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The effect of output impedance on load regulation?

T

Teece

Jan 1, 1970
0
Hi,

Does anyone have a reference for information on the effect of output
impedance on the load regulation capabilities of voltage regulators? I
realize that voltage regulators should be close to an ideal voltage source,
for the sake of efficiency, but I am not sure of the effect of output
impedance on the ability of the regulator to maintain a constant voltage.

Thank You
Tom
[email protected]
 
T

Tim Wescott

Jan 1, 1970
0
Teece said:
Hi,

Does anyone have a reference for information on the effect of output
impedance on the load regulation capabilities of voltage regulators? I
realize that voltage regulators should be close to an ideal voltage source,
for the sake of efficiency, but I am not sure of the effect of output
impedance on the ability of the regulator to maintain a constant voltage.

Thank You
Tom
[email protected]

That's going to depend on the voltage regulator in question. Any
voltage regulator is going to have an output stage with some real
impedance, and any VR worth it's salt is going to have a closed-loop
servo that holds the voltage constant with a PI or PID action. Thus the
regulation will be perfect for DC but will show some non-zero impedance
for higher frequencies -- so it'll look like an inductor in parallel
with a resistor, more or less. Stick a cap on the output and it'll be a
bandpass circuit (hopefully a stable one).

Any impedance that _you_ add such as parallel caps or resistors will
affect the regulation in a very predictable way.
 
G

Genome

Jan 1, 1970
0
| Hi,
|
| Does anyone have a reference for information on the effect of output
| impedance on the load regulation capabilities of voltage regulators? I
| realize that voltage regulators should be close to an ideal voltage
source,
| for the sake of efficiency, but I am not sure of the effect of output
| impedance on the ability of the regulator to maintain a constant
voltage.
|
| Thank You
| Tom
| [email protected]
|
|
|

I'm more interested in the load regulation capabilities of my asshole
when the 4 Niggers in this one toilet household are hogging the
bathroom. Two hours each for a shower and they still come out nigger
colored.

DNA
 
J

John Fields

Jan 1, 1970
0
I'm more interested in the load regulation capabilities of my asshole
when the 4 Niggers in this one toilet household are hogging the
bathroom. Two hours each for a shower and they still come out nigger
colored.

---
Tsk,tsk,tsk...

Unless used by a black person, "nigger" is such a politically
incorrect word here that the civil rightists (leftists?) have mandated
that we no longer call redbugs "chiggers", the acceptable word being
"chegroes".
 
T

Tim Wescott

Jan 1, 1970
0
John said:
---
Tsk,tsk,tsk...

Unless used by a black person, "nigger" is such a politically
incorrect word here that the civil rightists (leftists?) have mandated
that we no longer call redbugs "chiggers", the acceptable word being
"chegroes".
I hadn't heard that one. Why not "redbug"?

But yes, on the left side of the pond you can't even say the "n" word if
you're white (John's in trouble...). "African American" is currently in
vogue (that makes me a "European American", but everyone just says I'm a
White, or a honkey).

Perhaps it would be correct to use "African British"? Then you would be
a "Native British" to all but folks of Celtic descent, who would call
themselves "Native British" until accosted by Picts...
 
K

Ken Smith

Jan 1, 1970
0
Hi,

Does anyone have a reference for information on the effect of output
impedance on the load regulation capabilities of voltage regulators? I
realize that voltage regulators should be close to an ideal voltage source,
for the sake of efficiency, but I am not sure of the effect of output
impedance on the ability of the regulator to maintain a constant voltage.

It works (almost) by simple Ohm's law. The outut impedance isn't
resistive but, if it was, the drop would be simply I times R. Where the R
is the impedance. Life is more complex because the impedance is not
simply a resistance. It varies with frequency and has a phase angle.

