capacitor ESL measurement

[GSiu]

Hello,

Is there anyone know how to measure the ESL of film capacitor?

Will there be any reference standard?

Thanks,
GS

 

[Oliver Betz]

GSiu wrote:

Is there anyone know how to measure the ESL of film capacitor?

by checking the series resonance frequency.

Oliver
--
Oliver Betz, Munich
despammed.com is broken, use Reply-To:

 

[GSiu]

On Nov 30, 5:05 pm, Oliver Betz <ob...@despammed.com> wrote:

GSiu wrote:
Is there anyone know how to measure the ESL of film capacitor?

by checking the series resonance frequency.

Oliver
--
Oliver Betz, Munich
despammed.com is broken, use Reply-To:

Thanks Oliver.

Our capacitor seems to be cannot provide the series resonance
frequency.
Is there any equipment in the market that can measure the resonance
frequency?

Gsiu

 

[Oliver Betz]

GSiu wrote:

Is there anyone know how to measure the ESL of film capacitor?

by checking the series resonance frequency.

Our capacitor seems to be cannot provide the series resonance
frequency.

Sorry, I don't understand what you mean.

Is there any equipment in the market that can measure the resonance
frequency?

AC generator and AC meter, e.g. spectrum analyzer with tracking
generator.

Pay attention for low inductance connections and impedance matching. A
PCB is useful, but not mandatory.

If you don't completely understand the above, find someone doing it
correctly.

Oliver
--
Oliver Betz, Munich
despammed.com is broken, use Reply-To:

 

[Lostgallifreyan]

Oliver Betz <obetz@despammed.com> wrote in
news:5iu9f6h1opbiq17ilpv5lke42s1h4dpesh@z1.oliverbetz.de:

Is there any equipment in the market that can measure the resonance
frequency?

AC generator and AC meter, e.g. spectrum analyzer with tracking
generator.

Pay attention for low inductance connections and impedance matching. A
PCB is useful, but not mandatory.

Would a square wave with very fast edges do it? Looking at the ringing on a
fast oscilloscope might show it. I mean I'm sure it would, but I'm not sure
if it's easy to avoid seeing other sources of ringing. It's easy to get more
inductance in the wiring than in the capacitor! Which might be why few people
worry about it. Unless you're doing GHz signals, or making a fast flashlamp
laser pump, you usually don't need to deal with it.

Any chance of sidestepping the problem, by looking at capacitor choices in
existing equipment where this matters, and going with the same choices? That
way you might not have to measure, only to know that performance is ok.

 

[Lostgallifreyan]

Oliver Betz <obetz@despammed.com> wrote in
news:5iu9f6h1opbiq17ilpv5lke42s1h4dpesh@z1.oliverbetz.de:

GSiu wrote:

Is there anyone know how to measure the ESL of film capacitor?

by checking the series resonance frequency.

Our capacitor seems to be cannot provide the series resonance
frequency.

Sorry, I don't understand what you mean.

Nor do I, but it occurs to me that any resonance might be heavily damped.
With some dielectrics it might well be. There are several types of 'film'
capacitor, mylar, polyester, etc.. they likely differ a lot in the way small
transients are handled. I guess you just have to hit it hard with a very fast
transient at a regular rate and see if a scope catches the response. With
capacitance and inductance it ought to ring long enough even if damped, but I
have no idea if it rings loudly enough to detect it by eye onscreen.

 

[Oliver Betz]

Lostgallifreyan wrote:

Is there any equipment in the market that can measure the resonance
frequency?

AC generator and AC meter, e.g. spectrum analyzer with tracking
generator.

Pay attention for low inductance connections and impedance matching. A
PCB is useful, but not mandatory.


Would a square wave with very fast edges do it? Looking at the ringing on a

maybe, but it's much more complicated.

fast oscilloscope might show it. I mean I'm sure it would, but I'm not sure
if it's easy to avoid seeing other sources of ringing. It's easy to get more
inductance in the wiring than in the capacitor! Which might be why few people
worry about it. Unless you're doing GHz signals, or making a fast flashlamp
laser pump, you usually don't need to deal with it.

