Filter cap choice for ultra low ripple

[Jim Thompson]

On 09 Aug 2015 18:07:48 GMT, joe hey <joehey@mailinator.com> wrote:

On Sun, 09 Aug 2015 12:58:30 -0400, DecadentLinuxUserNumeroUno wrote:

On Sun, 09 Aug 2015 17:07:46 +0100, Pomegranate Bastard
PommyB@dsl.pipex.com> Gave us:

You are an imbecile.

Fuck off and die, pommy bitch cock sucking retard.

Jesus Christ, this guy really goes nuking around for even the slightest
of reasons...

joe (quickly hiding in the cabinet)

I suspect DecadentLoser is just another nom de plume of bloggs, or of
that ghost from the past... the infamous Robert... a real collection
of crazies >:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[rickman]

On 8/9/2015 1:25 PM, David Brown wrote:

On 09/08/15 16:27, Cursitor Doom wrote:
Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!


Decadent Linux may be extraordinarily rude, but he is right that there
is no answer to this question - we would need a lot more details to give
useful answers. Of particular importance are the frequency of noise to
be rejected, the type of currents and voltages involved, any unusual
circumstances or restrictions (such as wanting to be as small as
possible), and some information about the rest of the PSU design.

And a capacitor alone does not make a filter - you need it in
combination with something else (an inductance or resistance), and
usually in multiple stages with multiple filter components.

That is not strictly true. On the input of a switched cap PSU the
ripple is current. That will transform into voltage by the impedance of
the input supply, but the cap provides some of the current to reduce the
voltage ripple. A lower impedance of the input supply only improves the
situation, not worsen it.

On the output, the cap can be filtering the ripple from either the input
ripple residue, or the output ripple if a switched converter. Again, a
lower output impedance is better and a filtering cap will be taking
advantage of that impedance.

Any active circuit that acts as a filter has to be effective at the
frequency of interest. It is a common misconception that you can add a
linear regulator to the output of a switched converter to get rid of the
ripple. The frequency of ripple is often well outside the effective
frequency range of the linear regulators.

--

Rick

 

Troll question but anyway high capacity chemical batteries can offer very low noise. For example a 12v car battery. The leakage current in an electrolytic capacitor can be a source of noise. Probably a battery is better.

 

[DecadentLinuxUserNumeroUn]

On 09 Aug 2015 18:07:48 GMT, joe hey <joehey@mailinator.com> Gave us:

On Sun, 09 Aug 2015 12:58:30 -0400, DecadentLinuxUserNumeroUno wrote:

On Sun, 09 Aug 2015 17:07:46 +0100, Pomegranate Bastard
PommyB@dsl.pipex.com> Gave us:

You are an imbecile.

Fuck off and die, pommy bitch cock sucking retard.

Jesus Christ, this guy really goes nuking around for even the slightest
of reasons...

joe (quickly hiding in the cabinet)

Dude, the pommy retard has been stalking and trolling me for years, so
STFU about that which you are absolutely clueless please.

 

[DecadentLinuxUserNumeroUn]

On 09 Aug 2015 18:19:15 GMT, joe hey <joehey@mailinator.com> Gave us:

He reminds me of a quite (electronically) brilliant Finnish guy who got
poisoned from his mercury amalgam fillings,

Fuck you, you obtuse, know nothing about this group asswipe!

 

[DecadentLinuxUserNumeroUn]

On 09 Aug 2015 18:19:15 GMT, joe hey <joehey@mailinator.com> Gave us:

became 'as mad as a hatter',
tried to sue the (Finnish) government and the medical establishment,

I should 'sue' you with the penalty being that your ass ends up out in
the middle of the desert buried up to your neck right next to an ant
hill. Lets pour a bit of honey on top of your head as further 'suppers
ready' enticement for them.

For someone who has not frequented the group, you sure are one mouthy
little bitch.

 

[DecadentLinuxUserNumeroUn]

On 09 Aug 2015 18:19:15 GMT, joe hey <joehey@mailinator.com> Gave us:

It seems that mercury poisoning does that to your brain/constitution.

joe

It would be nice to see what my fist would do to your pussy boy face,
fucktard.

 

[DecadentLinuxUserNumeroUn]

On Sun, 9 Aug 2015 13:47:44 -0500, "Tim Williams"
<tmoranwms@charter.net> Gave us:

Best?

All things considered, same as always, electrolytic. Low cost, high value,
moderate to low ESR, reasonable life (when not run hot).

For any other considerations, it's up to you. Cost? Operating frequency?
Size? General *considerations*, yes, but no generalized *conclusion*.
That's what us designers get paid for. ;-)

Even more generally, however: you seem to dismiss system-level
considerations as obvious! But no, a signal generator is a system. The
power supply only needs to be as well-filtered as the PSRR of the output
stage, preamps and such require for the desired output noise level. And if
there's a regulator stage in there as well, even less (primary) filtering is
needed.

And you can locally filter and regulate stages that are unusually sensitive,
or rebuild them in terms of ratios and ground-referenced voltages, to
increase their PSRR.

