A wideband common-mode noise filter with a Mn-Zn ferrite and Cu/polyimide tape wound coil for switching power supplies used in electronic measuring instruments

This paper describes a wideband common-mode noise filter for switching power supply used in the electronic measuring instruments such as zero-flux type current tester. Since the current can be measured up to 50 MHz by using the current tester, the filter used for such application is required to have large common-mode noise rejection up to 100 MHz in frequency. The proposed common-mode filter consisted of an Mn-Zn ferrite core and Cu/polyimide tape wound coil, and operated as a coupled distributed constant circuit in the frequencies beyond 10 MHz. Such operation principle of the filter is same as the previous device. The device exhibited a common-mode rejection of 30 dB even at 100 MHz.