Choke Current Sensing Circuit for Accurate Bidirectional Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for measuring current through a choke, such as DCR current sensing, are limited in accuracy due to high production tolerances and temperature dependence of copper resistance, and cannot accurately measure bidirectional currents without additional circuit complexity and temperature compensation issues.
Innovation Solution
A device comprising an integrator circuit, an amplifier circuit with an NTC resistor in the feedback path, and a reference voltage source is used to decouple the NTC resistor from offset voltage generation, allowing for undistorted measurement of bidirectional currents while maintaining temperature compensation, using an operational amplifier for signal amplification and offset voltage coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If DCR current sensing is used to measure current through a choke, then unit costs are reduced and space requirements are minimized, but measurement accuracy is limited due to high production tolerances and temperature dependence of copper resistance
Solution Approach 1:
An NTC resistor is introduced as an intermediary component in parallel with the integrator capacitor to compensate for temperature effects. The NTC resistor's negative temperature coefficient counteracts the positive temperature coefficient of the copper resistance, thereby maintaining measurement accuracy across temperature variations without requiring separate temperature sensing or complex calibration circuits.
Solution Approach 2:
The measuring circuit parameters are made temperature-dependent through the NTC resistor to dynamically compensate for temperature effects. By selecting an NTC resistor with appropriate characteristics, the circuit automatically adjusts its response to maintain constant gain over temperature, transforming a static measurement system into one that adapts to environmental changes.
2Measurement precision
If an NTC resistor is used for temperature compensation in DCR current sensing, then temperature-dependent gain variations are compensated, but the circuit cannot accurately measure bidirectional currents without additional complexity
Solution Approach 1:
Instead of using the conventional approach of adding a bias offset voltage to shift the measurement range for bidirectional currents, this invention inverts the problem by properly grounding the reference potential and using the NTC resistor in a configuration that naturally handles both positive and negative currents. The center tap of the integrator circuit provides a true zero reference that works for bidirectional measurement without requiring additional offsetting circuitry.
Solution Approach 2:
The temperature compensation function is extracted and implemented separately through the NTC resistor in parallel with the integrator capacitor, independent of the bidirectional current measurement capability. This separation allows the circuit to handle bidirectional currents through proper reference potential establishment while temperature compensation occurs automatically through the NTC resistor's characteristics, eliminating the need for complex combined solutions.
3Adaptability or versatility
If a bias offset voltage is injected to extend measuring range for negative currents, then bidirectional current measurement is enabled, but temperature compensation using NTC resistor changes the offset voltage, causing incorrect current values
Solution Approach 1:
The temperature compensation function is extracted and implemented separately through the NTC resistor in parallel with the integrator capacitor, independent of the bidirectional current measurement capability. This separation allows the circuit to handle bidirectional currents through proper reference potential establishment while temperature compensation occurs automatically through the NTC resistor's characteristics, eliminating the need for complex combined solutions.
Solution Approach 2:
Instead of using the conventional approach of adding a bias offset voltage to shift the measurement range for bidirectional currents, this invention inverts the problem by properly grounding the reference potential and using the NTC resistor in a configuration that naturally handles both positive and negative currents. The center tap of the integrator circuit provides a true zero reference that works for bidirectional measurement without requiring additional offsetting circuitry.
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 solution enables accurate and efficient measurement of bidirectional currents through a choke, maintaining constant gain over temperature and frequency ranges, reducing measurement errors and complexity, and avoiding adverse effects from temperature changes.
Implementation Method 1
Temperature compensation can be achieved by means of an NTC resistor connected in parallel with the capacitor of the integrator circuit. The temperature-dependent gain factor of the sensor circuit is varied in such a way that it counteracts the temperature coefficient of the copper resistance of the choke
Implementation Method 2
the current through the choke is measured indirectly by detecting the voltage drop across the choke and continuously integrating it. The measured current is obtained by integrating the voltage. For this purpose, an integrator circuit is used
Implementation Method 3
The amplifier circuit comprises an inverting and a non-inverting amplifier input terminal and an amplifier output terminal. The non-inverting amplifier input terminal is supplied with an amplifier input signal depending on the integrator output signal. A voltage signal characterizing the current through the choke is present at the amplifier output terminal
Data Source
AI summary
The invention relates to a device (200) for measuring a current through a choke (130) of a voltage converter (100) comprising an integrator circuit (140), an amplifier circuit and an NTC resistor (160). The amplifier circuit comprises an inverting and a non-inverting amplifier input connection (152, 154) and an amplifier output connection (156). The non-inverting amplifier input connection (154) is supplied with an amplifier input signal according to an integrator output signal. A voltage signal characterising the current through the choke (130) is applied at the amplifier output connection (156) of the amplifier circuit. The NTC resistor (160) is arranged in the feedback path of the amplifier circuit between the inverting amplifier input connection (152) and the amplifier output connection (156).