Several switching power supplies in the market use this kind of cages to protect the circuit, however, i have this question,

A) Is this used as a faraday cage due to the high frequency used by it?

B) How important are EMI filters for this kind of power supply?

enter image description here

  • \$\begingroup\$ Faraday cage can help with radiated emissions. But it doesn't stop conducted emissions which propagate back into the mains. So, the EMI filters are as important as for open-frame power supplies. For instance, the power supply in the picture has a built-in EMI filter. \$\endgroup\$ Commented Oct 24, 2014 at 5:04
  • 1
    \$\begingroup\$ If it were a solid metal box would you be thinking it's a faraday cage? I belive the holes are to let excess heat out. \$\endgroup\$
    – Andy aka
    Commented Oct 24, 2014 at 8:56
  • \$\begingroup\$ Arent switched poower supplies efficient enough to not generate to much heat? thats why im wondering why do they have so many holes if they are supposed to be heat efficient \$\endgroup\$
    – GoatZero
    Commented Oct 24, 2014 at 13:56
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    \$\begingroup\$ Offline switching supplies are usually 2-stage converters: A PFC stage (maybe 90% efficient) and a DC-DC stage, maybe also around 90% efficient. Overall efficiency is therefore about 81% (ish). For a 400W supply that means about 93 watts of heat dissipation. So those holes are not there for nothing. (The average load is usually quite a bit less than the max rated load, but even 50W is significant dissipation.) \$\endgroup\$
    – John D
    Commented Apr 29, 2015 at 2:12

2 Answers 2


I do not believe the perforated metal cage is there to act as a Faraday Cage. It is there for safety reasons to prevent contact with the high voltages within. The hole sizes are required to be smaller than the standard finger defined in safety ratings. A perforated rather than solid part is used for ventilation and cooling.


Faraday cage ideally do not have any holes or very less number of holes. So, the above might be probably used for cooling and safety.


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