An Adaptive Adjustment Method for Suppressing PCB Electromigration and a PCB Automatic Control System

Abstract

The present invention discloses an adaptive adjustment method for suppressing PCB electromigration and a PCB automatic control system, which relates to the field of systems for adjusting electrical variables. The method dynamically adjusts current distribution and switches communication modes according to different situations and priorities. During the process of dynamically adjusting current distribution, a control strategy that mainly monitors the change in current density and supplemented by monitoring the change in temperature is used to switch the communication mode, preventing hot spots and electromigration problems caused by abnormal current / temperature, significantly improving the reliability and stability of the PCB and its electronic devices, reducing maintenance costs and repair frequencies, and adapting to variable application environments and load conditions. The present invention can be applied to intelligent electronic devices such as intelligent access control, smart home, smart switches, and smart locks.

Description

Technical Field

[0001] The present invention relates to the field of printed circuits, and particularly to an adaptive adjustment method for suppressing PCB electromigration. Background Art

[0002] Electromigration refers to the phenomenon that metal atoms in metal wires migrate due to the impact of current under high current density. This phenomenon was first discovered by Smol Studeen in the field of microelectronics in the 1950s. With the continuous increase of current density in integrated circuit and PCB designs, the electromigration phenomenon has become more and more serious, which can lead to problems such as wire breakage and signal failure, greatly affecting the reliability and service life of electronic devices.

[0003] Currently, methods such as increasing wire width and reducing current density are commonly used in PCB design to mitigate the impact of electromigration. However, these methods have certain limitations in high-density and miniaturized PCB designs. For example, increasing wire width may be restricted by space, while reducing current density may sacrifice the performance of the device. Therefore, it is necessary to provide a new method to effectively prevent the electromigration phenomenon in PCB layouts, improve the reliability and life of PCBs, and further improve the reliability and life of intelligent electronic devices such as intelligent access control, smart home, smart switches, and smart locks. Summary of the Invention

[0004] The purpose of the present invention is to provide an adaptive adjustment method for suppressing PCB electromigration and a PCB automatic control system, aiming to overcome the above problems existing in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] An adaptive adjustment method for suppressing PCB electromigration includes the following steps:

[0007] Step (1): Embed an adaptive current adjustment module in the main circuit path of the PCB and set up a standby circuit path;

[0008] Step (2): When the main device and the slave device on the PCB exchange data through the first communication method, the adaptive current adjustment module continuously monitors the current density of the main circuit path; if the current density exceeds the preset first threshold, the adaptive current adjustment module immediately dynamically adjusts the current distribution;

[0009] Step (3): After dynamic adjustment, if the current density does not exceed the first threshold, repeat Step (2) for the next round of dynamic current distribution adjustment; if the number of times of dynamically adjusting the current reaches the second threshold and the current density still exceeds the first threshold, then execute Step (4);

[0010] Step (4): The autonomous control module automatically switches the main circuit path to the standby circuit path, and at the same time converts the first communication mode to the second communication mode, enabling the master device and the slave device of the PCB to exchange data through the second communication mode, thereby reducing power consumption; until the communication ends.

[0011] Furthermore, in the above step (4), before switching the main circuit path to the standby circuit path, the main control module activates the electronic components in the standby path through a small current pulse signal to preheat the standby path, enabling it to enter a stable operating state in advance, reducing the delay and performance fluctuations during the switching.

[0012] Furthermore, the above adaptive current regulation module includes a current detection unit, a control unit, and an execution unit; in the above step (2), the current detection unit is responsible for continuously measuring the current density in the circuit and transmitting the data to the control unit; the control unit analyzes the current data and sends an adjustment signal to the execution unit according to a predetermined current regulation strategy; the execution unit adjusts the current distribution in the main circuit path according to the adjustment signal, and at the same time monitors the change of the current density in the main circuit path and feeds back the information to the control unit.

[0013] Furthermore, the above first communication mode is IIC communication, and the second communication mode is INT single - bus communication.

