Hi all,
I have a dozen of these common-mode chokes from EMI filters in my box, taken from old fluorescent lamp ballasts and other SMPS power supplies. There's an idea to modify one of them to a current transformer, its windings would be the secondary winding of a current transformer. This choke is made up of two windings, each with about 30-50 turns, and I just need to add a primary winding, which would consist of 2 or 4 turns. I could figure out the exact number of turns with a generator.
There would be about 30 mA of current in the primary winding of the transformer, with a frequency of around 200 kHz.
Is the ferrite on such chokes suitable for working at 200kHz? Has anyone done something similar?
Thanks in aticipation

 

Hi.
Chokes suitable to work at a given frequency depends on the material of the core. So you have to characterize the core at this frequency you want and also at the power you need. Because the hysteresis loss is dependent on the power you apply, and also the frequency, as 200 kHz is somewhat high. If the core is too slow responding to this stimulus, it leads to distortion, loss in output amplitude, lag, and heating up in the core.

Figure: the effects of a sinusoid being too fast for the core.