Difference Amplifier Current Sensing Under High Common-Mode Voltage
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Solution Overview
Problem
Conventional current measurement methods struggle with accurately measuring current in high voltage applications exceeding 400 volts due to the inability of standard circuit components to handle high common mode voltages, particularly in environments with high common mode voltages.
Innovation Solution
A current sensor circuit utilizing a difference amplifier with isolated power supply and separate ground references, coupled with an isolation DC-to-DC converter, effectively isolating the difference amplifier from high common mode voltages, allowing accurate current measurement up to 2000 volts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard circuit components are used for current measurement, then the circuit design is simple and cost-effective, but the components cannot handle high common mode voltages exceeding 400 volts
Solution Approach 1:
An isolation DC-to-DC converter is introduced as an intermediary component between the high voltage measurement circuit and the low voltage processing circuit. This converter provides galvanic isolation, allowing the difference amplifier to operate at high common mode voltages while the processing side remains at safe low voltages, thus resolving the contradiction between handling high voltages and maintaining simple circuit design
Solution Approach 2:
The measurement system is segmented into isolated high voltage and low voltage domains. The difference amplifier operates in the high voltage domain to measure current accurately, while the isolation converter and processing circuitry operate in the low voltage domain, allowing each segment to be optimized for its specific voltage range without compromising overall system reliability
2Measurement precision
If a difference amplifier with isolated power supply is used, then accurate current measurement in high voltage environments is enabled, but the device complexity increases
Solution Approach 1:
The isolation DC-to-DC converter acts as a mediator that enables the difference amplifier to achieve high measurement precision in high voltage environments by providing isolated power supply. This intermediary component accepts standard input voltage and provides isolated output voltage to the difference amplifier, allowing accurate measurement without directly increasing the complexity of the measurement core
Solution Approach 2:
The system changes the power supply parameters of the difference amplifier by providing isolated voltage through the DC-to-DC converter. This parameter change enables the amplifier to operate with high common mode rejection ratio and maintain measurement precision even in high voltage environments, while the isolation converter handles the complexity of voltage transformation externally
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
Enables precise current measurement in high voltage environments by maintaining common mode voltages below 5 volts, enabling the use of standard components and suitable for applications like high voltage electric vehicles.
Implementation Method 1
A difference amplifier, also known as a differential amplifier, is an electronic device that amplifies the difference between two input voltages while rejecting voltage that is common to both inputs (common mode voltage)
Implementation Method 2
As current flows through this sensing resistor, a voltage drop across the sensing resistor is directly proportional to the amount of current across the resistor and to the current provided to the circuit under test due to the relationship defined by Ohm's Law (V=IR)
Implementation Method 3
A low side power terminal of the difference amplifier is coupled to a second ground node that is galvanically isolated from the first ground node
Data Source
AI summary
A current sensor circuit includes a sensing resistor having a first node adapted to be coupled to a high side terminal of a voltage supply and a second node adapted to be coupled to a high side terminal of a DUT (device under test). A low side terminal of the DUT is coupled to a first ground node. The current sensor circuit includes a difference amplifier coupled to the first node and the second node of the sensing resistor. A low side power terminal of the difference amplifier is coupled to a second ground node, and the second ground node is coupled to the high side terminal of the DUT. The current sensor circuit also includes an isolation DC (direct current)-to-DC converter having an output coupled to a high side power terminal of the difference amplifier.