Capacitor

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <301q2dF2pdul4U1@uni-berlin.de>, mbmsv@yahoo.com says...
> > Sure I do, but I don't have to live in theory only, try it some time.
> > Take a regulator of your choice, the 7805 is a nice package, use an
> > input voltage of 24VDC and then 12VDC with a load of 500ma on the 5v
> > side - you won't notice the difference in temp.
>
> Sure, you don't. 7805 will either blow up or will go into internal thermal
> protection mode should you put it into such a circuit. It is a 100 mA
> regulator and there is no way it can dissipate (24-5)*0.5=9.5W of power or
> even 3.5W in case of 12V input.... Sorry.

Try again, the LM7805 will handle 1A if properly heatsinked.
http://www.national.com/pf/LM/LM7805C.html


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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

> Try again, the LM7805 will handle 1A if properly heatsinked.
> http://www.national.com/pf/LM/LM7805C.html

OK, I was looking at LM78L05, which is a lower power version of the LM7805.
With the original LM7805 you might be able to actually dissipate your 9.5W,
but take a look at the Maximum Power Dissipation graphs in the datasheet, it
will only work with a hefty heatsink or in a fridge. The bigger device
doesn't change the basics of the Ohm's law. It is actually bigger because of
these basics!


/MM

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <301uugF2rhsgmU1@uni-berlin.de>, mbmsv@yahoo.com says...
> > Try again, the LM7805 will handle 1A if properly heatsinked.
> > http://www.national.com/pf/LM/LM7805C.html
>
> OK, I was looking at LM78L05, which is a lower power version of the LM7805.
> With the original LM7805 you might be able to actually dissipate your 9.5W,
> but take a look at the Maximum Power Dissipation graphs in the datasheet, it
> will only work with a hefty heatsink or in a fridge. The bigger device
> doesn't change the basics of the Ohm's law. It is actually bigger because of
> these basics!

In looking at the T0-3 unit, with heat-sink, sitting near my desk in a
power supply, and another one with the TO-220 style package, with heat-
sink, also sitting here (since I have about 30 of the 7805 devices and
another 10 LM338 and 317's and a bunch of power transistors and others.
I can assure you that the TO-3 and TO-220 units can deliver a sustained
500MA draw with little problem using a normal heat-sink (even one from
RadioShack) and a minimal amount of HSP.

They can also provide a sustained 1A of power, but, with a standard
heat-sink, you do notice a little heat from the fins. I would imagine if
you were to push beyond 1A a cooling fan might be required.


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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

> I can assure you that the TO-3 and TO-220 units can deliver a sustained
> 500MA draw with little problem using a normal heat-sink (even one from
> RadioShack) and a minimal amount of HSP.

I've no doubt it can deliver 500 mA, the question is how big a voltage drop
it can handle with this load. Somehow you don't want to admit the obvious.
The maximum junction temperature for both of these cases (TO3 and TO220) is
150 C. The junction-to-case thermal resistance is 4 C/W. Assuming your
heatsink has 10C/W resistance to ambient (which is pretty good) we get 14
C/W junction-to-ambient minimum resistance. At 9.5W of power dissipation
you'll have 9.5*14=133 C temperature differential between the junction and
ambient. Since the temperature in a computer case is usually higher than in
a room, let's say 35 C, you will have your junction at 168 C, which is well
above the spec. Do you still want to try 1 A at 24VDC input (19W to
dissipate)? Let us know how well it worked.


/MM

 

[frank]

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

> If the caps are part of the switching power supply that converts the
> the power supply voltages to the core voltages of the CPU, then I
> doubt that your computer would still be working. However, the caps may
> be filter caps that are spread around the board to provide some
> additional filtering and noise reduction to the switching transients
> on the ground and power planes. This is a fairly standard board design
> practice. If that's the case, you'd probably never know the
> difference.
>


Thanks for all the answers. As for now I´m no good at soldering, I have no
warranty on these 2 machines. I got 2 spare boards in the closet, so I´m set
for all things that can happen. As the still work like a charm I´m not doing
anything by now. Thanks for all the help, again.