[0014] Furthermore, the above step (4) specifically includes:

[0015] Sub - step (4.1): Initialize and configure the single - bus data line and the controller, adjust the transmission rate, and send a reset pulse for initial communication;

[0016] Sub - step (4.2): Confirm whether the slave device responds to the reset pulse. If the slave device does not respond to the reset pulse, error handling is performed and the communication ends directly; if the slave device responds to the reset pulse, enter sub - step (4.3);

[0017] Sub - step (4.3): Decide whether it is necessary to send a ROM command to select a specific slave device. If not, directly send a function command; if so, send a ROM command to select the slave device.

[0018] Furthermore, the above step (4) specifically further includes:

[0019] Sub - step (4.4): Perform read and write operations of data between the master device and the slave device to complete data exchange;

[0020] Sub - step (4.5): After completing the data read and write operations, the master device sends an end signal to end the communication;

[0021] Sub-step (4.6): Close the INT single-bus communication interface and release resources.

[0022] Furthermore, the above-mentioned execution unit adjusts the current distribution in the resistance and / or voltage adjustment circuit.

[0023] Furthermore, the above-mentioned adaptive current regulation module dynamically adjusts the current distribution, specifically including the following steps:

[0024] S31: Define a cost function C to represent the unevenness of the current distribution; among them, the cost function C is defined as the variance of the current density of all paths:

[0025] ;

[0026] The optimization goal is to minimize the cost function C, that is ;

[0027] Among them, ; J i is the current density of the i-th path, and N is the number of paths;

[0028] Define the following constraint conditions:

[0029] ;

[0030] ;

[0031] ;

[0032] Among them, J max is the first threshold, I total is the total current, and I i is the current of the i-th path;

[0033] S32: Randomly initialize the current I of each path i , and calculate the initial current density J i ;

[0034] S33: Calculate the gradient of the cost function C with respect to each current I i :

[0035] ;

[0036] Among them, is the derivative of the current density J i with respect to the current I i ;

[0037] S34: Update the current of each path according to the gradient descent method:

[0038] ; where η is the learning rate;

[0039] S35. Ensure that the updated current I i new meets the constraint conditions; if not, make corrections;

[0040] S36. Repeat steps S33 - S35 until the cost function C converges to the minimum value.

[0041] Furthermore, the above - mentioned adaptive current regulation module further includes a temperature detection unit. Taking several main circuit paths equipped with current detection units as a monitored area, a temperature detection unit is equipped for this monitored area;

[0042] The above - mentioned step (2) further includes: The temperature detection unit monitors the temperature change of the monitored area in real - time and feeds back the temperature change to the control unit;

[0043] The above - mentioned step (3) further includes: After n times of dynamic adjustment of current distribution, when the current density does not exceed the first threshold, if the temperature change shows an upward trend in a subsequent period of time, then execute step (4); otherwise, execute step (2).

[0044] A PCB automatic control system for implementing any one of the above - mentioned adaptive adjustment methods; this PCB automatic control system includes a main control module, an adaptive current regulation module, and a standby circuit path integrated on the PCB. The above - mentioned adaptive current regulation module is used to dynamically adjust the current distribution according to a predetermined current regulation strategy when the current density of the main circuit path is greater than the first threshold; the above - mentioned main control module is used to enable the main device and the slave device of the PCB to exchange data through the second communication method using the standby current path when the current density is still greater than the first threshold after dynamically adjusting the current distribution.

[0045] Furthermore, the above - mentioned adaptive current regulation module includes a current detection unit, a control unit, and an execution unit; the above - mentioned current detection unit is used to continuously measure the current density in the circuit and transmit the data to the control unit. The control unit analyzes the current data and issues an adjustment signal to the execution unit according to a predetermined current regulation strategy; the execution unit is used to adjust the current distribution in the main circuit path according to the adjustment signal, and at the same time monitor the change of the current density in the main circuit path and feed back the information to the control unit.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] In the present invention, the adaptive current regulation technology effectively addresses the electromigration problem through real - time monitoring and dynamic adjustment of current distribution, greatly improving the reliability and stability of electronic devices, and thus reducing the work and costs of product after - sales maintenance, product recall, or factory repair.

[0048] First, in the method disclosed by the present invention, according to different situations and priorities, by dynamically adjusting the current distribution and switching the communication method, it can effectively address the hot spots and electron migration problems caused by abnormal current density, greatly improve the reliability and stability of the PCB and its electronic devices, reduce the maintenance cost and repair frequency, and adapt to the changing application environment and load conditions. The present invention can be applied to intelligent electronic devices such as intelligent access control, smart home, smart switches, and smart locks.

