies in the prior art, so as to solve the problem that the circuit in the prior art lacks a programmable control mechanism for current regulation.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: The present application provides an adjustable semiconductor laser constant current drive circuit, comprising a microcontroller, a DC / DC buck module, a semiconductor laser, and a current control module. The microcontroller is connected to the enable terminal of the DC / DC buck module, the input terminal of the DC / DC buck module is connected to an external power supply, and the output terminal is connected to the positive electrode of the semiconductor laser, the negative electrode of the semiconductor laser is connected to the current control module, and the current control module is connected to the ADC sampling interface of the microcontroller. The microcontroller is also connected to a digital-to-analog conversion module, the output terminal of the digital-to-analog conversion module is connected to the feedback terminal of the DC / DC buck module through the current control module; the microcontroller is also connected to a communication module for establishing stable data exchange with external devices or other circuit modules.

[0007] Based on the operating characteristics of semiconductor lasers, such as high sensitivity to drive current and amplification of small fluctuations, this invention constructs a closed-loop constant current drive link of "communication setting - digital-to-analog conversion - current feedback - error correction". It innovatively introduces a "soft adjustable + hard feedback" dual-path control mechanism to achieve precise regulation and stable maintenance of the semiconductor laser drive current. The communication module serves as the input channel, transmitting the setting instructions to the microcontroller through the bus to complete the injection of the current setting value; the digital-to-analog conversion module converts the setting instructions into a control voltage, driving the DC / DC buck module to adjust the voltage output, achieving soft adjustable control; the current control module and the microcontroller's ADC sampling interface form a detection path, monitoring the actual current value in real time and completing hard feedback; the microcontroller, as the closed-loop core, continuously calculates the deviation between the current setting value and the actual value, and dynamically updates the control voltage accordingly. This constant current drive system has the combined advantages of fast response speed, flexible setting, and high adjustment accuracy. It can effectively ensure the stable output and long-term reliable operation of the semiconductor laser, and meet the integration requirements of multi-node laser systems for dynamic and consistent performance.

[0008] Furthermore, the digital-to-analog conversion module is connected to the microcontroller via an I²C serial communication interface, which facilitates precise multi-byte configuration through timing control and enables stable transmission of setting instructions in electromagnetic interference environments, improving the resolution and consistency of the target current setting process.

[0009] Furthermore, the output voltage of the digital-to-analog conversion module corresponds to a preset target drive current, which is set to a value that matches the current response characteristics of the semiconductor laser under different operating conditions. This precise matching to the needs of the semiconductor laser helps to accurately and stably control the operating point near the threshold current, reducing the risk of output power drift and improving its luminous efficiency and spectral stability.

[0010] Furthermore, the communication module is provided with a CAN bus communication interface, the D pin of the communication module is connected to the CAN_TX pin of the microcontroller, and the R pin of the communication module is connected to the CAN_RX pin of the microcontroller.

[0011] Furthermore, the communication module supports a CAN bus communication rate of up to 1Mbps. This communication rate ensures the real-time and consistency of the constant current control link, ensuring that control commands can be issued in real time and responding to current offset requirements caused by semiconductor laser aging or thermal drift, thereby improving adaptive setting capabilities.

[0012] Furthermore, after receiving control instructions forwarded by the communication module, the microcontroller writes the corresponding digital control data to the digital-to-analog conversion module, updating the value of the module's internal output register and dynamically adjusting the output voltage. This mechanism enables real-time adjustment of the semiconductor laser drive current based on the upper control system, facilitating integrated deployment within multi-module collaborative or centrally managed system architectures.

