Surface mount current sensors measure to 30A for small-motor drives

June 19, 2017 // By Graham Prophet
Swiss transducer maker LEM recently released a series of surface mount, SO8 & SO16 packaged, isolated current transducers range with an integrated current conductor. These are open-loop Hall effect current transducers, based on a ASIC of LEM’s own design, that measure from 4A up to 30A DC, AC or pulsed.

LEM is responding to a demand it sees for integral drives in small, especially AC, motors. Drive designs have to be very compact, to fit in limited space. Current sensing must also be immune to external magnetic field influence, as the motor’s fields are in close proximity. This range of Hall-based sensors can compete with shunt-based techniques on costs and also on the insulation/isolation that LEM has achieved, with up to 3000 Vrms isolation test ratings.


Differential Hall sensing provides the external field immunity, along with a chopping measurement technique, to yield 1.3% accuracy, and a response time of 2 µsec. Good offset and gain drifts are also featured. Operating temperature range is from -40 to +125ºC. The integrated transducers are for AC and DC isolated current measurement up to 300 kHz. The GO series offers full isolation, despite their small size, by integrating the primary conductor for nominal current measurements of 4A, 6A, 8A, 10A, 12A, 16A, 20A or 30A with a measurement span of 2.5 times the nominal current. . Products in the GO series are able to support high overload currents up to 200A peak for short durations (1 msec).


Standard models provide an analogue voltage output with different sensitivity levels according to the models to achieve an output voltage of 800 mV @ IPN for 5V versions and 500 mV @ IPN for 3.3V versions. Ratiometric output is also an option though dedicated models.


GO transducers are not simple Open Loop Hall effect ASIC-based transducers; the series has been designed with unique primary integrated conductors for gradient measurement, to provide an immunity against the external fields found in power electronic applications.


These dedicated designs combine field proven techniques such as programmable internal temperature compensation (held in EEPROM), which ensure high-performance accuracy over the full range of temperature, from -40 to +125°C with a maximum of 3.74 %. Absence of a magnetic