Cascode Bidirectional Switch Topology for 1.2 kV Single-Gate Control
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Solution Overview
Problem
Existing GaN technology faces challenges in realizing a single discrete or bidirectional switch device with a breakdown voltage of at least 1.2 kV due to the need for multiple buffer layers, leading to inefficient utilization and higher costs in higher voltage applications like 3-phase matrix converters and current source inverters.
Innovation Solution
The implementation of a switch device using a cascode configuration with a normally-on and a normally-off transistor, where the drain of the normally-off transistor is connected to the source of the normally-on transistor, along with voltage blocking and overvoltage protection devices to actively control the cascode device with only one gate, optimizing voltage blocking and current conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If two 650V rated devices are stacked to realize a 1.2 kV switch, then the breakdown voltage is improved, but the device complexity increases and requires both gates to be driven exactly at the same time
Solution Approach 1:
The patent inverts the conventional approach by using a normally-on device instead of a normally-off device as one of the stacked components. This allows the device to be controlled by a single gate signal rather than requiring synchronized control of two gates, thereby reducing control complexity while maintaining the 1.2 kV breakdown voltage capability
Solution Approach 2:
The patent extracts the control function from one of the two stacked devices by using a normally-on device that requires no gate control. This leaves only one actively controlled gate in the stacked configuration, simplifying the control architecture while preserving the voltage blocking capability
2Adaptability or versatility
If two discrete bidirectional switches are arranged back-to-back to block in both directions, then bidirectional blocking capability is improved, but the current conducts through the semiconductor material of both devices leading to inefficient utilization
Solution Approach 1:
The patent uses normally-on devices in the bidirectional switch configuration, which inverts the conventional normally-off approach. This allows the current to conduct through only one device's semiconductor material at a time rather than both, improving current conduction efficiency while maintaining bidirectional blocking capability
Solution Approach 2:
The patent applies different characteristics to different parts of the bidirectional switch structure by using normally-on devices with specific threshold voltages. This ensures that current flows through the optimal path (one device at a time) while maintaining the required blocking capability in both directions
3Strength
If two 1.2 kV discrete devices are arranged back-to-back to realize a 1.2 kV bi-directional blocking device, then bidirectional blocking voltage is improved, but the die size increases approximately four times larger
Solution Approach 1:
The patent merges two lower-voltage devices (650V each) into a single stacked configuration that achieves 1.2 kV bidirectional blocking capability. This combined structure requires only one actively controlled gate and utilizes the semiconductor material more efficiently, reducing the overall die size compared to using two full 1.2 kV devices
Solution Approach 2:
By using normally-on devices in the stacked configuration, the patent reduces the number of actively controlled gates from two to one, which simplifies the control architecture and allows for more efficient use of the semiconductor material, thereby reducing the required die size
Data Source
AI summary
A switch device includes at least two bidirectional switches electrically connected in a cascode configuration. A first bidirectional switch and a second bidirectional switch of the at least two bidirectional switches each have a normally-on gate and a normally-off gate. Any remaining bidirectional switch of the at least two bidirectional switches cascoded between the first and second bidirectional switches has a first normally-on gate and a second normally-on gate. The switch device is actively controlled by the normally-off gate of the first bidirectional switch and the normally-off gate of the second bidirectional switch. Each normally-on gate of the at least two bidirectional switches is electrically connected to a source of another one of the at least two bidirectional switches by a voltage blocking device configured to block a portion of the voltage across the switch device when the switch device is off. Additional switch devices embodiments are described.