External Diode Temperature Sensing for High-Power FETs
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Solution Overview
Problem
In high-power field effect transistor (FET) applications, accurate temperature sensing is compromised when the temperature sensor is located far from the FET, leading to potential damage due to inadequate monitoring and control of the FET's temperature, especially in hybrid automobiles and computer servers where currents are high.
Innovation Solution
An external diode-based temperature sensing system is employed, utilizing a ΔVbe method that applies a first and second current to the diode, measuring the voltage difference to provide an accurate temperature reading, which is then used to control the FET and prevent overheating, with hysteresis to ensure reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the temperature sensor is located far from the FET, then the circuit layout is simplified and component placement is easier, but the temperature measurement accuracy deteriorates
Solution Approach 1:
The patent introduces an external diode as an intermediary temperature sensing element that can be placed near the FET to accurately measure its temperature, while the controller remains separately located. The diode acts as a mediator that transfers temperature information from the FET to the controller without requiring direct physical connection or proximity between the controller and FET, thus resolving the contradiction between measurement accuracy and circuit layout flexibility.
2Measurement precision
If the temperature sensor is placed proximate to the FET, then the temperature measurement accuracy is improved, but the device complexity and routing requirements increase
Solution Approach 1:
The external diode serves as a simple intermediary component that bridges the gap between the FET and controller. It requires minimal circuit routing - only a connection from the diode to the controller's temperature input pin - while enabling accurate temperature measurement. This approach avoids complex routing requirements that would arise from integrating the temperature sensor directly into the controller or requiring multiple signal paths.
3Device complexity
If a simple temperature sensing method is used, then the circuit complexity is reduced, but the temperature measurement accuracy deteriorates
Solution Approach 1:
The patent utilizes the temperature-dependent voltage characteristic of the external diode as a simple yet accurate temperature sensing mechanism. By measuring the diode's voltage drop at a known current, the system extracts temperature information without requiring complex circuitry. This parameter-based approach (using voltage as a temperature indicator) maintains circuit simplicity while achieving accurate temperature measurement, as the diode's voltage characteristic provides a direct and reliable temperature indicator.
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
The external diode system enhances temperature measurement accuracy, allowing for precise control of the FET's operating temperature range, preventing damage and ensuring reliable operation by accurately monitoring and managing the FET's temperature, even when the sensor is distant from the FET controller.
Implementation Method 1
utilizing a ΔVbe method that applies a first and second current to the diode, measuring the voltage difference to provide an accurate temperature reading
Data Source
AI summary
Described embodiments include a circuit for temperature sensing having a first current source coupled to a diode input terminal. The first current source provides a first current at a first current output. A second current source provides a second current at a second current output. The second current is larger than the first current. A first switch is coupled between the second current source output and the diode input terminal. A capacitor is coupled between the diode input terminal and a temperature output terminal. A second switch is coupled between the temperature output terminal and a ground terminal. The temperature output terminal provides a temperature signal having a voltage that is proportional to a temperature of a component.