Flyback Converter Resonant Frequency for Magnetic Tamper Detection

Solution Overview

Problem

Smart meters are vulnerable to magnetic tampering attacks, which can disrupt the operation of their integrated power supplies. Existing solutions, such as Hall effect sensors, increase costs and development efforts due to the additional circuitry required.

Innovation Solution

The system employs a flyback converter with a resonant frequency and discontinuous conduction mode, where a controller measures and monitors the resonant frequency. If the resonant frequency deviates from its normal condition, the controller triggers an event to detect and respond to magnetic tampering.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Hall effect sensors are placed near the transformer to detect magnetic tamper attacks, then magnetic tamper detection capability is improved, but device complexity and cost increase due to additional circuitry

Engineering Contradiction:

Improvemagnetic tamper detection capabilityVSAvoidcircuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The existing flyback converter circuit is made multi-functional by using its resonant frequency characteristics not only for power conversion but also for magnetic tamper detection. The controller monitors the resonant frequency of the flyback converter's LC circuit, which changes when external magnetic fields affect the transformer, thereby detecting tamper attempts without adding dedicated sensor circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The flyback converter's own resonant frequency characteristics are utilized for self-diagnosis of magnetic tampering. Instead of requiring external sensors, the system uses its inherent electrical characteristics (resonant frequency of the LC circuit formed by transformer inductance and capacitor) to detect changes caused by external magnetic fields, making the detection function self-contained within the existing power supply circuit.

Inventive Principle:

Principle #25Self-service

2Reliability

If Hall effect sensors are placed near the transformer to detect magnetic tamper attacks, then magnetic tamper detection capability is improved, but development effort and cost increase

Engineering Contradiction:

Improvemagnetic tamper detection capabilityVSAvoiddevelopment effort

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The existing flyback converter circuit is made multi-functional by using its resonant frequency characteristics not only for power conversion but also for magnetic tamper detection. The controller monitors the resonant frequency of the flyback converter's LC circuit, which changes when external magnetic fields affect the transformer, thereby detecting tamper attempts without adding dedicated sensor circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

Instead of using expensive Hall effect sensors and their associated circuitry, the invention uses the already-present flyback converter components (transformer, capacitor, controller) to perform detection. This approach eliminates the need for additional expensive components, reducing both development effort and manufacturing cost while maintaining detection functionality.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If additional circuitry is added to detect magnetic fields, then magnetic tamper detection capability is improved, but cost increases

Engineering Contradiction:

Improvemagnetic tamper detection capabilityVSAvoidcircuitry quantity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The existing flyback converter circuit is made multi-functional by using its resonant frequency characteristics not only for power conversion but also for magnetic tamper detection. The controller monitors the resonant frequency of the flyback converter's LC circuit, which changes when external magnetic fields affect the transformer, thereby detecting tamper attempts without adding dedicated sensor circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The flyback converter's own resonant frequency characteristics are utilized for self-diagnosis of magnetic tampering. Instead of requiring external sensors, the system uses its inherent electrical characteristics (resonant frequency of the LC circuit formed by transformer inductance and capacitor) to detect changes caused by external magnetic fields, making the detection function self-contained within the existing power supply circuit.

Inventive Principle:

Principle #25Self-service

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 approach allows for reliable detection of external magnetic fields without the need for additional circuitry, thereby reducing costs and enhancing the security of smart meters.

Implementation Method 1

determine whether the resonant frequency satisfies a condition

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

measure resonant frequency of electronic components to detect a magnetic tamper attack from an external magnetic field

Methodology Applied

Scientific EffectElectromagnetic Induction: Electromagnetic Induction

Data Source

PatentUS12292461B2Resonant frequency change detection

Publication Date: 2025.05.06 TEXAS INSTRUMENTS INC

AI summary

At a switch terminal of a flyback converter in a discontinuous conduction mode in a power meter, an apparatus determines a resonant frequency of the flyback converter. The apparatus determines whether the resonant frequency satisfies a condition. Through a controller, the apparatus triggers an event responsive to determining that the resonant frequency satisfies the condition.