Inversely Coupled MOS Transistors for Low Resistance Current Detection
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Solution Overview
Problem
The use of shunt resistors in bidirectional semiconductor switches for overcurrent detection increases the on-resistance of the circuit, hindering quick charging in rechargeable battery packs.
Innovation Solution
A semiconductor device with a configuration of inversely coupled main MOS transistors and sense MOS transistors, where the sense transistors detect the main current without the need for a shunt resistor, reducing the overall resistance and improving current detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is provided in series with the bidirectional switch for overcurrent detection, then current detection capability is improved, but the on-resistance of the entire circuit is increased
Solution Approach 1:
The patent divides the current detection function into separate sense MOS transistors (first and second sense MOS transistors) that are inversely coupled in series, allowing current detection without requiring a shunt resistor in the main current path. This segmentation enables the main MOS transistors to handle full current while sense transistors provide detection capability.
Solution Approach 2:
The patent introduces sense MOS transistors as intermediary elements that replicate the current flow characteristics without bearing the full load. These sense transistors are coupled through their sources to a common potential and their drains to opposite potentials, creating an intermediate detection path that doesn't add resistance to the main circuit.
2Measurement precision
If a shunt resistor is used for overcurrent detection, then current detection accuracy is improved, but charging speed is reduced
Solution Approach 1:
The current detection function is segmented into dedicated sense MOS transistors that operate in parallel with the main current path. The first sense MOS transistor detects current in one direction while the second sense MOS transistor detects current in the opposite direction, enabling accurate detection without impeding charging current flow.
Solution Approach 2:
The sense MOS transistors serve multiple functions: they detect overcurrent conditions, provide current direction sensing, and maintain low impedance paths during both charging and discharging operations. This multi-functionality eliminates the need for separate shunt resistors that would slow down charging.
3Loss of energy
If sense MOS transistors are inversely coupled in series with shared drain electrode, then current detection is achieved without shunt resistor, but device complexity increases
Solution Approach 1:
The patent merges the detection functions for both current directions into a single integrated structure where first and second sense MOS transistors are inversely coupled in series with a shared drain electrode. This combining approach reduces the total component count compared to using separate detection circuits for each direction.
Solution Approach 2:
The sense MOS transistors are configured with asymmetric coupling: their sources are coupled to a common potential while their drains are connected to opposite potentials. This asymmetric arrangement enables the transistors to function as a unified detection element that responds to current flow in either direction without requiring symmetric duplicate circuits.
Data Source
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AI summary
An object of the present invention is to suppress an increase in on-resistance of an entire circuit including a bidirectional semiconductor switch. A semiconductor device includes a first main MOS transistor and a second main MOS transistor of a vertical structure that are inversely coupled to each other in series by sharing a drain electrode and a first sense MOS transistor and a second sense MOS transistor of a vertical structure that are inversely coupled to each other in series by sharing a drain electrode. The first sense MOS transistor is used for detecting the main current of the first main MOS transistor, and the second sense MOS transistor is used for detecting the main current of the second main MOS transistor.