Frank

 

[frank]

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

.. Wenn nicht, arbeite
> solange es geht mit dem Board weiter und tausch es gegen ein Neues aus,
> sobald Fehler auftreten.
>
Hallo Carsten,

danke für die Hilfe, und genau das werde ich tun.

Gruß

Frank

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <30216dF2og258U1@uni-berlin.de>, mbmsv@yahoo.com says...
> > I can assure you that the TO-3 and TO-220 units can deliver a sustained
> > 500MA draw with little problem using a normal heat-sink (even one from
> > RadioShack) and a minimal amount of HSP.
>
> I've no doubt it can deliver 500 mA, the question is how big a voltage drop
> it can handle with this load. Somehow you don't want to admit the obvious.
> The maximum junction temperature for both of these cases (TO3 and TO220) is
> 150 C. The junction-to-case thermal resistance is 4 C/W. Assuming your
> heatsink has 10C/W resistance to ambient (which is pretty good) we get 14
> C/W junction-to-ambient minimum resistance. At 9.5W of power dissipation
> you'll have 9.5*14=133 C temperature differential between the junction and
> ambient. Since the temperature in a computer case is usually higher than in
> a room, let's say 35 C, you will have your junction at 168 C, which is well
> above the spec. Do you still want to try 1 A at 24VDC input (19W to
> dissipate)? Let us know how well it worked.

While you won't like my answer, and I'm sure you say it's not true, I've
been doing it for years. Almost always use +24 to the supply side for
the +15, +10, +5 supply circuits, and -24 for the -15, -10 circuits. The
have handled 500MA loads for years with the standard heat-sink and HSP.

You and I can both read the spec's, and I have never disagreed with
them, not once, but what works in the real world is different that the
specs many times. Heck, I even have one +/- 15vdc follower that I built
in the early 80's that still works (changed the caps a few years back),
and it still follows within about 3mv all day long.

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"Leythos" <void@nowhere.org> wrote in message
news:MPG.1c05bb2aa1024f3b989a7c@news-server.columbus.rr.com...
>
> While you won't like my answer, and I'm sure you say it's not true, I've
> been doing it for years. Almost always use +24 to the supply side for
> the +15, +10, +5 supply circuits, and -24 for the -15, -10 circuits. The
> have handled 500MA loads for years with the standard heat-sink and HSP.

You are a strange person I should say. There is a huge difference between
15V and 5V output in this case! With 5V at 500mA you are on the edge of what
can be done with a 7805. At 15V you do have some margin.

> You and I can both read the spec's, and I have never disagreed with
> them, not once, but what works in the real world is different that the
> specs many times.

If this happens, it usually means either error in measurements or in how
these measurements are being interpreted. Besides, this time you are
challenging much more than a spec, you are challenging one of the basic laws
of physics.

/MM

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <302gr6F2ptuihU1@uni-berlin.de>, mbmsv@yahoo.com says...
> "Leythos" <void@nowhere.org> wrote in message
> news:MPG.1c05bb2aa1024f3b989a7c@news-server.columbus.rr.com...
> >
> > While you won't like my answer, and I'm sure you say it's not true, I've
> > been doing it for years. Almost always use +24 to the supply side for
> > the +15, +10, +5 supply circuits, and -24 for the -15, -10 circuits. The
> > have handled 500MA loads for years with the standard heat-sink and HSP.
>
> You are a strange person I should say. There is a huge difference between
> 15V and 5V output in this case! With 5V at 500mA you are on the edge of what
> can be done with a 7805. At 15V you do have some margin.

Maybe I should have been more clear - the +15 and +10 are not done with
the LM78XX series. The 5V is and works fine, even at loads of 1A over
hours of continuous operation.

