Decouplers, Couplers and Back-Filters for Surge Testing a DC Supply Interface

March 7, 2019
10:35  -  10:55 am

Most people happily go to IEC 61000-4-5 for guidance on surge testing AC or DC supplies. In coming up with suitable test circuits for DC supplies the ITU-T members found that there are several test configuration omissions in IEC 61000-4-5. The ITU-T work established test circuits for floating systems, such as the 400 V (±200 V) system for data centres and 5G, and supply systems with remote single point earth-bonding. To understand DC supply system variants a list of system configurations is given. Testing requires the power source and powered equipment be suitably coupled and a method of applying a surge devised. This leads to an examination and discussion of commercially available decouplers, couplers and back-filters. Rather than ending up with collection of test circuits, UK Ofcom came up with a “one size fits all” test circuit, which, for simplicity, the ITU-T converted into one circuit for testing the powered equipment and a second circuit for testing the power sourcing equipment. As equipment ports often contain electronic functions, the port impedance may go low or high for the surge duration and the consequences of such events needs to be considered.

The presentation concludes with four examples of the likely surge conditions for different DC supply system variants.

Learning points:

  • DC power supply configurations
  • Decouplers, couplers and back-filters
  • Surge test circuit configurations
    • Powered equipment port
    • Power sourcing equipment port
  • Surge conditions for four DC supply system variants