FET Current Sensing via Temperature Compensation

Solution Overview

Problem

Current methods for monitoring current in battery management systems require additional components that increase impedance and waste energy, as they involve placing a resistor in series with the power source, which is unnecessary when not actively measuring current.

Innovation Solution

A battery management circuit using a Field-Effect Transistor (FET) as a current sensing device, where the control logic determines current by measuring voltage levels across the FET and adjusting for temperature variations, allowing accurate current measurement without additional resistance in the power path.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a resistor is placed in series with the power source to monitor current, then current measurement capability is achieved, but power consumption increases and system cost increases

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent extracts the current measurement function from a separate physical resistor component and integrates it into the existing FET device. By utilizing the FET's on-resistance characteristic, the measurement function is obtained without adding an external resistor to the power path, thereby eliminating the continuous power loss and cost associated with an always-present measurement resistor.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The FET device is made multi-functional by enabling it to serve both as a power switch and as a current sensing element. The same FET that controls power delivery also provides the resistance needed for current measurement, eliminating the need for a dedicated measurement resistor and reducing overall system component count and power consumption.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a resistor is placed in series with the power source to monitor current, then current measurement capability is achieved, but system component count increases

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidsystem component count

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the current measurement function with the existing FET power switch device. Instead of adding a separate resistor component to the power path for measurement purposes, the solution combines the measurement functionality with the FET's inherent resistance characteristic, thereby reducing the total component count and simplifying the system architecture.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The FET device is made multi-functional by enabling it to serve both as a power switch and as a current sensing element. The same FET that controls power delivery also provides the resistance needed for current measurement, eliminating the need for a dedicated measurement resistor and reducing overall system component count and power consumption.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If a resistor is placed in series with the power source to monitor current, then current measurement capability is achieved, but impedance in power path increases

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidimpedance in power path

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the current measurement function from a separate physical resistor component and integrates it into the existing FET device. By utilizing the FET's on-resistance characteristic, the measurement function is obtained without adding an external resistor to the power path, thereby eliminating the continuous power loss and cost associated with an always-present measurement resistor.

Inventive Principle:

Principle #2Taking out (Extraction)

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 measurement without adding unnecessary components or resistance, reducing energy consumption and costs, while maintaining system efficiency and compactness.

Implementation Method 1

Using Ohm's law, a value for the current may be determined from the resistance of the resistor and the voltage level across the resistor

Methodology Applied

Scientific EffectOhm's law: Ohm's Law

Implementation Method 2

The apparatus may further include a sensor configured to measure a temperature

Methodology Applied

Scientific EffectTemperature sensing:

Data Source

PatentUS9813063B2Method of using a field-effect transistor as a current sensing device

Publication Date: 2017.11.07 APPLE INC

AI summary

An apparatus may include one or more registers configured to store a plurality of values, and an analog-to-digital converter (ADC). Each value of the plurality of values may correspond to a characteristic of a transistor at a respective temperature value. The ADC may be configured to generate a digital value corresponding to a difference in voltage levels between a first terminal and a second terminal of the transistor. The apparatus may further include a sensor configured to measure a temperature, and control logic configured to generate a first voltage level at a control terminal of the transistor and receive the digital value from the ADC. The control logic may be further configured to determine, during a first operational mode, a current passing through the transistor dependent upon the digital value, at least one value of the plurality of values, and the temperature.