> > You and I can both read the spec's, and I have never disagreed with
> > them, not once, but what works in the real world is different that the
> > specs many times.
>
> If this happens, it usually means either error in measurements or in how
> these measurements are being interpreted. Besides, this time you are
> challenging much more than a spec, you are challenging one of the basic laws
> of physics.

Ah, the old, specs could be wrong, physics could be wrong, something
must be wrong, cause you can't explain how it can work on paper when it
works in real life.

Here's and Idea, instead of telling me something that I'm doing can't be
done, that the spec's don't allow for it, try it yourself, the LM7805C's
are cheap, pick your package type, and try it - just try it yourself
before you tell me what I'm doing isn't possible.

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"Leythos" <void@nowhere.org> wrote in message
news:MPG.1c05ee3e50bc0dc9989a7e@news-server.columbus.rr.com...
works in real life.
>
> Here's and Idea, instead of telling me something that I'm doing can't be
> done, that the spec's don't allow for it, try it yourself, the LM7805C's
> are cheap, pick your package type, and try it - just try it yourself
> before you tell me what I'm doing isn't possible.

I am doing this kind of thing pretty much every day. That's what I am being
paid to do. So far, I haven't been able to break the Ohm's law. Why don't
YOU try to load your perpetum mobile with a 5A load and feed it with 100VDC.
It shouldn't make any difference in heat, right? Go and measure your
voltages, currents and temperatures properly and then we can see whether
theory is coherent with practice.

/MM

 

[Guest]

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <Up-dnQw5WtrnpAHcRVn-pg@rogers.com>, mbmsv@yahoo.com says...
> "Leythos" <void@nowhere.org> wrote in message
> news:MPG.1c05ee3e50bc0dc9989a7e@news-server.columbus.rr.com...
> works in real life.
> >
> > Here's and Idea, instead of telling me something that I'm doing can't be
> > done, that the spec's don't allow for it, try it yourself, the LM7805C's
> > are cheap, pick your package type, and try it - just try it yourself
> > before you tell me what I'm doing isn't possible.
>
> I am doing this kind of thing pretty much every day. That's what I am being
> paid to do. So far, I haven't been able to break the Ohm's law. Why don't
> YOU try to load your perpetum mobile with a 5A load and feed it with 100VDC.
> It shouldn't make any difference in heat, right? Go and measure your
> voltages, currents and temperatures properly and then we can see whether
> theory is coherent with practice.

I hear that same rhetoric from people all the time. I don't care if
you're paid to do it, like that means your qualified. I don't care if
you just want to whine about it not being possible. I don't care if you
don't seem to understand that it's already being done and working. I've
been building power supply units since the 70's, and unlike you, I've
not been blinded by the "I can only do what the spec's say I can do"
mentality.

Like I said, try it yourself, put aside your big headed idea that it's
not possible, just try it, you might surprise yourself. What I've seen
from your replies is symptomatic of the typical "the spec's say it can't
work, so it can't work type of people". Open your eyes once and quit
being such a closed minded person and just try it, it's a simple
circuit, you should be able to build it in under an hour (even if you
have to solder it yourself). You might even have the parts, since you're
pretty much paid to do this this every day - if you don't have the TO-3
LM7805 you can order one for about $5 from suppliers.

One of these days you might want to actually try something before you
speak out that it's impossible, when you do try it you're going to look
funny posting that it did work (not that I expect that from someone like
you).


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"Leythos" <void@nowhere.org> wrote in message
news:MPG.1c0656948ac2f4fd989a80@news-server.columbus.rr.com...
>
> Like I said, try it yourself, put aside your big headed idea that it's
> not possible, just try it, you might surprise yourself.
>
You are not hearing me. I am trying this kind of thing every day and I am
not seeing the results you see. If you want me to try something be more
specific. What it is precisely you want me to try and what it is I will see?
What are the design goals/parameters:

Input voltage, load, max and min ambient temperature, heat sink thermal
resistance, etc?

