SiC MOSFET Main and Sense Cell Thresholds for Low-Temperature Stability
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Solution Overview
Problem
Existing silicon carbide semiconductor devices experience a decrease in main current at low temperatures due to unconsidered temperature-dependent properties of threshold voltage, leading to unstable current sensing operations.
Innovation Solution
The silicon carbide semiconductor device incorporates a main cell and a sense cell with different threshold voltages, where the threshold voltage of the main cell is set to be smaller than that of the sense cell, ensuring the temperature-dependent properties of the main current remain approximately flat at 0°C or less, thereby preventing a decrease in main current and maintaining stable current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold voltage of the sense cell is set larger than that of the main cell to suppress unbalance of current ratio, then the current sensing accuracy is improved, but the main current decreases at low temperature due to unconsidered temperature dependent properties
Solution Approach 1:
The patent applies parameter changes by setting different threshold voltage values for the main cell and sense cell, specifically optimizing the sense cell threshold voltage to be in the range of 2.0V to 3.5V. This parameter optimization compensates for temperature-dependent effects and maintains stable current characteristics across temperature variations, resolving the contradiction between sensing accuracy and low-temperature stability
Solution Approach 2:
The patent implements local quality by creating asymmetric threshold voltage characteristics between the main cell and sense cell. The sense cell is specifically designed with a higher threshold voltage than the main cell, giving each cell localized electrical properties tailored to its function. This local differentiation enables the sense cell to maintain accurate current sensing while the main cell preserves stable current output at low temperatures
2Stability of the object's composition
If the threshold voltage difference between main cell and sense cell is increased to improve current ratio balance, then the sensing operation stability is improved, but the sense current becomes excessively reduced at low temperature
Solution Approach 1:
The patent optimizes the threshold voltage parameter of the sense cell to a specific range (2.0V to 3.5V) that balances two competing requirements: maintaining operation stability through sufficient threshold voltage difference while preventing excessive sense current reduction at low temperatures. This precise parameter control resolves the contradiction between stability and current magnitude
Data Source
AI summary
An object of the present disclosure is to achieve a stable current sensing operation and suppress decrease in main current at a low temperature of 0° C. or less in a silicon carbide semiconductor device. An SiC-MOSFET includes: a main cell outputting main current; and a sense cell outputting sense current proportional to the main current, wherein temperature dependent properties of the main current differ in accordance with threshold voltage of the main cell, temperature dependent properties of the sense current differ in accordance with threshold voltage of the sense cell, the threshold voltage of the main cell is smaller than the threshold voltage of the sense cell, and in a temperature of 0° C. or less, an inclination of the temperature dependent properties of the main current is smaller than an inclination of the temperature dependent properties of the sense current.