Power supply, but no power???
U. Cortez
replaced it with a new 350W ATX PSU. After removing the burnt psu, I
screwed the new psu into the case, hooked the ATX power supply to the
motherboard, and hooked up power for various components (HD's,
CD-ROM's). The motherboard's pilot light turns on to signify that it's
getting power, but when I press the case's power button... nothing. No
fans, no sound, no disk spinning, no signs of life at all (besides that
pilot light being on). Am I forgetting something?
I inspected all the components (and the motherboard and cpu) and none
of them appear (or smell) to have been damaged.
Where do I go from here? Any help would be appreciated.
Motherboard: DFI AK70 (AMD 750 cpu).
-U.
PS, forgive the cross-post -- I don't have a news host and google is
giving me errors when I try to post to some of these groups
individually.
Wes Newell
> I believe a power surge toasted my power supply the other day, so I
> replaced it with a new 350W ATX PSU. After removing the burnt psu, I
> screwed the new psu into the case, hooked the ATX power supply to the
> motherboard, and hooked up power for various components (HD's,
> CD-ROM's). The motherboard's pilot light turns on to signify that it's
> getting power, but when I press the case's power button... nothing. No
> fans, no sound, no disk spinning, no signs of life at all (besides that
> pilot light being on). Am I forgetting something?
>
> Where do I go from here? Any help would be appreciated.
>
Double check the power button plug is plugged into the proper pins. If it
is and it still doesn't work, unplug it and short the 2 power button pins
on the MB for a second. It should turn on power. If not, then it may be a
bad MB or bad PSU. If it does come on that way, then the problem is in the
leads to, or the power button itself.
--
Abit KT7-Raid (KT133) Tbred B core CPU @2400MHz (24x100FSB)
My server http://wesnewell.no-ip.com/cpu.php
Verizon server http://mysite.verizon.net/res0exft/cpu.htm
w_tom
fact. What inside the power supply is blackened? However if
just assuming it was some surge and if assuming it was the
power supply, then you have much to learn. The power supply
'system' is many components. A power supply is only one
part. You could swap things forever until something works.
Or discover in but two minutes what is and is not damaged.
Procedures and concepts are provided in two previous posts:
"Computer doesnt start at all" in alt.comp.hardware on 10
Jan 2004 at
http://tinyurl.com/2t69q and
"I think my power supply is dead" in alt.comp.hardware on 5
Feb 2004 at
http://tinyurl.com/yvbw9
Just because a light is on does not mean sufficient voltage
is available. Lights can illuminate; fans spin; and still the
power supply is not working. But then a power supply might
shutdown because something else is defective. There is no
faster analysis than using a 3.5 digit multimeter. Two
minutes should suggest what is defective. Furthermore,
numbers that mean nothing to you could be the 'smoking gun'
solution for those with better knowledge. Without numbers,
you cannot tap the best sources on the other side of your
computer screen.
U. Cortez
> If the power supply is toasted, then you have an important
> fact. What inside the power supply is blackened? However if
>just assuming it was some surge and if assuming it was the
> power supply, then you have much to learn.
Yes, I know the PSU is toasted. Whether or not anything else is
damaged is what I don't know. I haven't bothered opening up the power
supply itself... and other than recognizing what resistors and
capacitors are, I'm not real familiar with the components _within_ a
psu. I don't know what caused the problem, but the circuit breaker was
thrown for the entire room (not only did computer shut down, all the
lights and clocks turned off, etc). However, it wasn't a brown- or
black-out.
> There is no faster analysis than using a 3.5 digit multimeter.
> Two minutes should suggest what is defective.
That'll be my next step. Thanks for the info.
pobo88
> On Thu, 07 Apr 2005 13:28:25 -0700, U. Cortez wrote:
>
> > I believe a power surge toasted my power supply the other day, so I
> > replaced it with a new 350W ATX PSU. After removing the burnt psu, I
> > screwed the new psu into the case, hooked the ATX power supply to the
> > motherboard, and hooked up power for various components (HD's,
> > CD-ROM's). The motherboard's pilot light turns on to signify that it's
> > getting power, but when I press the case's power button... nothing. No
> > fans, no sound, no disk spinning, no signs of life at all (besides that
> > pilot light being on). Am I forgetting something?
> >
> > Where do I go from here? Any help would be appreciated.
> >
> Double check the power button plug is plugged into the proper pins. If it
> is and it still doesn't work, unplug it and short the 2 power button pins
> on the MB for a second. It should turn on power. If not, then it may be a
> bad MB or bad PSU. If it does come on that way, then the problem is in the
> leads to, or the power button itself.
try taking all of the components out of your computer and runniong the
system out of the case, at least this mught remove the chance that
something is grounded.
U. Cortez
> fact. What inside the power supply is blackened?
