IGBT Freewheeling Diode Float Cell Ratio for Voltage Oscillation
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Solution Overview
Problem
Semiconductor devices with parallel switching devices face issues of voltage oscillation and waveform distortion due to parasitic inductance, which are difficult to address through resistance adjustments alone, as they involve tradeoffs with switching speed and turn-on voltage.
Innovation Solution
Incorporating a freewheeling diode for each IGBT device connected in parallel, with a specific configuration that includes active, dummy, and float cells, where the ratio of float cells to total active and dummy cells is between 5% and 35%, to reduce voltage oscillation and waveform distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching devices are connected in parallel to reduce switching loss and control output current, then productivity and power control are improved, but parasitic inductance generates voltage oscillation and current oscillation during switching
Solution Approach 1:
A freewheeling diode is introduced as an intermediary component for each switching device. The diode provides a dedicated current path during switching transitions, preventing current oscillation and voltage oscillation caused by parasitic inductance between parallel switching devices. This mediator absorbs the harmful effects without compromising the parallel connection configuration.
Solution Approach 2:
The patent divides the semiconductor device into multiple independent modules, each consisting of a switching device paired with its own freewheeling diode. This segmentation isolates the current paths of individual switching devices, preventing mutual interference and oscillation between parallel devices while maintaining overall system productivity.
2Object-affected harmful factors
If resistance is adjusted to reduce voltage oscillation, then voltage oscillation is reduced, but switching speed and turn-on voltage are adversely affected due to tradeoffs
Solution Approach 1:
The freewheeling diode serves as a mediator that provides a low-impedance current path during switching transitions, eliminating the need to adjust resistance values. This approach reduces voltage oscillation without introducing the tradeoffs associated with resistance changes, preserving both switching speed and turn-on voltage characteristics.
3Object-affected harmful factors
If freewheeling diode is added for each switching device, then voltage oscillation and current oscillation are reduced, but device complexity increases
Solution Approach 1:
The semiconductor device is segmented into modular units, each containing a switching device and its associated freewheeling diode. This modular segmentation makes the added complexity manageable and systematic, allowing each module to be designed and analyzed independently while maintaining overall current control.
Solution Approach 2:
The freewheeling diode is specifically positioned and configured for each individual switching device based on local requirements. This localized approach ensures that each switching device has optimal current path control, reducing current oscillation effectively without requiring global system redesign.
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 reduces voltage oscillation and waveform distortion while managing switching speed and turn-on voltage within the specified ratio range, enhancing the performance of semiconductor devices.
Implementation Method 1
Parasitic inductance may be generated between the switching devices in the semiconductor device in which the switching devices are connected in parallel. For this reason, an induced electromotive force may be generated during the switching to generate voltage oscillation and current osculation caused by the voltage oscillation.
Data Source
AI summary
A semiconductor device includes IGBT devices; and a freewheeling diode provided for each IGBT device. The IGBT devices are connected in parallel to be driven. Each IGBT device includes: a collector region; a drift region; a body region; a trench gate penetrating the body region; and an emitter region surrounded by the body region and in contact with the trench gate. Each IGBT device further includes an active cell with the emitter region; a dummy cell without the emitter region; and an active dummy cell without the emitter region. The active dummy cell has a float cell where the body region is in electrically-floating condition. A ratio of the number of float cell to the total number of the active cell and the active dummy cell is larger than or equal to 5% and is smaller than or equal to 35%.