AC sensor replaces 2 current transformers in power delivery systems

Austin, Tex. — Offering a space- and cost-savings alternative to traditional current transformers, Silicon Laboratories Inc. has introduced a next-generation ac current sensor family, housed in a small 4 x 4 x 1-mm package. The Si85xx ac current sensors, part of the company’s ISOpro isolation product portfolio, provide up to 5 kVrms of electrical isolation to ensure safety compliance for a variety of power delivery systems such as ac-dc switching power supplies, isolated dc-dc supplies, motor control applications and electronic lighting ballasts, said the company.

The Si85xx ac current sensors are designed as a replacement for larger and bulkier transformers that typically contribute to significant supply losses and parasitics that complicate system design, said the company. The highly integrated ISOpro ac current sensors feature a sophisticated architecture that minimizes the need for discrete components for filtering and reset circuitry.

With a measurement accuracy of better than 5 percent, the Si85xx ac current sensors are available in 5 A, 10 A and 20 A versions. They provide a large output signal level of 2.0 V 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 bill-of-materials (BOM) cost by more than $0.30, according to Silicon Labs.


Claiming 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, said Silicon Labs. The devices’ low resistance (<1.3 milliohms) and small parasitic inductance (<2 nH) result in more efficient power supplies that are easier and quicker to design, according to the company. Silicon Labs said the Si85xx current sensors also significantly improve system reliability by eliminating the need to hand wind or calibrate at assembly as required by mechanical transformers. 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 are available in two package sizes: a 4 x 4 x 1-mm QFN for space-constrained designs requiring an isolation rating up to 1 kVrms, and a 20-pin SOIC with a 5 kVrms isolation rating for systems intended for deployment in global markets that are powered from widely varying ac input supply voltage ranges. Availability: Samples are available now. Pricing: List pricing in quantities of 10,000 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 $99.00, respectively. Resources: Si85xx ac current sensors and development tools.