SMPS vs 50Hz Transformer noise

[Ebrahim]

Hello, SMPS power supplies are known for higher noise versus ordinary
50Hz transformers. I was thinking that because of high frequency of
these power supplies, it should be easy to filter their output with a
simple low pass filter. for example a 1.0 Ohm and 100uF produce a filter
with f(-3db) ~1600Hz and it can drastically reduce ripples but for 50Hz
size of such capacitor is not practical. I like to hear of your thoughts.

regards

 

[Ebrahim]

On Thu, 11 Jun 2009 17:56:38 +0430, Ebrahim wrote:

Audible noise? Electrical noise? Conducted? Radiated?

Mostly I mean radiated(Electromagnetic) and Electrical(Ripple)

Yes you can post-filter the output of a SMPS, to good effect. But before
you do that you have to pay careful attention to component parasitics and
circuit layout -- capacitors that don't act enough like capacitors won't
help, and trying to short out noise that has already escaped the
boundaries of your supply is futile.

you mean parasitic cap parallel to resistor of the filter and parasitic
inductor in series with capacitor of the filter, right?

I want to conclude a SMPS can more easily generate a ripple free output
than a 50Hz transformer.

 

[Ebrahim]

I'd like to see that 1 ohm resistor in a 20 amp 3.3V supply...

Well then it should have multiple filters for each let's say 1A and SMPS
Voltage should be higher to compensate drop.

 

[Phil Allison]

"Ebrahim"

Hello, SMPS power supplies are known for higher noise versus ordinary 50Hz
transformers.

** Totally false.

SMPS produce regulated, nealyr pure DC while 50Hz supplies do not.

I was thinking that because of high frequency of these power supplies, it
should be easy to filter their output with a simple low pass filter. for
example a 1.0 Ohm and 100uF produce a filter with f(-3db) ~1600Hz and it
can drastically reduce ripples but for 50Hz size of such capacitor is not
practical. I like to hear of your thoughts.

** A great many real electronic circuits have lots of something called PSRR
or Power Supply Rejection Ratio.

Look it up.

Learn something.



...... Phil

 

[Ebrahim]

** A great many real electronic circuits have lots of something called PSRR
or Power Supply Rejection Ratio.

Look it up.

Learn something.

What PSRR has to do with subject of this thread?
I'm comparing noise(especially ripple) of SMPS and 50Hz
transformers(After bridge). different components have like OpAmps have
different PSRR that has nothing do with subject of this thread.

 

[Phil Allison]

"Ebrahim"

** Do not snip my posts - you fucking ****.

What PSRR has to do with subject of this thread?

** Could hardly be more relavant to the issue of using 50Hz v SMPSs.

I'm comparing noise(especially ripple) of SMPS and 50Hz transformers(After
bridge).

** I don't give a flying **** what an IDIOT like YOU wrongly decides to
compare.

Comparing regulated and UNREGULATED supplies is STUPID !!

different components have like OpAmps have different PSRR that has nothing
do with subject of this thread.

** Listen up - you fucking tenth wit.

YOU do not own this thread.

NOBODY ever owns a usenet thread.

Go stick your pointy head up a dead bear's bum

you damn stinking TROLL !!!!!




...... Phil

 

[Ebrahim]

"Ebrahim"

** Do not snip my posts - you fucking ****.




** Could hardly be more relavant to the issue of using 50Hz v SMPSs.




** I don't give a flying **** what an IDIOT like YOU wrongly decides to
compare.

Comparing regulated and UNREGULATED supplies is STUPID !!



** Listen up - you fucking tenth wit.

YOU do not own this thread.

NOBODY ever owns a usenet thread.

Go stick your pointy head up a dead bear's bum

you damn stinking TROLL !!!!!




..... Phil

You have proved what a worthless idiot you are.
You are a stupid troll.
I was respectful and said your response has nothing to do with the
subject but you act more like a prostitute than an engineer.
I think you belong to brothels not a technical newsgroup.

I'm happy to ignore you forever.


PS: I apologize from all respectful people that read this but I had to
tell these to such a worthless animal.

 

[Ebrahim]

Phil A. has some psychological issues, which lead him to go over the
edge with some regularity. On the other hand, he knows a fair bit of
engineering--with scatological and anatomical references filtered out,
his posts are often worth reading, and he certainly adds colour and
personality to SED. It's just that prissiness is not his thing.

