Inductor Current Sensing via Low-Side Switch Slope Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional inductor current sensing methods in Switch Mode Power Supplies (SMPS) face challenges in accurately sensing current information due to high switching frequency, short on-time duty, and noise from switches, leading to poor accuracy and power loss, especially under light load conditions, and are temperature sensitive with increased costs for component replacement.
Innovation Solution
An inductor current sensing device that classifies current information into rising and falling slope information and average current, using a controller IC or stand-alone devices to process and merge these signals, allowing for accurate current monitoring by sensing only the low-side switch information, which includes a block diagram with LS current sensing, slope sensing, valley current sensing, operator, and current slope synthesis circuits to generate a triangular waveform proportional to the inductor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional inductor current sensing methods are used in SMPS with high switching frequency and short on-time duty, then the system can operate at higher frequency with smaller form factor, but the current sensing accuracy deteriorates due to noise from switches turning on and off
Solution Approach 1:
The patent extracts only the necessary current information from the low-side switch voltage signal by detecting the slope of the voltage waveform. Instead of sensing the entire current waveform directly, the method extracts slope information which contains the essential current characteristics while being immune to high-frequency switching noise. This extraction approach resolves the contradiction by obtaining accurate current information without being affected by the noise generated at high switching frequencies.
Solution Approach 2:
The patent uses the low-side switch voltage signal as an intermediary to indirectly obtain inductor current information. Rather than directly sensing the inductor current which is contaminated by switching noise, the method uses the clean voltage signal from the low-side switch as a mediator. The slope of this voltage signal serves as an intermediary representation that preserves current information while eliminating noise, thus resolving the accuracy problem at high switching frequencies.
2Measurement precision
If conventional current sensing methods are used, then current information can be obtained, but power loss increases especially under light load conditions
Solution Approach 1:
The patent employs self-service by utilizing the existing low-side switch and its inherent voltage signal for current sensing purposes. The low-side switch already exists in the circuit for its primary function, and its voltage signal naturally contains the current information needed. By making this existing component serve dual purposes (switching and sensing), the patent eliminates the need for separate sensing components that would consume additional power, thus resolving the power loss issue while maintaining measurement accuracy.
Solution Approach 2:
The low-side switch is made multi-functional by using it for both its primary switching function and as a current sensing element. The voltage signal generated by the low-side switch during its operation is universally used to extract current information. This universal usage of the low-side switch for dual purposes eliminates the need for dedicated sensing components, reducing overall power consumption while maintaining accurate current measurement even under light load conditions.
3Ease of manufacture
If conventional sensing methods are used, then current monitoring can be implemented, but the system becomes temperature sensitive and requires expensive component replacement
Solution Approach 1:
The patent extracts current information from the low-side switch voltage signal without relying on temperature-sensitive parasitic resistance measurements. By taking out only the essential slope information from the voltage waveform, the method avoids using components or measurements that are sensitive to temperature variations. This extraction approach eliminates the need for expensive temperature-compensated components while maintaining manufacturing simplicity and cost-effectiveness.
4Measurement precision
If parasitic resistance measurement is used for current sensing, then current information can be obtained, but precise measurement becomes difficult and costly
Solution Approach 1:
The patent uses the low-side switch voltage signal as an intermediary that provides current information without requiring direct parasitic resistance measurement. The voltage signal serves as a mediator that translates current information into a measurable form that is easy to obtain and process. This intermediary approach simplifies the measurement process by avoiding complex parasitic resistance measurements while maintaining accurate current sensing through slope detection of the voltage waveform.
Data Source
AI summary
Aspects of the present disclosure describe a SMPS system, comprising a SMPS and an inductor current sensing device. The SMPS comprise a high-side (HS) switch and a low-side (LS) switch coupled in series and an output filter including an inductor and a capacitor coupled to a switch node formed by the HS and LS switches. An inductor current is supplied by the inductor to a load. The inductor current sensing device coupled across the LS switch has a first input configured to receive a node signal indicating a voltage level at the switch node, a second input configured to receive an input voltage of the system and a third input configured to receive an output voltage of the system. The inductor current sensing device is configured to obtain a first constant DC slope information, a second constant DC slope information and a valley current information based on the first input, second and third inputs, and generate an output signal based on the first constant DC slope information, the second constant DC slope information and the valley current information. The output signal has a triangular waveform including a rising slope and a falling slope proportional to rising and falling slopes of the inductor current.