A full digital high-frequency LED constant current driving circuit and control method

Abstract

The application provides a full-digital high-frequency LED constant current driving circuit and a control method, which comprises a power unit, a feedback unit and a control unit.The power unit performs energy transmission and conversion in a switching mode of a half-bridge topology, charges and freewheels an inductor, and enables the LED to obtain continuous current.The feedback unit measures a DC bus voltage and an output current of the power unit, and sends the output current to the control unit for processing.The control unit calculates a pair of complementary PWM signals according to an external PWM signal and the output current measured by the feedback unit, and outputs the pair of complementary PWM signals to the power unit to control the power unit to perform energy transmission and conversion and feedback a working state.The power unit is directly controlled by a microcontroller, which greatly improves the flexibility of the algorithm and the controllability of the system, thereby realizing high-frequency, high-precision and wide-range current control, and meeting the requirements of high-frequency short exposure, wide-range precise adjustment occasions such as high-speed machine vision and digital pathology scanning for continuous and adjustable LED driving current and high-frequency non-flickering.

Description

Technical Field

[0001] The present invention relates to the field of electricity, and in particular to a full-digital high-frequency LED constant-current drive circuit and a control method. Background Art

[0002] In recent years, constant-current LED drive technology has matured. However, in applications requiring high-frequency, short-exposure, and wide-range precision adjustment, such as high-speed machine vision and digital pathology scanning, the LED current must not only be constant but also adjustable over a wide range to adjust its brightness. Even microsecond-level exposures, such as those used in high-speed camera capture, must be flicker-free. This places extremely high demands on precise LED current regulation and control: the current must be adjusted continuously and with low ripple across the full range.

[0003] Traditional LED dimming solutions often use constant current source chips or linear dimming technology: constant current source chips can only maintain the current at a fixed value. The microcontroller adjusts the average output current by periodically enabling / disabling it, so it cannot guarantee precise and continuous current when outputting low currents. Linear dimming technology can achieve a more stable current regulation effect, but it has low efficiency, high heat generation, difficulty in high-frequency control, and limited application scenarios. Summary of the Invention

[0004] In view of the defects in the prior art, the object of the present invention is to provide a fully digital high-frequency LED constant current drive circuit and control method.

[0005] According to the present invention, a fully digital high-frequency LED constant current drive circuit is provided, comprising:

[0006] Power unit: uses a half-bridge topology to transmit and convert energy, charging and freewheeling the inductor, so that the LED obtains continuous current;

[0007] Feedback unit: measures the DC bus voltage and the output current of the power unit and sends them to the control unit for processing;

[0008] Control unit: Based on the external PWM signal and the output current measured by the feedback unit, a pair of complementary PWM signals are calculated and output to the power unit, controlling the power unit to perform energy transmission and conversion, and providing feedback on the working status.

[0009] Preferably, the power unit includes:

[0010] Gate drive circuit: converts the pair of complementary PWM signals output by the control unit into a strong signal for driving the field effect transistor;

[0011] Field effect tube half bridge: connecting the gate drive circuit, the DC bus and the LED, driving the LED in a half-bridge topology;

[0012] Current sampling resistor: located at the high end of the power supply;

[0013] The inductor stores energy when the lower arm of the MOSFET half-bridge is turned on, and releases energy in the form of current when the lower arm of the MOSFET half-bridge is turned off, so that the current passing through the LED remains constant throughout the full PWM cycle.

[0014] Preferably, the feedback unit includes:

[0015] A voltage divider follower circuit is connected to the DC bus and the control unit, divides and filters the DC bus through a resistor-capacitor network, and reduces the output impedance of the voltage divider circuit;

[0016] Differential amplifier circuit: connected to the two ends of the sampling resistor and the control unit, amplifying the voltage difference between the two ends of the sampling resistor.

[0017] Preferably, the control unit comprises:

[0018] Microcontroller;

[0019] Input shaping circuit: connected to the microcontroller, filtering and shaping the external PWM signal;

[0020] Communication interface circuit: connecting the microcontroller with an external PC;

[0021] Clock line: connected to the microcontroller to provide a clock signal.

[0022] According to a control method of a full-digital high-frequency LED constant-current drive circuit provided by the present invention, the full-digital high-frequency LED constant-current drive circuit is used to perform the following steps:

[0023] Pulse command parsing step: capturing the external PWM signal and calculating the pulse width of the external PWM signal, and converting it into a control target given value of the constant current control algorithm after digital low-pass filtering;

[0024] Serial communication processing steps: according to the custom communication protocol, parse the received serial data and generate serial data frames that comply with the custom communication protocol;

[0025] Load parameter identification steps: voltage-current parameter table identification based on nonlinear discrete current observer;

[0026] Current control step: performing open-loop feedforward control based on a voltage-current parameter table and performing feedback control based on a current deviation to generate the pair of complementary PWM signals for half-bridge control;

[0027] Comprehensive functional steps: coordinate instructions, switch functions, detect faults and implement protection.

