Power supply design

[Franc Zabkar]

On Thu, 10 Feb 2005 21:38:12 GMT, john_c@tpg.com.au (John Crighton)
put finger to keyboard and composed:

On Fri, 11 Feb 2005 07:52:53 +1100, Franc Zabkar
fzabkar@optussnet.com.au> wrote:

On Thu, 10 Feb 2005 04:52:58 GMT, john_c@tpg.com.au (John Crighton)
put finger to keyboard and composed:

On Thu, 10 Feb 2005 04:25:00 +0000 (UTC), Wing Fong Wong
wing@tart.com.au> wrote:



Only problem with computer PS are that the voltages aren't always too
stable - especially cheap ones.

--

Wing Wong.
Webpage: http://wing.ucc.asn.au


Hello Wing,
that is interesting, tell me your experiences.
How bad was the instability that you found?
Regards,
John Crighton
Hornsby

Only the very high end PSUs appear to have independent regulation for
each of the supply rails. IME most PC PSUs regulate by sensing a
weighted average of the +5V and +12V rails. This means that load
variations on the +12V rail will affect the +5V supply. See this ATX
example:
http://www.pavouk.comp.cz/hw/en_atxps.html

Notice R25 and R26 in the feedback path. Whenever I modify a PC PSU
for +6V or 13.8V, I remove the appropriate resistor and recalculate
the remaining one.


- Franc Zabkar


Hello Frank,
thanks for pointing that out. Great to see actual diagrams
and descriptions.

Then see these DTK SMPS and motherboard circuits:
http://www.dtk.com.tw/tech/dtkfaq.html


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[quietguy]

Go to the tip and grab an old computer - convert the power supply to what you
need


David

Dejan Uzelac wrote:

Hi.

I need an adapter with an output of 5V 2A DC. I cant seem to find it
anywhere, and even if I do it costs minimum $50. Well, thats a bit much for
my application.

Highest output current adapter I have is a 9V 1A DC adapter.

Any idea how to convert this to 5V, 2A? how can I make a little power supply
circuit?

THANX

 

[Phil Allison]

"Rod Speed"
"Phil Allison"

The high current, 5 volt rail has the PWM feedback loop stabilising it
while the others do not and are unregulated.

More stricty they track the 5 volt rail which is regulated.

** If you adjust the voltage trim, then all rails will go up and down
together. But if the load on the 5 volt rail is varied then the opposite
happens.

The PWM duty cycle instantly increases to compensate voltage drop caused by
applying a greater load on the 5 volt rail - then that larger PWM duty
cycle immediately causes the voltage on the other rails to rise.




.............. Phil

 

[Rod Speed]

Phil Allison <philallison@tpg.com.au> wrote in
message news:372djnF532kvvU1@individual.net...

Rod Speed wrote
Phil Allison <philallison@tpg.com.au> wrote

The high current, 5 volt rail has the PWM feedback loop stabilising it while
the others do not and are unregulated.

More stricty they track the 5 volt rail which is regulated.

If you adjust the voltage trim, then all rails will go up and down together.
But if the load on the 5 volt rail is varied then the opposite happens.

Thats just plain wrong. As the 5V sags, the regulation jacks that up
and jacks up the other high power rails too, because the regulation
controls the switching side and the other high power rails come
off the same high freq transformer with their own windings on that.

The PWM duty cycle instantly increases to compensate voltage drop caused by
applying a greater load on the 5 volt rail - then that larger PWM duty cycle
immediately causes the voltage on the other rails to rise.

Thats the opposite of what you said previously and is now correct.

And that isnt unregulated with the other high power rails.

They dont all monitor just the 5V rail either.

 

[Phil Allison]

"Rod Speed"

Phil Allison


The high current, 5 volt rail has the PWM feedback loop stabilising it
while the others do not and are unregulated.

More stricty they track the 5 volt rail which is regulated.

If you adjust the voltage trim, then all rails will go up and down
together. But if the load on the 5 volt rail is varied then the opposite
happens.

Thats just plain wrong. As the 5V sags, the regulation jacks that up
and jacks up the other high power rails too,

** Where did "high power rails" come from ??????? The Rodbot is trying
to sneak that in through the back door.

The 5 volt rail holds voltage when loaded and the PWM jacks the others go
*up* if the load on them has not similarly increased.

