Thanks John,
Very good points added. * For the same L value(s) the capacitors of the T-config are divided by 2, so half the touch current. * The input (mains side) capacitor of the PI shunts and increases mains RF current, so contributes to parasitic RF current in the mains , where the series L of the T filter attenuates any RF current in the circuit. * The PI filter depends more on good ground quality as the T, due to higher (short circuit) RF currents in the input cap, or it needs 2 grounds.. * The capacitor of the T-filter is less prone to aging due to reduced RF currents and reduces surge and peak voltages. Gert -----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: Wednesday 22 July 2015 11:39 To: [email protected] Subject: Re: [PSES] GFCI Nuisance Tripping In message <[email protected] <mailto:[email protected]> >, dated Wed, 22 Jul 2015, "ce-test, qualified testing bv - Gert Gremmen" <[email protected] <mailto:[email protected]> > writes: > Filter specifications should not be made in 50 ohm environments but >in much lower impedance ranges (0.5 -5 Ohms), so the product will >better fulfil the expectations of their users See the less well-known CISPR 17 standard. > >* Filter manufacturers need to be aware of the existence of >emission and immunity regulations and create fully bi-directional >filters, for lower input currents (due to lower power consumptions of >modern devices) > >* Adequate input/output filters do not need high value touch >current capacitors. By using T-type of filters (LCL) instead of >PI-types (CLC) the values of decoupling caps can be heavily reduced (no >touch current), at increased cost of dual CM-inductors. But we are used >to that aren?t we? I did a quick simulation of T and Pi filters with 1 ohm impedance and normalized frequency, and I can't confirm that the capacitor in the T is smaller than those in the Pi. However, the inductors in the T are smaller than the one in the Pi. This seem logical to me, since at cut-off (-3 dB frequency) the T filter 'matches' zero impedance source and load, and the Pi filter 'matches' infinite impedances. So the T filter has a normalized C value of 2, with two L values of 1 in parallel, so LC = 2 x 0.5 = 1. The Pi filter has an L value 2 in series with two Cs of value 1, so LC is again 1. > >* Shunting a low impedance signal with high value capacitors is >NOT the way to go. Attenuation needs a high series impedance followed >by a low ground path, I think we all agree about that. This is a very important point. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk <http://www.jmwa.demon.co.uk> When I turn my back on the sun, it's to look for a rainbow John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html <http://www.ieee-pses.org/emc-pstc.html> Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ <http://product-compliance.oc.ieee.org/> can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> Instructions: http://www.ieee-pses.org/list.html <http://www.ieee-pses.org/list.html> (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html <http://www.ieee-pses.org/listrules.html> For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher: <[email protected] <mailto:[email protected]> > David Heald: <[email protected] <mailto:[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