/MM

 

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In article <WcudnZu1PdTDOwHcRVn-1Q@rogers.com>, mbmsv@yahoo.com says...
> "Leythos" <void@nowhere.org> wrote in message
> news:MPG.1c0656948ac2f4fd989a80@news-server.columbus.rr.com...
> >
> > Like I said, try it yourself, put aside your big headed idea that it's
> > not possible, just try it, you might surprise yourself.
> >
> You are not hearing me. I am trying this kind of thing every day and I am
> not seeing the results you see. If you want me to try something be more
> specific. What it is precisely you want me to try and what it is I will see?
> What are the design goals/parameters:
>
> Input voltage, load, max and min ambient temperature, heat sink thermal
> resistance, etc?

Here's what you've said:

Based on the spec's, the LM7805 can not provide reliable output of 5v at
500MA (or even 1A) with a standard heat sink with an supply voltage of
24VDC.

I said:

Wrong, it works, is working, and has worked on many systems for at least
about 20 years that I know of and have DIRECT experience with. I also
said that I have read and understand the technical specs, but that
sometimes you have to just believe what you see in the real world and
not just on paper.

I think you can figure out what you have to test based on the two
statements above.

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"Leythos" <void@nowhere.org> wrote in message
news:MPG.1c06bf4f8b968e0989a82@news-server.columbus.rr.com...
>
> Here's what you've said:
>
> Based on the spec's, the LM7805 can not provide reliable output of 5v at
> 500MA (or even 1A) with a standard heat sink with an supply voltage of
> 24VDC.
>
> I said:
>
> Wrong, it works, is working, and has worked on many systems for at least
> about 20 years that I know of and have DIRECT experience with. I also
> said that I have read and understand the technical specs, but that
> sometimes you have to just believe what you see in the real world and
> not just on paper.
>
> I think you can figure out what you have to test based on the two
> statements above.

1. What the hell is a "standard" heatsink?
2. What is the ambient temperature?

I don't have more time to spend on this BS. I've done my labs to prove the
Ohm's law many years ago in Grade 7 or 8. There is nothing to be gained from
this experiment. The last board I designed has 5 switching regulators and
over a dozen of linear ones. Every and each of them work according to the
known laws of physics and dissipate precisely the amount of heat I
calculated. Yes, you can run semiconductors at 150C or some even higher, but
reliable things are not designed this way. Have you ever heard of derating?
Have you ever seen a curve demonstrating failure frequency depending on
junction temperature? As I can see it, you look at a datasheet, notice the
max current and max input voltage and then you plug it in a circuit and
experiment. You might be lucky and it "works" most of the times, but have
you tried to qualify your circuit to work in avionics equipment where
ambient temperatures can easily reach 70 C and where cooling air coming from
a fan is sometimes just as hot? If people were doing designs your way we
would still be in a crystal radio age. Why do you believe the output voltage
spec and don't believe power and temperature rating specs? You don't expect
to see 7V or 17V output from your favorite 7805, but somehow you expect that
other parts of the spec along with fundamental laws of physics can be
stretched to whatever lengths. Finally, back to your 500mA 24VDC PSU. I
didn't say it can't work, but it is on the edge depending on your heatsink.
If you increase the current to 1A it will most likely fail (again depending
on the heatsink, ambient temperature and fan speed).

/MM


/MM

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <304g0cF2rjqo9U1@uni-berlin.de>, mbmsv@yahoo.com says...
> 1. What the hell is a "standard" heatsink?

Something you can find for sale in the common electronics supply
catalogs - not something that is the size of a Refrige.

> 2. What is the ambient temperature?

Room temp, don't ask what room, pick one in your house, on a normal day.

> I don't have more time to spend on this BS. I've done my labs to prove the
> Ohm's law many years ago in Grade 7 or 8. There is nothing to be gained from
> this experiment.

