Capacitance Measurement Using High-Frequency AC and Reference Capacitor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Accurate measurement of capacitance in electronic components, such as thyristors and bidirectional transient voltage suppressors, is challenging due to their voltage and time-dependent characteristics, leading to inaccurate capacitance values when using conventional measurement methods with low-frequency or low-voltage signals.
Innovation Solution
Applying an alternating current (AC) voltage with a high frequency and short period, significantly less than the component's characteristic time, to measure both voltage and current waveforms concurrently, allowing for the calculation of capacitance as a function of voltage using the ratio of current through the device to the change in voltage over time, or by using a reference capacitor to determine the capacitance of the device under test.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional low-frequency or low-voltage measurement methods are used, then the measurement process is simple, but the capacitance measurement accuracy deteriorates due to voltage and time-dependent characteristics
Solution Approach 1:
The patent applies parameter changes by using high-frequency AC voltage signals instead of conventional low-frequency signals. The measurement method changes the frequency parameter of the test signal to be significantly higher than the device's characteristic frequency, which prevents complete discharge during measurement and captures the voltage-dependent capacitance characteristics accurately.
Solution Approach 2:
The patent employs periodic action by applying AC voltage signals at high frequency. The periodic nature of the AC signal ensures that the device under test remains charged during each cycle, allowing accurate capacitance measurement. The period of the AC signal is chosen to be much shorter than the characteristic discharge time of the device.
2Measurement precision
If high-frequency AC voltage is applied to prevent complete discharge, then capacitance measurement accuracy improves, but the measurement setup complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a known capacitor in parallel with the device under test. This known capacitor serves as a reference to simplify the measurement setup and calculation process. The intermediary capacitor helps in determining the unknown capacitance through comparison, reducing the complexity of the overall measurement system.
3Measurement precision
If measurement frequency is increased to capture voltage-dependent characteristics, then measurement accuracy improves, but measurement time decreases available discharge time
Solution Approach 1:
The patent applies parameter changes by adjusting the frequency parameter of the measurement signal. By increasing the frequency to be significantly higher than the device's characteristic frequency, the measurement captures the voltage-dependent capacitance characteristics while the high frequency ensures the period is too short for complete discharge to occur during measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides more accurate capacitance measurements that reflect actual use conditions, reducing the likelihood of complete discharge during measurement and yielding characteristic capacitance curves useful for circuit design, which can help in selecting components with lower insertion losses and harmonics.
Implementation Method 1
a capacitance of the device is computed by multiplying a capacitance of the capacitor by a ratio of the instantaneous current through the device to the instantaneous current through the capacitor
Data Source
AI summary
A device and method of determining a capacitance of a device is provided, which in one embodiment includes connecting a first terminal of a capacitor having a known capacitance to the first terminal of the device, applying an AC voltage to the first terminal of the device and the first terminal of the capacitor, measuring a current through the capacitor, measuring a current through the device, determining a first voltage across the device as a function of time, computing a capacitance of the device as a function of time by multiplying the capacitance of the capacitor by the ratio of the current through the device to the current through the capacitor, determining a capacitance of the device as a function of voltage based on the capacitance as a function of time and the first voltage across the device as a function of time, and outputting data of the first capacitance of the device as a function of voltage.