Current Sense Circuit With Pull-Up Aging Matching
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Solution Overview
Problem
Power transistors experience uneven aging due to differing voltage drops when turned off, leading to inaccurate current sensing as they age, as the sense transistor does not experience the same level of voltage drop, resulting in a loss of proportionality between the sense current and power current.
Innovation Solution
A current sense circuit with a pull-up component connected between the input nodes of the power transistor and the sense transistor, which forces the sense transistor to experience a similar voltage drop to the power transistor when both are off, ensuring both transistors age at a similar rate and maintain proportional internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sense transistor is used to sense power current, then the current sensing function is achieved, but the sense transistor does not experience the same voltage drop as the power transistor when off, leading to uneven aging and loss of proportionality between sense current and power current
Solution Approach 1:
The pull-up component is configured to equalize the voltage at the input nodes of the power transistor and sense transistor when both are off, ensuring both transistors experience the same voltage drop and age at the same rate. This maintains the proportionality between sense current and power current over time, resolving the reliability issue while preserving measurement precision.
2Power
If the power transistor handles high voltage when off, then the power switching function is achieved, but the large voltage drop causes accelerated aging and increased internal resistance when on
Solution Approach 1:
By using the pull-up component to equalize voltages at the input nodes of both transistors when off, the power transistor experiences controlled voltage conditions that reduce excessive aging effects while maintaining its high power handling capability when on.
3Object-affected harmful factors
If the sense transistor input node voltage is kept low when off, then the sense transistor is protected from excessive voltage stress, but it does not experience the same voltage drop as the power transistor, causing differential aging
Solution Approach 1:
The pull-up component actively raises the sense transistor input node voltage to match the power transistor input node voltage when both are off, ensuring both transistors experience identical voltage stress and age uniformly, while the sense transistor remains protected during normal operation due to its smaller size and lower current handling requirements.
Data Source
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AI summary
A current sense circuit (100) that allows for accurate sensing of a power current that flows through a power transistor (110) as the power transistor ages. The circuit (100) includes the power transistor (110), a sense transistor (120) and a pull-up component (130). The control nodes of the power transistor (110) and the sense transistor (120) are connected, causing the power transistor (110) and sense transistor (120) to be on or off simultaneously. The pull-up component (130) is connected between the input node (112) of the power transistor (110) and the input node (122) of the sense transistor (120). When power is provided to the pull-up component (130), and when each of the power transistor (110) and sense transistor (120) are off, the pull-up component (130) forces a voltage present at the sense transistor input node (122) to be approximately equal to a voltage present at the power transistor input node (112), causing the sense and power transistors (120, 110) to age together.