Ferrous Silicon Aluminum Toroids 22UH

Ferrous Silicon Aluminum Toroids 22UH

It is often difficult to measure the saturation characteristics of the core (whole or part) of a common mode coil. A simple test shows to what extent the attenuation of a common-mode filter is affected by the inductance reduction caused by the 60Hz scheduling current. An oscilloscope and a differential mode suppression network (DMRN) are required for this test. First, the oscilloscope is used to monitor the line voltage. Input signals from channel A of the oscilloscope in the following way, set the time reference of the oscilloscope as 2ms/div, and then add the trigger signal to channel A. When the AC voltage reaches the peak, the wired current will be generated. At this time, the degradation of the filter efficiency is expected. The input of the DMRN is connected to the LISN, and the output is matched with an impedance of 50 and connected to the B-channel of the oscilloscope. When the common mode choke is operating in the linear region, during the input current fluctuation, the emission increment detected in the B channel does not exceed 6-10dB. During the peak in - line voltage, the bridge rectifier guides on and transmits the charging current.

If the common mode choke reaches saturation, then the emission will increase as the input surge increases. If the common mode choke reaches strong saturation, the emission intensity is the same as it would be without the filter, that is, it is easy to reach more than 40dB.

These experimental data can be interpreted in other ways. The emission minimum (when the line current is 0) is the effect shown when the filter has no bias current. The ratio of peak emission to minimum emission, the degradation factor, is used to measure the effect of the line current offset on the actual effect of the filter. A large degradation factor indicates that the common mode choke core is not used properly at all, and the "inherent degradation factor" of a better filter is roughly 2-4. It is caused by two phenomena: first, the decrease in inductance caused by the 60Hz charging current (as described above); Second, the forward and reverse guide of the bridge rectifier. The equivalent circuit of common-mode emission consists of a voltage source with an impedance of about 200pF, the diode impedance, and the common-mode impedance of the LISN. When the bridge rectifier is forward biased, a voltage division occurs between the source impedance, 25, and the LISN common-mode impedance. When the bridge rectifier is reverse-biased, there is a voltage division between the source impedance, the rectifier bridge reverse-biased capacitance, and the LISN. When the reverse bias capacitance of the diode rectifier bridge is small, it has a certain effect on common-mode filtering. When the rectifier bridge is biased forward, common-mode filtering is not affected.