Sure there is, but, as I figured, you don't like to be wrong, so you
absolve yourself of it by saying that your labs and specs are right.

> The last board I designed has 5 switching regulators and
> over a dozen of linear ones. Every and each of them work according to the
> known laws of physics and dissipate precisely the amount of heat I
> calculated.

And I never suggested that your designs don't work, never suggested that
Ohms law was wrong, or anything of the sort. If you want to boast about
your abilities, I was doing the above in the late 70's, and still have
parts cabinets full of chips - but who cares.

If you are going to make a statement that the LM7805 can not operate at
5V providing 500MA in a stable configuration with a supply voltage of +
24V then you ought to be able to prove it. I did, it works, got a couple
of them right here, working for years. I'm not asking you to take my
word for it alone, I'm saying that it works, is stable, and does not
fail, and that if you don't believe it, try it yourself. If you can't be
big enough to at least try it, then quit whining about how it can't
work!


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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

Re: "The onboard PSU is normally not a switching unit, the Switching
PSU's are the large metal units that you connect AC to."

That is totally wrong. The Vcore power supply for the CPU, which is on
the motherboard, most definitely IS a switching power supply.

The correct advice here is to remove AND REPLACE the bad capacitors.
Frankly, I'd replace any other SIMILAR capacitors at the same time.
About 2-3 years ago, the industry was flooded with several hundred
million bad electrolytic capacitors. It happened because a chemical
company that was going bankrupt, in an attempt to save money, left a
critical but expensive chemical out of their production of electrolyte
used by the capacitor makers in Taiwan. I'm guessing that you have some
of those caps.

There really is no solution other than to remove and replace them, which
will require soldering. You don't need an exact replacement. If in
doubt, get parts with higher capacitance and/or higher voltage. I have
an oscilloscope that I built in 1980 that I was into to replace a pilot
lamp, and I noticed a 3000 uF 15 volt capacitor blown completely apart,
the scope worked fine without it. I temporarily replaced it with a 1000
uf 25 volt part (closest I could come at radio shack), but later
installed a 3000 uf 30 volt part.


Leythos wrote:
> In article <dqWdndAEi68TEATcRVn-1Q@rogers.com>, mbmsv@yahoo.com says...
>
>>"Leythos" <void@nowhere.org> wrote in message
>>news:MPG.1c02dd7c4ad1dc9c989a57@news-server.columbus.rr.com...
>>
>>>Replace the CAP as soon as possible or at least remove it.
>>
>>Removing a cap from a switching power supply, where it is likely to belong,
>>might disable the board completely. I actually found a similar problem on my
>>old Aopen mobo (in my case the caps are definitely belong to the main CPU
>>switching power supply), so I went and bought a new ASUS mobo But I am
>>going to replace the caps on the old board and then build a second computer.
>
>
> The onboard PSU is normally not a switching unit, the Switching PSU's
> are the large metal units that you connect AC to. Most of the
> "regulators" on the motherboard have no PSU to them, they are just
> voltage regulators. A regulator, using the existing DC signal from the
> PSU, uses the CAP's to clean the ripple out of the "switched" DC supply
> from the PSU.
>
> Removing a CAP, from the PSU would indeed cause problems, as they use
> the caps to provide ripple rejection to the DC output.
>
> The caps on a motherboard, in almost every instance, are to spot signal
> filtering or for ripple rejection at the point.
>

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

The first poster was correct. Linear regulators, including 3-terminal
regulators like 7805's, drop the voltage by WASTING the excess as heat.
Essentially, they drop the voltage by putting an electronically
variable resistance between the higher voltage and the desired lower
voltage.