[0013] Furthermore, the current control module includes a first operational amplifier, a second operational amplifier, a first capacitor, a second capacitor, a first resistor, a second resistor, a third resistor, and a fourth resistor; the non-inverting input of the first operational amplifier is connected to the first capacitor and the first resistor, and to the negative electrode of the semiconductor laser; the reverse input of the first operational amplifier is connected to the second resistor and the third resistor; the third resistor is connected to the output of the first operational amplifier; and the output of the first operational amplifier is connected to the ADC sampling interface of the microcontroller; the non-inverting input of the second operational amplifier is connected to the second capacitor and the fourth resistor; the output of the digital-to-analog conversion module is connected to the non-inverting input of the second operational amplifier via the fourth resistor; the reverse input of the second operational amplifier is connected to its output; and the output of the second operational amplifier is connected to the feedback terminal of the DC / DC buck module. This structure constructs a current sampling and feedback control path through the operational amplifier, achieving stable output and precise regulation of the drive current.

[0014] Furthermore, the first resistor is connected in series between the cathode of the semiconductor laser and the ground, and is connected to the second resistor, for generating a detection voltage signal for the current flowing through the semiconductor laser.

[0015] Furthermore, the DC / DC buck module dynamically adjusts the duty cycle of the internal PWM control signal according to the voltage received at its feedback terminal to change the output voltage and achieve stable control of the semiconductor laser drive current.

[0016] Furthermore, the first resistor is a high-power, high-precision milliohm-level resistor, and the gain of the first operational amplifier is set by the second and third resistors connected to its input terminals. This configuration facilitates stable acquisition of voltage signals corresponding to small current changes. The milliohm-level first resistor meets the required detection sensitivity for small changes in laser drive current, improving the system's responsiveness to current disturbances and avoiding unnecessary jumps in output power.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) This application constructs a closed-loop constant current control system with flexible settings as the starting point, voltage control as the intermediary, real-time sampling as the feedback, and error correction as the core logic, which can effectively meet the operating requirements of semiconductor lasers for high precision, fast response and small fluctuation tolerance of driving current. By taking the microcontroller as the control center, the communication module, digital-to-analog conversion module, DC / DC buck module and current control module are coordinated with it to form a complete link, so that the target driving current has the ability to respond in real time, automatically correct and finely control, thus breaking through the control lag, setting rigidity and feedback separation caused by relying on static components and manual settings in traditional constant current driving solutions. This link not only improves the output stability and response consistency of semiconductor lasers under complex working conditions, but also enhances the system's ability to adapt to operating environment disturbances and device characteristic changes.

[0018] (2) This application adopts a modular control system structure. The communication module supports standard bus protocol connection, which can incorporate multiple semiconductor laser drive units into a unified control architecture to achieve multi-node access and centralized management. It has good scalability and system adaptability and is suitable for parallel driving, regional control and integrated deployment scenarios of complex systems of semiconductor lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of an adjustable semiconductor laser constant current drive circuit provided by the present invention; Figure 2 for Figure 1 Pin connection diagram of the chip used in the microcontroller; Figure 3 for Figure 1 Pin connection diagram of the chip used in the digital-to-analog conversion module; Figure 4 for Figure 1 Pin connection diagram of the chip used in the DC / DC step-down module; Figure 5 for Figure 1 Pin connection diagram of the chip used in the communication module.

[0020] Icon: 1-microcontroller; 2-DC / DC step-down module; 3-semiconductor laser; 4-current control module; 5-digital-to-analog conversion module; 6-communication module. DETAILED DESCRIPTION

[0021] In order to make the implementation process of the present invention clearer, it will be described in detail below with reference to the accompanying drawings.

[0022] Example 1: The present invention provides an adjustable semiconductor laser constant current drive circuit, such as Figure 1 As shown, it includes a microcontroller 1, a DC / DC buck module 2, a semiconductor laser 3, and a current control module 4. The microcontroller 1 is connected to the enable terminal of the DC / DC buck module 2. The input terminal of the DC / DC buck module 2 is connected to an external power supply, and the output terminal is connected to the positive electrode of the semiconductor laser 3. The negative electrode of the semiconductor laser 3 is connected to the current control module 4, and the current control module 4 is connected to the ADC sampling interface of the microcontroller 1. The microcontroller 1 is connected to a digital-to-analog conversion module 5, and the output terminal of the digital-to-analog conversion module 5 is connected to the feedback terminal of the DC / DC buck module 2 through the current control module 4. The microcontroller 1 is also connected to a communication module 6 for establishing stable data exchange with external devices or other circuit modules.

