Semiconductor Device With Asymmetric Switching Element Paths
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Solution Overview
Problem
Semiconductor devices with parallel IGBT and MOSFET configurations face challenges in resisting short-circuit currents, leading to increased MOSFET size and cost, particularly when using expensive silicon carbide materials.
Innovation Solution
The semiconductor device is designed with a second switching element positioned further from the terminals than the first switching element, creating a longer output current path with increased inductive reactance, directing short-circuit currents to the first switching element with lower reactance, thereby reducing resistance and MOSFET size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MOSFET is arranged adjacent to the power source line to handle short-circuit currents, then the short-circuit resistance is improved, but the MOSFET size and cost increase
Solution Approach 1:
The patent applies local quality by creating different path characteristics for different current types: the first output current path (through IGBT) has lower inductive reactance for normal operation, while the second output current path (through MOSFET) has higher inductive reactance that naturally limits short-circuit currents. This localized differentiation of path properties solves the contradiction by providing appropriate resistance characteristics only where needed without increasing overall device size
Solution Approach 2:
The patent changes the inductive reactance parameter of the output current paths by adjusting the wiring length and configuration. The second output current path is designed with higher inductive reactance compared to the first path, which transforms the MOSFET's role from actively resisting short-circuit currents (requiring large size) to passively limiting them through circuit parameters, thereby reducing MOSFET size while maintaining short-circuit protection
2Reliability
If the MOSFET is arranged adjacent to the power source line to ensure resistance to excess current, then the reliability under short-circuit conditions is improved, but the device cost increases due to larger MOSFET size
Solution Approach 1:
The patent creates local quality differences in the circuit paths where the IGBT path (first output current path) has lower inductive reactance for efficient power transmission, while the MOSFET path (second output current path) has higher inductive reactance that naturally limits excess currents. This localized differentiation provides excess current resistance through circuit topology rather than oversized components, reducing manufacturing cost
Solution Approach 2:
The patent introduces inductive reactance as an intermediary mechanism between the MOSFET and the short-circuit current. Instead of relying on the MOSFET alone to withstand excess currents (which requires large, expensive devices), the higher inductive reactance of the second output current path acts as an intermediary that naturally limits the magnitude of short-circuit currents, allowing the use of smaller, less expensive MOSFETs while maintaining reliability
3Reliability
If a longer output current path is used for the second switching element, then the inductive reactance increases to limit short-circuit currents, but the wiring length increases
Solution Approach 1:
The patent changes the inductive reactance parameter of the second output current path to achieve short-circuit current limitation. By carefully designing the wiring length and configuration of the second path (through MOSFET) to be longer than the first path (through IGBT), the patent achieves the desired inductive reactance increase without excessive wiring length, as the additional length is only what's necessary to create the reactance difference, not a uniform increase in all connections
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 configuration effectively suppresses short-circuit resistance in the MOSFETs, allowing for smaller silicon carbide MOSFETs and reduced costs while maintaining efficient operation.
Implementation Method 1
a wiring length from a first terminal to a second terminal via the second switching element is longer than a wiring length from the first terminal to the second terminal via the first switching element. Although a current path via each switching element forms a parasitic inductor, in the present disclosure, an inductive reactance of the second switching element with respect to the first terminal and the second terminal can be made greater than a reactance of the first switching element
Data Source
AI summary
A semiconductor device includes: a first switching element that controls an output current flowing between a power source and a load; a second switching element that is connected to the first switching element in parallel, and controls an output current flowing between the power source and the load; and a drive circuit that outputs control signals to the first switching element and the second switching element to individually control the first switching element and the second switching element. A second output current path that allows the output current to flow from a terminal connected to the power source to a terminal connected to the load via the second switching element is longer than a first output current path that allows the output current to flow from a terminal connected to the power source to a terminal connected to the load via the first switching element.