Bidirectional Switching Assembly With Cascode Loss Reduction
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Solution Overview
Problem
Conventional bidirectional switching units for power systems, such as those used in power converters and battery chargers, suffer from high voltage drop, high power loss, and large footprint requirements, making them inefficient and costly.
Innovation Solution
A bidirectional switching assembly comprising a first and second low-voltage MOSFET and a normally ON high-voltage semiconductor switch, such as a JFET or HEMT, arranged in series, where the high-voltage switch is sandwiched between the MOSFETs, allowing bidirectional control with reduced losses and smaller footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional bidirectional switching units use two MOSFET or IGBT devices in common source/collector or common drain/emitter configuration, then bidirectional control of current flow is achieved, but high voltage drop, high power loss, and large footprint requirements occur
Solution Approach 1:
The bidirectional switching unit is segmented into three separate switching units (first MOSFET, second MOSFET, and third high-voltage switch) connected in series, where each unit handles specific voltage and current conditions. This segmentation allows optimization of each component for its specific function, reducing overall power loss while maintaining bidirectional control capability.
Solution Approach 2:
Different switching units are positioned at different locations within the circuit to handle specific local conditions. The high-voltage switch is placed in the middle to handle voltage blocking, while MOSFETs are positioned at the ends for current conduction. This local optimization reduces voltage drop and power loss in specific regions of the circuit.
2Ease of operation
If conventional bidirectional switching units use two MOSFET or IGBT devices in common source/collector or common drain/emitter configuration, then bidirectional control of current flow is achieved, but large footprint requirements occur
Solution Approach 1:
By segmenting the bidirectional switch into three specialized units connected in series, the design allows for more compact arrangement compared to the conventional two-device configuration. Each switching unit can be optimized for its specific function, potentially reducing the overall footprint while maintaining bidirectional control capability.
3Ease of operation
If a normally ON high-voltage semiconductor switch is used with gates connected through high-voltage diodes, then the switch can be controlled bidirectionally, but the circuit complexity increases
Solution Approach 1:
High-voltage diodes are introduced as intermediary components to connect the gate of the high-voltage switch to the circuit. These diodes enable bidirectional gate control while protecting the gate from voltage spikes, achieving bidirectional switching capability with controlled complexity through the use of these intermediary protective elements.
4Loss of energy
If three switching units are arranged in series with the high-voltage switch sandwiched between MOSFETs, then voltage drop and power loss are reduced, but the number of components increases
Solution Approach 1:
Each switching unit is optimized for its specific local function: MOSFETs handle low-voltage current conduction at the circuit ends, while the high-voltage switch handles voltage blocking in the middle. This local optimization reduces voltage drop and power loss in specific regions, justifying the increased component count through improved overall efficiency.
Data Source
AI summary
A bidirectional switching assembly includes a first switching unit having a first low voltage MOSFET that includes a first gate, a second switching unit having a second low voltage MOSFET that includes a second gate, and a third switching unit having a normally ON high voltage semiconductor switch that includes a third gate connected through high-voltage diodes with an input side and an output side of the switching assembly. The switching units are arranged in series with the third switching unit sandwiched between the first and second switching units. In one direction, the second and third switching units form a cascode. In the other direction, the first and third switching units form a cascode. The switching assembly is configured to conduct a current in either direction when the third switching unit is switched on and block a current in either direction when the third switching unit is switched off.