[0023] Semiconductor laser 3 is highly sensitive to variations in drive current. The relationship between its optical output power and input current is bounded by a threshold current: when the input current is below the threshold current, the relationship exhibits a nonlinear relationship (with a low slope). Above the threshold current, the relationship enters a linear gain region. Within this linear gain region, the optical output power and input current are approximately directly proportional. Small current fluctuations are amplified into significant optical power drift, leading to wavelength instability and device lifetime degradation. In practical applications, this high-gain characteristic of the linear region is particularly pronounced in high-load scenarios such as multiple lasers in parallel and high-power continuous output. Current control errors can trigger cascading effects, including output power fluctuations, spectral broadening, and the risk of thermal runaway. Therefore, the drive system of semiconductor laser 3 must possess high-resolution current setting capabilities, real-time error correction, and fast-response dynamic control performance. This embodiment systematically optimizes the drive path based on these control requirements and operating characteristics, constructing a modular closed-loop control architecture centered on communication settings, fine voltage regulation, real-time sampling, and dynamic feedback to ensure that the drive current is stably maintained at the target set value within the critical linear operating region.

[0024] The microcontroller 1 is used to perform core control of the constant current drive process, and preferably uses an STM32F042F6P6 chip. The chip integrates a 12-bit analog-to-digital conversion module and a controller area network communication interface. Figure 2As shown, pins PA5 and PA6 are configured for I²C communication, connecting to the clock and data lines of digital-to-analog conversion module 5, respectively, for writing digital control data to the module. Pin PA0 is connected to the enable pin of DC / DC buck module 2, controlling the on / off switching of the output voltage of DC / DC buck module 2. Pin ADC_IN1 is an ADC sampling interface with analog-to-digital conversion capabilities, converting analog quantities into digital quantities. This ADC sampling interface is connected to the output of current control module 4 and is used to detect the current flowing through semiconductor laser 3 in real time. Based on the sampling results, microcontroller 1 can sense changes in optical power or thermal offsets that may be caused by small current fluctuations, and dynamically adjust voltage settings in the subsequent control process, achieving highly sensitive regulation of the drive current.

[0025] The digital-to-analog conversion module 5 is connected to the microcontroller 1 via an I²C serial communication interface. Figure 3 As shown, the digital-to-analog conversion module 5 includes a digital-to-analog conversion chip. This chip preferably uses the DAC8571, which has 16-bit conversion resolution and supports I²C bus communication in standard mode (100kbps) and fast mode (400kbps). It also features an address pin configuration function, which sets the 7-bit I²C device address by configuring the level (high / low) of the A0 pin, thereby enabling multi-device identification on the bus. For example, when the A0 pin is configured to a low level, its 7-bit address can be represented as 1001100 (binary); when the A0 pin is configured to a high level, its 7-bit address can be represented as 1001110 (binary). The SCL pin is the clock line, connected to the PA5 pin of the microcontroller 1, and the SDA pin is the data line, connected to the PA6 pin of the microcontroller 1. This chip is suitable for 3.3V or 5V power supply systems, with a supply voltage range of 2.7V-5.5V. Its VOUT pin outputs a voltage signal, suitable for connection to nodes with high input impedance in the feedback control path. In this embodiment, the voltage output terminal of the digital-to-analog conversion module 5 is connected to the current control module 4 and indirectly acts on the feedback terminal of the DC / DC buck module 2. Its output voltage is used to adjust the drive current of the semiconductor laser 3. The target drive current is set based on the current response characteristics of the semiconductor laser 3 under different operating conditions, with matching and dynamic properties. Setting different voltage output values ​​according to specific working requirements helps achieve precise drive and avoid optical power fluctuations, wavelength drift, or device performance degradation caused by current mismatch.

