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ESR in caps

Is a lower ESR always a better thing without qualification? That is to
say, no thinking has to be done, just change the caps.We are changing
some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
tant. Doesn't this change the inrush current when turning on the
device on empty caps?
 
M

Mook Johnson

Jan 1, 1970
0
ESR can be a good thing sometimes.

If your circuit has high inductance traces teh ESR can damp the resonant
tank circuit and reduce ringing. Also ESR may be required by some switching
regulators for stability.

So a sort answer, lower ESR is not ALWAYS better but it often is.
 
E

Eeyore

Jan 1, 1970
0
Is a lower ESR always a better thing without qualification? That is to
say, no thinking has to be done, just change the caps.We are changing
some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
tant. Doesn't this change the inrush current when turning on the
device on empty caps?

That depends on the source resistance.

Graham
 
J

Joerg

Jan 1, 1970
0
Mook said:
ESR can be a good thing sometimes.

If your circuit has high inductance traces teh ESR can damp the resonant
tank circuit and reduce ringing. Also ESR may be required by some switching
regulators for stability.

And in LDO regulators. Where they don't always tell you how critical the
lower limit is because the marketeers might think that wouldn't look good.

So a sort answer, lower ESR is not ALWAYS better but it often is.

Tantalums? I've had my fair share of kaboom experiences with them and
its back to electrolytics here.
 
J

John F

Jan 1, 1970
0
Joerg said:
Tantalums? I've had my fair share of kaboom experiences with them
and
its back to electrolytics here.

I once got hit by a piece... It punched through my skin and had to be
removed in a tiny surgery. Weird.
 
J

John Larkin

Jan 1, 1970
0
Is a lower ESR always a better thing without qualification? That is to
say, no thinking has to be done, just change the caps.We are changing
some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
tant. Doesn't this change the inrush current when turning on the
device on empty caps?

What's the operating voltage?

Tantalums have a bad habit of detonating when used as supply bypasses.
Inrush current heats up tiny asperites, then the tantalum becomes fuel
and the MnO2 is the oxidizer. Boom. A change in vendor, plus lower
esr, may introduce problems that you haven't seen before. Our rule is:
no tantalums on supply rails.

Some voltage regulators, both linear and switchers, get unstable with
low esr-loads.

John
 
E

Eeyore

Jan 1, 1970
0
John said:
What's the operating voltage?

Tantalums have a bad habit of detonating when used as supply bypasses.
Inrush current heats up tiny asperites, then the tantalum becomes fuel
and the MnO2 is the oxidizer. Boom. A change in vendor, plus lower
esr, may introduce problems that you haven't seen before. Our rule is:
no tantalums on supply rails.

Have you looked at the 'solid aluminium' types ?

Graham
 
J

John Larkin

Jan 1, 1970
0
Have you looked at the 'solid aluminium' types ?

Graham

I've been meaning to research polymer tantalums and polymer aluminums,
both of which are claimed to have very low esr and to be
detonation-proof. Haven't got around to it. For now, we just use
regular aluminums.

John
 
E

Eeyore

Jan 1, 1970
0
John said:
I've been meaning to research polymer tantalums and polymer aluminums,
both of which are claimed to have very low esr and to be
detonation-proof. Haven't got around to it. For now, we just use
regular aluminums.

Motherboard manufacturer Gigabyte has moved to using them FWIW.

Graham
 
F

Fred Bartoli

Jan 1, 1970
0
John F a écrit :
I once got hit by a piece... It punched through my skin and had to be
removed in a tiny surgery. Weird.

Then you are Robocap, aren't you?
 
F

Fred Bartoli

Jan 1, 1970
0
John Larkin a écrit :
I've been meaning to research polymer tantalums and polymer aluminums,
both of which are claimed to have very low esr and to be
detonation-proof. Haven't got around to it. For now, we just use
regular aluminums.

John

Check some Sanyo Oscons.
 
J

John F

Jan 1, 1970
0
Fred said:
John F a écrit :

Then you are Robocap, aren't you?

LOL
That one was good!

Another one: My girlfriend read over a page of my books that i had
left open on my desk. All over the day she was very silent and then
during dinner she asled: "Why do you read all that stuff about
Tantra-Capacitors? And that it brings a high capacity but is
dangerous? What are you preparing for?"