[0028] Preferably, the serial port communication processing step comprises:

[0029] A plurality of protocol frames composed of multiple bytes constitute a serial port instruction protocol set for issuing instructions, configuring parameters, and monitoring states.

[0030] According to the serial port instruction protocol set, the received serial port data is parsed to generate a data frame conforming to the serial port instruction protocol set.

[0031] Preferably, the current control step comprises:

[0032] Feedforward control: calculating open-loop feedforward control PWM duty cycle according to the voltage-current parameter table of the LED;

[0033] Feedback control: performing nonlinear PID control based on current deviation to calculate closed-loop feedback control PWM duty cycle.

[0034] Preferably, the load parameter identification step comprises:

[0035] Recording the voltage-current relationship of the LED to form a voltage-current parameter table, which is stored in the storage unit of the microcontroller;

[0036] Predicting the output current through a nonlinear discrete current observer, and feedback correcting the voltage-current parameters according to the actual current to iteratively calculate the real voltage-current parameter table.

[0037] Preferably, the comprehensive function step comprises:

[0038] Instruction coordination: selecting an external PWM signal or a serial port instruction;

[0039] Function switching: switching the function to normal output mode or load identification mode;

[0040] System fault detection: when the output current exceeds the preset range or the preset time, an overcurrent signal is given, the PWM output is placed in a safe state, and the gate drive circuit power supply is cut off through the ENA signal.

[0041] Compared with the prior art, the present application has the following advantages:

[0042] 1. Relying on a full-digital high-frequency LED constant current driving circuit and control method, current wide range and high precision regulation are realized, ensuring the requirements of continuous adjustable brightness, high-frequency non-flickering of LED light source in precision occasions;

[0043] 2. Compared with linear constant current source, the efficiency, precision, and high-frequency control performance of the power supply are greatly improved, thereby widening the application scenarios;

[0044] 3. The unique power supply control method improves the steady-state accuracy and response speed of current control, and enhances the scalability and flexibility of digital power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0046] Figure 1 This is a structural principle diagram of the fully digital high-frequency LED constant current drive circuit of the present invention;

[0047] Figure 2 This is a schematic diagram of the control method of the all-digital high-frequency LED constant current drive circuit of the present invention;

[0048] Figure 3 This is the output waveform diagram of the LED driving circuit of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0050] The structural principle diagram of a fully digital high-frequency LED constant current drive circuit is as follows: Figure 1 As shown, it includes: a power unit, a feedback unit, and a control unit.

[0051] The power unit is used for energy conversion; specifically, it consists of power tubes Q1 and Q2, an inductor L1, a sampling resistor R1, and a high-speed gate drive circuit. The power tubes Q1 and Q2 are alternately turned on and off to charge and freewheel the inductor L1 in a switching manner, forming a constant current and voltage on the load LED. Furthermore, by changing the conduction time of Q1 and Q2, that is, the duty cycle, the voltage of the load, and thus its current, can be controlled. Furthermore, the current forms a voltage difference on the sampling resistor R1, and the load current can be determined by measuring this voltage difference.

[0052] The feedback unit is used to measure the state quantity; specifically, it consists of a voltage divider follower circuit and a differential amplifier circuit, which respectively measures the DC bus voltage and the voltage across the two sets of current sampling resistors, and sends them to the control unit for processing.

[0053] The control unit, with a microprocessor as its core, receives external signals, such as PWM signals or serial communication signals, configures system parameters, samples the output of the feedback unit, outputs high-precision complementary PWM signals through calculations by an internal algorithm unit, directly controls the power unit for energy transmission and conversion, and feeds back the system status via a serial port. Specifically, it consists of an input shaping circuit, a communication interface circuit, a high-precision clock, and a microcontroller.

[0054] The power unit operates at a relatively high frequency and power, which places high demands on the selection of power transistors Q1 and Q2 and the selection of gate drive circuits. Low-resistance, high-speed power MOSFETs and high-speed, high-drive-capability gate drive circuits should be selected.

