Safeguard Meters from Magnetic Tampering with New LinkSwith-XT2 Design

By Taryn Engmark

Assistant Editor

Embedded Computing Design

August 19, 2021


Safeguard Meters from Magnetic Tampering with New LinkSwith-XT2 Design

Utility meters need to work without interruption and often under adverse conditions. From full load to light load, through line surges, or even when being tampered with, meters require rugged and efficient power supplies to deliver power without fail.

A new design example report (DER-711) addresses these challenges with a 6.6 W dual-output flyback converter using a LinkSwitch-XT2 offline switcher IC. With a low-RDS (ON) and 900 V MOSFET, LinkSwitch-XT2 improves efficiency at full load, maintains efficiency at light load, and resists magnetic tampering.

Meter tampering is often done by placing a strong magnet close to the meter’s power supply to interfere with transformer inductance. LinkSwitch-XT2 features an ON/OFF control that compensates for the primary inductance reduction by increasing operating frequency to maintain output power level. The ON/OFF control enables high efficiency at light load, allowing utility providers to minimize energy consumption during normal meter operation.

A Universal Design

The LinkSwitch-XT2 IC’s integrated 900 V MOSFET provides a valuable safety margin for meters in regions with high and unstable mains voltage. DER-711 has an ultra-wide 85-350 VAC input range and can withstand 6 kV of differential line surge.

No EMI or Thermal Issues

The DER-711 circuit design utilizes the current limit of LinkSwitch-XT2 to operate at very low frequency, making it capable of withstanding severe magnetic tampering. When operating frequency increases to 60 kHz due to proximity to a magnet, the design wouldn’t incur thermal or electromagnetic interference issues. In the extreme case when a magnet is in physical contact with the transformer, the drop in system efficiency is limited to 4-6%, and IC temperature increases by just 16°C at full load. The DER-711 board layout places the transformer in the center, maximizing distance from possible external magnetic interference.

For more information, visit Power Integrations.

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