MOSFET Drain-Source Resistance Temperature Detection Circuit
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Solution Overview
Problem
Existing temperature sensing methods for power MOSFETs, particularly in semiconductor devices, face challenges in detecting rapid temperature changes due to insufficient thermal coupling between the power switch and controller, leading to potential catastrophic failures and the inability to implement hysteretic thermal shutdown capabilities.
Innovation Solution
A low-side connected temperature detection circuit that measures the drain-source on-resistance (RDS(on)) of a power MOSFET directly, allowing for instantaneous thermal detection and hysteretic shutdown, by utilizing a sense-FET to monitor drain current and voltage, and comparing it to calibrated values to infer junction temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal coupling is achieved through high-side driver, then thermal detection capability is improved, but response speed to rapid temperature changes deteriorates
Solution Approach 1:
The patent introduces an intermediary mechanism by measuring drain-source on-resistance (RDS(on)) of the power MOSFET itself, which serves as a direct indicator of junction temperature. This RDS(on) measurement acts as an intermediary parameter that correlates with temperature but can be measured electrically without requiring thermal coupling to the controller, thus resolving the contradiction between thermal detection capability and response speed.
Solution Approach 2:
The patent replaces the mechanical/thermal coupling system (heat transfer from MOSFET junction to controller) with an electrical measurement system. By measuring the electrical parameter RDS(on)) which has a known temperature coefficient, the system directly obtains temperature information without relying on thermal conduction paths, thereby achieving fast response to transient temperature changes.
2Adaptability or versatility
If controller is separated from power MOSFET, then system modularity is improved, but thermal coupling and temperature monitoring capability deteriorates
Solution Approach 1:
The patent replaces the thermal coupling mechanism with an electrical measurement approach. By measuring RDS(on)) which can be done through electrical connections alone, the system maintains accurate temperature monitoring capability even when the controller is physically separated from the power MOSFET, thus enabling system modularity without sacrificing temperature monitoring precision.
Solution Approach 2:
The patent uses RDS(on)) as an intermediary parameter that bridges the gap between electrical measurement and thermal state. This intermediary allows the controller to infer junction temperature through electrical measurements alone, eliminating the need for direct thermal coupling and enabling separated modular architecture.
3Reliability
If latching shutdown is used for thermal protection, then device protection is improved, but operational flexibility and hysteretic shutdown capability deteriorates
Solution Approach 1:
The patent implements feedback by continuously monitoring RDS(on)) and comparing it against temperature-threshold-correlated values. This feedback mechanism enables the controller to make informed decisions about shutdown and restart operations, supporting both latching shutdown and hysteretic shutdown modes based on the application requirements, thus maintaining device protection while providing operational flexibility.
Solution Approach 2:
The patent introduces dynamics to the thermal protection system by enabling different shutdown modes (latching and hysteretic) and allowing restart after cooling. The system can dynamically switch between protection strategies and adapt its response based on the severity and duration of thermal conditions, providing both reliable protection and operational flexibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and rapid temperature monitoring, preventing transient overheating and allowing for hysteretic thermal shutdown, thus enhancing the protection of power MOSFETs during both steady-state and transient conditions.
Implementation Method 1
the forward voltage drop of the sense diode has a negative temperature coefficient such that the forward voltage drop is inversely proportional to the MOSFET junction temperature
Data Source
AI summary
An electronic circuit for sensing a temperature rise in a power transistor device, the temperature rise caused by a current flow in the power transistor device. The power transistor device and a sense-FET are disposed on a substrate. The sense-FET senses a fractional portion of the current flow and outputs a current signal. A JFET has its drain connected to the drain of the power transistor device. The gate of the JFET is connected to the source of the power transistor device, such that when the power transistor device is on, the JFET is also turned on, and a drain voltage signal of the power transistor device is output at a second node of the JFET. A detection circuit receives the drain voltage signal and the current signal and outputs an alarm signal when the drain-source resistance of the power transistor device exceeds a combined threshold limit.