Short Circuit Protected Composite Switch for Inverter Circuits
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Solution Overview
Problem
Conventional III-N high electron mobility transistors (HEMTs) in power inverter applications face challenges during short circuit conditions, where high voltage and current exceed their power handling capacity, leading to potential device failure due to increased on-resistance and reduced heat dissipation when attempting to reduce saturation current by decreasing gate width and die size.
Innovation Solution
A short circuit protected composite switch is configured by cascading a high current group IV FET with a III-N FET, incorporating an additional low current group IV FET to control the gate of the high current group IV FET, allowing the III-N FET to maintain operation while limiting current and preventing oscillations during short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate width and die size of the III-N HEMT are reduced to decrease saturation current, then the saturation current is reduced, but the on-resistance increases and heat dissipation capability deteriorates
Solution Approach 1:
The patent divides the single HEMT device into a composite structure consisting of a III-N HEMT and a group IV FET connected in series (cascoded configuration). The group IV FET is positioned to handle high current during normal operation, while the III-N HEMT operates at lower current levels, effectively segmenting the current handling functions between the two devices and protecting the HEMT from excessive current damage.
Solution Approach 2:
The group IV FET acts as an intermediary protective device between the power source and the III-N HEMT. During short circuit conditions, the group IV FET limits the current before it reaches the HEMT, serving as a current-limiting mediator that prevents the HEMT from experiencing damaging high current while maintaining the HEMT's low on-resistance and heat dissipation capabilities.
2Reliability
If the saturation current of the III-N HEMT is reduced to protect against short circuits, then short circuit protection is improved, but the device's power handling capacity and performance deteriorate
Solution Approach 1:
The composite switch segments the power handling function: the group IV FET handles high current and power during normal operation, while the III-N HEMT operates at lower power levels. This segmentation allows the system to achieve both short circuit protection and high power handling capacity by assigning different operational roles to each device based on their respective strengths.
Solution Approach 2:
The patent creates a composite device combining two different semiconductor materials (III-N HEMT and group IV FET) with complementary characteristics. The group IV FET provides high current capability and short circuit protection, while the III-N HEMT provides low on-resistance and high electron mobility. This composite structure achieves both short circuit protection and high power handling capacity that neither device could achieve alone.
3Reliability
If a composite switch configuration is used to protect the III-N HEMT, then short circuit protection is improved, but the device complexity increases
Solution Approach 1:
The patent merges the III-N HEMT and group IV FET into a single integrated composite switch device with unified source and drain terminals. This merging approach consolidates two protective mechanisms (the cascoded structure and the intrinsic body diode of the FET) into one device, achieving short circuit protection without requiring additional external protection circuits or components, thereby limiting the increase in overall system complexity.
Data Source
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AI summary
There are disclosed herein various implementations of a short circuit protected composite switch and a circuit including such a switch. In one exemplary implementation, such a short circuit protected composite switch includes a III-N field-effect transistor (FET) having a drain, a source, and a gate, and a high current group IV FET coupled in series with the III-N FET and configured to limit a current through the III-N FET. The short circuit protected composite switch also includes another group IV FET coupled between the gate and the source of the III-N FET, and another transistor coupled between the gate of the III-N FET and a source of the high current group IV FET.