The figures below show examples of the functions of respective noise
filters used in a switching power supply. To confirm these functions,
changes in the Mains Terminal Interference Voltage is broken down into
differential mode and common mode noise components.
Figure (a) shows data obtained when no noise filter is used. This
figure reveals that both the differential mode and common mode noise
components are high. Figure (b) shows data obtained when an X-capacitor
is used. This figure reveals that the differential mode noise component
is decreased. Figure (c) shows data obtained when both an X-capacitor
and Y-capacitor are used. This figure reveals that both the common mode
and differential mode noise components are decreased. Figure (d) shows
data obtained when an X-capacitor, Y-capacitor, and common mode choke
coil are all used. This figure reveals that the differential mode noise
component is further decreased as well as the common mode one. This is
because an actual common mode choke coil contains a certain amount of
differential mode inductance. |
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