High-Side Current Emulation via Inductance Sensing
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Solution Overview
Problem
Existing current sensing circuits in Switch Mode Power Supplies (SMPS) face challenges in accurately detecting high-side current information due to parasitic inductance and diode reverse recovery, leading to oscillation issues and the need for preset or estimated inductance values, which are not suitable for high-switching-frequency and low-duty-cycle applications.
Innovation Solution
A current detection and control circuit that includes a current sensing circuit for the low-side switching element, a sample and hold circuit, a current emulation circuit with an inductance sensing circuit and an AC emulation circuit to automatically convert and provide accurate high-side current information based on real-time inductor current rate of change, eliminating the need for preset inductance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing circuits are used for high-side switching elements, then the circuit structure is simple, but the current detection accuracy deteriorates due to parasitic inductance and diode reverse recovery
Solution Approach 1:
The patent introduces an intermediary approach by using the low-side current sensing circuit combined with mathematical modeling to indirectly obtain high-side current information. Instead of directly sensing the high-side current (which would require complex circuitry), the system uses the easily measurable low-side current and applies Kirchhoff's current law with inductance modeling to calculate the high-side current, thus avoiding direct exposure to parasitic inductance and diode reverse recovery effects
Solution Approach 2:
The patent replaces the direct electrical sensing mechanism with a computational approach. Instead of using physical current sensors that directly measure high-side current (which suffer from parasitic effects), the system substitutes this with a mathematical model that uses the low-side current measurement, switching signals, and inductance parameters to compute the high-side current through software processing and signal analysis
2Measurement precision
If preset inductance values are used for current emulation, then the device complexity is reduced, but the measurement precision deteriorates due to inductor degradation over time
Solution Approach 1:
The patent implements a feedback mechanism where the actual inductance value is continuously sensed and measured during operation. The inductance sensing circuit monitors the real-time inductance of the power inductor, and this measured value is fed back to the control system to dynamically adjust the current emulation calculations, ensuring accuracy even as the inductor degrades over time or under different operating conditions
Solution Approach 2:
The patent transitions from a static approach (using fixed preset inductance values) to a dynamic approach where the inductance value is continuously adapted based on real-time sensing. The system dynamically adjusts the emulation parameters according to the actual inductance measurement, allowing the current emulation to remain accurate despite changes in operating conditions, temperature, or inductor aging
3Productivity
If high switching frequency and low duty cycle are used, then the productivity is improved, but the measurement precision of high-side current deteriorates due to increased parasitic effects
Solution Approach 1:
The patent uses the low-side current as an intermediary measurement that is not affected by the same parasitic issues as direct high-side sensing. By measuring the low-side current (which has cleaner signal characteristics even at high switching frequencies) and using mathematical relationships to derive high-side current information, the system maintains measurement accuracy while supporting high switching frequencies and low duty cycle operations
Data Source
AI summary
A current detection circuit for detecting a current in a Switch Mode Power Supply (SMPS) having a first switch and a second switch coupled in series and an output filter including an inductor and a capacitor coupled to a switch node formed by the first and second switches, has a current sensing circuit for sensing a current across the second switch and generating a current sensing signal indicating current information of the second switch, and a current emulation circuit for emulating current information of the first switch. The current emulation circuit includes an inductance sensing circuit for acquiring a real-time rate of change in inductor current and an AC emulation circuit for computing the AC portion of the current information of the first switch based on the real-time rate of change in inductor current.