Thanks Phil H.,I'm not regretting to filtering him out. I have many
knowledgeable civil friends and I really prefer to hear polite and sane
knowledge from my friends.
I only want others to know I'm usually not such a person to say those
words unless someone provokes me beyond red line.
Anyway Thanks Phil Hobbs

Cheers

 

[Ebrahim]

Ebrahim wrote:

Define 'practical'. Classical (transformer, bridge, capacitor) power
supplies seem to do pretty well with a BFC as a ripple filter. Depending on
how you define 'pretty well', of course.

Sorry, I didn't understand what BFC is.
I think you are right and it can't be generalized to all modes and as
indicated before there are situations like low voltage high current SMPS
that a filter can't be practical.
I usually have a lot of problem with 50Hz ripple. In my current designs
output current may change anywhere from 1nA to 10A and voltage has to
remain constant within 10uV, previously I've built a device that it's
output current was 10uA-10A and voltage was within 100uV. It was
challenging and I used SMPS there and it worked but now for 1nA-10A I'm
also considering 50Hz transformer. If I use a 50Hz transformer + bridge,
capacitors will be extremely big >0.1F(in total).

PS: about building bridges, I like to build bridges but in a peaceful
territory not in a place constantly bombarded

 

[Rich Grise]

Sorry, I didn't understand what BFC is.

Big F*cking Capacitor.

Cheers!
Rich

 

[Ebrahim]

Big F*cking Capacitor.

LOL !

 

[Phil Allison]

"Ebrahim"


** You are a totally stupid pile of autistic shit, a waste of space a waster
of good people's valuable time.

**** off and DROP DEAD !!!










@gmail.com> wrote in message news:[email protected]...

 

[Phil Allison]

"Ebrahim"


** You are a totally stupid pile of autistic shit, a waste of space a waster
of good people's valuable time.

**** off and DROP DEAD !!!

 

[Phil Allison]

"John Larkin"

A 100 uF electrolytic cap will have lots of inductance

** Absoute BOLLOCKS.




..... Phil

 

[Phil Allison]

"Phil Hobbs"


** Why would a smart guy like you wanna tolerate and even feed stinking fed
trolls like these ?

SED has been destroyed by these total fools.

You proud of that ?



..... Phil

 

[Ebrahim]

Woah, 10A and 1 ohm.... I don't think that is going to work.... and
you want the voltage not to change by more than 10uV. Those look like
tough specs to me. (But I'm far from a power supply expert).

George, I didn't used 1Ohm in case of 10A I used 0.1 Ohm + 1000uF.
Well about my new design 10uV, It is not just a power supply. It is
device that has an power amplifier, various feedbacks,... but in power
supply section I want to make it quite as much as I can and as I said I
also consider 50Hz Transformer.

regards

 

[Jeroen Belleman]

Maybe billions of femtohenries???

Actually, I'd expect it to be in the double-digit nanoHenry
ballpark. Much depends on the details of manufacturing.

Jeroen Belleman

 

[Phil Allison]

"Phil Hobbs"

Nah, it's just that every time I prod D from BC he starts talking about
religion, and off we go for another thousand bad-tempered, unthinking, and
very ill-informed posts.

This guy showed enough glimmers of cluefulness that I thought it might be
worth showing him the ropes. We shall see.

Cheers

** Strewth - you realy are a first class fucking idiot.




..... Phil

 

[Phil Allison]

"Electronworks.co.uk"

"Phil Allison" "Ebrahim the TROLL "
Before Phil gets totally carried away (and I wish he would), it depends on
the design of each power supply as to which gives out more noise.

** Unregulated 50Hz supplies have far more noise than SMPS.

Generally well over 100 times more.

SMPSs do NOT give out pure dc.

** Not what I posted - fuckhead.

Far from it.

** Blatant lie #1.

With a switched mode power supply, you can choose what frequency you use,
hence can shift the frequency of the interference away from any spectrally
sensitive area of your circuit. Naturally, as they have a higher switching
frequency than 50Hz, the reactive components are smaller (magnetics and
capacitors), so very physically small designs can be achieved with an
SMPS. Compare a switched mode in a mobile phone (or a laptop cable) with
that of a 50Hz linear power supply and you can immediately see the
difference in capacitor size.

** Another blatant lie.

Filter electro values in SMPS are typically larger than for a similar size
50Hz supply.

Comparing regulation, you can get an SMPS to regulate very accurately and
very efficiently with very small components with output ripple of only
50mV or so. To get the output ripple with a 50Hz linear power supply would
mean a huge output cap.

** Or a small IC called a regulator.

Hope this helps

** You only added to the bullshit.

**** off - fool.



.... Phil