If you want for example power supply decoupling with 1 Ohm impedance
at 100MHz, what inductance is allowed?

Oliver
--
Oliver Betz, Muenchen (oliverbetz.de)

 

[Lostgallifreyan]

Oliver Betz <OBetz@despammed.com> wrote in
news:4cf55e66.13644140@z1.oliverbetz.de:

Lostgallifreyan wrote:

Is there any equipment in the market that can measure the resonance
frequency?

AC generator and AC meter, e.g. spectrum analyzer with tracking
generator.

Pay attention for low inductance connections and impedance matching. A
PCB is useful, but not mandatory.


Would a square wave with very fast edges do it? Looking at the ringing
on a

maybe, but it's much more complicated.

Is it? I was thinking it sound simpler than an "AC generator and AC meter,
e.g. spectrum analyzer with tracking generator." I thought most people
contemplating such measures might rustle up a scope and a fast square wave
transition somehow. The scope itself often provides one, though at 1V peak it
might want amplifying.

fast oscilloscope might show it. I mean I'm sure it would, but I'm not
sure if it's easy to avoid seeing other sources of ringing. It's easy to
get more inductance in the wiring than in the capacitor! Which might be
why few people worry about it. Unless you're doing GHz signals, or
making a fast flashlamp laser pump, you usually don't need to deal with
it.

If you want for example power supply decoupling with 1 Ohm impedance
at 100MHz, what inductance is allowed?

Oliver

As little as possible. So I wouldn't try to calculate it at all, parasitics
alone might complicate the picture. This is like asking House for a precise
diagnosis when it's easier to treat the patient. The results give you more
chance of the diagnosis later. That's why I'm asking if the measure is really
needed. I really don't know if the first poster is asking for a preventive
measure, or a precise value. The latter is hard to get whatever you do, and
it's not something I see that often in cap specs, I just checked four
datasheets, only one mentioned ESL at all. If the makers thought it easy or
required a lot, I think they'd all specify it as they do for ESR.

In the case you mention, I wouldn't try to measure because I haven't got a
few grand's worth of lab gear. But I'd use an SMT ceramic cap (possibly two,
a larger value with X7R dielectric, and a smaller one parallel, with COG) as
close to the IC or other parts as possible. After all, if 'allowed' means
permissible, context is everything. A filter rolls off, this sort hasn't got
a brick wall response curve so it's not very precise. It's not as bad as
asking 'how long is a piece of string', but it is almost certainly easier to
try the best shot and see how far it goes. Sometimes a simple question cannot
have a meaningful answer if it's reduced to the same simplicity. So I'd do
what is easy, safe and obvious and see if it was enough, then take it from
there if it wasn't.

If anything more precise is wanted about a specific capacitor, I'd identify
the cap exactly and get onto the makers for specific data beyond that in the
data sheets if it's not there. And if they could not or would not provide it
I'd consider it 'undefined' and maybe choose a part from someone who did,
because even if I did measure it, how could I guarantee the next cap I used
was the same?

I once had to handle retroreflective damage on laser diodes at a time when
the makers, distibuters, and damn near everyone else was in denial of the
problem. It cost my a few hundred pounds that no-one repaid me for, but we do
now have a mucg wider awareness that the problem exists. But that little
hazard pales beside the scale of testing that capcitors involve because
there are so many types, and time and gear cost so much, and I think that if
this matters, it is the makers' job to do it, not ours.

 

[Phil Allison]

"GSiu"

Is there anyone know how to measure the ESL of film capacitor?

Our capacitor seems to be cannot provide the series resonance
frequency.
Is there any equipment in the market that can measure the resonance
frequency?


** Depends on the type of capacitor - SMD ones are very tricky to measure.

But if it is a normal, leaded part you can assume an estimate of between
10nH and 20nH.

The actual value is very dependant on how YOU mount and use the cap in your
device - as the leads and the body size are what is causing ALL the
inductance.


...... Phil