Groups > sci.electronics.design > #453602

Re: A resistor network with a curious property

From	"Tim Williams" <tiwill@seventransistorlabs.com>
Newsgroups	sci.electronics.design
Subject	Re: A resistor network with a curious property
Date	2017-03-25 15:25 -0500
Organization	A noiseless patient Spider
Message-ID	<ob6jib$52j$1@dont-email.me> (permalink)
References	(1 earlier) <33j6dchmo1mnt300eat0c77hu6fesrhll1@4ax.com> <oavkb8$uul$1@dont-email.me> <qgq7dc5p2oroebe1vbvqi8clrddjivitj5@4ax.com> <ob59m0$uru$1@dont-email.me> <d9da8e97-7e1f-415b-adf4-0d65437fe7d7@googlegroups.com>

Show all headers | View raw

"George Herold" <gherold@teachspin.com> wrote in message 
news:d9da8e97-7e1f-415b-adf4-0d65437fe7d7@googlegroups.com...
> Ahh, OK I was wondering what the goal was...  Why is your network
> better than than just a string of ~10 20W TO-220's?  (With some other
> R's (in the Tee) to keep 50 ohms everywhere.)
> I don't know much about R's at high frequency.

The low-order equivalent circuit of a TO-220 resistor will be two series 
inductors, representing lead (and bond, if applicable) inductance, a 
resistance between them, and a distributed capacitance from the resistor to 
the heatsink tab and other surroundings.

Really, the leads will have a transmission line impedance on the order of 
150 ohms, which looks inductive at lower frequencies and lower impedances 
(say, relative to 50 ohms).  The resistive patch will have some transmission 
line characteristic as well, and if it evenly covers the substrate, it will 
have a low impedance, and therefore look capacitive at lower frequencies.

"Lower frequencies" being, those well below the equivalent electrical length 
of the elements in question.  So, for a TO-220, a couple cm -- a couple GHz.

At higher frequencies, you cannot so easily ignore the transmission line 
effects, and you have to build more and more complicated (higher order) 
lumped models (distributed L and C) to suit (or use transmission lines 
proper).

But at that point, you'll have so much trouble matching to these structures, 
and in keeping them consistent between assemblies (because we're talking 
lead geometry here), that you're better off giving up and declaring that as 
your upper frequency limit...

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

Thread

A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-22 20:23 -0500
  Re: A resistor network with a curious property George Herold <gherold@teachspin.com> - 2017-03-22 19:11 -0700
    Re: A resistor network with a curious property George Herold <gherold@teachspin.com> - 2017-03-22 19:49 -0700
      Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-22 23:43 -0500
    Re: A resistor network with a curious property Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-23 10:56 -0400
      Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 02:15 -0500
  Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-22 22:24 -0400
  Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-22 23:05 -0400
    Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-22 23:44 -0500
      Re: A resistor network with a curious property Jasen Betts <jasen@xnet.co.nz> - 2017-03-23 07:20 +0000
  Re: A resistor network with a curious property Robert Baer <robertbaer@localnet.com> - 2017-03-22 19:48 -0800
    Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-22 23:47 -0500
  Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-22 21:20 -0700
    Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-22 23:55 -0500
      Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-23 01:15 -0400
        Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 02:41 -0500
          Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-25 09:45 -0400
      Re: A resistor network with a curious property Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-23 09:16 +0000
        Re: A resistor network with a curious property Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-23 14:51 +0000
      Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-23 08:41 -0700
        Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 03:30 -0500
          Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-25 09:25 -0700
          Re: A resistor network with a curious property George Herold <gherold@teachspin.com> - 2017-03-25 09:59 -0700
            Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 15:25 -0500
    Re: A resistor network with a curious property Winfield Hill <hill@rowland.harvard.edu> - 2017-03-23 12:38 -0700
  Re: A resistor network with a curious property "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-23 06:41 +0000
  Re: A resistor network with a curious property Wanderer <wanderer@dialup4less.com> - 2017-03-23 05:53 -0700
    Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-23 13:41 -0400
    Re: A resistor network with a curious property rickman <gnuarm@gmail.com> - 2017-03-25 18:57 -0400
  Re: A resistor network with a curious property Jon Elson <jmelson@wustl.edu> - 2017-03-23 14:28 -0500
    Re: A resistor network with a curious property tabbypurr@gmail.com - 2017-03-23 20:59 -0700
      Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-25 09:27 -0700
    Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 02:58 -0500
      Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-25 09:31 -0700
        Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-25 15:32 -0500
          Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-25 13:54 -0700
            Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-25 17:26 -0400
              Re: A resistor network with a curious property "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-26 02:51 -0500
                Re: A resistor network with a curious property bitrex <bitrex@de.lete.earthlink.net> - 2017-03-26 12:18 -0400
            Re: A resistor network with a curious property whit3rd <whit3rd@gmail.com> - 2017-03-25 16:11 -0700
              Re: A resistor network with a curious property John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-26 11:36 -0700
    Re: A resistor network with a curious property rickman <gnuarm@gmail.com> - 2017-03-25 18:57 -0400
  Re: A resistor network with a curious property bloggs.fredbloggs.fred@gmail.com - 2017-03-24 09:08 -0700

csiph-web