[0049] Second, in the method disclosed by the present invention, during the process of dynamically adjusting the current distribution, the communication method is switched based on the control strategy of mainly monitoring the current change and supplemented by monitoring the temperature change, preventing the hot spots and electron migration problems caused by abnormal temperature after the dynamic adjustment of the current distribution, and further improving the reliability and stability of the PCB and its electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a flowchart of the method for preventing electron migration in the PCB layout in the present invention.

[0051] Figure 2 It is a simple structural block diagram of the PCB in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0052] The following describes the specific implementation manners of the present invention with reference to the drawings. To fully understand the present invention, many details are described below, but for those skilled in the art, the present invention can be implemented without these details.

[0053] As shown in Figure 1 and Figure 2 an adaptive adjustment method for suppressing electron migration in a PCB includes the following steps:

[0054] Step (1): Embed an adaptive current adjustment module in the main circuit path of the PCB and set up a standby circuit path.

[0055] In the PCB design stage, a multi-layer wiring technology is adopted to set up independent wiring layers for the main circuit path and the standby circuit path respectively, and ensure that there is a certain degree of isolation between them in the physical position to reduce mutual interference. At the same time, an adaptive current adjustment module is integrated at the key nodes of the main circuit path, and the module is packaged in a miniaturized form to save PCB space.

[0056] Preferably, the standby circuit path is optimized to have electrical characteristics similar to those of the main circuit path, including parameters such as impedance and inductance, to ensure that the performance of the circuit does not change significantly when switching to the standby path.

[0057] Step (2): When the master device and the slave device on the PCB exchange data through the first communication method, the adaptive current regulation module continuously monitors the current density of the main circuit path. If the current density exceeds the preset first threshold, the adaptive current regulation module immediately dynamically adjusts the current distribution to achieve dynamic adjustment of the current and ensure that the current is within a safe range.

[0058] Step (3): After dynamic adjustment, if the current density does not exceed the first threshold, repeat Step (2) for the next round of dynamic current distribution adjustment. If the number of times of dynamically adjusting the current reaches the second threshold and the current density still exceeds the first threshold, then execute Step (4).

[0059] Specifically, in a specific embodiment, the adaptive current regulation module immediately dynamically adjusts the current distribution, including the following steps:

[0060] Define that there are N main current paths on the PCB circuit, and the current density of each path is J i (i = 1, 2,..., N). The goal is to adjust the current distribution so that the current density of all paths is as uniform as possible without exceeding the preset first threshold J max .

[0061] Specifically:

[0062] S31. Define a cost function C to represent the non-uniformity degree of the current distribution. Among them, the cost function C can be defined as the variance of the current density of all paths:

[0063] , where is the average current density of all paths:

[0064] , J i is the current density of the i-th path, and N is the number of paths.

[0065] The optimization goal is to minimize the cost function C, that is: .

[0066] Define the constraint conditions as follows:

[0067] The current density J of each path i must be less than or equal to the first threshold J max :

[0068] ;

[0069] The total current I total remains constant: ; where I i is the current of the i-th path;

[0070] The current I of the path i Greater than zero: .

[0071] S32. Randomly initialize the current I of each path i , and calculate the initial current density J i ;

[0072] S33. Calculate the gradient of the cost function C with respect to each current I i :

[0073] ,

[0074] where is the derivative of the current density J i with respect to the current I i and can be obtained by calculating through a specific circuit model;

[0075] S34. Update the current of each path according to the gradient descent method:

[0076] ; where η is the learning rate, controlling the step size;

[0077] S35. Ensure that the updated current I i new meets the constraint conditions. If not, make corrections;

[0078] S36. Repeat steps S33 - S35 until the cost function C converges to the minimum value. Through the above mathematical model, the control unit can automatically calculate and adjust the current distribution to ensure that the current is more evenly distributed in the PCB circuit, thus preventing hot spots and electron migration problems.

[0079] An example is as follows:

[0080] Suppose there are 3 main current paths on the PCB, with initial currents I1 = 2A, I2 = 3A, I3 = 5A respectively, and the total current I total = 10A. The maximum allowable current density J max = 10A / mm 2 .

