Overcurrent Protection Circuit for Fast GaN Switch Turn-Off
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Solution Overview
Problem
GaN devices are more susceptible to overcurrent damage compared to conventional semiconductor devices, and existing overcurrent protection technologies are insufficient to protect GaN devices from overcurrent at high speeds.
Innovation Solution
An overcurrent protection circuit is designed using first and second transistors, where the first transistor is a PNP bipolar transistor and the second transistor is an NPN bipolar transistor, configured to rapidly turn off the switching element when the control voltage exceeds a predetermined threshold, thereby protecting the semiconductor switch from overcurrent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional overcurrent protection technologies (DESAT function, CT detection, or voltage threshold detection) are used, then the protection mechanism is simple and easy to implement, but the response speed is insufficient to protect GaN devices from overcurrent damage occurring within about 100 nanoseconds
Solution Approach 1:
The patent applies preliminary action by pre-configuring the protection circuit with a voltage divider network and comparator that continuously monitor the drain-source voltage before overcurrent damage occurs. When the voltage exceeds a predetermined threshold, the comparator immediately triggers the protection transistor to turn off the MOSFET, eliminating detection and processing delays. This preliminary monitoring and pre-positioned protection mechanism enables response within the critical 100 nanosecond window required for GaN device protection.
Solution Approach 2:
The patent replaces conventional mechanical or slow electronic protection mechanisms with a voltage-based electronic protection system. Instead of using current transformers or desaturation detection that rely on current flow changes, the invention directly monitors voltage across the MOSFET drain-source terminals and uses a voltage comparator for instantaneous detection. This substitution of detection methodology enables ultra-fast response by eliminating the time required for current buildup or saturation detection.
2Speed
If the protection circuit uses simple voltage threshold detection, then the circuit complexity is low, but the protection speed and reliability are insufficient for GaN devices
Solution Approach 1:
The patent introduces a voltage divider network as an intermediary between the MOSFET drain-source terminals and the voltage comparator. This divider network scales down the high voltage to a level suitable for the comparator while maintaining proportional relationship, enabling fast voltage threshold detection without exposing the comparator to high voltages. The intermediary also includes protection transistors that act as mediators to quickly disconnect the MOSFET when overvoltage/overcurrent is detected, balancing speed requirements with circuit protection.
Solution Approach 2:
The patent changes the detection parameter from current-based detection (CT detection, desaturation) to voltage-based detection. By monitoring the drain-source voltage and comparing it against a predetermined threshold voltage, the system achieves ultra-fast response. The voltage divider ratio and comparator threshold are carefully selected parameters that transform the high-voltage, fast-transient protection requirement into a low-voltage, manageable comparison operation, enabling nanosecond-level response without excessive circuit complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed overcurrent protection circuit effectively protects semiconductor switches from overcurrent at higher speeds than conventional methods, ensuring the reliability and longevity of GaN devices.
Implementation Method 1
first and second transistors, wherein the first transistor is a PNP bipolar transistor and has an emitter connected to the control voltage, and the second transistor that is an NPN bipolar transistor
Data Source
AI summary
The overcurrent protection circuit includes: a first transistor having an emitter connected to a control voltage; and a second transistor having a base connected to a collector of the first transistor, a collector connected to a base of the first transistor and pulled up to a voltage, and a grounded emitter. When the control voltage exceeds a first threshold voltage, the first and second transistors are turned on, the control voltage decreases as a result of decrease in the pull-up voltage, and a protection operation to turn a switching element off is started, and the overcurrent protection circuit includes a first diode connected between the control voltage and the emitter of the first transistor, and an element circuit connected between the emitter and the base thereof. The element circuit includes any of a second diode, a first resistor, and a parallel circuit including the second diode and the first resistor.