Low-Side N-Channel FET Transient Overvoltage Suppression

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Solution Overview

Problem

Existing transient voltage suppression circuits face issues with radio frequency emissions and high power dissipation due to the need for charge pumps or transformers to activate N-channel FETs, and P-channel FETs are limited by high ON resistance and power dissipation, making them unsuitable for larger power applications.

Innovation Solution

A transient overvoltage protection circuit using an N-channel FET connected in series with the low-side of the power source, which remains ON during normal operation but turns OFF to prevent voltage transients from propagating, eliminating the need for voltage boosting and reducing electromagnetic interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If an N-channel FET is used in series with the input line, then the FET can be operated with standard gate voltage, but additional voltage boosting hardware (charge pump/transformer) is required which generates radio frequency emissions

Engineering Contradiction:

ImproveFET gate voltage operationVSAvoidradio frequency emissions

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the voltage boosting hardware (charge pump or transformer) from the system by relocating the FET to the low-side position. This eliminates the need for gate voltage boosting and removes the source of radio frequency emissions while maintaining the N-channel FET's operational advantages

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of placing the FET on the high-side as conventionally done, the patent inverts the approach by placing the N-channel FET on the low-side. This inversion eliminates the need for voltage boosting hardware and its associated radio frequency emissions while maintaining effective transient voltage suppression

Inventive Principle:

Principle #13The other way round (Inversion)

2Object-generated harmful factors

If a P-channel FET is used to avoid voltage boosting hardware, then radio frequency emissions are reduced, but the FET generates high power dissipation due to high ON resistance

Engineering Contradiction:

Improveradio frequency emissionsVSAvoidpower dissipation

Core Design Contradiction:

Object-generated harmful factorsVSLoss of energy

Solution Approach 1:

The patent inverts the conventional approach by using an N-channel FET on the low-side instead of a P-channel FET. This allows the system to benefit from the low ON resistance and low power dissipation characteristics of N-channel FETs while eliminating the need for voltage boosting hardware that causes radio frequency emissions

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If a transient voltage suppression device is used to clamp input voltage, then voltage suppression is provided, but the load remains unprotected if the suppression device fails to activate

Engineering Contradiction:

Improvevoltage suppression reliabilityVSAvoidprotection circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the protection function by using the FET as a series switch that completely isolates the load from transient voltages. This segmentation approach provides more reliable protection compared to clamping devices, as the FET acts as a binary on/off switch that either connects or disconnects the load, eliminating the risk of partial protection failure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control circuit acts as an intermediary that monitors input voltage conditions and controls the FET state accordingly. This intermediary function ensures reliable activation of the FET during transient events while maintaining normal operation during steady-state conditions, providing robust protection without excessive complexity

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Effectively prevents transient voltages from damaging loads by isolating the power supply without the need for additional hardware, reducing radio frequency emissions and power dissipation, and ensuring reliable operation across a range of voltage conditions.

Implementation Method 1

an N-channel FET is connected in series with the low-side of the power source and is selectively activated in response to a detected transient voltage condition

Methodology Applied

Scientific EffectField effect transistor operation: Conduction (electrical)

Data Source

PatentUS8203815B2System and method to provide transient overvoltage suppression

Publication Date: 2012.06.19 HAMILTON SUNDSTRAND CORP

AI summary

Transient overvoltage suppression circuit prevents voltage surges from damaging an attached load. The suppression circuit includes a transistor connected in series with a low-side or return line of the load. A control circuit monitors the voltage on the input line (i.e., high-side) and in response to a detected voltage transient turns the transistor OFF to isolate the load from the transient voltage.