If the regulator has a feedback pin, you have to figure out what the
impedance is when the feedback is working. This is usually lower than the
natural output impedance of the power stage. To understand this think
about a simple regulator with feedback:

Real power stage
------------------------
! !
! Ideal (A) (B) !
-->! Power ---[ Zout ]-------- To load
! ! stage ! !
! ------------------------ !
! V
! ------------
! ! Feedback !
! ! divider !
! -----------
! --------- !
---! Servo !<---------------
! gain !
---------

Imagine that the load forces the output voltage (B) of the regulator to
vary by a small amount at some frequency. If you follow that variation
throught the "feedback divider" and the "Servo gain" and the "Ideal power
stage", you can figure out what the signal at (A) is. Since Zout has the
(A-B) voltage across it, you can figure out how much the current in Zout
must vary.

Once you know The variation in current for a given variation in voltage at
(B) it is just Ohms law to figure the impedance with feedback included.

Since each thing in this circuit is frequency dependant, you have to do
this calculation at each frequency you care about.
 
K

Kevin Aylward

Jan 1, 1970
0
Tim said:
I hadn't heard that one. Why not "redbug"?

But yes, on the left side of the pond you can't even say the "n" word
if you're white (John's in trouble...).

Oh good, that gives me immunity for one of my favourite jokes.

Q. What do you call a nigger in a suit?
A. The defendant.

"African American" is
currently in vogue (that makes me a "European American", but everyone
just says I'm a White, or a honkey).

Perhaps it would be correct to use "African British"? Then you would
be a "Native British" to all but folks of Celtic descent, who would
call themselves "Native British" until accosted by Picts...

This whole PC stuff, is of course complete bullshit. I doubt if many
actually know my heritage, despite my numerous posts here, so I'll
clarify a bit:

My fathers side is all white. My mother is physically as black as the
ace of spades. Her mother was white, but her dad was a black from
Nigeria. However, my mothers mothers husband, was white. This makes me
the son of a black bastard.

Now, I have a rather err.. healthy looking, strong Californian tan
(seems to trash the genetic idea that traits are digitally inherited),
and what with my mothers attributes, this lead essentially, throughout
school to being referred to as sambo, nigger, wog, paki etc, you name
it, I was called it. The deal is that it meant absolutely nothing to me,
by the time that your 8 years old, the "insults" go through one ear and
out the other. Certainly any adult that has a problem with name calling
is one sad motherfucker indeed. The only real issue I had, was when 30
school kids shouted out, lets all go and give that nigger a right good
kicking. As you can imagine, the use of a derogatory reference, was the
last thing that I was concerned about.

The fundamental point of freedom (e.g. of speech), is to be free to do
things that others find objectionable. If no one found something
objectionable, we wouldn't need the concept in the first place to
protect it. i.e. Freedom would be completely meaningless. The idea that
words are censored, is probably the most abhorrent violation of free
speech that there can be. Its incredible that merely saying things like
"nigger" "****" evokes such outrage and indeed, e.g. bleeped out on
television. People have a "right" to be racist in their beliefs and
sayings. If we don't protect peoples rights to say what others find
objectionable, there can be no protection for those beliefs that we
ourselves find reasonable, but others find objectionable due to their
brainwashed prudish childhoods. Now..where did I put my whips...

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
D

Don Pearce

Jan 1, 1970
0
Oh good, that gives me immunity for one of my favourite jokes.

Q. What do you call a nigger in a suit?
A. The defendant.

"African American" is

This whole PC stuff, is of course complete bullshit. I doubt if many
actually know my heritage, despite my numerous posts here, so I'll
clarify a bit:

My fathers side is all white. My mother is physically as black as the
ace of spades. Her mother was white, but her dad was a black from
Nigeria. However, my mothers mothers husband, was white. This makes me
the son of a black bastard.

Now, I have a rather err.. healthy looking, strong Californian tan
(seems to trash the genetic idea that traits are digitally inherited),
and what with my mothers attributes, this lead essentially, throughout
school to being referred to as sambo, nigger, wog, paki etc, you name
it, I was called it. The deal is that it meant absolutely nothing to me,
by the time that your 8 years old, the "insults" go through one ear and
out the other. Certainly any adult that has a problem with name calling
is one sad motherfucker indeed. The only real issue I had, was when 30
school kids shouted out, lets all go and give that nigger a right good
kicking. As you can imagine, the use of a derogatory reference, was the
last thing that I was concerned about.

