A micro-current acquisition circuit and method based on capacitance

Abstract

The present invention provides a micro-current acquisition circuit and method based on capacitance in the field of lithium battery pack protection board testing technology. The circuit includes a micro-control unit U1, an analog-to-digital conversion chip U2, a current acquisition module, a switch switching module and a constant current source V; one end of the analog-to-digital conversion chip U2 is connected to the micro-control unit U1, and the other end is connected to the current acquisition module; one end of the switch switching module is connected to the current acquisition module, and the other end is connected to the constant current source V; the micro-control unit U1 is connected to the current acquisition module and the switch switching module respectively. The advantage of the present invention is that the accuracy of micro-current acquisition is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery pack protection board testing, and in particular to a capacitor-based micro-current acquisition circuit and method. Background Art

[0002] After the production of lithium battery packs is completed, the protection board needs to be tested using testing equipment. With the advancement of technology, the testing equipment for protection boards is also developing towards convenience and miniaturization. Since a large number of protection boards need to be tested, frequent charging of the testing equipment is inevitable.

[0003] In order to extend the use time of the test equipment, there are two methods: increasing the battery capacity of the test equipment and reducing power consumption. Increasing the battery capacity is undoubtedly contrary to the development direction of convenience and miniaturization, so the method of reducing power consumption is generally adopted.

[0004] Reducing power consumption means reducing the operating current, static current, sleep current and power-off current. In order to better reduce power consumption, it is necessary to accurately collect the current first. For current collection, the following method is traditionally used: when the current flows through the sampling capacitor Cs, the change in the capacitor voltage within the unit time T is collected, and then the corresponding current is calculated. The calculation formula is as follows:

[0005]

[0006]

[0007] From the above formula, we can see that the final calculated current I in It is closely related to the value of the sampling capacitor Cs. However, in actual use, the capacitance of the sampling capacitor Cs will be affected by factors such as temperature, humidity, dust, vibration, and capacitor aging. If the capacitance has changed, the initial capacitance is still used to calculate the current I in , which will undoubtedly directly affect the accuracy of current acquisition.

[0008] Therefore, how to provide a capacitor-based microcurrent acquisition circuit and method to improve the accuracy of microcurrent acquisition has become a technical problem that needs to be solved urgently. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a capacitor-based microcurrent acquisition circuit and method to improve the accuracy of microcurrent acquisition.

[0010] In a first aspect, the present invention provides a capacitor-based micro-current acquisition circuit, comprising a micro-control unit U1, an analog-to-digital conversion chip U2, a current acquisition module, a switch module and a constant current source V;

[0011] One end of the analog-to-digital conversion chip U2 is connected to the microcontroller unit U1, and the other end is connected to the current acquisition module; one end of the switch switching module is connected to the current acquisition module, and the other end is connected to the constant current source V; the microcontroller unit U1 is connected to the current acquisition module and the switch switching module respectively.

[0012] Furthermore, the current acquisition module includes an operational amplifier U3, a switch K3 and a sampling capacitor Cs;

[0013] Pin 1 of the operational amplifier U3 is connected to the switch K3, the sampling capacitor Cs and the analog-to-digital conversion chip U2, pin 2 is connected to the switch K3, the sampling capacitor Cs and the switch K2, and pin 3 is grounded; the control end of the switch K3 is connected to the micro control unit U1.

[0014] Furthermore, the switch switching module includes a single-pole double-throw switch K1 and a switch K2;

[0015] Pin 1 of the SPDT switch K1 is connected to the constant current source V, and pin 2 is connected to one end of the switch K2; the other end of the switch K2 is connected to the current acquisition module; the control ends of the SPDT switch K1 and the switch K2 are both connected to the microcontroller unit U1.

