Your FAQ

Here you get answers to many questions around the topic electronic design.

Why is the rated current smaller than the saturation current for some inductors?

Because these two features are independent of each other by definition. The rated current is defined by the temperature rise, whereas the saturation current is defined by the drop in the inductance value. In the case of smaller packages, the core saturates before the inductor becomes hot, because we always strive to obtain a small RDC.

Why isn’t a standard SMT ferrite recommended the for use in circuits in which the maximum rated current is exceeded only for a very short time, e.g. inrush currents?

The multilayer structure of the internal layers may become damaged, which would result in interruptions of the circuit. The WE-MPSB ferrites can be used in these situations. They are the world’s first peak pulse specified multilayer SMT ferrites which are the best choice for such applications.

When does a common-mode choke saturate?

As long as the rated current flows through the two windings in the current-compensated mode, the saturation point will not be reached. Only when the current cannot be guaranteed to flow back and forth between both windings, would we speak of saturation. The common-mode noise current capable of bringing a common-mode choke to saturation must be extremely large.

How can a snap ferrite be replaced by a circuit-board solution in the redesign process?

As soon as a snap ferrite is used on a cable that conducts several lines, it fulfils the function of a common-mode choke. In this case, you must note which of the lines conduct the common-mode interference and place a common-mode choke in these lines on the PCB. If there are more than two lines that conduct this interference, a common-mode with multiple lines must be used.

Is a shielded case sufficient to pass the ESD test?

In most cases no, since the discharge creates an inward electromagnetic field and transports the charge onto the circuit board. We recommend using ESD suppressors or TVS diodes at the interfaces. When using a shielded case, we recommend the use of conductive seals from the WE-LT series in the intermediate spaces (cover-base) to create a sufficient shielding effect.