[0081] Initialization: Calculate the initial current density J i (assuming the cross-sectional areas of the paths are A1 = 1mm 2 , A2 = 1mm 2 , A3 = 1mm 2 ):

[0082] .

[0083] The cost function is calculated as follows:

[0084] .

[0085] Optimization: Adjust the current through the gradient descent method so that J i becomes more uniform without exceeding J max .

[0086] Step (4): The main control module automatically switches the main circuit path to the standby circuit path, and at the same time converts the first communication method to the second communication method to reduce power, enabling the master device and slave device of the PCB to exchange data through the second communication method, thereby reducing power loss; until the communication ends.

[0087] Preferably, before switching the main circuit path to the standby circuit path, the main control module activates the electronic components in the standby path through a small current pulse to preheat the standby path, enabling it to enter the stable working state in advance and reducing the delay and performance fluctuations during switching.

[0088] As Figure 1 and Figure 2 shown, in an embodiment, the above-mentioned adaptive current regulation module includes a current detection unit, a control unit, and an execution unit. In step (2), the current detection unit is responsible for continuously measuring the current density in the circuit and transmitting the data to the control unit; the control unit analyzes the current data and issues an adjustment signal to the execution unit according to a predetermined current regulation strategy; the execution unit adjusts the current distribution in the main circuit path according to the adjustment signal, and at the same time monitors the change of the current density in the main circuit path and feeds back the information to the control unit.

[0089] Among them, the current detection unit includes but is not limited to current sensors. High-precision current sensors, such as Hall effect sensors or current detection amplifiers, are deployed in key main circuit paths (such as important signal lines or data lines). Using differential measurement technology, the current in the main circuit path is monitored in real time, the change of the current is measured, and then according to the change of the current and the cross-sectional area of the main circuit path, the change of the current density is calculated. Among them, the sampling frequency of the current sensor can be dynamically adjusted according to the working frequency of the circuit and the signal change rate to ensure accurate current data acquisition.

[0090] In addition, the analog signal collected from the current sensor can be converted into a digital signal through an analog-to-digital converter (ADC) so that the control unit can perform digital signal processing. Digital signal processing technology can also be used to filter out noise and improve the accuracy and reliability of the measurement. Since the adaptive current regulation module continuously monitors the current density, it can make a quick response even when the circuit working conditions change. This real-time monitoring ensures the timeliness of the current data and provides a basis for dynamic adjustment.

[0091] The intelligent algorithms embedded in the control unit can automatically calculate and adjust the current distribution based on real-time current density data, making the current distribution in the PCB circuit more uniform. This helps prevent hotspots and electromigration problems caused by excessive local current. These algorithms include, but are not limited to, proportional-integral-derivative (PID) control, fuzzy logic control, or model-based predictive control to achieve optimal current regulation.

[0092] Once the control unit determines the required adjustment, the execution unit will respond quickly to adjust the current distribution in the circuit by changing the resistance and / or voltage. The execution unit specifically includes, but is not limited to, adjusting the variable resistor, switching the power path, or adjusting the operating state of the voltage regulator to achieve precise control of the current.

[0093] Of course, the adjusted current density will be monitored again by the current detection unit, and the data will be fed back to the control unit to form a closed-loop control. This closed-loop control ensures the effectiveness of the adjustment measures and makes further adjustments if necessary.

[0094] As Figure 1 and Figure 2 shown, in one embodiment, in addition to the current detection unit, control unit, and execution unit, the above adaptive current regulation module further includes a temperature detection unit. When designing the PCB, several main circuit paths equipped with current detection units are regarded as a monitored area, and a temperature detection unit is equipped for this monitored area. Among them, the temperature detection unit includes, but is not limited to, a temperature sensor, and the analog signal collected from the temperature sensor can be converted into a digital signal through an analog-to-digital converter (ADC) so that the control unit can perform digital signal processing. On this basis, the method for preventing electromigration in the PCB layout further includes:

[0095] In step (2), the temperature detection unit monitors the temperature change of the monitored area in real time and feeds back the temperature change to the control unit;

[0096] In step (3), after n times of dynamically adjusting the current distribution, when the current density does not exceed the first threshold, if the temperature change shows an upward trend in a subsequent period of time (such as 1s - 2s), then step (4) is executed; otherwise, step (2) is executed. Preferably, if the temperature change rises by more than the third threshold (such as 0.3℃ - 0.5℃) in a subsequent period of time (such as 1s - 2s), then step (4) is executed; otherwise, step (2) is executed.