Just for kicks, I opened up the old psu and it looks like a couple
capacitors blew. I'm not going to be all that dissappointed to see
that psu taken to the morgue, as it was old and cheap and possibly
under-powered. However, I won't be a happy puppy if my motherboard got
toasted too. I'll probably test it today and see...
-U.
w_tom
consistent with the circuit breaker tripping. Now here is
where we discover the technical knowledge of the guy who
selected that supply. Asian manufacturers have learned there
are many computer assemblers masguading as electrically
knowledgeable. So power supplies that are missing essential
functions are now dumped into the market at greater profit.
You know them by their lower price. These are functions where
were defacto standard even 30 years ago.
Any power supply that fails must not damage any other
computer part. But if the essential function was missing in
that supply, then you now may have other damage. A minimally
acceptable supply sells for about $65 full retail. Supplies
missing essential functions such as overvoltage protection
sell for less, earn greater profits for their manufacturers,
and can then cause disk drive and motherboard failure.
You have no other failures inside the computer IF the
original power supply was minimally acceptable; not selected
by a 'bean counting' computer assembler.
Wes Newell
> Any power supply that fails must not damage any other
> computer part. But if the essential function was missing in
> that supply, then you now may have other damage. A minimally
> acceptable supply sells for about $65 full retail. Supplies
> missing essential functions such as overvoltage protection
> sell for less, earn greater profits for their manufacturers,
> and can then cause disk drive and motherboard failure.
>
I think overload protection is a requirement for UL approval. And I've
never spent over $24 for a PSU.:-)
I've used a 600W similar to this for over a year now on my A64 system. But
it was $24 when I bought mine.
http://store.mrtechus.com/60ulapatxcop.html
DaveW
frequently happens when an inexpensive power supply unit is used in a
system. It passes the surge on to the motherboard, rather than absorb it
entirely.
--
DaveW
"U. Cortez" <goodbad...@yahoo.com> wrote in message
news:1112905705.1...@f14g2000cwb.googlegroups.com...
U. Cortez
the motherboard) and all the voltages were in their acceptable ranges.
So, I started to plug things back in 1 at a time, and... it all
worked! I'm typing this now on my working computer. There must have
just been a loose connection or something when I first installed my new
PSU. But when I took my computer apart (yes, I mean completely apart
-- even took the cooler off the cpu) and put it back together I must
have secured whatever was keeping it from starting up before.
So I guess the failed motherboard was a false alarm (whew!). Now the
first thing on my agenda: get a UPS so I don't have to worry about
circuit trips blowing my PSU again.
Thanks all for the help!
-U.
Franc Zabkar
<w.ne...@TAKEOUTverizon.net> put finger to keyboard and composed:
>On Fri, 08 Apr 2005 12:22:21 -0400, w_tom wrote:
>
>> Any power supply that fails must not damage any other
>> computer part. But if the essential function was missing in
>> that supply, then you now may have other damage. A minimally
>> acceptable supply sells for about $65 full retail. Supplies
>> missing essential functions such as overvoltage protection
>> sell for less, earn greater profits for their manufacturers,
>> and can then cause disk drive and motherboard failure.
>>
>I think overload protection is a requirement for UL approval. And I've
>never spent over $24 for a PSU.:-)
>
>I've used a 600W similar to this for over a year now on my A64 system. But
>it was $24 when I bought mine.
>http://store.mrtechus.com/60ulapatxcop.html
I'd be suspicious of that 600W rating. The combined output of the 3
major rails is 644W, a figure that doesn't appear to allow for proper
derating. If it's a Deer brand PSU, I'd be looking especially closely
at it. I've been stung by a 170W fake labelled as 400W.
Here are the claimed specs from the above URL:
===================================================================
ATX 600 Watt Power Supply for P4 ,PIII and AMD processor compatible
with ATX 2.03 standard.
DC Output:
+5V 50A +/-5% +3.3V 32A +/-4% +12V 24A +/-5%
-12V 1.0A +/-10% -5V 0.5A +/-10% +5Vsb 2.0A +/-5%
===================================================================
Having said the above, I'd be willing to bet that the PSU in a typical
system is never called upon to provide more than about 150W.
Until my recent experience with the fake PSU, I've always been well
served by generics. In fact, I contacted a dozen or so computer stores
in my area and was unable to find a single vendor who could supply
anything other than a generic ATX PSU. Most were selling Deers. I had
to go online to find a branded PSU.
- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
w_tom
obviously.
First, power supplies selling for $25 retail would quickly
forget that essential function. If is contains essential
functions such as overvoltage protection, then the
manufacturer would proudly note that function - and many
others. If is does not list overvoltage protection (as with
most sub $40 supplies), then it will also forget to install
overvoltage protection and many other essential functions.
