High-Voltage MOSFET Switch Isolation Under Parasitic Capacitance
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Solution Overview
Problem
High-voltage electronic switches face challenges in maintaining isolation and preventing parasitic capacitance-induced failures, especially under high slew rate conditions, and existing solutions either require complex structures or lead to harmonic distortion and increased power consumption.
Innovation Solution
The proposed solution involves a switching device with two high-voltage MOSFETs connected in cascaded fashion, using a control circuit with additional transistors and diodes to manage the gate and source nodes, ensuring robust off-state operation independent of HV supply voltages and minimizing parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex control structures are used to manage off-state operation, then isolation and reliability are improved, but device complexity increases
Solution Approach 1:
The circuit uses the inherent parasitic capacitances of the MOSFETs (CGS, CGD, CDS) as functional elements rather than treating them as harmful factors. The parasitic capacitances naturally provide the needed isolation during off-state operation, eliminating the requirement for complex external control structures. The circuit serves itself by utilizing its own parasitic elements for the isolation function.
Solution Approach 2:
The patent converts the harmful parasitic capacitances into beneficial functional elements. Instead of adding complex control circuits to counteract or manage these parasitic effects, the invention exploits them to achieve the desired isolation and off-state operation. The parasitic capacitances become the mechanism that enables reliable switching without additional complexity.
2Reliability
If parasitic capacitances are managed through complex off-state-driving blocks, then switching reliability is improved, but power consumption increases
Solution Approach 1:
The circuit achieves reliable switching by utilizing its own parasitic capacitances rather than requiring external active control circuits that would consume power. The natural electrical characteristics of the MOSFET parasitic elements provide the switching reliability needed without continuous power expenditure from complex driving blocks.
Solution Approach 2:
The invention extracts and utilizes the useful aspect of parasitic capacitances for switching operation, eliminating the need for separate power-consuming control circuits. By taking out the isolation function from external control blocks and embedding it in the inherent device physics, power consumption is reduced while maintaining reliability.
3Ease of manufacture
If nodes sensitive to parasitic capacitances are present, then design flexibility is maintained, but manufacturing precision and reliability decrease
Solution Approach 1:
The patent converts parasitic capacitances from harmful sensitivity factors into beneficial functional elements. By designing the circuit to exploit rather than fight against parasitic capacitances, the invention achieves both ease of manufacture (no special layout constraints needed) and high reliability (immunity to parasitic effects). The design is simplified because it works with natural device characteristics rather than requiring precise control or avoidance of them.
Solution Approach 2:
The invention changes the operational parameters and design approach to work with parasitic capacitances rather than against them. Instead of designing for low parasitic values or adding compensation circuits, the patent selects operating conditions and circuit topology that naturally utilize parasitic capacitances for desired functionality, simplifying manufacturing while improving reliability.
4Reliability
If isolation is increased to prevent parasitic effects, then reliability is improved, but device complexity and power consumption increase
Solution Approach 1:
The circuit achieves isolation by utilizing its own parasitic capacitances as the isolation mechanism. During off-state, the parasitic capacitances naturally provide the electrical isolation needed between different nodes, eliminating the requirement for additional isolation circuits or complex control structures. The device isolates itself through its inherent physical characteristics.
Solution Approach 2:
The patent converts parasitic capacitances into the isolation mechanism. Rather than adding complex isolation circuits to block parasitic effects, the invention uses the parasitic capacitances themselves to provide the needed isolation. This approach improves reliability through isolation while avoiding increased device complexity.
Data Source
AI summary
A high-voltage electronic switch includes first and second transistors defining a current flow path between an input and output of the switch. The transistors have a common point of the current flow path and a common control terminal. A control circuit includes a voltage line receiving a limit operating voltage and first and second branches coupled between the voltage line and the common point and common control terminal, respectively. Further transistors are activated, upon turning-off of the first and second transistors, for coupling the branches to the voltage line. The branches include a parallel connected resistor, diode, and string of diodes with opposite polarities. The diode of the first branch plus string of diodes of the second branch and diode of the second branch plus string of diodes of the first branch provide coupling paths between the voltage line and, respectively, the common point and common control terminal.