[0097] As Figure 1 and Figure 2As shown, in one embodiment, the first communication method is IIC communication; the second communication method is INT single-bus communication, which has lower power consumption. Step (4) specifically includes:

[0098] Sub-step (4.1): Initialize and configure the single-bus data line and the controller, adjust the transmission rate, and send a reset pulse for initial communication.

[0099] Sub-step (4.2): Confirm whether the slave device responds to the reset pulse. If the slave device does not respond to the reset pulse, perform error handling and directly end the communication; if the slave device responds to the reset pulse, enter sub-step (4.3).

[0100] Sub-step (4.3): Determine whether it is necessary to send a ROM command to select a specific slave device. If not, directly send a function command; if so, send a ROM command to select the slave device.

[0101] Sub-step (4.4): Perform data reading and writing operations between the master device and the slave device to complete data exchange;

[0102] Sub-step (4.5): After completing the data reading and writing operations, the master device sends an end signal to end the communication;

[0103] Sub-step (4.6): Close the INT single-bus communication interface and release resources.

[0104] INT single-bus communication usually has lower power consumption in low-speed and low-power application scenarios. Converting to low-power INT single-bus communication can further prevent hotspots and electromigration problems.

[0105] As Figure 1 and Figure 2 shown, the present invention also discloses and protects a PCB automatic control system for implementing the above adaptive adjustment method, which can be applied to intelligent electronic devices such as intelligent access control, smart home, smart switch, and smart lock. The PCB automatic control system includes a main control module, an adaptive current adjustment module, and a standby circuit path integrated on the PCB. The method for preventing electromigration in the PCB layout is executed through the main control module, the adaptive current adjustment module, and the standby circuit path. Among them, the above adaptive current adjustment module is used to dynamically adjust the current distribution according to a predetermined current adjustment strategy when the current density of the main circuit path is greater than the first threshold; the above main control module is used to use the standby current path to enable the master device and the slave device of the PCB to perform data exchange through the second communication method when the current density is still greater than the first threshold after dynamically adjusting the current distribution.

[0106] Further, the above-mentioned adaptive current regulation module includes a current detection unit, a control unit, and an execution unit; the current detection unit is used to continuously measure the current density in the circuit and transmit the data to the control unit, and the control unit analyzes the current data to issue a regulation signal to the execution unit according to a predetermined current regulation strategy; the execution unit is used to adjust the current distribution in the main circuit path according to the regulation signal, and at the same time monitor the change of the current density in the main circuit path and feedback the information to the control unit.

[0107] The above is only the specific implementation manner of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantive modification made to the present invention using this concept shall fall within the scope of infringement of the protection scope of the present invention.

Claims

1. An adaptive adjustment method for suppressing PCB electron migration, characterized in that: The following steps are involved: Step (1), embedding an adaptive current regulation module in the main circuit path of the PCB and setting a backup circuit path; Step (2), when the master device and the slave device of the PCB exchange data through the first communication mode, the adaptive current regulation module continuously monitors the current density of the main circuit path; If the current density exceeds a preset first threshold, the adaptive current regulation module dynamically adjusts the current distribution; Step (3): after dynamic adjustment, if the current density does not exceed the first threshold, repeat step (2) to perform the next round of dynamic adjustment of current distribution; if the number of dynamic current adjustments reaches the second threshold and the current density still exceeds the first threshold, execute step (4); Step (4), the main control module automatically switches the main circuit path to the backup circuit path, and at the same time converts the first communication mode into the second communication mode, so that the master device and the slave device of the PCB exchange data through the second communication mode, thereby reducing power loss; until the communication is terminated.

2. The method for adaptively adjusting PCB electron migration according to claim 1, characterized in that: The adaptive current regulation module comprises a current detection unit, a control unit and an execution unit; in the step (2), the current detection unit is responsible for continuously measuring the current density in the circuit and transmitting the data to the control unit; the control unit analyzes the current data and sends a regulation signal to the execution unit according to a predetermined current regulation strategy; the execution unit adjusts the current distribution in the main circuit path according to the regulation signal, monitors the change of the current density in the main circuit path, and feeds back the information to the control unit.