[0055] Furthermore, set Q1 and Q2 to be turned on at different times, set the lower tube (Q2) to be turned on when the state is 1, and the conduction time is , the state is 0 when the lower tube is turned off, and the off time is , then the relationship between the conduction state of Q2 and the output voltage and current is as follows Figure 3 As shown; the average voltage across the LED load is set to , set the DC bus voltage to , set the output current ripple , set the inductance to , the duty cycle is defined as , defines the switching frequency ; You can get the relationship: , According to the above two equations, increasing the duty cycle, inductance, and switching frequency can reduce current ripple. The duty cycle is related to the input voltage and LED properties (LED operating voltage). Therefore, choosing a suitable DC bus voltage, inductance, and switching frequency can significantly reduce current ripple.

[0056] In the feedback unit, the voltage follower circuit should select an appropriate voltage division ratio according to the DC bus voltage, and the differential amplifier circuit should consider its common mode range.

[0057] The control unit, whose core is a microcontroller, needs to generate high-precision PWM signals, so it requires a higher main frequency or a high-precision timer module, otherwise it will not be able to finely adjust the output voltage and thus cannot obtain fine current control.

[0058] Second, the control method and design points of the all-digital high-frequency LED constant current drive circuit of the present invention are explained.

[0059] A control method schematic diagram of a fully digital high-frequency LED constant current drive circuit is shown in the figure below: Figure 2As shown, it includes: a pulse instruction parsing module, a serial communication processing module, a current control module, a load parameter identification module, and a comprehensive function module.

[0060] The pulse instruction parsing module uses the input capture function of the timer to capture the moments of the rising and falling edges of the external pulse and calculate the high-level pulse width; the pulse width is converted into a given value of the current control module after digital low-pass filtering.

[0061] The serial port communication processing module includes two major functions: serial port protocol parsing and serial port data generation, and a serial port command protocol set; the serial port command protocol set specifies several protocol frames consisting of multiple bytes for issuing commands, configuring parameters, and status monitoring; the serial port protocol parsing function parses the received serial port data according to the serial port command protocol set; and the serial port data generation function generates data frames that comply with the serial port command protocol set.

[0062] The current control module includes a feedforward control module and a feedback control module. The feedforward control module performs open-loop feedforward control based on a voltage-current parameter table. The feedback control module performs nonlinear PID control based on current deviation and incorporates technologies such as integral limiting, control variable filtering, and differential signal extraction to improve control quality. The output of the feedforward control module is superimposed on the output of the feedback control module to obtain the final control output.

[0063] The load parameter identification module includes a voltage-current parameter table and a nonlinear discrete current observer. The voltage-current parameter table is a table that records the voltage-current relationship of the load LED and is stored in the storage unit of the microcontroller. The nonlinear discrete current observer obtains the deviation from the actual output by predicting the current output, and uses this deviation to feedback correct the parameter table, thereby obtaining more accurate load data.

[0064] The comprehensive functional module includes an instruction coordination module, a function switching module, and a system fault detection and protection module; the instruction coordination module is used to select the output instruction of the pulse instruction parsing module or the output instruction of the serial port protocol parsing module; the function switching module is used to control the switching system function to normal output mode or load identification mode; the system fault detection and protection module records the time when the output current exceeds the set current, judges and gives an overcurrent signal, puts the PWM output into a safe state, and cuts off the power supply of the gate drive circuit through the ENA signal.

[0065] The voltage-current parameter table should adopt the method of discrete key points + linear or nonlinear interpolation to obtain higher-precision feedforward and shorter identification time; when performing parameter identification, the identification curve should be ensured to be monotonic.

[0066] The parameter setting of the feedback correction of the nonlinear discrete current observer should be heuristic and should guarantee the convergence of the feedback correction; when the convergence cannot be guaranteed, the identification result should indicate an error and exit.

[0067] The nonlinear PID control should be properly configured according to actual needs; when high steady-state accuracy is required without requiring transient response speed, integral control can meet the demand; when a certain response speed is required, proportional control should be added; when a response without overshoot is required, differential control should be added; the segmented setting of PID parameters should be debugged according to actual conditions; the adjustment of PID parameters is also the same. The finally obtained output waveform is as shown in Figure 3

[0068] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0069] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict.​