[0016] In a second aspect, the present invention provides a method for collecting microcurrent based on capacitance, comprising the following steps:

[0017] Step S10, the micro control unit U1 controls the sampling capacitor Cs to discharge the stored electricity;

[0018] Step S20, the micro control unit U1 controls the constant current source V to input current I_cc to charge the sampling capacitor Cs;

[0019] Step S30, the micro control unit U1 collects the voltage Vo1 output by the current acquisition module at time T1 through the analog-to-digital conversion chip U2, and calculates the actual capacitance Cs1 of the sampling capacitor Cs based on T1, Vo1 and I_cc;

[0020] Step S40, the micro control unit U1 controls the sampling capacitor Cs to discharge the stored electricity;

[0021] Step S50, the micro control unit U1 controls the pin 2 of the single-pole double-throw switch K1 to input the current I_in to charge the sampling capacitor Cs;

[0022] Step S60 , the micro control unit U1 collects the voltage Vo2 output by the current collection module at time T1 through the analog-to-digital conversion chip U2 , and calculates the current value of the current I_in based on T1 , Vo2 and Cs1 .

[0023] Furthermore, the step S10 is specifically as follows:

[0024] The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

[0025] Furthermore, the step S20 is specifically as follows:

[0026] The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 1 and 3 of the single-pole double-throw switch K1, thereby controlling the constant current source V to input the current I_cc to charge the sampling capacitor Cs.

[0027] Furthermore, in step S30, the calculation formula of the actual capacitance Cs1 is:

[0028] Cs1 = -I_cc*T1 / Vo1.

[0029] Furthermore, the step S40 is specifically as follows:

[0030] The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

[0031] Furthermore, the step S50 is specifically as follows:

[0032] The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 2 and 3 of the single-pole double-throw switch K1, thereby controlling the input current I_in of the pin 2 of the single-pole double-throw switch K1 to charge the sampling capacitor Cs.

[0033] Furthermore, in step S60, the current value of the current I_in is calculated as follows:

[0034] I_in=-Cs1*Vo2 / T1.

[0035] The advantages of the present invention are:

[0036] By setting the single-pole double-throw switch K1, switch K2, switch K3 and constant current source V, the microcontroller unit U1 first discharges the electricity stored in the sampling capacitor Cs, and then controls the constant current source V to input current I_cc to charge the sampling capacitor Cs through the single-pole double-throw switch K1, switch K2 and switch K3 to calculate the actual capacitance Cs1 of the sampling capacitor Cs; then the electricity stored in the sampling capacitor Cs is discharged, and the sampling capacitor Cs is charged by inputting current I_in through pin 2 of the single-pole double-throw switch K1. The current value of the current I_in is calculated based on the actual capacitance Cs1 instead of using the initially calibrated Cs for calculation, thereby overcoming the problem of changes in the capacitance of the sampling capacitor Cs due to environmental factors, and ultimately greatly improving the accuracy of micro-current collection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0038] Figure 1 The present invention is a circuit diagram of a capacitor-based micro-current collection circuit.

[0039] Figure 2 It is a flow chart of a capacitance-based micro-current collection method of the present invention. DETAILED DESCRIPTION

[0040] The technical solution in the embodiment of the present application has the following general idea: the sampling capacitor Cs is charged by the input current I_cc from the constant current source V to calculate the actual capacitance Cs1 of the sampling capacitor Cs; the sampling capacitor Cs is then charged by the input current I_in from pin 2 of the single-pole double-throw switch K1, and the current value of the current I_in is calculated based on the actual capacitance Cs1 to improve the accuracy of micro-current collection.

[0041] Please refer to Figure 1 to Figure 2 As shown, a preferred embodiment of a capacitor-based micro-current acquisition circuit of the present invention includes a micro-control unit (MCU) U1, an analog-to-digital conversion chip (A / D chip) U2, a current acquisition module, a switch module and a constant current source V;

[0042] The microcontrol unit U1 is used to control the on and off of the single-pole double-throw switch K1, the switch K2 and the switch K3, receive the voltage signal output by the analog-to-digital conversion chip U2, and calculate the actual capacitance Cs1 of the sampling capacitor Cs and the current value of the current I_in. In specific implementation, it is sufficient to select a microcontroller unit that can realize this function from the prior art, and it is not limited to any model, such as the STM32F103 series MCU of ST Company, and the control program is well known to those skilled in the art, which can be obtained by those skilled in the art without creative work; the analog-to-digital conversion chip U2 is used to perform analog-to-digital conversion on the voltage signal output by the current acquisition module. In specific implementation, it is sufficient to select an analog-to-digital conversion chip that can realize this function from the prior art, and it is not limited to any model, such as AD9280, which can be obtained by those skilled in the art without creative work; the current acquisition module is used to amplify and collect the input current; the switch switching module is used to switch whether the input is I_cc or I_in, and to turn on and off the current input channel; the constant current source V is used to output a high-precision and fixed current I_cc.

