Inductor Current Sensing With Adaptive DCR Identification
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Solution Overview
Problem
Power converter circuits, such as switch mode power supplies, face challenges in determining inductor properties like DC resistance (DCR) and inductance, which can vary from specifications, affecting performance and requiring mechanisms to detect these properties, especially in applications where prior knowledge is not available and properties change with temperature and age.
Innovation Solution
A circuit with a tunable time constant control and DCR control circuit that adjusts gain based on average inductor current and current command signals, allowing the power converter to autonomously determine inductor properties, thereby optimizing performance and being immune to changes in inductor values or parasitic board resistances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If inductor properties are assumed to match specifications, then device complexity is reduced, but measurement precision and reliability deteriorate due to property variations
Solution Approach 1:
The power converter circuit performs self-identification of inductor properties by measuring its own operating characteristics (current, voltage, frequency) and calculating DCR and inductance values internally, eliminating the need for external measurement devices or user input while maintaining high precision
Solution Approach 2:
The circuit continuously monitors inductor current and voltage, uses this feedback to calculate actual inductor properties, and adjusts control parameters accordingly to compensate for property variations, ensuring reliable operation despite deviations from specification
2Measurement precision
If inductor properties are detected using external measurement devices, then measurement precision improves, but device complexity and ease of operation worsen due to additional components and calibration requirements
Solution Approach 1:
The power converter's control circuit performs multiple functions: it controls the switching operation, measures current and voltage, calculates inductor properties, and adjusts control parameters, eliminating the need for separate dedicated measurement devices while maintaining measurement precision
Solution Approach 2:
The inductor property measurement and control functions are merged into a single integrated control circuit that uses the same current and voltage sensors for both protection/control operations and inductor characterization, reducing overall system complexity
3Device complexity
If fixed control parameters are used, then device complexity is reduced, but adaptability worsens due to temperature and aging effects on inductor properties
Solution Approach 1:
The control circuit dynamically adjusts control parameters based on real-time measurements of inductor current and voltage, automatically adapting to temperature changes and aging effects without requiring manual recalibration or complex temperature sensing circuits
Solution Approach 2:
The circuit changes control parameters (such as switching frequency, duty cycle, or current limits) based on calculated inductor properties that vary with temperature and age, maintaining optimal performance across different operating conditions through automatic parameter adaptation
Data Source
AI summary
A circuit includes a current sensor circuit having inputs and an output. The current sensor inputs are adapted to be coupled to inductor terminals a power converter. The current sensor circuit includes a tunable time constant circuit coupled between the current sensor inputs and the current sensor output. A time constant control circuit is coupled to a tunable time constant circuit, and is configured to tune the time constant circuit responsive to the current sensor output and another signal representative of inductor current. An adjustable gain circuit has a first input coupled to the current sensor output. A direct current resistance (DCR) control circuit has an output coupled to a second input of the adjustable gain circuit, and the DCR control circuit is configured to provide a gain adjust signal at the output thereof responsive to an average current of the inductor and a current command signal for the power converter.