Say you are using a 7805 to drop 12 volts (which might be unregulated as
well) down to 5 volts. The extra 7 volts is across the 7805. If the
current draw at 5 volts is 100ma (0.1 amps), then you are "wasting" .7
watts in the regulator (7 volts across the regulator x .1 amps through
the regulator). That might not sound like much, but the load is only
using .5 watts (5 volts, 0.1 amps), so you are "wasting" more than you
are using. The wasted power appears as heat (the regulator gets hot,
and may require a heat sink).

3 terminal regulators can only dissipate about 2-3 watts total at most,
and only then with a good heat sink. So while a 7805 can supply 1 amp,
you can forget about it if you want to drop 24 volts to 5 volts, because
it would have to dissipate 19 watts (1 amp, 19 volts across the
regulator). On the other hand, if you were working from an 8 volt
supply, it could handle it, because the power dissipation would now only
be 3 watts (near the limit of the regulator, but manageable with a good
heat sink).

The whole reason for using a switching regulator is that they have high
efficiency, they don't waste power. That's because they don't "drop"
the output voltage from the input voltage, rather they generate the
output voltage "from scratch".


>
>>If they used a
>>linear regulator they would have to waste half of the power since core
>>voltages are so low and the lowest voltage available from the big PSU is
>>3.3V.
>
>
> What's wrong is that statement - you don't "waste" anything, the
> regulator doesn't "waste" anything from the PSU. You can easily drop the
> +12VDC supply down to any lower voltage without "wasting" anything.
>
>

 

[Guest]

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

Leythos, you are just totally wrong, and have no understanding of how
these parts work.


Leythos wrote:

> In article <VQomd.194$im.132@newsfe5-gui.ntli.net>,
> rogerspamignored@ttelmah.demon.co.uk says...
>
>>Do you understand how a linear regulator works?.
>
>
> Yea, I if I take the 7812, 7805, LM317, etc... regulator device, and
> look in my Linear data book, it's the same as it's been since the 80's.
> The device does not disapate heat or waste anything to provide the
> specified power from the supply voltage.
>
> I don't see it as disapating anything to provide the drop to the
> requested level, I see it disapating heat to provide the X volts at y
> MA, through the circuit. The drop doesn't generate the heat, the load on
> the regulator does.
>

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

The cap is probably neither open nor shorted, in fact it's quite
possibly still working .... as a capacitor.

The problem with the defective electrolyte that was used in a few
hundred million capacitors made a couple years ago was that a chemical
that reduced "gassing" was left out. The capacitors then could produce
excessive gas pressure and eventually the "can" would ruture somewhere.

While this can destroy the capacitor in either an open or a short mode,
sometime all that happens is that the can ruptures, electrolyte leaks
out, but the capacitor basically isn't catastrophically destroyed (at
least not immediately).

The loss of electrolyte will reduce the effective capacitance of the
capacitor, but this normally isn't critical until towards the end (when
either most of the electrolyte has leaked out or dried out). Also, as
was noted, the electrolyte is corrosive and can "eat through" the traces
on the circuit board. The capacitor should be replaced, but IN THIS
INSTANCE, it may well have neither shorted nor opened, and may, for the
moment, still be functioning "adequately".

[One other possibility is that it IS open, but these circuits often have
quite a few capacitors in parallel, and the remaining capacitors (which
have not failed YET) may be adequate to keep things working ok.]


>
> One thing to keep in mind, the OP said the cap was blown and in my
> experience, if it was part of the switching power circuit, it would
> almost certainly mean problems for his system.
>
> Since he's not having any problems with it, then it must be OPEN and not
> shorted and certainly not doing it's job. This leads me to believe that
> it's just for filtering ripple on the board at some critical point that
> requires flat voltage levels.
>
> One last thing, if I setup a 7805 or LM317 regulator, and supply it with
> 12VDC and set the output to 5V, the heat generated under a 1A load is no
> different than when I supply it with a 24VDC input.
>
>

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

First, you are wrong both in theory and in practice. A 7805 dropping 12
volts to 5 will dissipate more than twice as much power (heat) as one
dropping 8 volts to 5 (assuming the same current draw). And the
difference is VERY, VERY real.

