stardustsailor
Well-Known Member
ADDITIONAL (external ) EMC Filtering for Switching PSUs ( CC & CV )
A power supply or DC/DC converter will have an in-built input filter to
reduce the conducted emissions. It will have two parts; one to reduce
the common mode noise, the other to reduce the differential mode
noise. Common mode noise can be reduced by use of Y capacitors
between line and ground and another one between neutral and ground
in conjunction with a common mode inductor.
Differential mode noise can be reduced by use of an X capacitor
between the line and the neutral in conjunction with a differential mode
inductor. In some instances the differential mode inductor is formed
from the leakage inductance of the common mode inductor so that
there is only one visible wound component.
Sometimes the built-in filter will give an inadequate performance for a given application. This may be
where the power supply is designed to meet the lesser requirements of an industrial environment but
is being used in the more stringent light industrial or residential environment. Perhaps several power
supplies are being used in a single piece of equipment and the resulting emissions must be reduced,
or perhaps noise from the load itself is being coupled into the input of the power supply. In all these
instances some form of external filtering will be required.
Filter Selection
There are some basic steps to follow when choosing a filter,
some of which are straightforward and others less so.
Mechanical format
Is the filter going to be mounted within the equipment where it can be
fixed to a panel or should it also provide the extra functions of being the
mains input connector and perhaps contain an on/off switch?
If it is the former, a chassis mount filter can be used. These will generally have
faston terminals for easy connection but may also come with flying
leads. IEC inlet filters can have built-in on/off switches and even fuse
holders. They can be mounted by either screwing them down to the
equipment or by use of self locking lugs. Generally, for metal chassis
equipment, the bolt-down variety will provide a lower impedance earth
path for the circulating noise down to ground
Input current
The filter should be able to pass the maximum working current of the
equipment so as not to overheat but generally the lower the current
capacity within a filter series, the higher its filtering performance.
Attenuation required
A filter will be required to reduce the noise at certain frequencies. By
how much and at which frequencies is information which will not readily
be known without having first performed a conducted noise
measurement. Filters have differing amounts of attenuation and, for a
given current rating, the higher the attenuation the larger the filter. As
there will be a practical limit on the size of filter components, large
amounts of attenuation will require the use of multi-stage filters.
http://www.xppower.com/pdfs/techguide.pdf
A power supply or DC/DC converter will have an in-built input filter to
reduce the conducted emissions. It will have two parts; one to reduce
the common mode noise, the other to reduce the differential mode
noise. Common mode noise can be reduced by use of Y capacitors
between line and ground and another one between neutral and ground
in conjunction with a common mode inductor.
Differential mode noise can be reduced by use of an X capacitor
between the line and the neutral in conjunction with a differential mode
inductor. In some instances the differential mode inductor is formed
from the leakage inductance of the common mode inductor so that
there is only one visible wound component.
Sometimes the built-in filter will give an inadequate performance for a given application. This may be
where the power supply is designed to meet the lesser requirements of an industrial environment but
is being used in the more stringent light industrial or residential environment. Perhaps several power
supplies are being used in a single piece of equipment and the resulting emissions must be reduced,
or perhaps noise from the load itself is being coupled into the input of the power supply. In all these
instances some form of external filtering will be required.
Filter Selection
There are some basic steps to follow when choosing a filter,
some of which are straightforward and others less so.
Mechanical format
Is the filter going to be mounted within the equipment where it can be
fixed to a panel or should it also provide the extra functions of being the
mains input connector and perhaps contain an on/off switch?
If it is the former, a chassis mount filter can be used. These will generally have
faston terminals for easy connection but may also come with flying
leads. IEC inlet filters can have built-in on/off switches and even fuse
holders. They can be mounted by either screwing them down to the
equipment or by use of self locking lugs. Generally, for metal chassis
equipment, the bolt-down variety will provide a lower impedance earth
path for the circulating noise down to ground
Input current
The filter should be able to pass the maximum working current of the
equipment so as not to overheat but generally the lower the current
capacity within a filter series, the higher its filtering performance.
Attenuation required
A filter will be required to reduce the noise at certain frequencies. By
how much and at which frequencies is information which will not readily
be known without having first performed a conducted noise
measurement. Filters have differing amounts of attenuation and, for a
given current rating, the higher the attenuation the larger the filter. As
there will be a practical limit on the size of filter components, large
amounts of attenuation will require the use of multi-stage filters.
http://www.xppower.com/pdfs/techguide.pdf
