Bidirectional Current Sensing in Switching Regulators
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Solution Overview
Problem
Current current sensing circuits in switching regulators face challenges in accurately sensing bidirectional currents, particularly when the polarity of the switch current changes, and are complicated by manufacturing processes that can lead to inherent electrical connections between transistors, making it difficult to maintain robust current observations near transition regions.
Innovation Solution
The proposed solution involves a current sensing circuit that includes a replica transistor and a current sensing circuit configured to source and sink sense current, using a feedback circuit to control the voltage of the replica transistor's source, allowing bidirectional current sensing by generating appropriate currents based on the switch current's polarity, and using a sense resistor to change voltage in relation to the switch current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional current sensing circuit is used, then the circuit structure is simple, but the sensing accuracy deteriorates when bidirectional currents are present
Solution Approach 1:
The current sensing circuit is segmented into two separate sensing paths: one for positive current (first current sensing circuit) and one for negative current (second current sensing circuit). Each path is activated based on the polarity of the input current, allowing accurate sensing of bidirectional currents without interference. This segmentation resolves the contradiction by maintaining simple individual circuit structures while achieving high sensing accuracy for both current directions.
2Productivity
If the switching regulator operates near transition regions, then the switching efficiency is maintained, but the current observations become unreliable due to inherent electrical connections
Solution Approach 1:
An intermediary circuit is introduced between the switching regulator and the current sensing circuits. This intermediary includes isolation elements that prevent inherent electrical connections from affecting the sensing accuracy. The intermediary maintains the switching efficiency by allowing normal operation while ensuring reliable current observations by isolating the sensing circuits from parasitic connections during transition regions.
3Adaptability or versatility
If the drain voltage transitions between power supply voltages, then the switching regulator adapts to varying load conditions, but the current sensing accuracy deteriorates
Solution Approach 1:
The current sensing circuit employs dynamic switching mechanisms that adapt the sensing path based on the drain voltage level and current polarity. When the drain voltage transitions between power supply voltages, the circuit dynamically selects the appropriate sensing configuration, maintaining accurate current measurements throughout the voltage transition range and under varying load conditions.
Data Source
AI summary
Apparatus and methods for current sensing in switching regulators are provided. In certain implementations, a switching regulator includes a switch transistor, a replica transistor, a sense resistor, and a current sensing circuit. The drain and gate of the switch transistor can be electrically connected to the drain and gate of the replica transistor, respectively. The current sensing circuit can generate an output current that varies in response to a sense current from a source of the replica transistor. Additionally, the current sensing circuit can sink the sense current when the sense current flows from the drain to the source of the replica transistor and source the sense current when the sense current flows from the source to the drain of the replica transistor. The sense resistor can receive the output current such that the voltage across the sense resistor changes in relation to the current through the switch transistor.