Cascode Switch Overcurrent Protection Using Node Voltage Plateau
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Solution Overview
Problem
Modern power converters using low on-resistance cascode switches, such as GaN or SiC, face challenges in rapidly detecting overcurrent conditions following turn-on due to the rapid nature of excessive current events, which traditional protection circuits with leading edge blanking are unable to detect effectively.
Innovation Solution
A protection circuit is implemented that includes a cascode configuration with a depletion mode and enhancement mode field effect transistors, utilizing a comparator and logic AND gate to detect overcurrent faults by observing a plateau in the cascode node voltage for a threshold time duration, allowing for rapid detection and corrective action.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional protection circuits with leading edge blanking are used, then the circuit structure is simple, but the overcurrent detection speed is slow and cannot detect rapid excessive current events
Solution Approach 1:
The protection circuit is segmented into multiple functional blocks: overcurrent detection circuit (comparator), control circuit (logic AND gate), and drive circuit (multiple stage gate drive). Each block performs a specific function, allowing the system to achieve fast detection without overwhelming complexity in a single circuit.
Solution Approach 2:
The protection circuit performs preliminary detection of overcurrent conditions immediately upon switch turn-on, before the excessive current can cause damage. The comparator continuously monitors the cascode node voltage and is ready to trigger protection actions within nanoseconds of detecting an abnormal condition.
2Measurement precision
If multiple stage gate drive is used, then the switch turn-on is controlled precisely, but the control circuit complexity increases
Solution Approach 1:
The gate drive signal is dynamically adjusted through multiple stages: a first stage provides a weak turn-on signal to gradually activate the switch, and a second stage provides a strong turn-on signal to fully activate the switch quickly. This dynamic control allows precise management of the turn-on process, enabling accurate current sensing while controlling circuit complexity through standardized gate drive components.
Data Source
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AI summary
Fast turn-on protection of a cascode switch is presented herein. A cascode circuit includes a depletion mode field effect transistor and an enhancement mode field effect transistor electrically coupled in cascode. During turn-on, a protection circuit detects an overcurrent fault by observing a plateau of a cascode node voltage. An overcurrent fault may be detected in response to the plateau existing for greater than a threshold time duration.