[0043] One end of the analog-to-digital conversion chip U2 is connected to the microcontroller unit U1, and the other end is connected to the current acquisition module; one end of the switch switching module is connected to the current acquisition module, and the other end is connected to the constant current source V; the microcontroller unit U1 is connected to the current acquisition module and the switch switching module respectively.

[0044] The current acquisition module includes an operational amplifier U3, a switch K3 and a sampling capacitor Cs; the operational amplifier U3 is used to amplify the input current. In specific implementation, it is sufficient to select an operational amplifier that can realize this function from the prior art, and is not limited to any model, such as TL082, which can be obtained by those skilled in the art without creative labor;

[0045] Pin 1 of the operational amplifier U3 is connected to the switch K3, the sampling capacitor Cs and the analog-to-digital conversion chip U2, pin 2 is connected to the switch K3, the sampling capacitor Cs and the switch K2, and pin 3 is grounded; the control end of the switch K3 is connected to the micro control unit U1.

[0046] The switch switching module includes a single-pole double-throw switch K1 and a switch K2; the single-pole double-throw switch K1 is controlled by the microcontroller unit U1, and can conduct pins 1, 3 or 2, 3 as needed, and the current to be measured is input from pin 2;

[0047] Pin 1 of the SPDT switch K1 is connected to the constant current source V, and pin 2 is connected to one end of the switch K2; the other end of the switch K2 is connected to the current acquisition module; the control ends of the SPDT switch K1 and the switch K2 are both connected to the microcontroller unit U1.

[0048] A preferred embodiment of a method for collecting microcurrent based on capacitance of the present invention comprises the following steps:

[0049] Step S10, the micro control unit U1 controls the sampling capacitor Cs to discharge the stored electricity;

[0050] Step S20, the microcontroller unit U1 controls the constant current source V to input the current I_cc to charge the sampling capacitor Cs; the current value of the current I_cc is known;

[0051] Step S30, the microcontroller unit U1 collects the voltage Vo1 output by the current acquisition module at time T1 through the analog-to-digital conversion chip U2, and calculates the actual capacitance Cs1 of the sampling capacitor Cs based on T1, Vo1 and I_cc; that is, the capacitance of the sampling capacitor Cs is recalibrated through the high-precision constant current source V to improve the current acquisition accuracy;

[0052] Step S40, the microcontroller unit U1 controls the sampling capacitor Cs to discharge the stored electricity; by discharging the stored electricity of the sampling capacitor Cs before calculating the actual capacitance Cs1 and current collection, the current collection accuracy is guaranteed;

[0053] Step S50, the microcontroller unit U1 controls the pin 2 of the single-pole double-throw switch K1 to input the current I_in to charge the sampling capacitor Cs; the current value of the current I_in is unknown and is the current value to be measured;

[0054] Step S60, the microcontroller unit U1 collects the voltage Vo2 output by the current acquisition module at time T1 through the analog-to-digital conversion chip U2, and calculates the current value of the current I_in based on T1, Vo2 and Cs1. The duration of the time T1 can be set as needed. If the charging time of the sampling capacitor Cs has not reached the time T1, it needs to be continuously charged until the time T1.

[0055] The step S10 is specifically as follows:

[0056] The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

[0057] The step S20 is specifically as follows:

[0058] The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 1 and 3 of the single-pole double-throw switch K1, thereby controlling the constant current source V to input the current I_cc to charge the sampling capacitor Cs.

[0059] Furthermore, in step S30, the calculation formula of the actual capacitance Cs1 is:

[0060] Cs1 = -I_cc*T1 / Vo1.

[0061] The step S40 is specifically as follows:

[0062] The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

[0063] The step S50 is specifically as follows:

[0064] The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 2 and 3 of the single-pole double-throw switch K1, thereby controlling the input current I_in of the pin 2 of the single-pole double-throw switch K1 to charge the sampling capacitor Cs.

[0065] In the step S60, the current value of the current I_in is calculated as follows:

[0066] I_in=-Cs1*Vo2 / T1.