The fundamental point of freedom (e.g. of speech), is to be free to do
things that others find objectionable. If no one found something
objectionable, we wouldn't need the concept in the first place to
protect it. i.e. Freedom would be completely meaningless. The idea that
words are censored, is probably the most abhorrent violation of free
speech that there can be. Its incredible that merely saying things like
"nigger" "****" evokes such outrage and indeed, e.g. bleeped out on
television. People have a "right" to be racist in their beliefs and
sayings. If we don't protect peoples rights to say what others find
objectionable, there can be no protection for those beliefs that we
ourselves find reasonable, but others find objectionable due to their
brainwashed prudish childhoods. Now..where did I put my whips...

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Hear hear!

I don't like you because you are ...................

Insert derogatory noun or adjective from, but not limited to:

tall, short, black, white, ginger, freckled, bald, hairy, stupid,
clever, thin, fat...

The list goes on, and for me they all carry equal weight. For me
racism is the politically correct use of race to deny somebody the
right to air his feelings without censure.

I once saw a chat show with a participating audience of teenagers. One
black girl was asked a question and she said "Well, I'm not a racist".
Then she gave an embarrassed giggle and followed up "well, I couldn't
be,really, could I?". For me, that was the most racist comment I had
heard in a long time - all the more dangerous for the fact that nobody
- including the presenter - picked her up on it.

d
Pearce Consulting
http://www.pearce.uk.com
 
K

Kevin Aylward

Jan 1, 1970
0
Hear hear!

I don't like you because you are ...................

Insert derogatory noun or adjective from, but not limited to:

tall, short, black, white, ginger, freckled, bald, hairy, stupid,
clever, thin, fat...

The list goes on, and for me they all carry equal weight. For me
racism is the politically correct use of race to deny somebody the
right to air his feelings without censure.

I once saw a chat show with a participating audience of teenagers. One
black girl was asked a question and she said "Well, I'm not a racist".
Then she gave an embarrassed giggle and followed up "well, I couldn't
be,really, could I?". For me, that was the most racist comment I had
heard in a long time -

Yes. I agree.


Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
J

John Fields

Jan 1, 1970
0
This whole PC stuff, is of course complete bullshit. I doubt if many
actually know my heritage, despite my numerous posts here, so I'll
clarify a bit:

My fathers side is all white. My mother is physically as black as the
ace of spades. Her mother was white, but her dad was a black from
Nigeria. However, my mothers mothers husband, was white. This makes me
the son of a black bastard.

Now, I have a rather err.. healthy looking, strong Californian tan
(seems to trash the genetic idea that traits are digitally inherited),
and what with my mothers attributes, this lead essentially, throughout
school to being referred to as sambo, nigger, wog, paki etc, you name
it, I was called it. The deal is that it meant absolutely nothing to me,
by the time that your 8 years old, the "insults" go through one ear and
out the other. Certainly any adult that has a problem with name calling
is one sad motherfucker indeed. The only real issue I had, was when 30
school kids shouted out, lets all go and give that nigger a right good
kicking. As you can imagine, the use of a derogatory reference, was the
last thing that I was concerned about.

The fundamental point of freedom (e.g. of speech), is to be free to do
things that others find objectionable. If no one found something
objectionable, we wouldn't need the concept in the first place to
protect it. i.e. Freedom would be completely meaningless. The idea that
words are censored, is probably the most abhorrent violation of free
speech that there can be. Its incredible that merely saying things like
"nigger" "****" evokes such outrage and indeed, e.g. bleeped out on
television. People have a "right" to be racist in their beliefs and
sayings. If we don't protect peoples rights to say what others find
objectionable, there can be no protection for those beliefs that we
ourselves find reasonable, but others find objectionable due to their
brainwashed prudish childhoods. Now..where did I put my whips...
 
