Cascoded Switching Circuit for Stable Gate Voltage and Fast Turn-Off
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Solution Overview
Problem
Conventional power semiconductor switches using wide bandgap materials like SiC and GaN face challenges in controlling the turn-off speed and voltage level of high voltage normally-on switching elements, and suffer from significant reverse recovery losses, limiting their application in high frequency circuits.
Innovation Solution
A switching circuit design that includes a normally-on switching element, a normally-off switching element, and a switching unit, where the drain of the normally-off switching element is connected to the source of the normally-on switching element, and the power source and switching unit form a serial-connected branch, allowing for controlled voltage levels and improved switching performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional direct driving method is adopted for high voltage normally-on switching elements, then the circuit structure is simple, but the turn-off speed is low under small current and the gate voltage cannot be controlled steadily
Solution Approach 1:
The patent introduces a low voltage normally-off switching element as an intermediary component between the control signal and the high voltage normally-on switching element. This intermediary element enables precise control of the gate voltage of the high voltage element, improving turn-off speed and controllability while maintaining relatively simple circuit structure.
2Reliability
If a cascade circuit of high voltage normally-on switching element and low voltage normally-off switching element is adopted, then the gate voltage control is improved, but significant reverse recovery loss occurs due to parasitic capacitance
Solution Approach 1:
The patent utilizes the parasitic capacitance of the low voltage normally-off switching element not as a harmful factor but as a beneficial element for voltage control. By carefully designing the cascade connection, the parasitic capacitance helps stabilize the gate voltage of the high voltage element while the switching element is turned off, reducing reverse recovery losses through controlled voltage clamping.
3Speed
If the switching response time of normally-on switching element is improved under different working current requirements, then the switching performance is enhanced, but the circuit complexity increases
Solution Approach 1:
The low voltage normally-off switching element serves multiple functions simultaneously: it acts as a control switch for the high voltage element, provides gate voltage clamping during turn-off, and utilizes its parasitic capacitance to improve switching response time across different current conditions. This multi-functionality achieves enhanced switching performance without proportionally increasing circuit complexity.
Data Source
AI summary
A switching circuit is disclosed. The switching circuit includes a normally-on switching element, a normally-off switching element, a switching unit and a power source. The drain of the normally-off switching element is electrically connected to the source of the normally-on switching element. The source of the normally-off switching element is electrically connected to the gate of the normally-on switching element. The power source and the switching unit are configured to form a serial-connected branch. A first terminal of the serial-connected branch is electrically connected to the drain of the normally-off switching element. A second terminal of the serial-connected branch is electrically connected to the source of the normally-off switching element.