Transistor Junction Temperature Estimation via Turn-off Voltage
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Solution Overview
Problem
Existing methods for estimating the junction or die temperature of transistors, particularly in transient operations, are not sufficiently accurate for control applications in inverters driving electric motors, necessitating an improved real-time temperature estimation method.
Innovation Solution
A system and method that measure turn-off voltage change and peak voltage across a transistor, determining intermediate parameters like turn-off and turn-on currents and on-state voltage drop, and then estimate the average junction or die temperature based on energy loss, inverter system temperature, and thermal characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermally sensitive resistor is spaced apart from the semiconductor die to provide electrical insulation and reduce noise, then reliability and noise immunity are improved, but measurement precision of junction temperature deteriorates
Solution Approach 1:
The patent uses turn-off voltage change (dvce/dt) as an intermediary parameter to indirectly measure junction temperature. Instead of directly measuring temperature with a spaced thermistor, the method measures the voltage change rate during transistor turn-off, which is temperature-dependent, and uses this as a mediator to infer the actual junction temperature without requiring direct thermal contact.
Solution Approach 2:
The patent changes the measurement parameter from direct temperature sensing to measuring the rate of voltage change (dvce/dt) during switching. This parameter change allows temperature estimation through electrical characteristics that vary with temperature, eliminating the need for physical proximity between the sensor and the semiconductor die.
2Ease of operation
If conventional current sensors are used to measure turn-off current, then current measurement is achieved, but measurement precision deteriorates due to sensor errors
Solution Approach 1:
The patent replaces mechanical/current sensors with an electrical measurement approach. Instead of using conventional current sensors that introduce errors, the method uses voltage measurements across the transistor terminals and calculates the turn-off current from the measured dvce/dt and known circuit parameters, substituting direct current sensing with voltage-based indirect measurement.
Solution Approach 2:
The transistor itself serves as the measurement element. The voltage change during turn-off, which is inherently generated by the transistor's switching behavior, is used to extract both current and temperature information. The device under test provides its own measurement signal, eliminating the need for external sensing components that introduce errors.
3Productivity
If temperature estimation methods are simplified for real-time operation, then productivity and response time are improved, but measurement precision deteriorates
Solution Approach 1:
The patent performs preliminary characterization of the transistor's dvce/dt versus temperature relationship during manufacturing or initial operation. This pre-established relationship is stored and used during real-time operation to quickly convert measured voltage change rates into temperature estimates, enabling fast real-time measurement without complex calculations while maintaining precision through pre-calibrated data.
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 provides improved accuracy in estimating transistor temperatures during both steady-state and transient operations, eliminating errors from conventional current sensors and maintaining reliability across a wide temperature range, suitable for silicon carbide power semiconductor devices.
Implementation Method 1
measures turn-off voltage change (e.g., a rate of voltage rise or dvce/dt) with respect to change in time between a collector and emitter (or drain and source, respectively) of a transistor
Implementation Method 2
thermal characteristic of an inverter system (e.g., thermal resistance of a liquid cooled system) for the inverter
Implementation Method 3
observed inverter system temperature (e.g., coolant temperature of a coolant in a coolant system) for cooling the inverter
Data Source
AI summary
A detector measures turn-off voltage change with respect to change in time between a collector and emitter of a transistor and peak voltage of the transistor at the collector. An electronic data processor determines intermediate parameters of turn-off current, the turn-on current and on-state voltage drop based on the turn-off voltage change and the peak voltage. The data processor determines the power or energy loss for one switching cycle of the transistor based on the turn-off current, the turn-on current and on-state voltage drop between the collector and emitter of the transistor. The data processor estimates an associated average die temperature for the transistor over the switching cycle.