Second, just not possible to sell a supply at $25 retail,
earn a profit, and include essential functions.
Third, UL only cares about you getting hurt. UL does not
care for an instant how destructive that power supply is to
any transistors. Overvoltage protection does nothing for
human safety.
Fourth, then there is the common problem with counterfeit UL
stickers. No way a $25 supply is going to include functions
considered essential even 30 years ago.
w_tom
shorted through solder mask. Example of why one does not swap
parts. You fixed (permanently or temporarily) the problem and
don't even know why it existed. In the future, get the
numbers before disassembling anything. At least we would have
a much short list of suspects. If failure is seen on meter,
then you could disconnect some things and test until the
problem is resolved. Knowing which voltage was problematic
could have also been more helpful.
Just a better way to approach the problem next time.
Historically, such intermittents tend to return slightly more
often than not.
Wes Newell
> Overvoltage protection is not required for UL approval -
> obviously.
>
If you say so.
>
> Second, just not possible to sell a supply at $25 retail,
> earn a profit, and include essential functions.
>
So, you don't think they could spent an extra 25 cents to do this in a $25
PSU. Interesting.
> Third, UL only cares about you getting hurt. UL does not
> care for an instant how destructive that power supply is to any
> transistors. Overvoltage protection does nothing for human safety.
>
Again, if you say so.
> Fourth, then there is the common problem with counterfeit UL
> stickers. No way a $25 supply is going to include functions considered
> essential even 30 years ago.
>
Well, This psu says it has overload protection, and I have no basis for
calling them liars. It's retail price is over $40, but it's sale price is
only $18. They also have a 300W unit that states it has overload
protection they sell for $9 (Retail price of $24).
U. Cortez
psu's out there that completely ignore the need for overvoltage
protection. On the contrary, there are probably some inexpensive psu's
that have the protection. While it appears that the psu that wes found
does have protection, I'd still be a little skeptical of a psu that
claims to push 600w but only cost $18. Personally, I'll stick with
name-brand psu's.
w_tom
required of power supplies. Does that $25 supply really have
overload protection? The specs are quite clear about this.
Short all outputs together and turn on power. Power supply
must not be damaged. That demonstrates overload protection
which is completely different from overvoltage protection
which, in turn, has nothing to do with UL approval.
This is basic electrical knowledge that anyone should
understand before making power supply recommendations.
Overvoltage and overload (or overpower) protection are
completely different functions. Power supplies must meet
both, and other standards such as FCC. Just another standard
that many discounted power supplies may violate to sell at
profit.
Franc Zabkar
<w.ne...@TAKEOUTverizon.net> put finger to keyboard and composed:
>On Sun, 10 Apr 2005 06:07:31 -0400, w_tom wrote:
>
>> Overvoltage protection is not required for UL approval -
>> obviously.
>>
>If you say so.
>>
>> Second, just not possible to sell a supply at $25 retail,
>> earn a profit, and include essential functions.
>>
>So, you don't think they could spent an extra 25 cents to do this in a $25
>PSU. Interesting.
In fact the additional cost can be nil. Deer PSUs have a single IC
that does it all - PWM control, PS-ON control, +3.3V regulation,
+5/+12V regulation, Power Good generation, and overvoltage sensing.
See this circuit diagram:
"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip
Franc Zabkar
<fza...@optussnet.com.au> put finger to keyboard and composed:
>On Sun, 10 Apr 2005 11:38:53 GMT, Wes Newell
><w.ne...@TAKEOUTverizon.net> put finger to keyboard and composed:
>
>>On Sun, 10 Apr 2005 06:07:31 -0400, w_tom wrote:
>>
>>> Overvoltage protection is not required for UL approval -
>>> obviously.
>>>
>>If you say so.
>>>
>>> Second, just not possible to sell a supply at $25 retail,
>>> earn a profit, and include essential functions.
>>>
>>So, you don't think they could spent an extra 25 cents to do this in a $25
>>PSU. Interesting.
>
>In fact the additional cost can be nil. Deer PSUs have a single IC
>that does it all - PWM control, PS-ON control, +3.3V regulation,
>+5/+12V regulation, Power Good generation, and overvoltage sensing.
Here is the data for an all-in-one IC (not the same as in the Deer
PSU):
http://www.systemgeneral.com/semiGP/sg6105_E.asp
w_tom
that power supply at electro-tech.narod.ru . Overvoltage
protection means something must be able to short out a (about)
25 amp output with no damage. Not a cheap component and
definitely not possible inside an Integrated Circuit.
The IC SG6105 contains many functions previously performed
by multiple chips. This is a minor cost decrease. But, for
example, the galvanic isolation necessary for some of those
functions is not inside this chip either. Things such as
optocoupler are still another separate component.
