Active Current Sensing Circuit with Feedback Protection
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Solution Overview
Problem
Conventional current sensing circuits face challenges in achieving a large current measuring range while maintaining a low burden voltage, as the burden voltage increases with the subject current, limiting the signal-to-noise ratio due to the need for small shunt resistors and fuses.
Innovation Solution
A current sensing circuit design with a shunt resistor and an amplifier having a feedback path with an over-current protection device, where the burden voltage is independent of the voltage drop across the shunt resistor and over-current protection device, allowing for a large shunt resistor to be used, thereby maintaining a low burden voltage and improving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large shunt resistor is used to improve signal-to-noise ratio, then measurement precision is improved, but burden voltage increases
Solution Approach 1:
The patent introduces an intermediary mechanism (op-amp based voltage follower circuit) between the shunt resistor and the measurement system. This intermediary buffers the voltage signal from the shunt resistor, allowing the use of a larger shunt resistor for better signal-to-noise ratio without proportionally increasing the burden voltage impact on the measured circuit.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by using an operational amplifier to actively manage the voltage signal. The op-amp circuit transforms the relationship between shunt resistor value and burden voltage, enabling parameter optimization where a larger resistance can be used without linearly increasing the voltage drop impact.
2Loss of energy
If a small shunt resistor is used to reduce burden voltage, then burden voltage is reduced, but signal-to-noise ratio deteriorates
Solution Approach 1:
The voltage follower circuit acts as an intermediary that decouples the relationship between shunt resistor size and signal quality. It provides high input impedance to the shunt resistor, allowing maximum voltage signal extraction without loading effects, while providing low output impedance to drive the measurement system.
3Loss of energy
If a fuse with small impedance is used to reduce burden voltage, then burden voltage is reduced, but the fuse requires frequent replacement
Solution Approach 1:
The patent introduces a current sensing resistor as an intermediary element that handles the voltage measurement function, allowing the fuse to be optimized for protection function rather than minimal impedance. The current sensing resistor absorbs the impedance requirements, freeing the fuse from the constraint of needing ultra-low impedance.
Solution Approach 2:
The patent segments the circuit functions by separating the current measurement function (handled by current sensing resistor) from the protection function (handled by fuse). This segmentation allows each component to be optimized for its specific function without compromise.
4Adaptability or versatility
If the burden voltage is reduced to improve measurement range, then current measuring range is extended, but signal-to-noise ratio is affected
Solution Approach 1:
The op-amp based voltage follower serves as an intermediary that enables the circuit to adapt to a wide range of current values while maintaining signal quality. The high input impedance buffer allows accurate voltage measurement across different current levels without the burden voltage constraint limiting the measurement range.
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 measurement of large currents with a substantially low burden voltage, enhancing the signal-to-noise ratio and efficiency, and using a resettable fuse for over-current protection that does not require replacement, improving measurement efficiency.
Implementation Method 1
a shunt resistor coupled in the current path for converting the subject current into an output voltage difference across the shunt resistor
Data Source
Figure 1~2
Figure 3~4
AI summary
The current sensing circuit (50) comprises a first input terminal (51) and a second input terminal (53) for introducing a subject current that flows in a current path; a shunt resistor (55) coupled in the current path for converting the subject current into an output voltage difference across the shunt resistor; an amplifier (57) having a first input node (59) coupled to the first input terminal, a second input node (61) coupled to the second input terminal, an output node (63), and a feedback path (67) comprising an over-current protection device (65), wherein the feedback path is coupled between the output node and the first input terminal; and an output terminal (69) coupled to the second input terminal and the shunt resistor to output the output voltage difference. The current sensing circuit has a relatively large current measuring range and a small burden voltage. A measurement device is also described.