I spent a whole night showing her what the difference between Tantal-
and Tantra- was... Rather on the Tantal- side (to stay OT here) :)
 
M

mg

Jan 1, 1970
0
Is a lower ESR always a better thing without qualification? That is to
say, no thinking has to be done, just change the caps.We are changing
some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
tant. Doesn't this change the inrush current when turning on the
device on empty caps?

Low ESR (and ESL) capacitors should be used whenever you need a fast
surge or frequency response like in most low-voltage (3.3V and lower)
circuits, for instance.

When using electrolytics, by the way, one should pay attention to load
life and temperature ratings if you care about reliability and
longevity.
 
M

Mike

Jan 1, 1970
0
I once got hit by a piece... It punched through my skin and had to be
removed in a tiny surgery. Weird.

Very strange - I use tantalums on almost 100% of my boards, and have
only destroyed one. That happened when a 12V battery lead got shorted
to the 3.3V supply regulated supply which had a tantalum on it. I
think the tantalum was rated for about 6V. It just smoked and got a
crack in it. A part next to it was more interesting, however. I can't
remember the part number, but I had a TI CAN 3.3V transceiver in a
SOIC-8 package nearby - and about half of the package blew out,
leaving a gigantic hole in the chip. (and lots of magic smoke in my
lab). That was exciting.

But anyways - under normal usage - I have never, ever had a tantalum
explode, crack, or have any other problems.

-Mike
 
J

John F

Jan 1, 1970
0
Mike said:
Very strange - I use tantalums on almost 100% of my boards, and have
only destroyed one. That happened when a 12V battery lead got
shorted
to the 3.3V supply regulated supply which had a tantalum on it. I
think the tantalum was rated for about 6V. It just smoked and got a
crack in it.

:) Great luck there was not 'nuf dI/dt in that...
A part next to it was more interesting, however. I can't
remember the part number, but I had a TI CAN 3.3V transceiver in a
SOIC-8 package nearby - and about half of the package blew out,
leaving a gigantic hole in the chip. (and lots of magic smoke in my
lab). That was exciting.

Had that with a BC548 once. It kept on glowing in the crater :)
But anyways - under normal usage - I have never, ever had a tantalum
explode, crack, or have any other problems.

Don't try to use it in SMPS. Never ... <looking around suspiciously>
.... ever.
 
Is a lower ESR always a better thing without qualification? That is to
say, no thinking has to be done, just change the caps.We are changing
some bulk decoupling caps to a part with 50% lower ESR. 150uF 16V
tant. Doesn't this change the inrush current when turning on the
device on empty caps?

Thanks to all that replied. It turned out that the LDO would be
unstable with a low ESR cap on its output. As a kind of manager, I
really had to put the brakes on the "lower ESR is always better"
idea....
 
A

Alex

Jan 1, 1970
0
My thoughts
It must allways be best with low ESR .
Remember that the ESR will disipate heat in the capacitor, and this
heat is damaging the cap in short time.. If there is no heat ,then a
electronic circuit can live forever.
Heat is also a waist of power, and we always try to design to the
lowest power-use.
If a circuit will be unstable ,if the caps is changed with better
caps, then the design is bad.. if resistors was needed ,then you put a
resistor, and do not use the ESD resistor.

Alex in Denmark
I'm new to this group, so I introduce myself here as an engineer
working in the electronic field..( in most countries , think my degree
would be like BSC ), I have 30 Y experience in repair of electronics,
and 2Y experience with taking care of a electronic lab at university..
I live in Sonderborg Denmark..
 
M

mg

Jan 1, 1970
0
Thanks to all that replied. It turned out that the LDO would be
unstable with a low ESR cap on its output. As a kind of manager, I
really had to put the brakes on the "lower ESR is always better"
idea....

With power supplies, the first and most difficult problem is to
determine the characteristics of the load, i.e., the surge current or
frequency response required. Once that's done, it's just a matter of
going shopping for the correct regulator and then following the
vendor's application notes in regard to what capacitors to use, and
how many, to insure that the regulator is stable while at the same
time providing a fast frequency response.
 
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