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Tiny AC current sensor replaces big transformers

Posted: 06 Jan 2010 ?? ?Print Version ?Bookmark and Share

Keywords:current sensor? transformer? AC/DC? power supply?

Silicon Laboratories Inc. grows its ISOpro line of isolation products with an AC current sensor family. The Si85xx AC current sensors replace traditional current transformers, providing up to 5kVrms of electrical isolation to ensure safety compliance for a variety of critical power delivery systems. The devices suit AC/DC switching power supplies, isolated AC/DC supplies, motor control applications and electronic lighting ballasts.

The Si85xx AC current sensors provide a more reliable, cost-effective alternative to antiquated transformers for today's modern power delivery systems. Traditional transformers are large, bulky magnetic components that contribute significant supply losses and have parasitics that complicate system design. The highly integrated ISOpro AC current sensors feature a sophisticated architecture that minimizes the need for costly discrete components for filtering and reset circuitry. An available small-footprint QFN package eases PCB space constraints with a small 4mm x 4mm x 1mm profile.

With a measurement accuracy of better than 5 percent, the Si85xx AC current sensors are available in 5-, 10- and 20A versions. They provide a large output signal level of 2V at full-scale output range, eliminating the need for an external amplifier. A "ping-pong" output mode enables one sensor to replace two current transformers and associated components in full-bridge applications, reducing board footprint by more than 50 percent and BOM cost by more than $0.30.

Offering the industry's lowest parasitic losses, the Si85xx current sensors enable designers to maximize system efficiency and meet aggressive power budgets for green energy standards. The devices' low resistance ("Silicon Labs' ISOpro Si85xx isolated AC current sensors provide a space- and cost-saving alternative to traditional transformers and their associated external components," said Dave Bresemann, vice president of Silicon Laboratories. "The new Si85xx current sensors also greatly improve system reliability. Based on mainstream CMOS process technology, the Si85xx devices require no hand winding or calibration at assembly unlike conventional mechanical transformers, which suffer from electrical and mechanical variations that reduce reliability and cause manufacturing headaches."

To ease the design process, the Si85xx AC sensor family is supported by a complete set of development tools including the Si85xx-EVB evaluation board and the OPENLPPOL-EVB open-loop point-of-load reference design.

The Si85xx ISOpro devices integrate the entire current sensing BOM into two space-saving package types:

A 20-pin SOIC with a 5kVrms isolation rating for systems intended for deployment in global markets that are powered from widely varying AC input supply voltage ranges.

A compact 4mm x 4mm x 1mm QFN package for space-constrained designs requiring an isolation rating up to 1kVrms. This QFN device is one-fourth the size of the smallest competitive product and five times thinner than a traditional transformer.

Samples of the Si85xx AC current sensors are available now. List pricing in 10,000-unit quantities ranges from $0.56 to $1.07 depending on isolation rating, package type, current range and output mode. The Si85xx-EVB and OPENLPPOL-EVB boards are priced at $19.95 and $99, respectively.

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