[0026] The DC / DC step-down module 2 includes a DC / DC step-down chip, preferably LM5116MHX, such as Figure 4As shown in the figure, this chip supports a maximum operating frequency of 1MHz and a maximum output current of 20A. It integrates multiple functions, including overcurrent protection, overtemperature protection, undervoltage lockout, and soft-start, making it suitable for high-reliability power supply scenarios. Its EN pin is the enable pin and uses level-triggered control, meaning it enters normal operation mode when the voltage is above 3.3V. The DC / DC buck chip is controlled by a high-level output from the microcontroller 1 to the enable pin. The chip's VIN pin connects to an external power supply, while the VOUT pin outputs a stepped-down voltage signal, which serves as the power source for the semiconductor laser 3 and is connected to its positive terminal. The negative terminal of the semiconductor laser 3 is connected to ground through the current control module 4, forming a complete current path. The FB pin serves as the feedback input and is connected to the voltage output of the digital-to-analog converter module 5. When the microcontroller 1 sets a new target drive current, the digital-to-analog converter module 5 outputs a corresponding analog voltage signal, which acts on the FB pin and participates in the chip's internal feedback control loop. By comparing the FB pin voltage with an internal reference voltage, the chip adjusts the error amplifier output, dynamically adjusting the duty cycle of the pulse-width modulation (PWM) controller and controlling the power transistor's on-time, enabling real-time regulation of the DC / DC step-down output. This regulation mechanism ensures that the output voltage precisely follows the set value, thereby stabilizing the drive current flowing through semiconductor laser 3 and achieving indirect closed-loop regulation of the voltage-controlled drive current.

[0027] The LM5116 chip used in the DC / DC buck module 2 in this embodiment has a built-in periodic overcurrent protection mechanism, which helps to protect the semiconductor laser 3 from damage in sudden situations such as communication failure or control abnormality. The chip constructs a current detection path through its CS pin and CSG pin, and sets a detection resistor in series between the source of the low-side power tube and the ground for real-time monitoring of the output current. When the current flowing through the detection resistor causes the voltage across it to exceed the overcurrent threshold set inside the chip, the LM5116 chip will forcibly shut down the power switch during the current PWM switching cycle, terminating the conduction process, thereby limiting the output current from continuing to rise. If the overcurrent state persists, the chip will enter the shutdown protection state and automatically restart after the current returns to normal. This hardware-level overcurrent protection mechanism does not require intervention from the microcontroller 1, has strong real-time performance and fast response speed, and can effectively prevent the semiconductor laser 3 from overcurrent shocks caused by output short circuits, load mutations, etc., thereby improving the safety and reliability of system operation.

[0028] Considering that the semiconductor laser 3 is highly sensitive to changes in the driving current, and is particularly susceptible to voltage fluctuations under conditions such as parallel operation, high power, and continuous output, this embodiment selects the LM5116MHX chip as the core component of the DC / DC buck module 2 because it has excellent feedback optimization capabilities. The chip supports external compensation networks and feedforward mechanisms to further enhance dynamic response performance. Its COMP pin is connected to a capacitor-resistor network, which can set the zero-pole position of the feedback system, adjust the loop gain and phase margin, and maintain stable output when the load changes. The RAMP pin injects a slope compensation signal, which, combined with the voltage feedforward path, can improve the system's response speed to voltage disturbances and load step changes and shorten the steady-state recovery time. The above characteristics enable the chip to exhibit better current regulation accuracy and dynamic stability when driving the highly sensitive semiconductor laser 3, meeting the stringent requirements of the semiconductor laser 3 for low noise, fast adjustment, and high consistency.