[0067] In summary, the advantages of the present invention are:

[0068] By setting the single-pole double-throw switch K1, switch K2, switch K3 and constant current source V, the microcontroller unit U1 first discharges the electricity stored in the sampling capacitor Cs, and then controls the constant current source V to input current I_cc to charge the sampling capacitor Cs through the single-pole double-throw switch K1, switch K2 and switch K3 to calculate the actual capacitance Cs1 of the sampling capacitor Cs; then the electricity stored in the sampling capacitor Cs is discharged, and the sampling capacitor Cs is charged by inputting current I_in through pin 2 of the single-pole double-throw switch K1. The current value of the current I_in is calculated based on the actual capacitance Cs1 instead of using the initially calibrated Cs for calculation, thereby overcoming the problem of changes in the capacitance of the sampling capacitor Cs due to environmental factors, and ultimately greatly improving the accuracy of micro-current collection.

[0069] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A micro-current collection circuit based on capacitance, Features: It includes a micro control unit U1, an analog-to-digital conversion chip U2, a current acquisition module, a switch module and a constant current source V; One end of the analog-to-digital conversion chip U2 is connected to the microcontroller unit U1, and the other end is connected to the current acquisition module; one end of the switch module is connected to the current acquisition module, and the other end is connected to the constant current source V; the microcontroller unit U1 is connected to the current acquisition module and the switch module respectively; The current acquisition module includes an operational amplifier U3, a switch K3 and a sampling capacitor Cs; Pin 1 of the operational amplifier U3 is connected to the switch K3, the sampling capacitor Cs and the analog-to-digital conversion chip U2, pin 2 is connected to the switch K3, the sampling capacitor Cs and the switch K2, and pin 3 is grounded; the control end of the switch K3 is connected to the micro control unit U1.

2. A capacitor-based micro-current collection circuit as claimed in claim 1, Features: The switch switching module includes a single-pole double-throw switch K1 and a switch K2; Pin 1 of the SPDT switch K1 is connected to the constant current source V, and pin 2 is connected to one end of the switch K2; the other end of the switch K2 is connected to the current acquisition module; the control ends of the SPDT switch K1 and the switch K2 are both connected to the microcontroller unit U1.

3. A micro-current collection method based on capacitance, Features: The method requires the use of the acquisition circuit as described in any one of claims 1 to 2, and comprises the following steps: Step S10, the micro control unit U1 controls the sampling capacitor Cs to discharge the stored electricity; Step S20, the micro control unit U1 controls the constant current source V to input current I_cc to charge the sampling capacitor Cs; Step S30, the micro control unit U1 collects the voltage Vo1 output by the current acquisition module at time T1 through the analog-to-digital conversion chip U2, and calculates the actual capacitance Cs1 of the sampling capacitor Cs based on T1, Vo1 and I_cc; Step S40, the micro control unit U1 controls the sampling capacitor Cs to discharge the stored electricity; Step S50, the micro control unit U1 controls the pin 2 of the single-pole double-throw switch K1 to input the current I_in to charge the sampling capacitor Cs; Step S60 , the micro control unit U1 collects the voltage Vo2 output by the current collection module at time T1 through the analog-to-digital conversion chip U2 , and calculates the current value of the current I_in based on T1 , Vo2 and Cs1 .

4. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: The step S10 is specifically as follows: The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

5. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: The step S20 is specifically as follows: The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 1 and 3 of the single-pole double-throw switch K1, thereby controlling the constant current source V to input the current I_cc to charge the sampling capacitor Cs.

6. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: In step S30, the calculation formula of the actual capacitance Cs1 is: Cs1 = -I_cc*T1 / Vo1.

7. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: The step S40 is specifically as follows: The micro control unit U1 closes the switch K3 and opens the switch K2, thereby controlling the sampling capacitor Cs to discharge the stored electricity.

8. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: The step S50 is specifically as follows: The microcontrol unit U1 opens the switch K3, closes the switch K2, and turns on the pins 2 and 3 of the single-pole double-throw switch K1, thereby controlling the input current I_in of the pin 2 of the single-pole double-throw switch K1 to charge the sampling capacitor Cs.

9. A method for collecting microcurrent based on capacitance as claimed in claim 3, Features: In the step S60, the current value of the current I_in is calculated as follows: I_in=-Cs1*Vo2 / T1.

Images