Common mode filters

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Common mode filters

The common mode filter is based on two coupled inductors (Figure 5).

Figure 5. Symbol of the common mode filter

The couple coefficient is called k. If L1 and L2 are two inductance values and M the mutual

inductance, the following equation is given:

Equation 1

their impedances are as follows:

Equation 2

and

Equation 3

Equation 4

k

M

L

1

L

2

×

----------------------

=

Z

1

R

1

j

ωL

1

j

ωM

I

2

I

1

----

×

++

=

Z

2

R

2

j

ωL

2

j

ωM

I

1

I

2

----

×

++

=

Mk

L

1

L

2

×

×

=