Current Sensing Circuit Thermal Error Correction
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Solution Overview
Problem
Current sense circuits in switching power supplies face inaccuracies in current measurement due to temperature fluctuations in sense resistors, as traditional temperature sensors struggle to accurately detect the actual temperature of sense resistors, especially when separated by thermal media with a significant thermal time constant.
Innovation Solution
A current sensing circuit that calculates the actual resistance of the sense resistor using a temperature sensor's measurement, thermal resistance, and power dissipation, iteratively updating the current calculation to account for temperature errors, allowing for accurate current determination through feedback circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is placed proximate to the sense resistor to measure temperature for resistance correction, then temperature sensing capability is provided, but measurement precision deteriorates due to thermal time constant delays in the medium between the sensor and resistor
Solution Approach 1:
The patent introduces a thermal model as an intermediary that mathematically relates the sense resistor temperature to the temperature sensor reading through thermal resistance and thermal time constant parameters. This model compensates for the thermal delay without requiring physical contact between the sensor and resistor, thus maintaining measurement precision while accounting for the time delay.
Solution Approach 2:
The patent transforms the temperature measurement problem by changing from direct temperature sensing to indirect temperature estimation through power dissipation calculation. By calculating power dissipation (P = I²R) and using thermal model parameters (thermal resistance θ and thermal time constant τ), the system computes the sense resistor temperature as Tsense = Tsensor + θ·P, eliminating the need for fast thermal response.
2Adaptability or versatility
If the sense resistor is separated from the temperature sensor by a thermal medium, then device layout flexibility is improved, but measurement precision worsens due to inaccurate temperature sensing
Solution Approach 1:
The thermal model acts as an intermediary that bridges the physical separation between the temperature sensor and sense resistor. By incorporating thermal resistance θ and thermal time constant τ of the medium between them, the model accurately translates the sensor reading to the resistor temperature, maintaining measurement precision despite physical separation and enabling layout flexibility.
Solution Approach 2:
The patent segments the temperature measurement function into two independent parts: the temperature sensor that can be placed anywhere in the circuit, and the thermal model that calculates the actual resistor temperature using the sensor reading plus thermal compensation. This segmentation allows independent optimization of sensor placement and resistor location.
3Measurement precision
If iterative feedback calculation is used to update current and power values, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements iterative feedback where the calculated current is used to update power dissipation, which in turn updates the temperature estimate, which then refines the resistance calculation, and finally improves the current measurement. This closed-loop feedback continuously converges to accurate values without requiring complex hardware, as the iterations can be performed in software or simple digital logic.
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
Significantly improves current measurement accuracy by correcting for both steady-state and transient temperature measurement errors, providing precise current calculations even with physical separation between the sense resistor and temperature sensor.
Implementation Method 1
The medium between the sense resistor and the temperature sensor cannot quickly conduct the resistor temperature to the temperature sensor due to the thermal time constant of the medium
Implementation Method 2
The sense resistor itself is generating heat, and the temperature sensor is separated from the sense resistor
Data Source
AI summary
In one embodiment, a current sensing circuit corrects for the transient and steady state temperature measurement errors due to physical separation between a resistive sense element and a temperature sensor. The sense element has a temperature coefficient of resistance. The voltage across the sense element and a temperature signal from the temperature sensor are received by processing circuitry. The processing circuitry determines a power dissipated by the sense element, which may be instantaneous or average power, and determines an increased temperature of the sense element. The resistance of the sense element is changed by the increased temperature, and this derived resistance Rs is used to calculate the current through the sense element using the equation I=V/R or other related equation. The process is iterative to continuously improve accuracy and update the current.