Hybrid Si MOSFET-GaN Switch Control for Reverse Loss Reduction
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Solution Overview
Problem
Wide-bandgap devices, such as GaN HEMTs, face challenges in high-current applications due to limited current capability and high reverse conduction loss, leading to increased system cost and efficiency limitations when used in power electronics systems.
Innovation Solution
A hybrid switch apparatus is developed, where a fast GaN HEMT is paralleled with a slower silicon MOSFET, with a control scheme that synchronizes gate drive signals to minimize conduction loss by switching the fast switch only during short durations, allowing the slower switch to handle most of the current conduction and reducing the power rating of the fast switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple WBG switches are paralleled to achieve high current capability, then the current capability is improved, but the system cost increases
Solution Approach 1:
The patent combines a WBG switch and a silicon switch in a hybrid parallel configuration. The WBG switch provides high-frequency switching capability while the silicon switch provides low-cost current conduction path, achieving high current capability without paralleling multiple expensive WBG devices.
Solution Approach 2:
The patent assigns different functional roles to different switches based on their local characteristics: the WBG switch is optimized for switching operations while the silicon switch is optimized for current conduction, allowing each component to operate in its optimal performance regime.
2Speed
If GaN HEMT is used to achieve high switching frequency, then the switching frequency capability is improved, but the reverse conduction loss increases
Solution Approach 1:
The silicon switch acts as an intermediary that provides a low-loss reverse conduction path. When the WBG switch needs to block reverse current, the silicon switch conducts instead, eliminating the high reverse conduction loss inherent in GaN HEMT devices.
Solution Approach 2:
The patent extracts the reverse conduction function from the WBG switch and assigns it to the silicon switch, allowing the WBG device to focus solely on high-frequency switching while the silicon device handles the detrimental reverse conduction.
3Ease of manufacture
If the power rating of WBG device is reduced to lower cost, then the system cost is reduced, but the current capability decreases
Solution Approach 1:
The patent merges a lower-power WBG switch with a silicon switch in parallel. The WBG switch operates at reduced power rating (lowering cost) while the silicon switch supplements the current capability, achieving both cost reduction and maintained current capability.
Data Source
AI summary
A hybrid switch apparatus includes a standard semiconductor switch and a fast semiconductor switch electrically arranged in parallel to form a joint output current path for carrying a load current. The standard switch may be a silicon (Si) MOSFET while the fast switch may be a GaN high electron mobility transistor (HEMT). A means for producing first and second gate drive signals includes a pulse former. The first gate drive signal is applied the standard switch for selectively turning the standard switch on and off. The pulse former outputs the second gate drive signal for driving the fast switch, where the pulse former generates the second gate drive signal as a switch-on pulse starting synchronously with each transition of the first gate drive signal and which generates the second gate drive signal in an OFF state in between pulses to avoid incurring a conduction loss in the fast switch.