Aging-Matched Current Sense Circuit for Power Transistors
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Solution Overview
Problem
Power transistors experience aging due to high electric fields, leading to increased internal resistance and inefficiency, which is not accurately reflected by accompanying sense transistors, as they are not exposed to the same voltage drop, resulting in inaccurate current sensing over time.
Innovation Solution
A current sense circuit with a connected power and sense transistor, and a pull-up component that equalizes the voltage at the sense transistor input node to that of the power transistor when both are off, ensuring both transistors age similarly, maintaining proportional resistance and accurate current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a sense transistor is used to measure power current, then current sensing becomes easier and more safe, but the sensing accuracy deteriorates over time due to differential aging between power and sense transistors
Solution Approach 1:
The patent applies equipotentiality by connecting the drain of the sense transistor to the drain of the power transistor, ensuring both transistors experience identical voltage drops and electric field conditions. This equalizes their aging rates, maintaining accurate current proportionality over time. The sense transistor operates under the same stress conditions as the power transistor, eliminating the measurement accuracy degradation caused by differential aging.
2Power
If power transistor handles high voltage, then power transmission capability increases, but aging effect increases due to high electric fields
Solution Approach 1:
The patent uses a sense transistor as a scaled-down copy of the power transistor, with identical structural characteristics but smaller size. This copy experiences the same voltage drop and electric field conditions, allowing it to replicate the aging behavior of the power transistor. By monitoring the sense transistor's current, the system can accurately track the power transistor's aging without directly measuring the high-power device.
3Quantity of substance
If sense transistor is smaller than power transistor, then current proportionality is maintained, but sensing accuracy deteriorates due to different aging rates
Solution Approach 1:
The patent resolves the aging rate discrepancy by connecting the drains of both transistors, ensuring they experience identical voltage drops and electric field intensities. This equipotential connection causes both transistors to age at the same rate despite their size differences, maintaining the current proportionality relationship over time. The sense transistor's smaller size allows easy measurement while its identical stress conditions ensure accurate long-term sensing.
Data Source
AI summary
A current sense circuit that allows for accurate sensing of a power current that flows through a power transistor as the power transistor ages. The circuit includes the power transistor, a sense transistor and a pull-up component. The control nodes of the power transistor and the sense transistor are connected, causing the power transistor and sense transistor to be on or off simultaneously. The pull-up component is connected between the input node of the power transistor and the input node of the sense transistor. When power is provided to the pull-up component, and when each of the power transistor and sense transistor are off, the pull-up component forces a voltage present at the sense transistor input node to be approximately equal to a voltage present at the power transistor input node, causing the sense and power transistors to age together.