DC Leakage Detector Excitation Circuit for Accurate Voltage Switching
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Solution Overview
Problem
Existing DC leakage detectors face accuracy issues due to the use of single operational amplifiers with high input offset voltages and ON resistance in the excitation unit, limiting the freedom of selection and increasing costs.
Innovation Solution
A DC leakage detector with an excitation unit that includes a comparison circuit and a voltage switching circuit, utilizing a CMOS operational amplifier with low input offset voltage and an analog switch with low ON resistance, allowing for accurate voltage level switching between high and low voltage values based on detection voltage and threshold comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single operational amplifier is used in the excitation unit to compare detection voltage with threshold voltage and output excitation voltage, then the device complexity is reduced, but the detection accuracy of DC leakage current decreases due to input offset voltage and ON resistance effects
Solution Approach 1:
The excitation unit is divided into two separate functional modules: a comparison circuit for comparing detection voltage with threshold voltage, and a voltage switching circuit for outputting excitation voltage based on the comparison result. This segmentation isolates the functions that were previously combined in a single operational amplifier, allowing each module to be optimized independently for its specific function, thereby improving overall detection accuracy while maintaining reasonable device complexity.
2Measurement precision
If high-performance operational amplifiers with low input offset voltage and low ON resistance are used in the excitation unit, then the detection accuracy of DC leakage current increases, but the freedom of selection of parts decreases and costs increase
Solution Approach 1:
Different parts of the excitation unit are designed with different functional requirements: the comparison circuit focuses on accurate voltage comparison, while the voltage switching circuit focuses on clean voltage level switching. This allows selection of components optimized for their specific local function rather than requiring a single high-performance operational amplifier to excel at both tasks, thereby increasing freedom of part selection while maintaining detection accuracy.
3Adaptability or versatility
If the input offset voltage of the operational amplifier increases, then the freedom of selection of parts increases, but the accuracy of comparison between detection voltage and threshold voltage decreases
Solution Approach 1:
The comparison function is separated from the voltage output function. The comparison circuit can use operational amplifiers with higher input offset voltage that are easier to select and more cost-effective, while the voltage switching circuit handles the critical voltage level transitions. This segmentation allows the use of components with more relaxed specifications in the comparison stage, increasing freedom of part selection without compromising overall system accuracy.
4Adaptability or versatility
If the ON resistance between high-side switch and low-side switch of the operational amplifier increases, then the freedom of selection of parts increases, but the accuracy of the voltage level of excitation voltage decreases
Solution Approach 1:
The voltage switching circuit is designed as a separate module that takes the comparison result as input and generates the excitation voltage output. This segmentation allows the voltage switching circuit to use switches with higher ON resistance that are easier to select and more cost-effective, while the critical voltage level accuracy is maintained through the dedicated switching architecture rather than relying on the operational amplifier's internal switch characteristics.
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 configuration enhances the detection accuracy of DC leakage currents, increases the freedom of selecting parts for the excitation unit, and reduces costs by ensuring precise voltage level switching and improved detection performance.
Implementation Method 1
an excitation coil 22 wound around the core 21. The excitation unit 23 applies, to the excitation coil 22, an excitation voltage
Implementation Method 2
a current-detecting resistor 24 that converts a current flowing through the excitation coil 22 into a detection voltage
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
An object of the present invention is to provide a DC leakage detector and electric leakage detector with the ability to increase the freedom of selection of parts that form an excitation unit. An excitation unit (23) applies, to an excitation coil (22), an excitation voltage with a voltage level alternately changing between a first high voltage value (VH1) higher than a reference voltage value (Vr) and a first low voltage value (VL1) lower than the reference voltage value (Vr). The excitation unit (23) includes a comparison circuit (231) and a voltage switching circuit (232). The comparison circuit (231) outputs a comparison signal having a voltage level switching between a high level and a low level depending on whether a detection voltage (Vd) is greater than, or equal to or less than, a threshold voltage (Vth). The voltage switching circuit (232) switches the voltage level of the excitation voltage between the first high voltage value (VH1) and the first low voltage value (VL1) according to the voltage level of the comparison signal.