MOSFET Temperature Calculation Using Parasitic Diode
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Solution Overview
Problem
Existing methods for accurately monitoring the temperature of metal oxide field effect transistor (MOSFET) switches in electric motor control systems require detailed knowledge of device parameters, leading to inaccuracies due to manufacturing variations and increased costs from using external temperature sensors.
Innovation Solution
A system and technique that calculates the operating temperature of MOSFET switches by measuring electrical signals, specifically drain-source voltage and current, at two different times, using an equation dependent on physics constants and these measurements, eliminating the need for precise knowledge of device characteristics and leveraging the intrinsic parasitic diode within the MOSFET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external temperature sensors are used to monitor MOSFET temperature, then temperature measurement accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The MOSFET's intrinsic parasitic diode is utilized to perform temperature measurement functions without requiring external temperature sensors. The diode's forward voltage characteristic naturally varies with temperature, allowing the MOSFET to self-monitor its own temperature through electrical measurements during normal operation.
Solution Approach 2:
The parasitic diode, which normally serves as a freewheeling path for motor current, is given an additional function of temperature sensing. By measuring the forward voltage across the diode during freewheeling periods, the same component performs both current recirculation and temperature monitoring duties.
2Measurement precision
If device parameters are used for temperature calculation, then temperature monitoring is enabled, but manufacturing variations cause measurement inaccuracies
Solution Approach 1:
The system measures the actual forward voltage of the parasitic diode during operation and uses this feedback to calculate temperature. This real-world measurement approach compensates for manufacturing variations because it directly observes the actual electrical characteristics of the specific MOSFET being monitored, rather than relying on predetermined parameter values.
Solution Approach 2:
The method exploits the temperature-dependent change in the diode's forward voltage parameter. As temperature varies, the forward voltage changes in a predictable manner, allowing temperature to be inferred from voltage measurements without needing to know the diode's absolute forward voltage characteristic, which varies with manufacturing.
3Measurement precision
If two electrical signal measurements are taken at different times, then temperature calculation accuracy is improved without requiring device parameters, but measurement time increases
Solution Approach 1:
The temperature measurement is performed by taking electrical signal measurements during periodic freewheeling intervals that occur naturally during motor operation. The control system captures forward voltage measurements at two different freewheeling periods, utilizing the periodic nature of motor commutation to obtain the necessary data without requiring dedicated measurement cycles.
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 accurate temperature calculations with ±5°C accuracy, enabling reliable motor operation over a wider temperature range and reducing manufacturing costs by eliminating the need for external sensors and precise parameter knowledge.
Implementation Method 1
Accurately monitoring the temperature of the MOSFET can have significant advantages in operating range and cost savings
Implementation Method 2
the motor control unit uses an equation to calculate the temperature that depends only on some physics constants and the first and second forward voltage and current values
Data Source
AI summary
Systems and techniques are described for monitoring the operating temperature of one or more circuit elements, such as a metal oxide field effect transistor (MOSFET) switch, where the circuit element is used to control at least one phase of an electric motor. The systems and techniques may calculate temperature by determining at least two electrical signals from the circuit element taken at least two different times. This results in an accurate temperature calculation without requiring precise knowledge of the particular characteristics of each respective circuit element.