Unidirectional Hybrid Switch Circuit for Low-Loss High-Current Switching
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Solution Overview
Problem
Existing electrical systems face challenges in efficiently switching high voltages and currents, particularly in applications like electric vehicles, due to high switching losses and cost inefficiencies when using multiple silicon carbide (SiC) switches in parallel, which result in slower turn-on and turn-off times and increased die area.
Innovation Solution
A hybrid switch incorporating bidirectional double-base bipolar junction transistors (BDB BJTs) and silicon carbide (SiC) devices, which selectively conduct forward current through FET and BJT switches while non-selectively conducting reverse current through diodes, reducing the number of switches needed and minimizing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If silicon carbide (SiC) switches are used to handle high currents, then the switching capability and voltage handling are improved, but the cost and die area increase significantly
Solution Approach 1:
The patent divides the current handling function into two segments: SiC devices handle the high-voltage blocking and switching initiation, while BDB BJTs handle the bulk of the current conduction. This segmentation allows each device type to operate in its optimal performance range, reducing the need for large-area SiC devices while maintaining high-power capability.
Solution Approach 2:
The hybrid switch circuit is designed to perform multiple functions using different device types: SiC devices provide fast switching and high-voltage blocking, BDB BJTs provide low-loss current conduction, and diodes provide reverse-current handling. This multi-functionality allows the system to achieve high-power capability without requiring all components to be large-area SiC devices.
2Power
If silicon carbide (SiC) switches are used to handle high currents, then the switching capability is improved, but the cost increases
Solution Approach 1:
The patent segments the cost burden by using expensive SiC devices only for functions where they provide unique value (fast switching, high-voltage blocking) and using cheaper BDB BJTs for current conduction. This reduces the total system cost while maintaining high-power capability.
Solution Approach 2:
The patent employs cheaper BDB BJTs and diodes to handle portions of the current conduction and reverse-current flow, reducing dependence on expensive SiC devices. This substitution with lower-cost components achieves cost reduction while maintaining overall system performance.
3Power
If current sharing during load transients is implemented, then the current handling capability is improved, but the control complexity increases
Solution Approach 1:
The patent merges the control of multiple devices (SiC switches and BDB BJTs) into a unified hybrid switch circuit topology where current sharing is achieved through the inherent circuit configuration rather than complex external control logic. The cascode and parallel connections automatically facilitate current distribution based on device characteristics.
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 hybrid switch achieves low conduction losses during the 'on-state' by using BDB BJTs to conduct majority of the current, while leveraging SiC devices for fast switching, thereby reducing costs and improving switching efficiency.
Implementation Method 1
selectively conducting a forward current from the upper terminal to the lower terminal by sharing the forward current between a FET switch and a BJT switch
Implementation Method 2
when the hybrid switch is reversed biased, non-selectively conducting a reverse current from the lower terminal to the upper terminal
Data Source
AI summary
Unidirectional hybrid switch. At least one example is a method operating a hybrid switch, the method comprising: sensing a voltage across an upper terminal and a lower terminal of the hybrid switch, the hybrid switch is forward biased when the upper terminal has higher voltage, and the hybrid switch is reverse biased when the lower terminal has higher voltage; when the hybrid switch is forward biased, selectively conducting a forward current from the upper terminal to the lower terminal by sharing the forward current between a FET switch and a BJT switch, the selectively conducting when a control terminal is asserted; and when the hybrid switch is reversed biased, non-selectively conducting a reverse current from the lower terminal to the upper terminal.