Semiconductor Current Detection Circuit for Rapid Short-Circuit Protection
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Solution Overview
Problem
Current semiconductor devices face challenges in accurately detecting high-speed arm shorting currents and high-accuracy load currents in three-phase two-level inverters, with existing methods either lacking in speed or accuracy due to limitations in comparator speed and operational amplifier performance.
Innovation Solution
A semiconductor device design that connects the output of a current sensing cell to the inverting input terminal of an operational amplifier, with a non-inverting input terminal connected to the source of a main cell with a source-bias voltage, utilizing a current/voltage conversion circuit and error detection circuits to rapidly detect arm shorting currents and accurately detect load overcurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a comparator is used for current detection, then detection speed is improved, but detection accuracy deteriorates due to voltage drops across the current detection means
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary device between the current sensing cell and the comparator. The operational amplifier performs current-to-voltage conversion with high precision, eliminating the direct connection between the current detection means and the comparator input. This intermediary conversion process resolves the contradiction by enabling accurate current measurement without the voltage drop issues that plague direct comparator-based detection methods.
Solution Approach 2:
The patent replaces the direct electrical connection method (comparator-based detection) with an operational amplifier-based current-to-voltage conversion system. This substitution allows for high-precision current measurement by converting the current signal into a voltage signal that can be accurately processed, thereby resolving the accuracy-speed trade-off inherent in direct comparator detection.
2Measurement precision
If an operational amplifier is used for current detection, then detection accuracy is improved, but detection speed deteriorates due to limited slew rate
Solution Approach 1:
The patent segments the detection function into two distinct pathways: one for high-speed detection (direct comparator path) and one for high-accuracy detection (operational amplifier conversion path). This segmentation allows each detection method to operate in its optimal performance regime, with the system selecting the appropriate path based on the detection requirements, thereby resolving the speed-accuracy trade-off.
Solution Approach 2:
The patent implements a dynamic detection system that can switch between different detection modes based on the operational requirements. The system dynamically selects between the high-speed comparator path and the high-accuracy operational amplifier path, allowing optimal performance for different types of current detection events (e.g., rapid fault detection vs. precise load monitoring).
3Device complexity
If a current sensing cell is connected directly to a comparator, then simple circuit structure is achieved, but voltage differences between main transistor and current-detection transistor cause accuracy loss
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary device that buffers and converts the current signal from the sensing cell before it reaches the comparator. This intermediary conversion process eliminates the direct voltage comparison issues between the main transistor and current-detection transistor, as the operational amplifier creates a virtual ground that equalizes the voltage conditions, thereby resolving the accuracy problem while maintaining reasonable circuit complexity.
Data Source
AI summary
In a semiconductor device utilizing a power semiconductor element provided with a main cell and a current sensing cell, a load overcurrent is accurately detected and a short circuit current is rapidly detected. The output of a current sensing cell is connected to an inverting input terminal of an operational amplifier, and a non-inverting input terminal of the operational amplifier is connected to the source of the main cell. A current/voltage conversion circuit configured with the operational amplifier and a sensing resistor converts an output current of the current sensing cell into a sensing voltage. A first error detection circuit compares the sensing voltage with a first reference voltage and outputs an error signal. A second error detection circuit compares a voltage at the inverting input terminal of the operational amplifier with a second reference voltage set to be higher than a source-bias voltage and outputs an error signal.