FreeLists / si-list / [SI-LIST] Re: resend - Specctraquest model: mounted inductance

["Nick" <nick@xxxxxxxxxxxx>]

Bart,
 

Self-inductance is a property of current loops. A copper wire does not have
a self-inductance. A thin copper wire has a well-defined self partial
inductance, but self partial inductance is pretty much meaningless unless
you also know the self and mutual partial inductances for the rest of the
loop. These quantities can't be measured directly, they can only be
calculated. 

 

The quantity that you described (total magnetic flux generated by an
alternating current in a wire segment divided by the current) is not the
self inductance or the self partial inductance. I'm not sure whether this
quantity has a name, but it would have little value in any real application.
It can't be measured and it can't readily be used to determine the
inductance of a loop containing that wire segment.

 

The ESL values published by capacitor manufacturers are not meaningful or
helpful unless the test fixture and test method are well defined. If you
want to determine the ESL of a capacitor for a particular application (e.g.
decoupling), it is important to measure the ESL in a fixture where the
capacitor is mounted in a manner that emulates your application. Any attempt
to extract an 'intrinsic' inductance, attributable to the capacitor only,
will result in a number that is of little use to anybody.

 

Nick

 

-----Original Message-----
From: Bart Bouma [mailto:bart.bouma@xxxxxxxxx] 
Sent: Wednesday, June 11, 2003 2:56 AM
To: nick@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: resend - Specctraquest model: mounted inductance

 


Hi Nick, 

I think, but I might wrong, that Inductance is not only a property of
current loops: 
e.g. a copper wire also has self-inductance: 
imagine a piece of copper wire, and assume an ac-current flowing through it.

This results in an alternating magnetic flux, which will  induce a current
flowing in opposite direction in the wire which will try to cancel the
original current. 
Is this not the definition of self-inductance? And it can be defined. 

From this view a capacitor has self inductance too. Isn't it this my
intrinsic inductance? 

I agree with you that in case of decoupling capacitors the current loop is
the determining factor for total inductance. 

Bart Bouma
http://www.yageo.com 

-----Original Message-----
My idea of intrinsic inductance is that this is the inductance of the 
capacitor itself, and that this inductance is determined by the capacitor, 
and solely the capacitor itself. So not by its environment like a 
copper-plane. The intrinsic inductance  - in my opinion - is determined by 
the capacitor's mechanical properties like length, width, heigth, internal 
structure (e.g. number of layers) etc.
Like the inductance one can calculate for a small rectangular piece of 
copper with known dimensions. Independent wether it is mounted on a pcb or 
floating in vacuum.


Bart,

You've identified the main problem with trying to assign a value of
inductance to a capacitor independent of its mounting. Inductance is a
property of current loops! The inductance of a small rectangular piece of
copper cannot be defined or measured independent of its environment.

For a small rectangular piece of copper, you could calculate a matrix of
self and mutual partial inductance parameters, but you would not be able to
use this matrix to find an actual measurable inductance until you defined
the rest of the loop.

Nick


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu