Capacitance measuring circuit and measuring method for microfarad-level electrolytic capacitor of sound box mainboard

Abstract

The invention discloses and provides a capacitance measuring circuit and a capacitance measuring method for a microfarad-level electrolytic capacitor of a sound box mainboard. The capacitance measuring circuit is simple in structure, low in cost, wide in applicability and high in measuring efficiency. The device comprises a programmable DC power supply module, a relay, a current sampling resistor, an instrument operational amplifier, an ADC voltage acquisition module and a master control module. The programmable direct-current power supply module is connected to the relay, the relay is connected to the current sampling resistor, the current sampling resistor is connected to the positive electrode of the sound box mainboard microfarad-level electrolytic capacitor, and the programmable direct-current power supply module is connected to the sound box mainboard microfarad-level electrolytic capacitor; the instrument operational amplifier is connected to two ends of the current sampling resistor, the instrument operational amplifier is connected with the ADC voltage acquisition module, and the main control module is respectively connected with the ADC voltage acquisition module, the programmable DC power supply module and the control end of the relay. Current change data in the charging process is obtained by using the sampling resistor, and an electronic load module is not needed. The method is applied to the technical field of capacitance measurement of the electrolytic capacitor.

Description

Technical Field

[0001] This invention relates to a capacitance measurement circuit and method for electrolytic capacitors, and particularly to a capacitance measurement circuit and method for microfarad-level electrolytic capacitors on a speaker motherboard. Background Technology

[0002] Smart speakers are becoming increasingly popular, with more and more comprehensive functions, playing an increasingly important role in people's daily work, life, and entertainment. Some speaker motherboards incorporate large electrolytic capacitors, typically in the microfarad range. These large electrolytic capacitors are usually placed on the main power rail of the speaker motherboard. The power amplifier chip requires a stable DC power supply, and the electrolytic capacitors act as filters and regulators, removing high-frequency noise from the power supply to prevent interference with the power amplifier chip and other circuits, thus preventing issues such as background noise and current hum. For smart speakers to function properly, it is often necessary to test the electrolytic capacitors. Currently, the main focus of electrolytic capacitor testing is checking whether the capacitance is within acceptable limits.

[0003] One existing testing method for electrolytic capacitors involves charging the capacitor with a DC power supply, disconnecting the power supply after charging, using an electronic load module to discharge the capacitor at a constant current, and simultaneously measuring the voltage across the capacitor with a multimeter. The capacitance is then calculated using the obtained voltage data and the constant current. However, using an electronic load module is costly and the system is complex, requiring configuration of discharge modes (e.g., constant current), parameters (current value, stop conditions), and trigger logic. Furthermore, it necessitates calibrating current accuracy, verifying response speed, and ensuring synchronization with the multimeter, significantly extending test preparation time and resulting in low test efficiency. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a capacitance measurement circuit and method for microfarad-level electrolytic capacitors on speaker motherboards that is simple in structure, low in cost, widely applicable, and highly efficient in measurement.

[0005] The technical solution adopted in this invention is as follows: A capacitance measurement circuit for a microfarad-level electrolytic capacitor on a speaker motherboard includes a programmable DC power supply module (DC), a relay (S), a current sampling resistor (R), an instrumentation operational amplifier (U), an ADC voltage acquisition module (ADC), and a main control module (MCU). The positive terminal of the programmable DC power supply module (DC) is connected to the input terminal of the relay (S), the output terminal of the relay (S) is connected to one end of the current sampling resistor (R), the other end of the current sampling resistor (R) is connected to the positive terminal of the microfarad-level electrolytic capacitor (C) on the speaker motherboard, and the negative terminal of the programmable DC power supply module (DC) is connected to the negative terminal of the microfarad-level electrolytic capacitor (C) on the speaker motherboard. The two input terminals of the instrumentation operational amplifier (U) are respectively connected to the two ends of the current sampling resistor (R), the output terminal of the instrumentation operational amplifier (U) is connected to the input terminal of the ADC voltage acquisition module, and the main control module (MCU) is connected to the control terminals of the ADC voltage acquisition module (ADC), the programmable DC power supply module (DC), and the relay (S).

[0006] Furthermore, the instrumentation operational amplifier U is model AD8253ARMZ.

[0007] Furthermore, the main control module MCU controls the programmable DC power supply module DC via SPI and I2C buses, and the main control module MCU controls the ADC voltage acquisition module ADC via SPI bus, thereby realizing the power supply control and the acquisition of voltage data corresponding to the charging current.

[0008] Furthermore, the main control module MCU controls the relay S via GPIO.

[0009] The measurement method for the capacitance measurement circuit of the microfarad-level electrolytic capacitor on the speaker motherboard is as follows: When the programmable DC power supply module DC supplies power to the microfarad-level electrolytic capacitor C on the speaker motherboard, a voltage drop will be generated across the current sampling resistor R. The instrumentation amplifier U collects the voltage drop across the resistor and converts it into a single-ended voltage signal, which is then sent to the ADC voltage acquisition module for data acquisition. The specific steps are as follows: a. The main control module MCU controls the relay S to close, thus completing the circuit; b. The main control module MCU controls the ADC voltage acquisition module to start the data acquisition function, and the acquisition time is 2 seconds; c. The main control module MCU controls the programmable power supply module to output 5V voltage, and at this time it begins to charge the microfarad electrolytic capacitor C on the speaker motherboard. d. After the data acquisition time is up, disconnect relay S and turn off the power supply. e. Based on the collected voltage data of the sampled current, select any two points during the current decrease process, namely (t1, V1) and (t2, V2), and substitute the data of these two points into the capacitance calculation formula, i.e. C = |(t1-t2) / R*[ln(V1 / V2)]|. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the principle of the present invention; Figure 2 This is a schematic diagram of the charging / discharging current variation curve of an RC series circuit capacitor. Figure 3 This is the actual waveform of the capacitance test according to the present invention; Figure 4 These are the measured capacitance data of this invention; Figure 5 This is a circuit diagram of the switching path for the current sampling resistor voltage difference signal; Figure 6 It is a circuit diagram of the power supply processing and reference voltage for each circuit; Figure 7 This is the circuit diagram for an instrumentation operational amplifier; Figure 8 This is a circuit diagram for selecting the output path of an instrumentation operational amplifier; Figure 9 This is a circuit diagram of the interface between the current sampling signal and the signal processing module; Figure 10 It is a circuit diagram of relay control, current sampling resistor, and its connection to the product. Detailed Implementation

[0011] like Figures 1 to 10 As shown, in this embodiment, the present invention includes a capacitance measurement circuit comprising a programmable DC power supply module (DC), a relay (S), a current sampling resistor (R), an instrumentation operational amplifier (U), an ADC voltage acquisition module (ADC), and a main control module (MCU). The positive terminal of the programmable DC power supply module (DC) is connected to the input terminal of the relay (S), the output terminal of the relay (S) is connected to one end of the current sampling resistor (R), the other end of the current sampling resistor (R) is connected to the positive terminal of a microfarad electrolytic capacitor (C) on the speaker motherboard, and the negative terminal of the programmable DC power supply module (DC) is connected to the negative terminal of the microfarad electrolytic capacitor (C) on the speaker motherboard. The two input terminals of the instrumentation operational amplifier (U) are respectively connected to the two ends of the current sampling resistor (R), the output terminal of the instrumentation operational amplifier (U) is connected to the input terminal of the ADC voltage acquisition module (ADC), and the main control module (MCU) is connected to the control terminals of the ADC voltage acquisition module (ADC), the programmable DC power supply module (DC), and the relay (S). This invention employs a series circuit structure of resistor R and capacitor C. At the instant of power-on, due to the capacitor's characteristic of "voltage not changing instantaneously," it behaves similarly to a "short circuit." At this moment, the current changes drastically within a short time, forming an exponential curve that gradually decreases in speed, starting at (0, 1) and eventually approaching 0 (i.e., a horizontal asymptote). Figure 2As shown in the diagram, the voltage change follows an exponential curve with a gradually decreasing rate of increase, starting at (0,0) and eventually approaching Vsupply (i.e., the horizontal asymptote). See voltage reference. Figure 3 The actual waveform of the capacitor test. We know that the charging and discharging curves of the capacitor in the same RC series circuit have different current directions, but the trend of change is the same (see...). Figure 2 As shown in the figure, the capacitance can be calculated using the formula for capacitor discharge.

[0012] The capacitor discharge formula is V c =V supply e^(-t / τ), τ=RC (time constant), converted to the formula for solving the capacitance C, is C=t / R*[-ln(V c / (V supply ))], Furthermore, we can obtain C = t / R * [ln(V supply / (V c ))).

[0013] Based on the voltage and current change characteristics and calculation methods of capacitor charging described above, the specific process of this scheme is described below: When power is supplied to the electrolytic capacitor, a voltage drop is generated across the sampling resistor R (100 ohms, selected based on the relatively small charging current of the electrolytic capacitor being tested). The instrumentation operational amplifier AD8253 can acquire this voltage drop and convert it into a single-ended voltage signal, which is then sent to the ADC voltage acquisition module for data acquisition. The AD8253 instrumentation operational amplifier features an adjustable gain function (four levels: x1, x10, x100, x1000), allowing for the selection of the appropriate gain based on the voltage drop level of the sampling resistor. The specific operating steps are as follows: a. The main control module controls relay S to close, thus completing the circuit; b. The main control module controls the ADC voltage acquisition module to start the data acquisition function, and the acquisition time is 2 seconds. c. The main control module controls the programmable power supply module to output 5V voltage, at which point it begins to charge the electrolytic capacitor. d. After the data acquisition time is up, disconnect relay S and turn off the power supply. e. Based on the voltage data of the sampled current, we can select any two points during the current decrease process, namely (t1, V1) and (t2, V2) (see...). Figure 2 (Charging / discharging diagram). Substitute the data from these two points into the capacitance calculation formula, i.e. C = |(t1-t2) / R*[ln(V1 / V2)]| In this scheme, the electrolytic capacitor used on the motherboard of the speaker under test has a capacitance of 2mF (i.e., 2000uF, composed of two 1000uF capacitors connected in parallel). The capacitance measured by this method is as follows: Figure 4 As shown, the test results are quite close to the theoretical values.

[0014] This invention utilizes the charging characteristics of a capacitor, acquiring current change data during the charging process through a sampling resistor, eliminating the need for an electronic load module. The DC power supply uses a programmable power module, offering greater flexibility in voltage setting and control, and wider applicability. Finally, current acquisition employs an ADC voltage acquisition module, providing a high data collection rate without impacting production efficiency. Therefore, this invention features a simple circuit, a universal method, and high measurement efficiency.

[0015] Although the embodiments of the present invention are described with reference to actual solutions, they do not constitute a limitation on the meaning of the present invention. Modifications to the embodiments and combinations with other solutions based on this specification will be obvious to those skilled in the art.

Claims

1. A capacitance measurement circuit for microfarad-level electrolytic capacitors on a speaker motherboard, characterized in that: The capacitance measurement circuit for a microfarad-level electrolytic capacitor on a speaker motherboard includes a programmable DC power supply module (DC), a relay (S), a current sampling resistor (R), an instrumentation operational amplifier (U), an ADC voltage acquisition module (ADC), and a main control module (MCU). The positive terminal of the programmable DC power supply module (DC) is connected to the input terminal of the relay (S), the output terminal of the relay (S) is connected to one end of the current sampling resistor (R), the other end of the current sampling resistor (R) is connected to the positive terminal of the microfarad-level electrolytic capacitor (C) on the speaker motherboard, and the negative terminal of the programmable DC power supply module (DC) is connected to the negative terminal of the microfarad-level electrolytic capacitor (C) on the speaker motherboard. The two input terminals of the instrumentation operational amplifier (U) are respectively connected to the two ends of the current sampling resistor (R), the output terminal of the instrumentation operational amplifier (U) is connected to the input terminal of the ADC voltage acquisition module (ADC), the programmable DC power supply module (DC), and the relay (S).

2. The capacitance measurement circuit for a microfarad-level electrolytic capacitor on a speaker motherboard according to claim 1, characterized in that: The instrumentation operational amplifier (U) is model AD8253ARMZ.

3. The capacitance measurement circuit for a microfarad-level electrolytic capacitor on a speaker motherboard according to claim 1, characterized in that: The main control module (MCU) controls the programmable DC power supply module (DC) via SPI and I2C buses, and the main control module (MCU) controls the ADC voltage acquisition module (ADC) via SPI bus to realize the power supply control and the acquisition of voltage data corresponding to the charging current.

4. The capacitance measurement circuit for a microfarad-level electrolytic capacitor on a speaker motherboard according to claim 1, characterized in that: The main control module (MCU) controls the relay (S) via GPIO.

5. A method for measuring the capacitance of a microfarad-level electrolytic capacitor on a speaker motherboard as described in claim 1, characterized in that: The measurement method is as follows: When the programmable DC power supply module (DC) supplies power to the microfarad-level electrolytic capacitor (C) on the speaker motherboard, a voltage drop will be generated across the current sampling resistor (R) as it passes through the current sampling resistor. The instrumentation operational amplifier (U) collects the voltage drop across the resistor and converts it into a single-ended voltage signal, which is then sent to the ADC voltage acquisition module (ADC) for data acquisition. The specific steps are as follows: a. The main control module (MCU) controls the relay (S) to close, thus completing the circuit; b. The main control module (MCU) controls the ADC voltage acquisition module (ADC) to start the data acquisition function, and the acquisition time is 2 seconds; c. The main control module (MCU) controls the programmable power supply module to output 5V voltage, at which point it begins to charge the microfarad electrolytic capacitor (C) on the speaker motherboard; d. After the data acquisition time is up, disconnect the relay (S) and turn off the power supply. e. Based on the collected voltage data of the sampled current, select any two points during the current decrease process, namely (t1, V1) and (t2, V2), and substitute the data of these two points into the capacitance calculation formula, i.e. C = |(t1-t2) / R*[ln(V1 / V2)]|.

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