New Standard Series of Current Sense Transformers

„Current Sense Transformers (CSTs) stand out among the various methods used to measure AC currents. CSTs allow for galvanic isolation of the detection circuit. The current to be determined is fed into the primary winding of a transformer and a voltage proportional to the primary current is measured on the secondary side. This technology has a number of other advantages over a shunt resistor, namely minimized losses, a very rugged construction and simple implementation of the subsequent electronics.

CSTs are used in applications requiring a current regulator, a protection circuit or a load detector.

EPCOS has developed two CST series whose SMT versions are particularly suited for compact DC/DC converters. The aim was to offer a stand alone solution in which the primary winding is already integrated. The components may be mounted on a circuit board using standard SMDT processing techniques.

The EE5 series is a compatible solution for existing designs based on an EE5 core. The E4.2 series is even more miniaturized. It uses the extremely compact E4.2 core. In contrast to the EE5 series, the primary winding is already integrated in the coil former. The space saving is evident. Thus the E4.2 requires only 33% of the area or 23% of the volume of its counterpart in the EE5 series.

Both variants have only a single winding on the primary side. Depending on the resolution required for the current measurement, a choice of 20, 30, 40, 50, 60, 70, 100 or 125 windings is available on the secondary side. If high measurement frequencies are required, it makes sense to select a variant with a correspondingly small number of secondary windings. Due to the parasitic capacitance of the secondary winding, the intrinsic resonant frequency – that has a limiting effect – is greater in variants with a lower turn count of the secondary winding.

CSTs are preferably used in conjunction with switching controllers. They replace the resistor in front of the source of the switching transistor and considerably reduce the power dissipation in this part of the circuit.

For detailed information please contact your local SPOERLE Branch Office.