Direct-Drive D-Mode GaN Half-Bridge With Fail-Safe High-Side Protection
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Solution Overview
Problem
There is a need for improved or alternative power semiconductor switching devices that take advantage of the performance characteristics of GaN-based semiconductor materials, particularly for high power switching applications, which require increased current per unit die area and reduced cost while ensuring failsafe operation during start-up and fault conditions.
Innovation Solution
A direct drive D-mode half-bridge power module is implemented, comprising a high-side switch and a low-side switch connected in a half-bridge configuration, where the high-side switch is a D-mode GaN transistor in series with an E-mode Si MOSFET, and the low-side switch is a D-mode GaN transistor. The Si MOSFET acts as a protection FET to hold the high-side switch in an off-state during start-up and fault conditions, using a control circuit to manage operational modes based on UVLO and overcurrent signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If D-mode GaN transistors are used for high-side and low-side switches, then switching speed and efficiency are improved, but failsafe operation during start-up and fault conditions deteriorates
Solution Approach 1:
The high-side switch is segmented into two independent GaN transistors (Q1 and Q2) with separate gate control. This allows Q1 to be directly driven for fast switching while Q2 can be controlled to provide failsafe protection during start-up and fault conditions, resolving the contradiction between switching speed and reliability.
Solution Approach 2:
An intermediary control mechanism is introduced where the gate driver circuit monitors system conditions and selectively controls the gating of Q2. This intermediary layer enables the system to switch between direct-drive mode (for speed) and protected mode (for reliability) based on operational requirements.
2Loss of energy
If wide bandgap semiconductor technologies (SiC, GaN) are used, then efficiency and switching frequency are improved, but semiconductor cost increases significantly
Solution Approach 1:
The invention changes the operational parameters of GaN transistors by using direct-drive gating for the high-side switch, allowing operation in depletion mode during normal conditions to minimize switching losses while maintaining compatibility with standard gate driver circuits, thus reducing overall system cost.
Solution Approach 2:
The patent employs a composite switching structure combining two GaN transistors with different control strategies - one for optimal performance and one for protection - creating a hybrid approach that balances performance benefits with cost considerations through intelligent device utilization.
3Productivity
If D-mode GaN transistors are directly driven, then current driving capability is increased, but protection during fault conditions becomes more complex
Solution Approach 1:
The direct-drive configuration allows the GaN transistors to self-regulate their switching behavior through inherent device characteristics, reducing the need for complex external protection circuits while maintaining high current driving capability.
Solution Approach 2:
The protection function is merged into the gate driver circuit itself, which monitors system conditions and automatically adjusts transistor gating. This integration eliminates the need for separate protection circuits, reducing overall complexity while maintaining robust fault protection.
Data Source
AI summary
A protected direct-drive depletion-mode (D-mode) GaN semiconductor half-bridge power module is disclosed. Applications include high power inverter applications, such as 100 kW to 200 kW electric vehicle traction inverters, and other motor drives. The high-side switch is a normally-on D-mode GaN semiconductor power switch Q1 in series with a normally-off LV Si MOSFET power switch M1 and the low-side switch is a normally on D-mode GaN semiconductor power switch Q2. The gates of both Q1 and Q2 are directly driven. M1 in series with Q1 provides a high-side switch which is a normally-off device for start-up and fail-safe protection. M1 may also be used for current sensing and overcurrent protection. For example, a control circuit determines an operational mode of M1 responsive to a UVLO signal and a voltage sense signal indicative of an overcurrent event. Examples of single phase and three-phase half-bridge modules and driver circuits are described.