Second, actually, the capacitor is NOT necessarily being used as a
ripple filter here, but rather as an "energy storage reservoir". There
is no ripple in the output of a linear regulator whose input is DC. And
while the output of a switching power supply would have ripple, the
frequency is VERY high (80-120 KHz is a common range) and is easily
filtered with small, tiny capacitors.

The reason for the large electrolytic caps is the same as the reason for
using 1 FARAD $200 capacitors in ultra-powerful automotive stereo
systems (the ones that you can FEEL when the guy whose car it's in parks
next to you). The reason is that the peak, instantaneous current
requirements of some modern CPU and video chips is tremendous. Some
Pentium 4's have peak Vcore current requirements in excess of 70 amps.
But these peaks last for nanoseconds or microseconds. The power
supplies, by themselves, can't supply that kind of power, and the large
electrolytic caps are present meet these demands, not to filter ripple.


Leythos wrote:

> In article <2vurf5F2rc889U1@uni-berlin.de>, me@privacy.net says...
>
>>It should be clear that the difference between Vin and Vout directly
>>and linearly impacts heat dissipation in the device.
>
>
> You would think so, and technically, I agree that I'm wrong, but in
> practice it does not appear so. I have the same books, even the ones
> from the 80's on those devices, and they say the same thing. What I see,
> in the lab does not show what the book states.
>
> And, yes, I clearly understand that a switching PSU is more efficient
> that a linear one, that was never a question.
>
> The question is that the OP posted that a cap had burst, that the
> solution had leaked, and that he noticed no difference in operation.
> While I am wrong on in power dissipation, I'm not wrong in the
> reason/use of the caps on the board. The caps are used to filter the
> ripple out of the supply source being used on the board. Since the cap
> has not caused any noticeable difference, it's safe to assume that the
> cap is Open and not shorted, that he could remove it without any change
> in current operation, and that it most likely has nothing to do with a
> switching power circuit on the board.
>
>

 

[mm]

Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

"Leythos" <void@nowhere.org> wrote in message
news:MPG.1c06da7b78658b87989a86@news-server.columbus.rr.com...
>
> If you are going to make a statement that the LM7805 can not operate at
> 5V providing 500MA in a stable configuration with a supply voltage of +
> 24V then you ought to be able to prove it.

I haven't made this statement. I believe it will work in a room temperature
with an adequate heatsink. Are you happy now? However, using a linear
regulator this way is generally a bad design practice these days unless
there are very strong reasons for it.

I think we should stop here. This is way OT for this newsgroup. It should be
moved to the sci.electronics.basics should you wish to continue.

/MM

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <419D4570.50807@neo.rr.com>, WatzmanNOSPAM@neo.rr.com says...
> Leythos, you are just totally wrong, and have no understanding of how
> these parts work.

Um, lets see - build 24V DC output, connect to basic LM7805 circuit,
load to 500MA, leave loaded and running for weeks. Leave DVM connected
to PC tracking output in 30 second intervals over 12 hour period, record
shows stable output at each point - logged data represents real world
experience.

So, what part am I missing? It seems to me that while no one here is
arguing the specs, the physics behind it, or the heat, that what you are
failing to understand is that it's working, running fine, and has worked
for many years. I can't make it any simpler for you, it just works!


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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

Linear regulators (eg Series 80nn) MAY waste huge amount of power
(power means watts or volt-amps or whatever you understand)..under
several situations.

If the diff. between Vin and Vout is significant...I'l use the text
book case where it specifies that Vin should be at least 3 volts over
the desired Vout.

The regulation can and will generate tons of heat...but this is reated
to the current (A) being drawn by the load connected to Vout.

If, forexample, you use a TO-220 package 7805 regulator, and feed it
say 9volts and consume ~ 1A@ 5Volts...you'll feel some real heat!!!

