Some typical noise suppression
circuit designs
The following diagrams illustrate
some commonly-used noise
suppression circuit designs.
Application engineers are available
throughout Schaffner’s worldwide
network of support centres to help
customers choose and design
optimal circuits for specific EMC
problems.
Single-phase power control.
The circuit
in Figure 9 controls the amount of power
delivered to the load. The use of a filter
based on a saturating-type choke (from
the RI Series) - sited as close as possible
to the switching element - provides short-
duration impedance to suppress the noise
precisely at the times of switching.
Controller
P
Cx
Suppressing common-mode
interference.
The circuit in Figure 11
illustrates the use of a current-
compensated type choke (from the RN
Series) in conjunction with a few discrete
components, to provide an economic filter
to suppress common-mode interference
between the AC mains and a switched-
mode power supply.
P
Load
N
Cy
Cy
RN
RI
Cx
Cx
N
Cy
Cy
Power
supply
E
E
Figure 9.
Application of a saturating
choke in a single-phase system
Three-phase power control.
The circuit
in Figure 10 illustrates the use of a filter
based on saturating-type chokes (from the
RI Series) in a three-phase rectifier with a
resistive load. Sited as close as possible to
the thyristor switching elements, the
chokes provide short-duration impedance
to suppress noise precisely at the times of
switching.
Suppressing differential and common-
mode noise.
The circuit in Figure 12 adds
another stage to the previous circuit to
combat differential-mode interference.
This is achieved by means of a filter based
on non-saturating rod-cored chokes from
the RF Series, which are ideal for removing
lower frequency noise such as that
RI
L1
Cx
Figure 11.
Simple powerline filer to
remove common-mode noise, based on a
current-compensated choke
generated at typical power supply
switching frequencies.
RF
P
RN
RI
RI
RI
Cx
Cx
RI
Cy
L2
L3
E
RI
Cx
N
RF
Cx
Cx
Equipment
Cy
Cy
Cy
Cy
Load
E
Figure 10.
Application of saturating
chokes in a three-phase system
Figure 12.
Two-stage powerline filter with
differential- and common-mode
suppression
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