There should be absolutely no excuse for excruciatingly clean DC, not since
tubes have gone the way of the dodo. Complementary semiconductors (and good
constant current characteristics) free us from the burden of B+ referenced
signals and low PSRR.

Tim

Isn't the term you were searching for 'PARD'?

 

[DecadentLinuxUserNumeroUn]

On Sun, 09 Aug 2015 11:58:12 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> Gave us:

I suspect DecadentLoser is just another nom de plume of bloggs, or of
that ghost from the past... the infamous Robert... a real collection
of crazies >:-}

...Jim Thompson

Jim Thompson is an absolute idiot who should assume nothing, since he
can't even put together what the fastest currently in use CPU is,
despite google being at his mundane brained fingertips.

 

[whit3rd]

On Sunday, August 9, 2015 at 7:29:32 AM UTC-7, Cursitor Doom wrote:

Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?

Output buffer amplifiers (transistor follower type) are insensitive to power
supply ripple and noise. Other parts of a 'signal generator' may need
any amount of current, or voltage regulation, or isolation from other
stages. So, it's too complex a problem for 'choice of filter capacitor'.

 

[krw]

On Sun, 09 Aug 2015 15:35:39 -0400, rickman <gnuarm@gmail.com> wrote:

On 8/9/2015 1:25 PM, David Brown wrote:
On 09/08/15 16:27, Cursitor Doom wrote:
Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!


Decadent Linux may be extraordinarily rude, but he is right that there
is no answer to this question - we would need a lot more details to give
useful answers. Of particular importance are the frequency of noise to
be rejected, the type of currents and voltages involved, any unusual
circumstances or restrictions (such as wanting to be as small as
possible), and some information about the rest of the PSU design.

And a capacitor alone does not make a filter - you need it in
combination with something else (an inductance or resistance), and
usually in multiple stages with multiple filter components.

That is not strictly true. On the input of a switched cap PSU the
ripple is current. That will transform into voltage by the impedance of
the input supply, but the cap provides some of the current to reduce the
voltage ripple. A lower impedance of the input supply only improves the
situation, not worsen it.

Absolutely. If the impedance of the source is increased, it has to be
lowered again with more input capacitance. This is often helpful,
though, to get rid of conducted emissions.

On the output, the cap can be filtering the ripple from either the input
ripple residue, or the output ripple if a switched converter. Again, a
lower output impedance is better and a filtering cap will be taking
advantage of that impedance.

The output ripple is current too. The same issues apply. After the
regulator (after the output capacitors), some impedance my help filter
noise, though. Often a ferrite bead (and ceramic cap) work well.

Any active circuit that acts as a filter has to be effective at the
frequency of interest. It is a common misconception that you can add a
linear regulator to the output of a switched converter to get rid of the
ripple. The frequency of ripple is often well outside the effective
frequency range of the linear regulators.

That's generally true but there are wideband "regulators", if you're
really worried about such things. Also, while the ripple may be
outside a linear regulator's bandwidth, switching regulators tend to
be noisy. A linear regulator often helps.

 

[M Philbrook]

In article <jkgfsat3d7rljm1ovi50vr1jo294l9qp1p@4ax.com>, DLU1
@DecadentLinuxUser.org says...

On Sun, 09 Aug 2015 11:58:12 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> Gave us:

I suspect DecadentLoser is just another nom de plume of bloggs, or of
that ghost from the past... the infamous Robert... a real collection
of crazies >:-}

...Jim Thompson

Jim Thompson is an absolute idiot who should assume nothing, since he
can't even put together what the fastest currently in use CPU is,
despite google being at his mundane brained fingertips.

what a fopdoodle

Jamie

 

On Sun, 9 Aug 2015 14:27:50 +0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!

tia,
cd

In addition to the actual filter/regulation, you really need to watch
out for the PCB layout. Make sure that the ripple current only flows
in the loop of secondary, rectifier and (first) storage capacitor.
This means that the rest of the circuit (both positive and ground)
must be powered directly from the capacitor terminals.

Getting the regulator input from capacitor terminal and the ground
return to somewhere on the PCB ground track between the rectifier
terminal and ground capacitor terminal, now the ripple current is
flowing through a common ground resistance, causing all kinds of hum
problem.

With additional regulation and filter sections, take the signal ground
PCB track at the output at the last filter stage, thus all ripple and
filtered noise will be circulating in the secondary, rectifier,
storage capacitor, regulator, additional filter loop and not pollute
the actual signal ground.

 

[mike]

On 8/9/2015 7:27 AM, Cursitor Doom wrote:

Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!

tia,
cd

You continue your history of under-specifying.
Specs have numbers.
"...as humanly possible" is not a number, or even a useful
concept.

Bottom line is that you can't afford enough caps to
solve a ripple problem. It's a system issue.

Back in the day, a bunch of us built TEK spectrum analyzers
from a big box of rejected parts. One of my tasks was to build
a current source to screen YIG oscillators. Boy, was that
an eye-opener. Turns out that noise comes from everywhere
at that level.