[0029] The microcontroller 1 is connected to a communication module 6, which includes a controller area network (CAN) bus communication chip for data exchange with an external control system. The TJA1050 chip is preferably used, as it supports a differential signal transmission rate of up to 1 Mbps, has strong anti-interference capabilities, accurate logic level matching, and short-circuit self-recovery characteristics, and is suitable for data communication requirements with high real-time performance and high reliability in industrial environments. Figure 5 As shown, the TJA1050 chip's D pin (TXD function) and R pin (RXD function) are connected to the CAN_TX and CAN_RX pins of microcontroller 1, respectively, enabling bidirectional data transmission. The CANH and CANL pins are connected to the differential signal lines of the CAN bus, with parallel termination resistors at both ends to suppress signal reflections and improve bus integrity. Control commands are transmitted via the CAN bus to communication module 6. After completing differential signal conversion and protocol parsing, the communication chip sends valid data to microcontroller 1. Microcontroller 1 integrates a CAN controller unit, and registers are used to configure the communication rate, receive filtering rules, and buffer parameters to ensure stable and reliable communication. Depending on the communication frequency and system configuration, microcontroller 1 can receive commands through an interrupt response mechanism or direct memory access (DMA) mode. The interrupt response mechanism, with its fast triggering and priority determination capabilities, is suitable for low-frequency update scenarios. The DMA mode is suitable for high-frequency communication needs and can complete data transfer without interrupting the main program execution, reducing the core load and improving the overall communication efficiency of the system.

[0030] The response relationship between the output optical power and the drive current of the semiconductor laser 3 is highly sensitive to changes in ambient temperature. Under continuous operation or high power density conditions, the internal junction temperature of the semiconductor laser 3 rises, which may cause the threshold current to change, the emission wavelength to shift, and the quantum efficiency to decrease. Without current compensation adjustment, problems such as output power fluctuation, spectral drift, and even thermal runaway are prone to occur. Therefore, this embodiment introduces a temperature compensation mechanism based on the microcontroller 1, establishing a closed-loop control strategy that automatically corrects the drive current as the temperature changes, so as to maintain the semiconductor laser 3 operating within the set parameter range.

[0031] Specifically, the microcontroller 1 executes the compensation control process at a fixed period, typically set between 100 and 500 milliseconds to balance regulation response speed and control stability. During each control cycle, the microcontroller 1 collects real-time temperature sensor measurements and calculates a corrected target drive current value based on an internally pre-set temperature-current model. This model sets a compensation slope based on the device characteristics of the semiconductor laser 3, typically adjusting the compensation slope by 0.05 mA to 0.2 mA per degree Celsius to ensure that temperature changes do not cause undesirable current deviations. The microcontroller 1 then converts the corrected target drive current value into digital control data and writes it to the digital-to-analog converter module 5 via a serial communication interface, updating its output register contents. The digital-to-analog converter module 5 outputs a corresponding analog voltage, which serves as the input signal for the current control module 4. This analog voltage is connected to the feedback terminal of the DC / DC step-down module 2, thereby enabling dynamic regulation of the drive current. This periodic temperature compensation mechanism maintains the stability of the drive current of the semiconductor laser 3 under fluctuating ambient temperature conditions, reducing output offset caused by temperature variations. It is suitable for complex applications requiring long-term operation or high reliability requirements.

[0032] This embodiment constructs a complete closed-loop control path for regulating the drive current of semiconductor laser 3, achieving constant current control and regulation of semiconductor laser 3. An external control system sends control instructions to communication module 6 via the CAN bus. After receiving and parsing the instructions, microcontroller 1 extracts the target drive current setting value, converts it into digital control data according to a preset format, and writes it to digital-to-analog conversion module 5 via a serial communication interface. Based on the control data, digital-to-analog conversion module 5 outputs a linear and stable analog voltage signal. This voltage signal serves as the input to the feedback pin of DC / DC buck module 2 and participates in the control process of its internal error amplifier, thereby changing the PWM duty cycle and dynamically adjusting the output voltage at VOUT. The voltage signal regulated by DC / DC buck module 2 serves as the drive voltage and is applied to the positive terminal of semiconductor laser 3. The negative terminal of semiconductor laser 3 is connected to current control module 4 and grounded, forming a stable drive current path. Current control module 4 also detects the actual operating current and transmits the detection result as an analog voltage to the ADC pin of microcontroller 1 for sampling. Microcontroller 1 periodically reads the sampled data and compares it with the target drive current setting. If any deviation occurs, it regenerates corrected control data and updates it to digital-to-analog conversion module 5, achieving closed-loop correction of the drive current. Through this process, the system can achieve high-precision drive current setting, rapid response, and real-time stable maintenance under dynamic operating conditions, meeting the stringent requirements of semiconductor laser 3 for low-fluctuation, highly consistent power supply.

