Hybrid Si-GaN Switching Circuit for Thermal-Limited Current Handling
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Solution Overview
Problem
Existing hybrid switching circuits using Si MOSFETs and GaN HEMTs are limited by GaN's poor thermal characteristics due to its small die size and poor thermal conduction, restricting current capabilities and requiring complex control for optimal performance.
Innovation Solution
A power converter design where silicon-based devices primarily conduct during the conduction phase, while wide bandgap (WBG) devices like GaN HEMTs are used only briefly to manage voltage stress and take advantage of their fast fall time, reducing thermal stress on silicon-based devices and allowing higher current absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If multiple GaN HEMT devices are used in parallel to increase current capability, then switching speed and E off loss are improved, but thermal management becomes difficult due to poor thermal conduction and small die size
Solution Approach 1:
The patent combines Si MOSFET and GaN HEMT devices in a hybrid parallel configuration where Si MOSFET handles high-current conduction phases and GaN HEMT handles switching transitions, merging the thermal stability of Si with the speed advantages of GaN to resolve the thermal management issue while maintaining high switching speed
Solution Approach 2:
The patent assigns different operational roles to different devices based on their local characteristics: Si MOSFET is optimized for high-current conduction with better thermal handling, while GaN HEMT is optimized for fast switching transitions, creating local quality optimization where each device operates in its most efficient regime
2Loss of energy
If GaN HEMT devices are used to reduce E off loss with faster fall time, then switching losses are reduced, but current capability is limited due to poor thermal characteristics
Solution Approach 1:
The hybrid switching circuit merges Si MOSFET and GaN HEMT in parallel, where GaN HEMT provides fast fall time and low E off loss during switching transitions while Si MOSFET provides high current capability during conduction phases, achieving both low switching losses and high current capability simultaneously
Solution Approach 2:
The patent implements dynamic switching control where the operational role of each device changes based on the switching phase: GaN HEMT is activated for fast turn-off transitions to minimize E off loss, while Si MOSFET handles the high-current conduction period, creating a dynamic system that optimizes both switching losses and current capability
3Reliability
If complex control strategies are implemented to optimize hybrid switching operation, then switching performance is improved, but device complexity increases
Solution Approach 1:
The patent employs preliminary action by pre-charging and pre-discharging gate capacitors through auxiliary circuits before main switching events, and by using resonant inductors to pre-position energy, which simplifies the main switching control logic while improving switching performance and reducing E off loss
Data Source
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AI summary
A power converter is provided. The power converter includes two or more hybrid switching circuits electrically connected to a source or storage element. Each switching circuit includes a wide bandgap device that is parallel-connected to a silicon-based device. The converter further includes a controller that is operatively coupled to each device of the first and second switching circuits. The controller is configured to operate each hybrid switching circuit by (i) activating the silicon-based device for an activation period, (ii) activating the wide bandgap device for a predetermined duty cycle less than the activation period, (iii) deactivating the silicon-based device while the wide bandgap device is activated, and (iv) deactivating the wide bandgap device. The hybrid switching circuits are sequentially operated to convert an alternating current of a power supply into a link voltage for a power converter, for example.