 

[Clifford Heath]

On 10/08/15 00:27, Cursitor Doom wrote:

Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!

I'm surprised Phil Hobbs hasn't jumped in here with his beloved
capacitance multipliers. But perhaps, since he's just been talking about
them and you haven't taken notice of that, he assumes that you're just
not a good listener?

In a nutshell: filter with whatever, then regulate your way to smoothness.

 

[DecadentLinuxUserNumeroUn]

On Mon, 10 Aug 2015 18:21:15 +1000, Clifford Heath <no.spam@please.net>
Gave us:

On 10/08/15 00:27, Cursitor Doom wrote:
Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!

I'm surprised Phil Hobbs hasn't jumped in here with his beloved
capacitance multipliers. But perhaps, since he's just been talking about
them and you haven't taken notice of that, he assumes that you're just
not a good listener?

In a nutshell: filter with whatever, then regulate your way to smoothness.

You obviously do not know how to read a thread.

 

On Sun, 09 Aug 2015 11:34:46 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Sun, 9 Aug 2015 14:27:50 +0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

What is currently the best choice of filter capacitor for the PSU section
of a high-end signal generator the output of which (obviously) really
needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!

tia,
cd

Generally one buys enough filter cap to get the ripple down to maybe 1
volt p-p, then adds a regulator to stabilize the voltage and greatly
reduce ripple. A second regulator or c-multiplier can be used to
further reduce noise and ripple, to power the more sensitive signal
generator stages.

Since the same charge needs to be transferred during the mains half
cycle, using huge storage capacitors will result a smaller conduction
angle and hence large peak currents. High peak current will cause many
problems, including strong stray magnetic fields that can be coupled
into various circuitry.

If low noise and not maximum efficiency is the goal, use moderate size
storage capacitors with possibly additional series resistance and the
peak currents remain small. Of course, this requires higher secondary
voltages, but the increased peak rectified voltage can be limited with
any conventional regulator.

 

[Pomegranate Bastard]

On Sun, 09 Aug 2015 12:58:30 -0400, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

On Sun, 09 Aug 2015 17:07:46 +0100, Pomegranate Bastard
PommyB@dsl.pipex.com> Gave us:

You are an imbecile.

Fuck off and die, pommy bitch cock sucking retard.

You are an utter imbecile.

 

[Pomegranate Bastard]

On Sun, 09 Aug 2015 17:07:30 -0400, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

On 09 Aug 2015 18:07:48 GMT, joe hey <joehey@mailinator.com> Gave us:

On Sun, 09 Aug 2015 12:58:30 -0400, DecadentLinuxUserNumeroUno wrote:

On Sun, 09 Aug 2015 17:07:46 +0100, Pomegranate Bastard
PommyB@dsl.pipex.com> Gave us:

You are an imbecile.

Fuck off and die, pommy bitch cock sucking retard.

Jesus Christ, this guy really goes nuking around for even the slightest
of reasons...

joe (quickly hiding in the cabinet)

Dude, the pommy retard has been stalking and trolling me for years, so
STFU about that which you are absolutely clueless please.

You really shouldn't flatter yourself, Nymbecile old girl. Do you
really consider yourself worth stalking?

 

[Pomegranate Bastard]

On 09 Aug 2015 18:19:15 GMT, joe hey <joehey@mailinator.com> wrote:

On Sun, 09 Aug 2015 13:40:35 -0400, DecadentLinuxUserNumeroUno wrote:

On Sun, 09 Aug 2015 19:25:14 +0200, David Brown
david.brown@hesbynett.no> Gave us:

On 09/08/15 16:27, Cursitor Doom wrote:
Gentlemen,

What is currently the best choice of filter capacitor for the PSU
section of a high-end signal generator the output of which (obviously)
really needs to be as ripple-free as humanly possible?
Just in *GENERAL* terms, please guys; don't want to get bogged down in
specifics and calculations at this stage, please!


Decadent Linux may be extraordinarily rude,

(O.T.)

He reminds me of a quite (electronically) brilliant Finnish guy who got
poisoned from his mercury amalgam fillings, became 'as mad as a hatter',
tried to sue the (Finnish) government and the medical establishment, did
probably some other things wrong too, and finally had to leave the
country due to harassment/persecution and went to the USA with his
electronics knowledge, where he continued ranting around where and
whenever he got the opportunity and at the slightest provocation.

It seems that mercury poisoning does that to your brain/constitution.

joe

Well done Joe, you scored a 3'er.

but he is right that there
is no answer to this question - we would need a lot more details to give
useful answers. Of particular importance are the frequency of noise to
be rejected, the type of currents and voltages involved, any unusual
circumstances or restrictions (such as wanting to be as small as
possible), and some information about the rest of the PSU design.

And a capacitor alone does not make a filter - you need it in
combination with something else (an inductance or resistance), and
usually in multiple stages with multiple filter components.

With that information, someone should be able to give you more helpful
answers. (Not me, probably - it's not really my field.)

The term for the day is "envelope tracking".

Not a postal service term.