FET Reliability Monitoring Using Body Diode Voltage Signatures
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Solution Overview
Problem
Field-effect transistors (FETs) degrade over time due to power delivery, reducing their reliability, and existing methods require complex temperature sensor circuits for diagnostic analysis.
Innovation Solution
A system and method that uses control logic to apply different gate voltages to FETs, sampling voltages across the device to determine degradation levels without separate temperature sensors, by comparing signatures from current paths through the channel and body diode, and using junction temperature to establish a reference voltage for non-degraded states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate temperature sensor circuits are used for diagnostic analysis, then temperature measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The FET device itself is used to generate temperature information through its inherent voltage characteristics. By measuring the voltage across the FET at different gate voltages, the device provides its own temperature data without requiring external temperature sensors, thus eliminating the need for separate temperature measurement circuits while maintaining measurement capability
Solution Approach 2:
The existing FET device performs multiple functions: it acts as both the power switching device and the temperature sensing element. The same FET structure that controls power delivery also generates the voltage signatures used for thermal diagnostics, combining two functions into one component to reduce overall system complexity
2Reliability
If separate temperature sensor circuits are used for diagnostic analysis, then temperature monitoring capability is improved, but manufacturing cost increases
Solution Approach 1:
The FET device provides its own temperature monitoring capability through its intrinsic voltage characteristics. By utilizing the voltage across the FET channel and body diode at different gate voltages, the system obtains temperature information without requiring additional temperature sensor components, thereby reducing part count and manufacturing cost
Solution Approach 2:
The temperature sensing function is extracted from a separate component and integrated into the FET device itself. The voltage measurements taken from the FET's inherent electrical characteristics contain temperature information, allowing the temperature monitoring function to be obtained from the existing power device without adding separate sensing elements
3Measurement precision
If multiple voltage measurements are taken at different gate voltages, then degradation assessment accuracy is improved, but measurement complexity increases
Solution Approach 1:
The measurement process uses periodic application of different gate voltages to the FET. By sequentially applying first and second gate voltages and measuring the corresponding voltages at these discrete time points, the system obtains multiple data points for degradation assessment without requiring complex simultaneous multi-parameter measurement circuits
Solution Approach 2:
The system performs preliminary voltage measurements at different gate voltages to establish temperature information before conducting the final degradation assessment. This preliminary action of measuring voltage at multiple gate voltage states allows the derivation of temperature data that is then used to interpret the degradation measurements accurately
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
This approach simplifies circuit design, reduces costs, and provides accurate temperature measurement directly from FET voltages, enabling reliable degradation assessment and maintenance triggers without dedicated temperature sensors.
Implementation Method 1
A measurement circuit is configured to sample a first voltage across the FET in response to a first state of the drive signal and configured to sample a second voltage across the FET in response to a second state of the drive signal. The control logic is configured to determine a junction temperature for the FET based on the second voltage.
Implementation Method 2
The control logic is configured to determine a difference between the first voltage and a reference voltage. The control logic is configured to compare the difference to a degradation threshold to determine a level of degradation of the FET. The reference voltage is determined based on the second voltage.
Data Source
AI summary
A device includes an output circuit configured to drive a gate of a field effect transistor (FET) in response to a drive signal. The FET includes a body diode. Control logic is configured to generate the drive signal to control the output circuit to drive the FET. A measurement circuit is configured to sample a first voltage across the FET in response to a first state of the drive signal and configured to sample a second voltage across the FET in response to a second state of the drive signal. The second state of the drive signal is different from the first state. The control logic is configured to determine a difference between the first voltage and a reference voltage. The control logic is configured to compare the difference to a degradation threshold to determine a level of degradation of the FET. The reference voltage is determined based on the second voltage.