FET Protection Circuit Using Temperature-Based Current Sensing
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Solution Overview
Problem
Existing protective circuits for field-effect transistors lack the capability for accurate evaluation of electrical currents, particularly in identifying short circuits, and are often costly due to the need for additional measuring resistors.
Innovation Solution
A protective circuit comprising field-effect transistors, temperature sensors, and a control device that determines electrical resistance and current based on temperature changes, eliminating the need for additional measuring resistors by using a linear relationship between temperature and resistance, and incorporating an analog-digital converter for precise current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional measuring resistors are used to accurately evaluate electrical currents, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The field-effect transistor's own temperature-dependent resistance is utilized as the measurement parameter. The transistor's channel resistance naturally changes with temperature, and this inherent property is exploited to determine current flow without requiring external measuring resistors. The control unit reads the voltage at the source terminal, which reflects the transistor's resistance state, thereby achieving self-measurement functionality.
Solution Approach 2:
The invention utilizes the temperature-dependent resistance characteristic of the field-effect transistor as a variable parameter for current measurement. By monitoring how the transistor's resistance changes with temperature and applying the known relationship between voltage, resistance, and current, the system determines electrical current through parameter variation rather than direct measurement with additional components.
2Measurement precision
If additional measuring resistors are used to accurately evaluate electrical currents, then measurement precision is improved, but cost increases
Solution Approach 1:
The field-effect transistor's own temperature-dependent resistance is utilized as the measurement parameter. The transistor's channel resistance naturally changes with temperature, and this inherent property is exploited to determine current flow without requiring external measuring resistors. The control unit reads the voltage at the source terminal, which reflects the transistor's resistance state, thereby achieving self-measurement functionality.
Solution Approach 2:
The invention replaces expensive precision measuring resistors with the field-effect transistor itself, which already exists in the circuit and has inherent temperature-dependent resistance characteristics. This substitution eliminates the need for additional costly components while maintaining measurement capability through the transistor's natural electrical properties.
3Reliability
If temperature monitoring is used to protect the FET, then reliability is improved, but the ability to accurately evaluate electrical currents is reduced
Solution Approach 1:
The temperature sensor serves dual purposes: it monitors the transistor's temperature for protection purposes and simultaneously enables current measurement through the temperature-dependent resistance relationship. The same temperature data that protects the device also provides the basis for accurate current evaluation, eliminating the need for separate measurement functionality.
Solution Approach 2:
The control unit continuously monitors the voltage at the source terminal and uses the known temperature-resistance relationship to calculate current flow in real-time. This feedback mechanism allows dynamic adjustment and accurate determination of electrical parameters while maintaining protection capabilities through continuous temperature monitoring.
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
Enables accurate and cost-effective evaluation of electrical currents, allowing for timely identification of short circuits and appropriate operational decisions, such as continuing or interrupting the circuit operation, while reducing the need for expensive measuring resistors.
Implementation Method 1
Based on this temperature, the control unit can determine the first electrical resistance of the first field-effect transistor and, consequently, the first electrical current flowing through it
Data Source
Figure 1
AI summary
The invention relates to a protective circuit (1) which is at least provided with the first field-effect transistor (2) comprising a first drain connection (3), a first source connection (4) and a first gate connection (5), a control appliance (6) by means of which an electrical first voltage (7) between the first drain connection (3) and the first source connection (4) can be determined, and a first temperature sensor (8) by means of which a variable first temperature (9) of the first field-effect transistor (2) can be detected, wherein a first resistance (10) of the first field effect transistor (2) and an electrical first current (11) conducted via the first field-effect transistor (2) can be determined by the control appliance (6) on the basis of the first temperature (9).