According to the two formulas, the current ripple can be reduced by improving the duty ratio, the inductor size and the switching frequency, and the duty ratio is related to the input voltage and the LED property (LED working voltage), so that the current ripple is reduced by selecting a proper direct-current bus voltage and selecting a proper inductor and switching frequency.

According to different direct-current bus voltages, the feedback unit should select a proper voltage division proportion for the voltage division follower circuit, and the differential amplifier circuit should consider the common mode range.

The core of the control unit is a microcontroller, which requires a high main frequency due to the need of generating a high-precision PWM signal, or has a high-precision timer module, otherwise, the output voltage cannot be finely adjusted, and thus fine current control cannot be obtained.

Secondly, the control method and the design key points of the all-digital high-frequency LED constant current drive circuit are explained.

A schematic diagram of a control method of an all-digital high-frequency LED constant current driving circuit is shown in fig. 2, and includes: the device comprises a pulse instruction analysis module, a serial port communication processing module, a current control module, a load parameter identification module and a comprehensive function module.

The pulse instruction analysis module captures the time of the rising edge and the falling edge of an external pulse by adopting the input capture function of a timer and calculates the high-level pulse width; the pulse width is digitally low-pass filtered and converted to a given value for the current control module.

The serial port communication processing module comprises a serial port protocol analysis module and a serial port data generation module, wherein the serial port protocol analysis module and the serial port data generation module generate two functions and a serial port instruction protocol set; the serial port instruction protocol set specifies a plurality of protocol frames consisting of a plurality of bytes and is used for issuing instructions, configuring parameters and monitoring states; the serial port protocol analysis function is used for analyzing the received serial port data according to a serial port instruction protocol set; and a serial port data generation function for generating a data frame conforming to a serial port instruction protocol set.

The current control module comprises a feedforward control module and a feedback control module. The feedforward control module carries out open-loop feedforward control on the basis of the voltage-current parameter table; the feedback control module performs nonlinear PID control based on the current deviation and comprises the technologies of integral amplitude limiting, control quantity filtering, differential signal extraction and the like, so that the control quality is improved; the feedforward control module outputs are overlapped with the feedback control module outputs to obtain the final control output.

The load parameter identification module comprises a voltage-current parameter table and a nonlinear discrete current observer; the voltage-current parameter table is a table for recording the voltage-current relation of the load LED and is stored in a storage unit of the micro-control; the nonlinear discrete current observer obtains the deviation from the actual output by predicting the current output, and the deviation is used for carrying out feedback correction on the parameter table, so that more accurate load data is obtained.

The comprehensive function module comprises an instruction coordination module, a function switching module and a system fault detection and module; the instruction coordination module is used for selecting an output instruction of the pulse instruction analysis module or an output instruction of the serial port protocol analysis module; the function switching module is used for controlling the switching system function to be in a normal output mode or a 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, places the PWM output in a safe state, and cuts off the power supply of the grid drive circuit through an ENA signal.

The voltage-current parameter table should adopt a mode of discrete key points + linear or nonlinear interpolation to obtain higher-precision feedforward and shorter identification time; when performing parameter identification, it should be ensured that the identification curve is monotonous.

The nonlinear discrete current observer is used for setting the feedback correction parameters in a heuristic manner and ensuring the convergence of the feedback correction; when convergence is not guaranteed, the recognition result should indicate an error and exit.

The nonlinear PID control is properly configured according to actual needs; when the requirement on the steady-state precision is high and the transient response speed is not required, the requirement can be met by adopting integral control; when a certain response speed is required, proportional control should be added; when no overshoot in response is required, differential control should be added; setting PID parameters in a segmented mode, and debugging according to actual conditions; the adjustment of the PID parameters is also possible. The resulting output waveform is shown in fig. 3.

In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.