W

Winfield Hill

Jan 1, 1970
0
Tim Wescott wrote...
Well, the regulator's output impedance is calculated from its measured
load regulation properties. Most regulator ICs have a Load Regulation
spec. For example the popular LM317 spec is 0.1% typ for 10mA to Imax.
Since Imax = 1A, a 10V LM317 regulator (note 0.1% of 10V = 10mV) has
R_out = 10mV / 1A = 0.010 ohms, or 10 milliohms, as we like to say.
That's going to depend on the voltage regulator in question. Any
voltage regulator is going to have an output stage with some real
impedance, and any VR worth it's salt is going to have a closed-loop
servo that holds the voltage constant with a PI or PID action. Thus
the regulation will be perfect for DC but will show some non-zero
impedance for higher frequencies -- so it'll look like an inductor
in parallel with a resistor, more or less.

Zout looks like an inductor in series with the DC output resistance.

Tom, look at the LM317's Output Impedance plot, which shows a rising
impedance (an inductor) = 0.3 ohms at 10kHz. L = XL / 2pi f = 4.8uH,
so the LM317 Zout at 10V and 500mA is 5uH in series with 10 milliohms.
Get the datasheet, http://www.national.com/ds.cgi/LM/LM117.pdf (One
more point, an LM317's Zout is proportional to its operating voltage,
e.g., at 5V it'd be lower, 2.5uH in series with 5 milliohms. OK, one
more point, the LM317's output inductance can be further reduced to
0.6uH, independent of operating voltage, by bypassing the ADJ pin.)
Stick a cap on the output and it'll be a bandpass circuit (hopefully
a stable one).

For our LM317 example, an optional 10uF (the recommended minimum)
output capacitor will resonate at f = 1/(2pi sqrt LC) = 23kHz. At
this frequency the resonant impedance is 0.7 ohms, times the Q.

Stability results primarily from the capacitor's esr, or the internal
"equivalent series resistance," limiting the LC circuit's resonant Q.
For example, a 25V Panasonic FC series 10uF aluminum cap has an esr
of 2 ohms, max, so the resonant Q would be about 2/0.7 = 3. Note,
if we use a *very* low esr cap, say 0.1 ohms, a Q = 7 would be worse.
If we use a 35V 27uF FC series cap, esr = 0.9 ohms, then our res-freq
would be lowered to 14.5kHz and X_LC = 0.44 ohms, so we get Q = 2.

Keep in mind these are all quite nice low supply impedance levels,
and a little peak at 15, 20 or 25kHz is not usually any problem.

Say we used a single 0.1uF ceramic bypass with our LM317, then the LC
resonance frequency would be 230kHz, X_LC = 7 ohms, and the ceramic
cap's low esr would mean we'd have a very high Q, and step changes in
the load current would cause severe ringing at 230kHz. But, if we add
a klunky old aluminum electrolytic, bam, the messy old ringing is gone!

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
B

Berge Duravin

Jan 1, 1970
0
dated Sat, 03 Jul 2004 09:14:58 -0500,

SNR

Need to scroll to see your answer.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Kevin Aylward
lueyonder.co.uk>) about 'The effect of output impedance on load
regulation?', on Sat, 3 Jul 2004:
Yes. I agree.

So do I. Now, Kevin, would you please check your e-mail for a message
from me that quotes one that I sent you several months ago and did not
receive a reply. It's got, like, a bit more urgent now. (;-)
 
K

Kevin Aylward

Jan 1, 1970
0
John said:
I read in sci.electronics.design that Kevin Aylward


So do I. Now, Kevin, would you please check your e-mail for a message
from me that quotes one that I sent you several months ago and did not
receive a reply. It's got, like, a bit more urgent now. (;-)

I did send you a reply with the appropiate enclosure a while back. email
me back again with a valid email address and I will repeat the
enclosure. I dont keep emails that long.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
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