Current Sense Circuit With Lead-Frame Shunt Temperature Compensation
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Solution Overview
Problem
Current sense circuits face challenges in accurately measuring current with thermally stable shunt resistors, as they are often too large and expensive, making them unsuitable for certain applications, and their size complicates packaging with voltage measurement circuitry.
Innovation Solution
A current sense circuit package is designed with a lead-frame serving as the shunt resistance, coupled with a differential amplifier that includes an input resistor with a composite temperature coefficient matching the lead-frame's temperature coefficient, allowing the amplifier's gain to compensate for temperature-induced variations in shunt voltage, thereby maintaining accurate current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermally stable shunt resistor is used for accurate current measurement, then measurement precision is improved, but the size and cost of the circuit increases
Solution Approach 1:
The patent combines the shunt resistor and differential amplifier into a single integrated package, where the shunt resistor is formed as part of the lead-frame structure and the amplifier is mounted directly on it. This integration eliminates the need for separate large-area thermally stable resistors while maintaining measurement accuracy through temperature compensation.
Solution Approach 2:
The patent changes the temperature coefficient parameter of the amplifier's input resistor to match the lead-frame's temperature coefficient. By selecting an input resistor with a specific temperature coefficient that compensates for the lead-frame's thermal drift, the system maintains accurate current measurements without requiring large, expensive thermally stable shunt resistors.
2Measurement precision
If a thermally stable shunt resistor is used for accurate current measurement, then measurement precision is improved, but the cost of the circuit increases
Solution Approach 1:
The integration of shunt resistor and amplifier into one package reduces component count and assembly complexity, lowering manufacturing costs while maintaining measurement precision through the temperature compensation mechanism.
Solution Approach 2:
By changing the input resistor's temperature coefficient to match the lead-frame's coefficient, the system achieves thermal stability using standard, low-cost components rather than expensive specialized thermally stable resistors.
3Area of stationary object
If the shunt resistor size is reduced for compact packaging, then device complexity is reduced, but temperature-induced measurement variations increase
Solution Approach 1:
The patent compensates for the thermal drift of small shunt resistors by matching the input resistor's temperature coefficient to the shunt resistor's temperature coefficient. This parameter matching ensures that both components drift together with temperature, maintaining accurate current measurements despite the reduced shunt resistor size.
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 approach enables accurate current measurement across a temperature range without the need for large, expensive shunt resistors, reducing the size and cost of the current sense circuit while maintaining measurement accuracy.
Implementation Method 1
the shunt resistance having a variation with temperature according to a lead-frame temperature coefficient
Implementation Method 2
an input resistor having a composite temperature coefficient configured to match the lead-frame temperature coefficient such that an output of the differential amplifier is a measurement of the shunt voltage and such that the output is compensated to remove the variation caused by the lead-frame temperature coefficient
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A package for a current sense circuit may include a lead-frame having a shunt resistance configured to generate a shunt voltage, which can be used to measure a current through the lead-frame. The shunt resistance associated with the lead-frame may be highly variable with temperature, which can cause errors in the current measurement. Accordingly, a current sense circuit can include an amplifier with an input resistor having a composite temperature coefficient configured to match a lead-frame temperature coefficient so that an output of the amplifier is compensated to remove variations in the shunt resistance of the lead-frame due to temperature.