GaN Transistor Overvoltage Protection via Silicon Cascode Mediator
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Solution Overview
Problem
Gallium nitride (GaN) transistors lack inherent avalanche capability and short-circuit withstand ability, making them susceptible to damage in switch circuit applications, and existing solutions are costly or inefficient.
Innovation Solution
A driver and current source circuit configuration that includes a gallium nitride transistor and a low voltage silicon transistor in a cascode configuration, allowing for controlled overvoltage and overcurrent protection by conducting sink current to prevent permanent damage, with the driver circuit operating in multiple modes to manage these conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If GaN transistors are used for high efficiency switching, then system efficiency and output power are improved, but the transistors become susceptible to damage from overvoltage and short-circuit conditions due to lack of inherent avalanche capability
Solution Approach 1:
A silicon transistor is introduced as an intermediary protective device in series with the GaN transistor. The silicon transistor's inherent avalanche capability acts as a safety mechanism that absorbs overvoltage spikes and short-circuit energy, protecting the GaN transistor from damage while allowing the GaN device to operate at high efficiency
Solution Approach 2:
The circuit is designed with overvoltage protection circuitry and current source circuits that activate before the GaN transistor can be damaged. The silicon transistor is pre-positioned in the circuit to provide avalanche protection, and control circuits are prepared to sink current during overvoltage conditions, cushioning the GaN device from harmful electrical stress
2Device complexity
If GaN transistors operate without overvoltage protection, then device complexity is reduced, but the transistors cannot withstand breakdown conditions
Solution Approach 1:
The protection circuitry is merged with the GaN transistor to form an integrated device. The silicon transistor, driver circuit, and overvoltage protection elements are combined into a single packaged unit, reducing overall system complexity while providing comprehensive breakdown protection
Solution Approach 2:
The silicon transistor serves multiple functions: it acts as a current source during normal operation, provides avalanche protection during overvoltage conditions, and functions as a protective element during short-circuit events. This multi-functionality reduces the need for separate protection circuits
3Reliability
If excessive breakdown voltage margin is used to protect GaN transistors, then transistor reliability is improved, but system cost increases and excessive voltages are subjected to the system
Solution Approach 1:
Instead of changing the GaN transistor's breakdown voltage parameter to provide excessive margin, the invention changes the protection mechanism by introducing a silicon transistor with complementary avalanche capability. This allows the GaN device to operate at its optimal breakdown voltage without costly over-design
4Productivity
If GaN transistors are designed for short-circuit withstanding, then productivity and application versatility are improved, but current GaN fabrication techniques cannot provide adequate short-circuit withstand ability
Solution Approach 1:
The silicon transistor serves as a mediator that absorbs short-circuit current and energy, protecting the GaN transistor from damage. This intermediary approach enables GaN devices to be used in applications requiring short-circuit withstanding capability without modifying the GaN fabrication process
Data Source
AI summary
Disclosed examples include methods, integrated circuits and switch circuits including a driver circuit and a silicon transistor or other current source circuit coupled with a gallium nitride or other high electron mobility first transistor, where the driver operatives in a first mode to deliver a control voltage signal to the first transistor, and in a second mode in response to a detected overvoltage condition associated with the first transistor to control the current source circuit to conduct a sink current from the first transistor to affect a control voltage to at least partially turn on the first transistor.