EMC inquiry

Discussion in 'General Electronics Chat' started by Skeebopstop, Nov 1, 2012.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    Dear All,

    I have been considering applying a power amplifier design with switched 24V outputs running on a 100kHz carrier with 20nS rise times without shielding or filtering. I have done it in the past up to 200nS rise times with 800V but we used shielding (no choice to filter given power being exported to motors).

    My inquiry in this situation, is related to my understanding that shielding will not be required based on:

    20nS rise time => highest harmonic of risetime 0.5*(1/Tr) => 25MHz

    25MHz @ ~1.8*10^8 m/s propogation velocity in copper => Wavelength = (1/25MHz)*(1.8*10^8 m/s) = 7.2 meters.

    Given that calculating exact transmission power of wires is quite difficult, I have the understanding that ensuring nothing longer than 1/20 the wavelength (i.e. 1/5th the quarter wavelength) will result in minimal radiation and simple calculation, so 0.36 meters is my unshielded cabling maximum.

    Shielding will then be reserved as my fallback plan for EMC compliance.

    What say ye to my analysis? Any better insight to be provided or people generally agree with this?

    Many thanks in advance,

    Last edited: Nov 1, 2012