[0033] Example 2: In Example 2, Figure 1 As shown, the current control module 4 is further refined based on Example 1 and can be divided into two parts: a current acquisition unit and a feedback control unit. The current acquisition unit includes a first operational amplifier U1, a first capacitor C1, a first resistor R1, a second resistor R2, and a third resistor R3; the feedback control unit includes a second operational amplifier U2, a second capacitor C2, and a fourth resistor R4.

[0034] In the current acquisition unit, the non-inverting input of the first operational amplifier U1 is connected to the first end of the first capacitor C1 and the first end of the first resistor R1. The second end of the first capacitor C1 and the second end of the first resistor R1 are grounded. The inverting input of the first operational amplifier U1 is connected to the first end of the second resistor R2 and the second end of the third resistor R3. The second end of the second resistor R2 is grounded, and the first end of the third resistor R3 is connected to the output of the first operational amplifier U1. The first resistor R1 is connected in series between the cathode of the semiconductor laser 3 and ground, and is used to generate a voltage difference proportional to the drive current across it, which is output as a current detection signal. The output of the first operational amplifier U1 is connected to the ADC sampling interface of the microcontroller 1, enabling real-time detection of the drive current of the semiconductor laser 3. In the feedback control unit, the non-inverting input of the second operational amplifier U2 is connected to the first end of the second capacitor C2 and the first end of the fourth resistor R4. The second end of the second capacitor C2 is grounded, and the second end of the fourth resistor R4 is connected to the output of the digital-to-analog conversion module 5. The inverting input terminal of the second operational amplifier U2 is connected to its output terminal to form a unity gain buffer structure, and the output terminal of the second operational amplifier U2 is connected to the feedback terminal of the DC / DC buck module 2, which is used to stably transmit the regulated voltage to the feedback control path to achieve constant current output control.

[0035] The current control module 4 acquires the drive current of the semiconductor laser 3 in real time through a front-end current acquisition unit and outputs a voltage signal corresponding to the current change to the microcontroller 1. The microcontroller 1 analyzes and processes this signal to generate digital control data for updating the drive current and adjusts the output voltage of the digital-to-analog conversion module 5 accordingly. The control voltage output by the digital-to-analog conversion module 5 is received by the feedback control unit and stably transmitted to the feedback terminal of the DC / DC buck module 2. It is compared with the internal reference voltage of the DC / DC buck chip to adjust its output voltage, indirectly achieving closed-loop control of the drive current of the semiconductor laser 3. The internal reference voltage of the DC / DC buck chip is a fixed value preset at the factory. The feedback control unit is equipped with a unity-gain buffer structure, which provides low output impedance driving capability while maintaining a constant control voltage amplitude. This effectively isolates the impedance coupling between the digital-to-analog conversion module 5 and the internal feedback loop of the DC / DC buck chip, preventing feedback signal distortion or disturbance caused by load fluctuations, temperature drift, or external interference. Compared to directly connecting the digital-to-analog conversion module 5 to the feedback terminal of the DC / DC buck module 2, the provision of a buffer structure enhances the driving capability and noise immunity of the feedback path, improving the response consistency and current output accuracy of the control process under variable operating conditions. This current control mechanism can quickly respond to small changes in the drive current, maintaining the operating stability of the semiconductor laser 3 and effectively improving the accuracy and reliability of current control during system operation.

