SMPS Current Detection Circuit Emulation for Inductor Accuracy
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Solution Overview
Problem
Existing current detection methods in switching mode power supplies (SMPS) are inaccurate due to variations in inductor resistance and temperature, leading to potential damage from short conditions and inefficiencies in current sensing across parasitic resistances.
Innovation Solution
A current detection circuit comprising a current sensing circuit and a current emulation circuit, which senses and emulates the inductor current based on PWM signal states, providing a continuous and accurate detection signal without the need for trimming, using a combination of current sensing and emulation signals during different periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inductor current is sensed by sensing the DC voltage across inductor using serially coupled resistor and capacitor, then current detection is achieved, but measurement precision deteriorates due to variation of inductor resistance and temperature
Solution Approach 1:
The patent creates a copy of the inductor current through a current mirror circuit. The sensing circuit measures the current through the low-side switch, and this sensed current is copied to generate an emulation signal that represents the inductor current. This copying approach eliminates the need to directly sense voltage across the inductor, thereby avoiding errors from inductor resistance variations and temperature effects.
Solution Approach 2:
The patent introduces an intermediary current emulation circuit that acts as a mediator between the switch current sensing and the inductor current detection. Instead of directly measuring inductor current through voltage sensing across the inductor (which is affected by resistance variations), the system uses the low-side switch current as an intermediary to generate an emulation signal that accurately represents the inductor current without being affected by inductor resistance changes.
2Measurement precision
If current is detected through parasitic resistance of inductor, then current sensing is achieved, but measurement precision deteriorates due to temperature dependence of resistance
Solution Approach 1:
The system copies the switch current characteristics to emulate the inductor current behavior. By using a current mirror to create a copy of the sensed current and integrating it through a capacitor, the system generates an emulation signal that tracks the inductor current without being affected by temperature-induced resistance changes in the inductor or sensing resistors.
Solution Approach 2:
The patent replaces the traditional voltage-based current sensing method (which relies on measuring voltage across parasitic resistance) with a current-based emulation method. Instead of using Ohm's law (V=IR) which is temperature-dependent, the system uses current mirroring and capacitive integration to directly emulate the current waveform, eliminating the temperature sensitivity inherent in resistance-based sensing.
3Measurement precision
If current detection signal is determined solely by current sensing circuit, then circuit complexity is reduced, but measurement precision deteriorates during switching transitions
Solution Approach 1:
The patent segments the current detection process into two distinct parts: a current sensing portion that measures the switch current, and a current emulation portion that generates the inductor current representation. This segmentation allows each part to perform its specific function optimally - the sensing circuit captures accurate switch current data, while the emulation circuit processes this data to generate the inductor current signal, improving overall precision during switching transitions.
Solution Approach 2:
The system performs preliminary current sensing during the off-state of the high-side switch, before the inductor current needs to be detected. By sensing the low-side switch current in advance and using it to generate an emulation signal through current mirroring and integration, the system prepares the current detection data ahead of time, ensuring accurate current information is available during critical switching transitions without adding excessive complexity.
Data Source
AI summary
A current detection circuit for detecting a current in a SMPS which has a first switch and a second switch; a current sensing circuit sensing a second switch current flowing through the second switch and providing a current sensing signal; and a current emulation circuit which generates a first current according to the current sensing signal and generate a second current according to the first current source, and the current emulation circuit further providing a current emulation signal based on the first current source and the second current source; wherein a current detection signal during a first period is proportional to the current emulation signal, and the current detection signal during a second period is proportional to the current sensing signal.