Switched-Capacitor Inductor Current Sensing Without Filter Delay
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Solution Overview
Problem
Existing switched-power circuits face inefficiencies and long delay times in measuring inductor charging current due to the need for complex voltage measurement circuits and low-pass filters, which affect accuracy and introduce losses.
Innovation Solution
A method and circuit using a pair of capacitors to sample output voltage at different cycle times of the inductor current waveform, sharing charge between them to provide a measurement voltage indicative of the average inductor charging current, eliminating the need for complex filters and reducing measurement delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement via sense resistors or auxiliary windings is used, then inductor charging current can be measured, but efficiency is sacrificed due to losses introduced by series elements
Solution Approach 1:
The patent uses an intermediary measurement approach by sampling the output voltage waveform instead of directly measuring inductor current through series elements. The capacitors C1 and C2 sample voltage at different phases, and the charge sharing process indirectly provides current information without introducing lossy series components into the power path.
Solution Approach 2:
The patent replaces the traditional electrical measurement method (using sense resistors or current transformers) with a voltage sampling and charge sharing mechanism. This substitution eliminates the need for direct current sensing elements that would introduce power losses.
2Measurement precision
If low-pass filter with long time constant is used to remove harmonics, then measurement accuracy is improved, but delay time increases
Solution Approach 1:
The patent uses periodic sampling of the voltage waveform at specific phases (peak and valley points) rather than continuous filtering. By sampling at strategically chosen moments during each switching cycle and using charge sharing, the circuit obtains accurate average current information without the time delays associated with long time constant filters.
Solution Approach 2:
The measurement circuit proactively samples the voltage waveform at predetermined phases before the need for measurement results is required. The capacitors are charged at specific moments in the switching cycle, and the charge sharing operation prepares the measurement voltage in advance, eliminating delays.
3Measurement precision
If complex voltage measurement circuits are used, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent divides the measurement function into discrete sampling stages using separate capacitors C1 and C2 for different phases, followed by a charge sharing operation. This segmentation simplifies each individual component while achieving the overall measurement function through coordinated operation of simple elements.
Solution Approach 2:
The patent changes the measurement parameter from direct current measurement to voltage sampling at different phases. By measuring voltage at peak and valley points and using charge sharing to derive average current information, the circuit achieves accurate measurement with simpler components.
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
Enables efficient measurement of average inductor charging current without introducing inefficiencies or delays, allowing for accurate load current determination and efficient mode switching in switched-mode power supplies.
Implementation Method 1
a first capacitor and a first switch that sample an output voltage of the power output stage at a first cycle time of an inductor current waveform and a second capacitor and a second switch that sample the output voltage at a second cycle time
Implementation Method 2
at least one third switch that connects the first capacitor to the second capacitor to provide a measurement voltage indicative of the average inductor charging current by sharing charge between the first capacitor and the second capacitor
Data Source
AI summary
Techniques for measuring average inductor charging current in a switched-power circuit avoid incurring measurement delay or a requirement of a complex filter. An inductor charging current measurement circuit coupled to a power output stage of the switched-power circuit measures an average charging current in an inductor of the switched-power circuit using pair of capacitors to sample an output voltage of the power output stage at different cycle times of an inductor current waveform. The measurement circuit includes a switch that connects the pair of capacitors together to provide a measurement indicative of the average inductor charging current by sharing charge between the first capacitor and the second capacitor to provide the measurement voltage. The provided measurement voltage is indicative of an average of an estimated peak and an estimated valley of the inductor current waveform, which may be used to make determinations regarding a magnitude of the load current.