Power Transistor Junction Temperature via Desaturation Sensing
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Solution Overview
Problem
Current methods for determining the junction temperature of power transistors in electric vehicles are inaccurate, leading to suboptimal operation and increased costs due to reliance on heatsink temperature measurements and additional equipment, which do not account for manufacturing variations and require extra space.
Innovation Solution
A measurement circuit device that includes a clamp, an analog-to-digital converter, and a microcontroller to directly measure the junction temperature of power transistors by converting the voltage across the transistor during its on-state, allowing for real-time adjustment of current capacity based on temperature, thereby optimizing transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If heatsink temperature measurement is used to estimate junction temperature, then cost is reduced and simplicity is improved, but measurement precision deteriorates
Solution Approach 1:
The power transistor itself serves as the temperature sensor by utilizing its inherent electrical characteristics (on-state voltage) that vary with temperature. The existing transistor structure and parameters are leveraged to provide self-diagnosis of junction temperature, eliminating the need for separate temperature sensing devices and reducing system complexity while improving measurement accuracy.
Solution Approach 2:
The invention exploits the temperature-dependent electrical parameters of the power transistor, specifically the on-state voltage (Vds) which changes predictably with junction temperature. By monitoring this electrical parameter instead of thermal parameters, the system achieves accurate temperature measurement through electrical characterization rather than thermal sensing.
2Measurement precision
If additional temperature sensing equipment is added to measure heatsink temperature, then measurement capability is improved, but cost increases
Solution Approach 1:
The power transistor provides its own temperature measurement capability through its inherent electrical characteristics. No external temperature sensors, PTC devices, or RTD elements are required. The transistor's own on-state voltage serves as the measurement parameter, eliminating the need for additional sensing components and reducing manufacturing costs.
Solution Approach 2:
The power transistor performs multiple functions: power switching and temperature sensing. By utilizing the same device for both power transmission and temperature measurement, the invention eliminates the need for dedicated temperature sensing equipment, reducing component count, manufacturing cost, and system complexity.
3Measurement precision
If additional temperature sensing equipment is added, then measurement capability is improved, but space requirements increase
Solution Approach 1:
The power transistor measures its own temperature using its inherent electrical characteristics, requiring no external sensing components. This eliminates the physical space that would be required for separate temperature sensors, mounting hardware, and associated circuitry, while maintaining accurate junction temperature measurement capability.
Solution Approach 2:
The temperature measurement function is merged with the power transistor itself. The same physical component that handles power transmission also provides temperature sensing through its electrical parameters. This consolidation eliminates the need for separate sensing equipment and the space it would occupy.
4Reliability
If worst-case thermal resistance and peak power loss assumptions are used, then reliability is improved, but productivity deteriorates due to operating below full capacity
Solution Approach 1:
The system continuously monitors the actual junction temperature through real-time measurement of the transistor's on-state voltage and uses this feedback to dynamically adjust the current capacity limits. This closed-loop control allows the transistor to operate at optimal capacity levels matched to actual temperature conditions, maximizing productivity while maintaining reliability through real-time safety monitoring.
Solution Approach 2:
The current capacity limits are made dynamic rather than static. Instead of using fixed worst-case assumptions, the system continuously adapts the allowable current capacity based on real-time junction temperature measurements. This enables the transistor to operate at higher capacities when cool and reduces capacity when hot, optimizing both productivity and reliability.
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 solution provides accurate junction temperature measurement and real-time capacity adjustment, ensuring optimal transistor performance, reducing the risk of overheating, and minimizing additional equipment costs, thus enhancing the reliability and efficiency of electric vehicle power systems.
Implementation Method 1
a voltage measurement circuit coupled to the power transistor that measures a voltage across the power transistor
Implementation Method 2
an analog-to-digital converter that converts the measured voltage from an analog value to a digital value
Implementation Method 3
Power transistors may be mounted on a heatsink in order to conduct energy (i.e., heat) away from the transistor to reduce temperature rise
Data Source
AI summary
A measurement circuit device for a vehicle includes a power transistor and a voltage measurement circuit coupled to the power transistor that measures a voltage across the power transistor. The measurement circuit device also includes a microcontroller that determines a junction temperature using the measured voltage and adjusts a capacity of the power transistor based on the determined junction temperature. In some embodiments, the measurement circuit device may include a clamping device that clamps the voltage across the transistor when the transistor is off. The measurement circuit device may also include an analog-to-digital converter that converts the measured voltage from an analog value to a digital value.