DC Leakage Detector Excitation Circuit with Split Compare-Switch Stages
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Solution Overview
Problem
Existing DC leakage detectors face accuracy issues due to the use of single operational amplifiers in the excitation unit, leading to low detection accuracy and limited part selection freedom, especially with increasing input offset voltage and ON resistance.
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 to improve detection accuracy, then the detection accuracy of DC leakage current increases, but the freedom of selection of parts and cost increase
Solution Approach 1:
Different parts of the excitation unit are designed with different functional requirements: the comparison circuit focuses on voltage comparison accuracy, while the voltage switching circuit focuses on voltage level switching performance. This allows selection of standard, cost-effective components for each module based on their specific local requirements, rather than requiring all components to meet high-performance specifications across all functions, thereby improving part selection freedom and reducing cost while maintaining detection accuracy.
3Reliability
If the operational amplifier's ON resistance increases, then the voltage level of excitation voltage deviates from supply voltage or ground potential, but using low ON resistance components increases cost
Solution Approach 1:
The voltage switching circuit acts as an intermediary between the comparison circuit and the excitation coil. It receives the comparison result and generates the appropriate excitation voltage level by switching between supply voltage and ground potential. This intermediary structure isolates the excitation coil from the direct impact of operational amplifier ON resistance, allowing the use of standard components while maintaining reliable voltage level accuracy through the switching mechanism.
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 and increases the freedom of selecting parts for the excitation unit, reducing costs and improving performance across varying temperature ranges.
Implementation Method 1
a magnetic core, a winding, an excitation unit... The magnetic core is electromagnetically coupled to a pair of electrically conductive paths... The winding is wound around the magnetic core. The excitation unit supplies an excitation current as an alternating current to the winding.
Implementation Method 2
The current-detecting resistor converts a current flowing through the excitation coil into a detection voltage.
Data Source
AI summary
An excitation unit applies, to an excitation coil, an excitation voltage with a voltage level alternately changing between a first high voltage value higher than a reference voltage value and a first low voltage value lower than the reference voltage value. The excitation unit includes a comparison circuit and a voltage switching circuit. The comparison circuit outputs a comparison signal having a voltage level switching between a high level and a low level depending on whether a detection voltage is greater than, or equal to or less than, a threshold voltage. The voltage switching circuit switches the voltage level of the excitation voltage between the first high voltage value and the first low voltage value according to the voltage level of the comparison signal.