AC Switch Using Compound Semiconductor MOSFETs
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Solution Overview
Problem
Existing AC switches for bidirectional current applications, particularly in hybrid and electric vehicles, face challenges with mechanical contact relays such as chattering, operating sounds, and reliability issues due to overcurrent, and silicon semiconductor switches struggle to achieve both high withstand voltage and low on-resistance.
Innovation Solution
The development of a semiconductor relay using compound semiconductor MOSFETs, specifically SiC or GaN, which are connected in series with body diodes to create an AC switch capable of bidirectional current switching, offering high withstand voltage and low on-resistance without increasing chip size, and incorporating current detection and overcurrent protection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical contact relays are used for bidirectional current switching, then the relay unit can be implemented with conventional technology, but the device suffers from chattering, operating sounds, contact melting/fixation, and reduced reliability
Solution Approach 1:
The patent replaces mechanical contact relays with semiconductor switches (MOSFETs or IGBTs) to eliminate mechanical chattering, operating sounds, and contact wear. The semiconductor-based AC switch unit uses electronic switching elements controlled by gate signals, substituting the mechanical moving contact system with a solid-state electronic system that has no physical wear or chattering issues.
2Reliability
If precharging relay and current limiting resistor are added to protect mechanical contacts, then contact melting/fixation is reduced, but the relay unit size and weight increase
Solution Approach 1:
The patent eliminates the need for precharging relays and current limiting resistors by using semiconductor switches with inherently low on-resistance. The MOSFETs or IGBTs can handle rush currents without requiring external protection components, thereby reducing the overall device size and weight while maintaining reliability.
Solution Approach 2:
The patent changes the electrical parameters of the switching element by using semiconductor devices with controllable on-resistance. The semiconductor switches can be designed with specific Rds(on) values to naturally limit inrush current without requiring external resistors, and can be controlled through gate voltage to manage current transitions smoothly.
3Reliability
If silicon semiconductor switches are used to replace mechanical relays, then mechanical problems are solved, but achieving 400 V withstand voltage increases chip size and on-resistance
Solution Approach 1:
The patent employs compound semiconductor materials (SiC or GaN) instead of conventional silicon. These compound semiconductors enable the fabrication of power devices that can withstand 400 V or higher voltages while maintaining small chip sizes and low on-resistance. The material properties of SiC and GaN allow for higher breakdown voltages and lower resistivity, resolving the contradiction between voltage rating and device size.
4Stress or pressure
If silicon semiconductor switches with 400 V withstand voltage are used, then high voltage capability is achieved, but on-resistance increases above 20 mΩ
Solution Approach 1:
The patent uses compound semiconductor materials (SiC or GaN) that simultaneously provide high breakdown voltage capability and low resistivity. These materials enable the construction of power switches that can withstand 400 V or higher while maintaining on-resistance below 20 mΩ, thereby reducing conduction losses and improving overall system efficiency compared to conventional silicon devices.
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
This solution provides an AC switch with a high withstand voltage of at least 400 V and on-resistance of less than 20 mΩ, addressing the reliability and size concerns of previous technologies while preventing overcurrent and ensuring efficient current control.
Implementation Method 1
a first compound semiconductor MOSFET and a second compound semiconductor MOSFET whose sources are connected with each other
Data Source
AI summary
An AC switch includes a first compound semiconductor MOSFET and a second compound semiconductor MOSFET whose sources are connected with each other, a first output terminal connected to the drain of the first compound semiconductor MOSFET, and a second output terminal connected to the drain of the second compound semiconductor MOSFET. The withstand voltage between the first output terminal and the second output terminal in an off state is not less than 400 V. The resistance between the first output terminal and the second output terminal in an on state is not more than 20 mΩ.