The PWM duty cycle instantly increases to compensate voltage drop caused
by applying a greater load on the 5 volt rail - then that larger PWM
duty cycle immediately causes the voltage on the other rails to rise.

Thats the opposite of what you said previously and is now correct.

** The Rodbot needs reading lessons.

And that isnt unregulated with the other high power rails.

** The other rails are let wander up and down when loaded or the 5 volt is
loaded - that is the very definition of unregulated.




.............. Phil

 

[Dejan Uzelac]

read:
http://www.pavouk.comp.cz/hw/en_atxps.html


"Phil Allison" <philallison@tpg.com.au> wrote in message
news:372us6F584j5hU1@individual.net...

"Rod Speed"
Phil Allison


The high current, 5 volt rail has the PWM feedback loop stabilising it
while the others do not and are unregulated.

More stricty they track the 5 volt rail which is regulated.

If you adjust the voltage trim, then all rails will go up and down
together. But if the load on the 5 volt rail is varied then the opposite
happens.

Thats just plain wrong. As the 5V sags, the regulation jacks that up
and jacks up the other high power rails too,


** Where did "high power rails" come from ??????? The Rodbot is
trying to sneak that in through the back door.

The 5 volt rail holds voltage when loaded and the PWM jacks the others go
*up* if the load on them has not similarly increased.


The PWM duty cycle instantly increases to compensate voltage drop caused
by applying a greater load on the 5 volt rail - then that larger PWM
duty cycle immediately causes the voltage on the other rails to rise.

Thats the opposite of what you said previously and is now correct.


** The Rodbot needs reading lessons.


And that isnt unregulated with the other high power rails.


** The other rails are let wander up and down when loaded or the 5 volt
is loaded - that is the very definition of unregulated.




............. Phil

 

[Rod Speed]

Phil Allison <philallison@tpg.com.au> wrote in
message news:372us6F584j5hU1@individual.net...

Rod Speed wrote
Phil Allison wrote

The high current, 5 volt rail has the PWM feedback loop stabilising it
while the others do not and are unregulated.

More stricty they track the 5 volt rail which is regulated.

If you adjust the voltage trim, then all rails will go up and down together.
But if the load on the 5 volt rail is varied then the opposite happens.

Thats just plain wrong. As the 5V sags, the regulation jacks that up and
jacks up the other high power rails too,

Where did "high power rails" come from ???????

Thats what the OP wanted, a higher power supply, cretin.

The Rodbot is trying to sneak that in through the back door.

Caught lying. Again.

The 5 volt rail holds voltage when loaded and the PWM jacks the others go *up*
if the load on them has not similarly increased.

OK, thats a lot clearer than you originally
said. In fact the 5V is jacked up too.

The PWM duty cycle instantly increases to compensate voltage drop caused by
applying a greater load on the 5 volt rail - then that larger PWM duty
cycle immediately causes the voltage on the other rails to rise.

Thats the opposite of what you said previously and is now correct.

The Rodbot needs reading lessons.

The Toaster Molesting Ape needs to repeat English 101.

And that isnt unregulated with the other high power rails.

The other rails are let wander up and down when loaded or the 5 volt is
oaded - that is the very definition of unregulated.

Not a fucking clue, as always.

 

[Phil Allison]

"Rod Speed"

Phil Allison

Where did "high power rails" come from ???????

Thats what the OP wanted, a higher power supply, cretin.

** Pure fiction.

The 5 volt rail holds voltage when loaded and the PWM jacks the others go
*up* if the load on them has not similarly increased.

OK, thats a lot clearer than you originally said.

** = the Rodbot finally got it.

In fact the 5V is jacked up too.

** Not a fucking clue .



............. Phil

 

[Rod Speed]

Some fuckwit toaster molesting ape claiming to be
Phil Allison <philallison@tpg.com.au> desperately attempted
to bullshit its way out of its predicament wrote in message
news:375635F57h4ghU1@individual.net...
and fooled absolutely no one at all. As always.

No wonder it got the bums rush.