Example 1: PFC Choke with nano crystalline core

The single phase PFC Choke with nano crystalline core in this example is dedicated for an active 3-phase power factor correction and has a rated inductance of 500 µH and a rated current of 40 ARMS (peak current in the real application up to 70 A at rated RMS current). The ribbon core consists of nano crystalline alloy with high saturation flux density.

The inductance of this choke decreases moderately up to 60 A (approximately 20%), which makes sense for the economical point of view and is not critical for the application. Beyond 60 A the inductance decreases much faster.

At 90 A, the inductor has an incremental inductance of no more than 120 µH! The circuit designer needs to take this into account for overload operation, even if a short overload operation wouldn’t cause thermal problems to the inductor.

In the current application, however, this would result in such high switching frequencies that the switching transistors would be overloaded.