High-Voltage MOSFET Switch Isolation Using 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 during high-voltage and high-slew-rate conditions, leading to potential harmonic distortion and increased power consumption.

Innovation Solution

The implementation of a switching device structure using two high-voltage MOSFETs with a control circuit that includes additional transistors and diodes, allowing for efficient turning-off and isolation by limiting voltage and utilizing parasitic capacitances to maintain the off-state without complex reference voltage generation, and minimizing power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional high-voltage switch structures are used, then basic switching function is achieved, but parasitic capacitances cause isolation failures and harmonic distortion under high-voltage and high-slew-rate conditions

Engineering Contradiction:

Improveisolation effectivenessVSAvoidparasitic capacitance effects

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful parasitic capacitances into beneficial elements by connecting them to a negative voltage rail, where they actively contribute to maintaining the off-state through capacitive coupling effects that reinforce isolation rather than compromise it

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent applies preliminary anti-action by pre-charging the parasitic capacitances to the negative voltage rail before switching operations, and by using clamping diodes to prevent voltage excursions that could compromise isolation, thereby counteracting potential harmful effects before they occur

Inventive Principle:

Principle #9Preliminary anti-action

2Ease of operation

If complex control circuits with reference voltage generation are used, then switching control is improved, but device complexity and power consumption increase

Engineering Contradiction:

Improveswitching control capabilityVSAvoidcontrol circuit structure

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent implements self-service by using the switch's own parasitic capacitances and existing voltage rails (including the negative voltage rail) to maintain the off-state, eliminating the need for external reference voltage generation circuits and complex control logic

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The negative voltage rail serves multiple functions simultaneously: it provides the reference potential for parasitic capacitances, enables off-state maintenance through capacitive coupling, and supports the operation of clamping diodes, thereby eliminating the need for separate dedicated control circuits

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Power

If conventional switch structures are used, then basic conduction is achieved, but power consumption increases under maximum criticality conditions

Engineering Contradiction:

Improveswitching capabilityVSAvoidpower consumption

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The patent converts the previously harmful parasitic capacitances into energy-saving elements by charging them to the negative voltage rail, where they actively maintain the off-state through capacitive coupling, thereby reducing the need for continuous power consumption to sustain isolation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 enhances the switching efficiency and reliability by maintaining effective isolation and reducing power consumption, even under maximum criticality conditions, while preventing harmonic distortion and ensuring robust operation across varying input voltages.

Implementation Method 1

the parasitic capacitances present in the structure are charged to a negative voltage level, it being possible for these same parasitic capacitances to contribute, through capacitive coupling effects, to the maintenance of the off-state of the switch

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Data Source

PatentUS9722596B2Electronic switch, and corresponding device and method

Publication Date: 2017.08.01 STMICROELECTRONICS SRL

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.