Inductor Current Estimation Circuit for Low-Loss Power Converters

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Solution Overview

Problem

Existing bridgeless AC-to-DC power converters face challenges in efficiently sensing inductor current, particularly due to the need for expensive high-frequency current sensing transformers or Hall-effect sensors, which increase costs and complexity, especially in low-power applications.

Innovation Solution

A current estimating circuit is introduced, which includes a current estimating resistor and capacitor coupled in series with a sense resistor, allowing for the synthesis of a current signal proportional to the inductor current without the need for continuous current sensing through a sense resistor, thereby reducing power dissipation and cost.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If high-frequency current sensing transformers or Hall-effect sensors are used to sense inductor current, then measurement precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improveinductor current sensing accuracyVSAvoidcircuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent creates an analog copy of the inductor current waveform using passive RC components. The current sensing circuit generates a voltage signal that replicates the inductor current profile without requiring direct current measurement, thereby simplifying the circuit while maintaining measurement accuracy for control purposes

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces complex electromagnetic sensing mechanisms (transformers and Hall-effect sensors) with a simpler electronic voltage division and RC integration system. This substitution eliminates the need for magnetic components and complex isolation requirements while achieving the necessary current information for control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If continuous current sensing through a sense resistor is implemented, then measurement precision is improved, but power dissipation increases

Engineering Contradiction:

Improveinductor current sensing accuracyVSAvoidpower dissipation

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent implements current sensing only during the switch off-time period rather than continuously. The RC circuit integrates the voltage across the sense resistor during the on-time and holds this value during the off-time, enabling periodic sampling that reduces average power dissipation while maintaining adequate measurement precision for control loop operation

Inventive Principle:

Principle #19Periodic action

3Ease of manufacture

If bridgeless AC-to-DC power converter topology is used, then manufacturing precision is improved, but ease of operation worsens due to current sensing challenges

Engineering Contradiction:

Improveconverter assembly simplicityVSAvoidcurrent sensing implementation

Core Design Contradiction:

Ease of manufactureVSEase of operation

Solution Approach 1:

The patent introduces an RC integrating circuit as an intermediary between the sense resistor and the control input. This intermediary circuit processes the sense resistor voltage to generate the appropriate control signal waveform, simplifying the overall sensing implementation in bridgeless topology while maintaining control accuracy

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

The proposed solution effectively estimates the inductor current with reduced power dissipation and cost, eliminating the need for expensive isolation components and enhancing the efficiency and robustness of the power converter, particularly in low-power applications.

Implementation Method 1

a current estimating resistor and capacitor converted the current into a voltage that was proportional to the current

Methodology Applied

Scientific EffectOhm's Law: Ohm's Law

Implementation Method 2

a current estimating resistor and capacitor converted the current into a voltage

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS20250038637A1System and method for estimating a current in an inductor of a power converter

Publication Date: 2025.01.30 TEXAS INSTRUMENTS INC

AI summary

In an example, a current estimating circuit includes a current estimating resistor coupled in series with a current estimating capacitor. The current estimating resistor and the current estimating capacitor are configured to provide a voltage across the current estimating capacitor during a first portion of a switching cycle, in which the voltage across the current estimating capacitor is proportional to an inductor current that flows through an inductor. The current estimating circuit includes a sense resistor configured to provide a sensed voltage across the sense resistor during a second portion of the switching cycle. The current estimating circuit includes a switch configured to apply the sensed voltage to the current estimating capacitor to provide the voltage across the current estimating capacitor during the second portion of the switching cycle.