Cascode Compound Switch Coupling for Slew Rate and EMI Control
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Solution Overview
Problem
High-voltage cascode compound switches suffer from excessively rapid transitions, leading to unwanted electromagnetic interference (EMI) and potential damage to motor windings, due to uncontrolled slew rates during switching operations in high-power applications.
Innovation Solution
Incorporating additional slew rate control circuitry, including diode or transistor coupling, to independently control the cascode and switching transistors, allowing for controlled slew rate management during both 'on' to 'off' and 'off' to 'on' transitions, thereby reducing EMI and protecting motor windings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cascode compound switch is used for high-voltage switching, then voltage blocking capability and current handling are improved, but slew rate becomes excessively high causing EMI and insulation damage
Solution Approach 1:
The patent segments the single switching operation into two distinct phases by using two transistors (first transistor for voltage blocking, second transistor for current switching). This segmentation allows independent control of voltage handling and current commutation, enabling slew rate control during switching while maintaining high voltage blocking capability through the first transistor.
Solution Approach 2:
The first transistor acts as an intermediary between the high-voltage node and the second transistor. It provides a controlled path for voltage transitions, mediating the slew rate by isolating the high-voltage node from rapid voltage changes occurring at the second transistor, thereby reducing EMI while maintaining voltage blocking capability.
2Productivity
If switching speed is increased for high-power delivery, then power conversion efficiency is improved, but displacement currents increase causing EMI radiation
Solution Approach 1:
The patent segments the switching function into two transistors where the first transistor handles voltage blocking and the second handles current switching. This allows the second transistor to operate rapidly for efficient power conversion while the first transistor's capacitance isolates the high-voltage node, preventing rapid voltage changes that would generate displacement currents and EMI.
3Productivity
If rapid switching is implemented for electrical power conversion, then switching efficiency is improved, but motor winding insulation may be damaged
Solution Approach 1:
The first transistor is positioned beforehand to cushion the high-voltage node from rapid voltage transitions. Its inherent capacitance acts as a buffer that slows down voltage changes at the high-voltage terminal, protecting motor winding insulation from voltage spikes while allowing the second transistor to switch rapidly for efficient power conversion.
Data Source
AI summary
A high-voltage (HV) compound switch can include coupling circuitry to help provide better slew rate (dV/dt) control, such as to limit electromagnetic energy radiation during switching, which can cause undesirable EMI. Further, efficiency and on-state resistance can be improved by controllably forward-biasing the “normally on” JFET when the compound switch is in an “on” state. In such an on-state, the JFET temperature can be monitored, such as by monitoring the gate-source junction voltage or the gate current of the JFET. Such temperature information can be used for control or other purposes.