DC Source Impedance measurement - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th February 2004, 06:49 PM   #1
diyAudio Member
 
Join Date: Jan 2002
Location: Williamsport, PA
Send a message via AIM to hugeli60
Default DC Source Impedance measurement

I have a challenege for you analog guru's out there.

Let's say I have a DC source with some internal impedance (kinda like a battery). This impedance is complex is nature with more than one equiv. C, L and R' inside. Given that this impedance will be on the order of milliohms at any particular frequency:

Does anyone out there know of a simple circuit that could accruately measure the impedance of this source. Keep in mind this is AC impedance. What I am looking for are say curves from 1hz - 10kHz for example.

This is a difficult measurement because the magnitude of the impedance is so small!
  Reply With Quote
Old 12th February 2004, 07:32 PM   #2
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Hmm... a couple of quick 'duh' questions:

1) If your source is DC, why are you interested in your AC impedances?

2) If your source impedance is known to be on the order of milliohms, then what does the value matter. As long as your input impedance is 1-ohm or more, it'll be significantly larger than your source impedance and your attenuation won't really matter.
  Reply With Quote
Old 12th February 2004, 07:35 PM   #3
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
If you have a quality setup like an Audio Precision, this would
not be a problem, as you can drive the DC source with an
AC signal through a big cap and precisely measure the AC
voltages which appear across the DC source. Even milliohms
would not be particularly daunting. You can insert a known
impedance in series with the AP output, or use its internal
25, 50, or 600 ohm source solely.

If you don't have such a refined measurement apparatus, drive
the DC source through a cap and resistor, but with a big fat
power amplifier, and use a less sensitive, but wide band, AC
voltameter.
  Reply With Quote
Old 12th February 2004, 07:43 PM   #4
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Add a reasonable value series resistor and a DC blocking capacitor.

Drive the circuit it with an AC source and measure the AC voltage across the DC source.

This will give its impedance, assuming the R effects a current source.

sreten.
  Reply With Quote
Old 12th February 2004, 08:59 PM   #5
diyAudio Member
 
Join Date: Jan 2002
Location: Williamsport, PA
Send a message via AIM to hugeli60
That is the way I do it now. The problem is that I am trying to condense the circuit were a large cap is not needed. I am trying to fit all of this cicuitry into oa very small package. The big cap right now hatkes up all of the space. I am looking for an all op-amp solution.

Thanks!
  Reply With Quote
Old 12th February 2004, 09:06 PM   #6
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Are you building a super smart auto-correcting zero-impedance power supply?? Admit it!!

Jan Didden
  Reply With Quote
Old 12th February 2004, 10:01 PM   #7
diyAudio Member
 
Join Date: Jan 2002
Location: Williamsport, PA
Send a message via AIM to hugeli60
No, I am actually measuring AC impedance output imp. of a DC source. For most practical situations this information is meaningless.
  Reply With Quote
Old 13th February 2004, 04:07 AM   #8
diyAudio Member
 
Join Date: Jan 2004
Location: Perth
Default Measuring output impedance

To measure the output impedance of a generator (ac or dc) you can use the load substitution method and Ohms law.

See http://www.mitedu.freeserve.co.uk/Theory/inzoz.htm
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Impedance measurement jig for SpeakerWorkshop Tenson Multi-Way 10 24th November 2007 11:56 PM
Impedance curve measurement bobsinclar Multi-Way 5 16th November 2006 01:17 PM
Impedance measurement Doug Everything Else 2 9th August 2003 05:50 AM
Having a problem with impedance measurement. prash Multi-Way 29 17th December 2002 05:24 AM
Vifa Impedance Measurement. Dave Multi-Way 27 2nd December 2001 02:55 AM


New To Site? Need Help?

All times are GMT. The time now is 09:25 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2