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AC-DC Converters for Communication Cards

Inductive components and EMC for telecommunication systems

Inductive components and EMC for telecommunication systems

Alongside the focal areas of renewable energies, industrial applications and medical systems, the market segment of telecommunication technology is of strategic significance for PRAX.

PRAX develops and produces inductive components and EMC filters for base stations, data centers and transmission devices.

A key factor in most of telecomm devices is low profile needed. Several modules are mounted in racks and therefore available height is limited.

DC-DC converters for telecommunication system are part of such rack devices. Input voltage comes from 48Vdc bus and the output voltage varies from different voltage levels because it is used to power up the electronic devices inside the base stations. DC-DC converters power levels are in the range from 80 W up to 450 W.

In order to minimize size, weight and profile high frequency switching techniques are applied, so it is common to use frequency levels higher than 300kHz by topologies like forward (with active clamp), dual forward, push-pull, half bridge and full bridge.

Main isolation transformer is one of the key components for base stations DC-DC converters and must accomplish technology needs like: Low profile, high efficiency, low losses at high frequency and isolation. The best magnetic solution is called planar technology. PRAX know-how in design and manufacturing allows proposing reliable planar transformers and output chokes.

Planar technology consists in a magnetic component where windings, instead of standard round wire, are built with heavy copper multi-layer PCBs. Mounting process is based in automatic wave soldering, allowing a high reliability and cost-effective solution. As windings are based on thin copper tracks stacked together, skin and proximity effect, plus leakage inductance are reduced by a factor of 10 compared to standard winding technology. PRAX capability in heavy copper is up to 250um thickness in a multi-layer PCB up to 16 layers.

Isolation requirements for DC-DC converters in telecommunication systems are based on the international standard EN-60950. The specified creepage and isolation requirement is achieved by the insulation between PCB layers.

Advantages of Planar transformers versus classic technology are as follows:

  • Low profile & weight
  • Reduced dimensions.
  • Low leakage inductance (<0,5%) and interwinding capacitance
  • Low losses
  • Higher power handling
  • Excellent repetivity
  • High reliability
  • Cost effective
  • Easier cooling
  • Better resistance to impact and vibration
  • Automatic assembly
  • Reduced noise

Among planar transformers and inductors, PRAX also provides design and manufacturing of filtering inductors, high frequency current transformers and gate drive transformers.

In some applications for transmissions devices, it is used a small switch mode power supply, usually in Flyback topology, for the control unit or the stand-by mode. Power range varies from 2 Watts up to 50 Watts. Main difference from the DC-DC converters is that input power comes from the mains line (high voltage) while the output voltage is considered as a SELV (Safety Extra Low Voltage). PRAX designs and manufactures customized flyback transformers meeting telecommunication safety standard (EN 60950).