Highfrequency Filtering of DC Power Lines

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High-frequency Filtering of DC Power Lines

• Technical, constructional and practical issues
  with filtering on dc power lines
• Wolfgang L. KlampferManager Training Center

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Contents

• EMC issues for base stations
• Filtering at high frequencies
• Contacting under high load
• Conventional solutions
• A new approach

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Basestations and EMC

• Standard requirements in Europe
• Noise sources and distribution

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Requirements for Base Stations
Radio Interface
Enclosure
Antenna
DC Supply
AC Mains
Other lines
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Requirements for Base Stations
Radio Interface
Enclosure

• Emission
• EN 55022CISPR 16-1
• Immunity
• EN 61000-4-4
• EN 61000-4-6

Antenna
DC Supply
AC Mains
Other lines
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Conducted Emission according to EN 55022, CISPR
16-1
Supply
EUT
DC LISN
PE
EMI Receiver
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Differential mode noise
L N PE
L
R
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Parasitic components as cause for differential
mode noise
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Characteristics for differential mode noise

• Current through ESL and ESR
• Lower frequencies
• Switching frequency and harmonics
• Loop structures

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Common mode noise
L N PE
L
R
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Insulation as cause for common mode noise
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Characteristics of common mode noise

• Usually high frequency problems, e.g.
  switching/oscillating at higher frequencies
• Affected by circuit layout, e.g. heat sinks
• Cables

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Differential to common mode conversion

• Perfectly balanced
• only differential mode
• no radiation
• Slight unbalance
• differential to common mode conversion
• conducted and radiated noise at high frequencies

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Filtering at high frequencies

• Problems with resonances and solutions
• Special filter requirements for base stations

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Capacitors and chokes for noise suppression

• Two metal plates, separated by insulation
• Often realised by 2 metallized plastic foils

• Wire wound to a coil
• Usually winding is placed on magnetic material
  (core)

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Frequency response of capacitors and chokes
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Use of capacitors and chokes in circuits
C
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Resonances of capacitors and chokes
Inductors can have significant capacitance
between windings
Connection leads of capacitors work like small
series inductances
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Frequency response of feedthrough capacitors
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Filters for Base Stations

• Special Requirements
• Customized power requirements
• Mixed AC and DC configurations
• Environmental stress
• High attenuation
• Special enclosure forms

AC Mains
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Power Layout
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Environmental Requirements

• Corrosion resistance
• Thermal shock
• Vibration
• Impact resistance
• Transportation shock and vibration
• Earthquakes

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Attenuation Requirements

• Insertion Loss, Line to GND, 50W
• 1.0 MHz 5.0 MHz ³ 20 dB
• 5.0 MHz 10.0 MHz ³ 30 dB
• 10.0 MHz 30.0 MHz ³ 40 dB
• 30.0 MHz 4.0 GHz ³ 40 dB

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Contacting at high loads

• Special issues and requirements for contacts

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Requirements for dc power connections

• Reliable contact
• Easy connect/disconnect
• Low contact resistance
• High number of connect-disconnect cycles
• Hot-pluggable

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Potential threats and problems

• Reliable contact
• Force of contacts over time
• Easy connect/disconnect
• Installation/maintenance time
• Low contact resistance
• Risk of overheating
• High number of connect-disconnect cycles
• Wear-out of contact surface
• Hot-pluggable
• Arcing between male and female connector
  destruction of contacts

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Specialties about a proper contact
Fixed beams
Surround spring (Activates only cantilevered
beams)
Cantilevered beams
Crimp barrel
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Function of the surround spring
Male pin engaging fixed beams hot plug surface
Male pin engaging cantilevered beams

• assists cantilevered beams at operating
  temperatures gt 80 C
• provides high mechanical shock/vibration
  stability with no contact bounce

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Function of the beams

• Fixed beams
• provide mechanical guidance
• thermal conductivity
• sacrificial hot plug / hot swap location
• Cantilevered beams
• low contact resistance
• low current density
• optimum insertion force

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Contact material selection for power connectors

• High conductivity copper low temperature rise
• Good manufacturing process
• Copper with good spring properties at contact
  interface normal force
• Copper with good formability for crimping to
  finely stranded copper conductors

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Conventional solution

• Standard approach for dc filtering and connecting

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Traditional installation until today
DC Power to Filter
Filter to Bus Bar
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Some considerations for the conventional solution

• 8 parts with 10 (!) connection points
• Necessary extra provisions for capacitor
  grounding
• Overall attenuation relies on quality of
  connection
• Work- and cost-intensive installation
• Many connections means many potential failure
  sources

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Relation between attenuation and earth resistance
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A new approach

• Advanced filtering and contacting solution

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Requirements for a contacting-filtering solution

• Easy connect and disconnect under full-load
• Easy and quick installation
• Reduced number of connection points
• Reliable filtering up to several GHz
• Protection against reverse polarity
• Protection against wrong connections in case of
  several power lines

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The solution ACARA

• 2 parts with 2 connection points
• High-quality contacts for connection and
  disconnection under full-load
• Time/cost/space saving solution

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Frequency response of ACARA
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Reverse polarity protection and code keying
Pins for keying of connector pairs
6 positions for keying pins
Protection against reverse polarity
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Thank you very much for your attention
Any questions?