Composite Power Switch Current Sensing With Closed-Loop Voltage Matching
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Solution Overview
Problem
Existing methods for detecting conduction current through power switches are inaccurate due to variations in gate-to-source and drain-to-source voltages, which prevents precise control of currents flowing through inductors and can lead to magnetic saturation.
Innovation Solution
The proposed solution involves an apparatus comprising a composite power switch formed by NMOS transistors, a voltage detector, a current detector, and a closed-loop controller. This setup ensures that power switches have approximately the same gate-to-source and drain-to-source voltages, allowing for a proportional relationship between conduction current and output current, thus enabling accurate detection of conduction current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If power switches N1 and N2 are used to detect conduction current, then current detection can be implemented, but measurement precision deteriorates due to voltage variations
Solution Approach 1:
The patent introduces an intermediary circuit that couples the first power switch and second power switch through a controlled connection. This intermediary mechanism ensures that both power switches experience identical voltage conditions (gate-to-source voltage and drain-to-source voltage) during current detection, thereby maintaining the reliability of the proportional relationship between their conduction currents while enabling accurate measurement.
2Adaptability or versatility
If power switches have different source voltages, then circuit operation is flexible, but measurement precision deteriorates
Solution Approach 1:
The patent applies the equipotentiality principle by ensuring that both power switches operate at the same voltage potential during the detection phase. The coupling mechanism equalizes the gate-to-source voltage and drain-to-source voltage across both switches, creating equipotential conditions that enable precise current measurement while preserving circuit flexibility through controlled switching sequences.
3Measurement precision
If prior art method is used for current detection, then device complexity is low, but measurement precision is insufficient
Solution Approach 1:
The patent merges the detection functions of two power switches into a unified detection system. By coupling the switches and utilizing their proportional current relationship under identical voltage conditions, the system achieves high-precision current detection without requiring separate independent detection circuits for each switch, thus improving measurement precision while controlling overall device complexity.
Data Source
AI summary
Disclosed is an apparatus for detecting a conduction current flowing through a power switch with a control node, a channel node and a reference node. The apparatus has a voltage detector, a current detector and a close-loop controller. The voltage detector transmits a channel voltage at the channel node to a voltage detection node as a detection voltage when the power switch is turned ON, makes the detection voltage different from the channel voltage when the power switch is turned OFF. The current detector is coupled to the control node and the reference node to form a current mirror with a current detection node. The close-loop controller provides an emulation current to the current detection node to make a controlled voltage at the current detection node equal to the detection voltage.