3. The adaptive adjustment method for suppressing PCB electron migration according to claim 1, characterized in that: In step (4), before switching the main circuit path to the backup circuit path, the main control module activates the electronic components in the backup path through a small current pulse signal, preheats the backup path, and enables it to enter a stable working state in advance, thereby reducing delays and performance fluctuations during switching.

4. The method for adaptively adjusting PCB electron migration according to claim 3, characterized in that: The step (4) specifically includes: Sub-step (4.1), initializing and configuring the single bus data line and the controller, adjusting the transmission rate, and sending a reset pulse to initialize communication; Sub-step (4.2), confirm whether the slave device responds to the reset pulse. If the slave device does not respond to the reset pulse, error processing is performed and the communication is terminated directly; if the slave device responds to the reset pulse, enter sub-step (4.3); Sub-step (4.3), determine whether it is necessary to send a ROM command to select a specific slave device. If not, directly send a function command; if necessary, send a ROM command to select a slave device.

5. The method for adaptively adjusting PCB electron migration according to claim 4, characterized in that: The step (4) specifically further includes: Sub-step (4.4), performing data reading and writing operations between the master device and the slave device to complete data exchange; Sub-step (4.5), after completing the data read and write operation, the master device sends an end signal to end the communication; Sub-step (4.6), close the INT single bus communication interface to release resources.

6. The adaptive adjustment method for suppressing PCB electron migration according to claim 2, characterized in that: The execution unit adjusts the current distribution in the circuit by changing the resistance and / or the voltage.

7. The adaptive adjustment method for suppressing PCB electron migration according to claim 1, characterized in that: The adaptive current regulation module dynamically adjusts the current distribution, specifically including the following steps: S31. Define a cost function C to represent the unevenness of the current distribution. The cost function C is defined as the variance of the current density of all paths: ； The optimization goal is to minimize the cost function C, that is ; in, ; J i is the current density of the ith path, N is the number of paths; Define the constraints as follows: ； ； ； Among them, J max is the first threshold, I total is the total current, I i is the current of the ith path; S32, randomly initialize the current I of each path i , and calculate the initial current density J i ; S33, calculate the cost function C for each current I i The gradient is: ； in, is the current density J i For current I i The derivative of S34. Update the current of each path according to the gradient descent method: ; where η is the learning rate; S35, ensure the updated current I i new Satisfy the constraints; if not, make corrections; S36, repeat steps S33-S35 until the cost function C converges to a minimum value.

8. The method for adaptively adjusting PCB electron migration suppression according to claim 2, characterized in that: The adaptive current regulation module further includes a temperature detection unit, wherein a plurality of main circuit paths equipped with the current detection unit are used as a monitored area, and the monitored area is equipped with a temperature detection unit; The step (2) further comprises: using a temperature detection unit to monitor the temperature change of the monitored area in real time, and feeding back the temperature change to the control unit; The step (3) further includes: after the current distribution is dynamically adjusted n times, when the current density does not exceed the first threshold, if the temperature change shows an upward trend in a subsequent period of time, executing step (4); otherwise, executing step (2).

9. A PCB automatic control system, characterized in that: Used to implement the adaptive adjustment method as described in any one of claims 1 to 8; the PCB automatic control system includes a main control module integrated in the PCB, an adaptive current adjustment module and a backup circuit path, wherein the adaptive current adjustment module is used to dynamically adjust the current distribution according to a predetermined current adjustment strategy when the current density of the main circuit path is greater than a first threshold; The main control module is used to use the backup current path to allow the master device and the slave device of the PCB to exchange data through the second communication method when the current density is still greater than the first threshold after the current distribution is dynamically adjusted.

10. A PCB automatic control system according to claim 9, characterized in that: The adaptive current regulation module includes a current detection unit, a control unit and an execution unit; the current detection unit is used to continuously measure the current density in the circuit and transmit the data to the control unit, the control unit analyzes the current data and sends a regulation signal to the execution unit according to a predetermined current regulation strategy; the execution unit is used to adjust the current distribution in the main circuit path according to the regulation signal, while monitoring the change of current density in the main circuit path, and feeding back the information to the control unit.

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