That's why the databooks indicate heatsink requiremnets and so
forth...Linear regulators...under real load...are not very efficient
and the lost efficiency makes heat!!







On Tue, 16 Nov 2004 16:34:53 GMT, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk> wrote:

>
>"Leythos" <void@nowhere.org> wrote in message
>news:MPG.1c03ee1a9bee7388989a69@news-server.columbus.rr.com...
>> In article <MPG.1c03e7d2c54a749989a68@news-server.columbus.rr.com>,
>> void@nowhere.org says...
>> > In article <VQomd.194$im.132@newsfe5-gui.ntli.net>,
>> > rogerspamignored@ttelmah.demon.co.uk says...
>> > > Do you understand how a linear regulator works?.
>> >
>> > Yea, I if I take the 7812, 7805, LM317, etc... regulator device, and
>> > look in my Linear data book, it's the same as it's been since the
>80's.
>> > The device does not disapate heat or waste anything to provide the
>> > specified power from the supply voltage.
>> >
>> > I don't see it as disapating anything to provide the drop to the
>> > requested level, I see it disapating heat to provide the X volts at y
>> > MA, through the circuit. The drop doesn't generate the heat, the load
>on
>> > the regulator does.
>It is the product of the current, and the voltage drop.
>
>> One thing to keep in mind, the OP said the cap was blown and in my
>> experience, if it was part of the switching power circuit, it would
>> almost certainly mean problems for his system.
>>
>> Since he's not having any problems with it, then it must be OPEN and not
>> shorted and certainly not doing it's job. This leads me to believe that
>> it's just for filtering ripple on the board at some critical point that
>> requires flat voltage levels.
>>
>> One last thing, if I setup a 7805 or LM317 regulator, and supply it with
>> 12VDC and set the output to 5V, the heat generated under a 1A load is no
>> different than when I supply it with a 24VDC input.
>You really don't understand it do you. On a 1A load from a 12v input, a
>7805, will have to dissipate 7W. From a 24v supply, it'll have to
>dissipate 19W. The heat most definately _is_ different.
>
>

 

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

In article <305im6F2taohgU1@uni-berlin.de>, mbmsv@yahoo.com says...
> I believe it will work in a room temperature
> with an adequate heatsink.

I agree.

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Archived from groups: alt.comp.periphs.mainboard.asus (More info?)

I suspect that what you think is happening, really isn't.

If you are getting 5 volts from a 7805 whose input is 24 volts, there is
19 volts across the 7805. That's not speculation or theory -- it's
simple physics, e.g. it's both theory AND real-world practice.

If you are pulling 500ma through ANY device with 19 volts across it,
it's GOING to dissipate 9.5 watts. Again, that's not speculation or
theory -- it's simple physics, e.g. it's both theory AND real-world
practice.

You can't dissipate 9.5 watts in a device the size of a 7805 without
some serious thermal considerations (and you may not be able to do it at
all, period).

My suggestion is that either the voltage or the current are not what you
say they are (or even believe that they are), or that you are just
making this up and have not really tried it.

[which, among other things, leaves me wondering if you know how to use a
multi-meter, especially to measure current]


Leythos wrote:

> In article <419D4570.50807@neo.rr.com>, WatzmanNOSPAM@neo.rr.com says...
>
>>Leythos, you are just totally wrong, and have no understanding of how
>>these parts work.
>
>
> Um, lets see - build 24V DC output, connect to basic LM7805 circuit,
> load to 500MA, leave loaded and running for weeks. Leave DVM connected
> to PC tracking output in 30 second intervals over 12 hour period, record
> shows stable output at each point - logged data represents real world
> experience.
>
> So, what part am I missing? It seems to me that while no one here is
> arguing the specs, the physics behind it, or the heat, that what you are
> failing to understand is that it's working, running fine, and has worked
> for many years. I can't make it any simpler for you, it just works!
>
>