I want to select a common mode choke. This will be placed at the input of a buck regulator. Now, assuming conducted noise or common mode noise, will be at a certain frequency and I will need common mode chokes that have high impedance at that frequency. For eg / I have a buck running at 100kHz. Then I will need a common mode choke tof high impedance at 100kHz and at harmonics of that fundamental frequency. The fundamental is 100kHz. Now, when terming harmonics, what is the max multiple that should be a worry ? Is it the 3rd harmonic ,so 300kHz ?
Also, when it is said we need high impedance at fundamental frequency and its harmonics, what exactly can be termed as high impedance ? WHat is the value and what is the basis for that value ?