Low-cost 50A current transducers improve on shunt measurement techniques

Paul Boughton
LEM's new HLSR series of current transducers provide alternative to resistive shunt/optocoupler configurations for insulated current measurements up to 50 Amps.

The five new HLSR transducers will satisfy application requirements in, for example, industrial inverters and motor drives; switch-mode and uninterruptible power supplies; specialist power supplies such as welding units; air conditioning; home appliances; but also in renewable-energy systems, for example, in solar combiner boxes and in solar inverters to track the maximum-power-point (MPPT).
LEM's HLSR series uses open-loop Hall-effect current sensing technology, to measure AC, DC or pulsed currents with nominal values of 10, 20, 32, 40 or 50 ARMS. LEM's proven expertise in open-loop Hall-effect technology allows these new devices to achieve a response time of only 2.5 µsec, with very low gain and offset drift over their operating temperature range of -40 to 105°C.[Page Break]
HLSR transducers deliver their output as an analogue voltage proportional to the primary measured current. In most applications, this voltage will be converted to a digital value by an analogue-to-digital converter: LEM has equipped the HLSR with an internal voltage reference of 1.65 or 2.5 V made available on a dedicated pin for use by an external device such as A/D converter, for example, or designers can choose to use an external reference from 0.5 to 2.65 V.

The voltage reference is just one feature of the new ASIC (Application-Specific Integrated Circuit) that LEM's designers created for this development, which enables the HLSR series to deliver typical accuracy of  ±1% at +25 °C, and ±3.4% at +105 °C, with a bandwidth of 100 kHz (-3 dB). LEM offers versions that operate from either + 3.3 or + 5 V single supplies.
LEM packaged the five models of the HLSR series in a compact and innovative outline that occupies only 387 mm2 of PCB area representing less surface than many solutions based on resistive shunts.[Page Break]

Variants of the package cater for either surface-mount or through-hole connection of both primary conductor path and signal/power connections. The low-profile package weighs just 5.5g, and is less than 12mm high.
Safe measurements are assured with a high level of insulation between primary and measurement circuitry thanks to long creepage and clearance distances (8mm as standard and 14mm on request), and a comparative tracking index (CTI) of 600. HLSR transducers are CE marked,  conform to the EN 50178 standard for industrial applications, and are granted of a five-year warranty.
For more information, visit www.lem.com