[0036] In the above structure, the first resistor R1 is connected in series between the cathode of the semiconductor laser 3 and ground, and is used to sample the voltage of the drive current of the semiconductor laser 3. According to Ohm's law, the voltage V1 developed across the first resistor R1 is proportional to the drive current I flowing through the semiconductor laser 3, satisfying the relationship: V1 = I × R1. To achieve high-precision drive current detection without affecting the normal power supply of the semiconductor laser 3, the first resistor R1 is a milliohm-level ultra-low resistance device. This device produces only a small but measurable voltage drop under high operating current conditions, thereby avoiding significant interference with the anode-cathode voltage of the semiconductor laser 3 and ensuring that the semiconductor laser 3 is always in a stable power supply state. Furthermore, since the first resistor R1 will withstand high current for a long time during operation, its power consumption level and resistance stability are directly related to the accuracy of the sampled signal and the response reliability of the constant current control. If the resistor performance fluctuates or has significant temperature drift, it may introduce current misjudgment, resulting in drive current deviation, and affecting the optical power and wavelength stability output by the semiconductor laser 3. Therefore, the first resistor R1 is preferably a high-precision sampling resistor with high power handling capability, low temperature drift coefficient, and resistance deviation less than 1%, so as to ensure the long-term stability of sampling accuracy and feedback regulation, thereby improving the output consistency of the semiconductor laser 3 under different working conditions and the overall control accuracy of the system.

[0037] Because the resistance of first resistor R1 is relatively small, V1 is typically in the millivolt range. To facilitate subsequent acquisition and processing, this voltage signal needs to be amplified. After amplification by first operational amplifier U1, the output voltage is V2. The gain of first operational amplifier U1 is determined by second resistor R2 and third resistor R3 connected to its input terminals, with an amplification factor of (1 + R3 / R2). Therefore, the output voltage V2 of first operational amplifier U1 satisfies the relationship: V2 = (1 + R3 / R2) × V1. Therefore, the output voltage V2 of first operational amplifier U1 and the drive current I of semiconductor laser 3 are related as follows: V2 = (1 + R3 / R2) × R1 × I. After acquiring the amplified voltage V2, microcontroller 1 uses a formula to infer the actual drive current value I based on preset circuit parameters (the values ​​of R1, R2, and R3), enabling real-time assessment of the actual operating status of semiconductor laser 3. Therefore, to ensure the accuracy of the drive current evaluation results, the first operational amplifier U1 should have performance parameters such as low input offset voltage, low noise density and high linearity to avoid introducing additional errors in the signal amplification process, which will cause the drive current sampling value to deviate from the actual current, and then cause control quantity drift or misjudgment in closed-loop feedback regulation, inducing system steady-state offset or even regulation oscillation, affecting the stability of constant current output.

[0038] Based on the above calculation formula, the microcontroller 1 calculates the current actual drive current value from the collected amplified voltage signal and compares it with the system's target drive current setting to calculate the deviation between the two. Based on this deviation, the microcontroller 1 generates a control instruction to adjust the output voltage of the digital-to-analog conversion module 5. This output voltage is applied to the feedback terminal of the DC / DC buck module 2 via the feedback control unit, acting as a control signal to influence its output state, thereby indirectly regulating the drive current of the semiconductor laser 3. Specifically, when the actual drive current value exceeds the target drive current setting, the microcontroller 1 increases the output voltage of the digital-to-analog conversion module 5, causing the feedback voltage detected at the feedback terminal to increase. To bring the feedback voltage back toward its internally set reference voltage, the DC / DC buck chip reduces the duty cycle of the PWM control signal, thereby lowering its output voltage. This reduces the drive current of the semiconductor laser 3 and gradually converges the system toward the target state. Conversely, when the actual drive current value is less than the target drive current setting, the microcontroller 1 reduces the output voltage of the digital-to-analog conversion module 5. When the DC / DC buck chip senses a drop in feedback voltage, it increases the PWM duty cycle, boosting its output voltage and thereby increasing the drive current of semiconductor laser 3. Through this closed-loop regulation process, the system continuously corrects current deviations, keeping the drive current of semiconductor laser 3 stable within the target range, achieving excellent dynamic response and steady-state control.