Claims

1. A fully digital high-frequency LED constant current drive circuit, characterized in that: include: Power unit: uses a half-bridge topology to transmit and convert energy, charging and freewheeling the inductor, so that the LED obtains continuous current; Feedback unit: measures the DC bus voltage and the output current of the power unit and sends them to the control unit for processing; Control unit: Based on the external PWM signal and the output current measured by the feedback unit, a pair of complementary PWM signals is calculated and output to the power unit, controlling the power unit to perform energy transmission and conversion, and providing feedback on the working status; The power unit includes: Gate drive circuit: converts the pair of complementary PWM signals output by the control unit into a strong signal for driving the field effect transistor; Field effect tube half bridge: connecting the gate drive circuit, the DC bus and the LED, driving the LED in a half-bridge topology; Current sampling resistor: located at the high end of the power supply; The inductor stores energy when the lower arm of the MOSFET half-bridge is turned on, and releases the energy in the form of current when the lower arm of the MOSFET half-bridge is turned off, so that the current passing through the LED remains constant throughout the full PWM cycle; The feedback unit includes: A voltage divider follower circuit is connected to the DC bus and the control unit, divides and filters the DC bus through a resistor-capacitor network, and reduces the output impedance of the voltage divider circuit; Differential amplifier circuit: connected to the two ends of the sampling resistor and the control unit, amplifying the voltage difference between the two ends of the sampling resistor; The voltage divider follower circuit selects an appropriate voltage divider ratio, and the differential amplifier circuit takes the common mode range into consideration to measure the DC bus voltage and the voltage across the two sets of current sampling resistors, respectively, and sends them to the control unit for processing; The FET half-bridge includes power transistors Q1 and Q2. These transistors alternately conduct, charging and freewheeling the inductor in a switching manner, creating a constant current and voltage across the LED. By varying the conduction time of the power transistors Q1 and Q2, the LED voltage, and thus the LED current, is controlled. The current creates a voltage difference across the current sampling resistor, and measuring this voltage difference yields the LED current. The control unit comprises: Microcontroller; Input shaping circuit: connected to the microcontroller, filtering and shaping the external PWM signal; Communication interface circuit: connecting the microcontroller with an external PC; Clock circuit: connected to the microcontroller to provide a clock signal; Set the power tubes Q1 and Q2 to be turned on at different times. Set the power tube Q2 to be turned on at state 1 and the on time to be t on , the state of power tube Q2 is 0 when it is turned off, and the off time is t off , set the average voltage across the LED load to u led , set the DC bus voltage to u bus , set the output current ripple ΔI, set the inductance size to L, and define the duty cycle as Defining the switching frequency Get relationship: u led =u bus ×D, 2. A control method for a fully digital high-frequency LED constant current drive circuit, characterized in that: The all-digital high-frequency LED constant current drive circuit according to claim 1 is used to perform the following steps: Pulse command parsing step: capturing the external PWM signal and calculating the pulse width of the external PWM signal, and converting it into a control target given value of the constant current control algorithm after digital low-pass filtering; Serial communication processing steps: according to the custom communication protocol, parse the received serial data and generate serial data frames that comply with the custom communication protocol; Load parameter identification steps: voltage-current parameter table identification based on nonlinear discrete current observer; Current control step: performing open-loop feedforward control based on a voltage-current parameter table and performing feedback control based on a current deviation to generate the pair of complementary PWM signals for half-bridge control; Comprehensive functional steps: coordinate instructions, switch functions, detect faults and implement protection.

3. The control method of the full-digital high-frequency LED constant current drive circuit according to claim 2, characterized in that: The serial communication processing steps include: It stipulates that multiple protocol frames consisting of multiple bytes constitute the serial port command protocol set, which is used to issue commands, configure parameters, and monitor status; According to the serial port command protocol set, the received serial port data is parsed and a data frame that complies with the serial port command protocol set is generated.

4. The control method of the full-digital high-frequency LED constant current drive circuit according to claim 2, characterized in that: The current control step includes: Feedforward control: Calculate the open-loop feedforward control PWM duty cycle based on the LED voltage-current parameter table; Feedback control: Perform nonlinear PID control based on current deviation and calculate the closed-loop feedback control PWM duty cycle.

5. The control method of the full-digital high-frequency LED constant current drive circuit according to claim 2, characterized in that: The load parameter identification step includes: Record the voltage-current relationship of the LED to form a voltage-current parameter table, which is stored in the memory unit of the microcontroller; The output current is predicted by a nonlinear discrete current observer, and the voltage-current parameters are feedback-corrected according to the actual current to iteratively calculate the real voltage-current parameter table.

6. The control method of the full-digital high-frequency LED constant current drive circuit according to claim 2, characterized in that: The integrated functional steps include: Command coordination: select external PWM signal or serial port command; Function switching: switch the function to normal output mode or load identification mode; System fault detection: When it is detected that the output current exceeds the preset current range or the preset time, an overcurrent signal is given, the PWM output is placed in a safe state, and the gate drive circuit power supply is cut off through the ENA signal.

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