Pass FET Current Sensing Across the Full Vds Range

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Solution Overview

Problem

Current sense circuits for pass FETs are limited in their ability to accurately sense current through the transistor for both small and large differences between source voltage (Vsource) and supply voltage (Vcc), restricting their operational range.

Innovation Solution

An electronic circuit with dual sense circuits, one for small and one for large differences between Vsource and Vcc, utilizing FETs and sense amplifiers to enable current sensing through a pass FET for the full range of Vsource from Vcc to ground, with switches and amplifiers configured to activate or deactivate based on voltage conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a single current sense circuit is used, then the circuit structure is simple, but the sensing capability is limited to either small or large voltage differences between Vsource and Vcc

Engineering Contradiction:

Improvesensing capability across voltage rangeVSAvoidcircuit structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The current sense circuit is divided into two separate sense circuits: a first sense circuit for sensing when the voltage difference between Vsource and Vcc is small, and a second sense circuit for sensing when the voltage difference is large. Each sense circuit is optimized for its specific voltage range, allowing the system to accurately sense current across the full voltage range from Vcc to ground.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If dual sense circuits are used to cover full voltage range, then sensing capability is improved, but device complexity increases

Engineering Contradiction:

Improvevoltage range coverageVSAvoidnumber of sense circuits

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The system dynamically switches between the first and second sense circuits based on the voltage difference between Vsource and Vcc. Control logic activates the appropriate sense circuit according to the operating conditions, ensuring optimal sensing performance across different voltage ranges while managing the complexity of having dual circuits.

Inventive Principle:

Principle #15Dynamics

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

Enables accurate current sensing through a pass FET for any drain-source voltage (Vds), overcoming the limitations of existing circuits by allowing sensing across the full range of Vsource from Vcc to ground, ensuring reliable operation in various voltage scenarios.

Implementation Method 1

a first sense circuit configured to pass a first sense current in case a difference between a supply voltage and a source voltage of the pass FET is small

Methodology Applied

Scientific EffectVoltage detection: Electric Field

Data Source

PatentEP4478058A1System for sensing current through a pass fet

Publication Date: 2024.12.18 NEXPERIA BV

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AI summary

An electronic circuit for sensing a current through a pass FET, wherein a first sense circuit passes a first sense current in case a difference between a supply voltage and a source voltage of the pass FET is small, and wherein a second sense circuit passes a second sense current in case the difference between the supply voltage and the source voltage of the pass FET is large. The first sense current and the second sense current are representative of the current through the pass FET.