[0039] The adjustable constant current drive circuit described in this embodiment is suitable for centralized control systems of multiple laser arrays, stable laser driving in industrial automation equipment, and medical imaging devices with high requirements for current control accuracy and operational reliability. It can achieve constant current power supply to different types of semiconductor lasers 3 in complex operating environments, meeting their comprehensive performance requirements in terms of dynamic response, thermal drift compensation, and overcurrent protection.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An adjustable semiconductor laser constant current drive circuit, comprising a microcontroller, a DC / DC step-down module, a semiconductor laser, and a current control module, wherein the microcontroller is connected to an enable terminal of the DC / DC step-down module, the input terminal of the DC / DC step-down module is connected to an external power supply, and the output terminal is connected to the positive electrode of the semiconductor laser, the negative electrode of the semiconductor laser is connected to the current control module, and the current control module is connected to the ADC sampling interface of the microcontroller, characterized in that: The microcontroller is connected to a digital-to-analog conversion module, and the output end of the digital-to-analog conversion module is connected to the feedback end of the DC / DC buck module through the current control module; the microcontroller is also connected to a communication module for establishing stable data exchange with external devices or other circuit modules.

2. The adjustable semiconductor laser constant current drive circuit according to claim 1, characterized in that: The digital-to-analog conversion module is connected to the microcontroller via an I²C serial communication interface.

3. The adjustable semiconductor laser constant current drive circuit according to claim 2, characterized in that: The output voltage of the digital-to-analog conversion module corresponds to a preset target driving current, and the target driving current is set to a value that matches the current response characteristics of the semiconductor laser under different working states.

4. The adjustable semiconductor laser constant current drive circuit according to claim 3, characterized in that: The communication module is provided with a CAN bus communication interface, the D pin of the communication module is connected to the CAN_TX pin of the microcontroller, and the R pin of the communication module is connected to the CAN_RX pin of the microcontroller.

5. The adjustable semiconductor laser constant current drive circuit according to claim 4, characterized in that: The communication module supports a CAN bus communication rate of up to 1 Mbps.

6. The adjustable semiconductor laser constant current drive circuit according to claim 5, characterized in that: After receiving the control instruction forwarded by the communication module, the microcontroller writes the corresponding digital control data to the digital-to-analog conversion module to update the value of the output register inside the digital-to-analog conversion module to achieve dynamic regulation of the output voltage.

7. The adjustable semiconductor laser constant current drive circuit according to claim 6, characterized in that: The current control module includes a first operational amplifier, a second operational amplifier, a first capacitor, a second capacitor, a first resistor, a second resistor, a third resistor, and a fourth resistor; the non-inverting input terminal of the first operational amplifier is connected to the first capacitor and the first resistor, and is connected to the negative electrode of the semiconductor laser, the reverse input terminal of the first operational amplifier is connected to the second resistor and the third resistor, the third resistor is connected to the output terminal of the first operational amplifier, and the output terminal of the first operational amplifier is connected to the ADC sampling interface of the microcontroller; the non-inverting input terminal of the second operational amplifier is connected to the second capacitor and the fourth resistor, the output terminal of the digital-to-analog conversion module is connected to the non-inverting input terminal of the second operational amplifier through the fourth resistor, the reverse input terminal of the second operational amplifier is connected to its output terminal, and the output terminal of the second operational amplifier is connected to the feedback terminal of the DC / DC buck module.

8. The adjustable semiconductor laser constant current driving circuit according to claim 7, characterized in that: The first resistor is connected in series between the cathode of the semiconductor laser and the ground, and is connected to the second resistor, and is used to generate a detection voltage signal for the current flowing through the semiconductor laser.

9. The adjustable semiconductor laser constant current driving circuit according to claim 8, characterized in that: The DC / DC buck module dynamically adjusts the duty cycle of the internal PWM control signal according to the voltage received at its feedback terminal to change the output voltage and achieve stable control of the semiconductor laser drive current.

10. The adjustable semiconductor laser constant current driving circuit according to claim 9, characterized in that: The first resistor is a milliohm-level high-power and high-precision resistor, and the gain of the first operational amplifier is set by the second resistor and the third resistor connected to the input end of the first operational amplifier.

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