Overvoltage protection is not a part of that chip. In fact,
Intel specs demand that overvoltage protection be part of a
separate circuit.
The SG6105 does contain circuits once provided by multiple
inexpensive components. A power supply once selling for less
than $100 now costs only $65 retail. Expensive components are
still required for other and necessary functions such as
overvoltage protection. Supplies containing necessary
functions such as overvoltage protection cannot sell for $25
retail at profit. Those would be supplies dumped into the
market missing essential functions.
Franc Zabkar
finger to keyboard and composed:
> I don't see the overvoltage protection circuit anywhere in
>that power supply at electro-tech.narod.ru . Overvoltage
>protection means something must be able to short out a (about)
>25 amp output with no damage.
The chip senses all the rails, including the negative ones, and shuts
down the oscillator if there is a fault condition. No oscillator means
no output. AFAICS, there is no need to crowbar the affected rail(s).
Pins 3,4, and 6 provide the OV functions. Pin 5 is probably equivalent
in function to the OPP (over power protection) pin of the SG6105.
> Not a cheap component and
>definitely not possible inside an Integrated Circuit.
Crowbar SCRs/zeners were used in the old days with linear supplies,
but these days most supplies are switchmode. The crowbar would protect
the load from a shorted pass transistor by blowing a fuse, but IMO a
switchmode supply doesn't really need such protection, unless there is
a possibility that the OV sense circuitry itself could fail.
> The IC SG6105 contains many functions previously performed
>by multiple chips. This is a minor cost decrease. But, for
>example, the galvanic isolation necessary for some of those
>functions is not inside this chip either. Things such as
>optocoupler are still another separate component.
>Overvoltage protection is not a part of that chip. In fact,
The chip's datasheet states that the chip performs under- and
overvoltage sensing/protection, as well as overpower and short circuit
protection. The overpower pin (OPP) requires some inexpensive external
components including a diode and some passives.
>Intel specs demand that overvoltage protection be part of a
>separate circuit.
True, but I suspect Intel is just playing it safe. I have no problem
with a single-chip PSU, especially if the cost savings could be
applied to properly rated parts, particularly the capacitors, diodes,
and magnetics on the DC side.
> The SG6105 does contain circuits once provided by multiple
>inexpensive components. A power supply once selling for less
>than $100 now costs only $65 retail. Expensive components are
>still required for other and necessary functions such as
>overvoltage protection. Supplies containing necessary
>functions such as overvoltage protection cannot sell for $25
>retail at profit. Those would be supplies dumped into the
>market missing essential functions.
I don't recall seeing any such expensive components in any PC SMPS.
All the PSUs I've seen shut down the PWM controller if there is an OV
condition, but then I've only ever seen generic PSUs. What components
do the more expensive branded PSUs use?
>Franc Zabkar wrote:
>> In fact the additional cost can be nil. Deer PSUs have a single IC
>> that does it all - PWM control, PS-ON control, +3.3V regulation,
>> +5/+12V regulation, Power Good generation, and overvoltage sensing.
>>
>> See this circuit diagram:
>>
>> "LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
>> http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip
w_tom
voltage monitoring function (that is now part of the single
IC). A function completely different from the overvoltage
protection circuit - which was also in that IBM PC. Some
power supply controller failures can cause overvoltage.
Totally unacceptable 30 years ago as today. The crowbar (or
equivalent) is required today as it was 30 years ago on switch
mode power supplies. Even the Intel spec (which is only for
switch mode power supplies) says
> The overvoltage sense circuitry and reference shall reside
> in packages that are separate and distinct from the
> regulator control circuitry and reference. No single point
> fault shall be able to cause a sustained overvoltage
> condition on any or all outputs. The supply shall provide
> latch-mode overvoltage protection as defined below.
Nothing new in this requirement. However when dumping
product into a marketplace dominated by 'bean counter'
mentalities, then profits are just too great. How to suspect
a defective power supply? No long list of numerical
specification and no specific listing of overvoltage
protection? Then it is a power supply for the market of 'bean
counting' computer assemblers.
That schematic is further proof that many power supplies are
missing essential functions. Some power supplies fail and
then destroy computer peripherals. A failure directly
traceable to a human who buys on price rather than learn basic
electrical principles. In a market where so many 'experts'
don't even know how how electricity works, then many clone
computers do have $25 power supplies. When a supply fails due
to a manufacturing defect, that 'computer assembler' instead
blames disk drive and motherboard damage on mythical
transients. Why? Most don't even know what electronic part
has failed; let alone know why. Better to just blame
something mythical that others will quickly believe.
Does the power supply provide a long list of numerical
specifications? Many do not provide specs which means
essential overvoltage protection is not required. Its called
dumping. Made profitable by computer assemblers don't even
understand why component manufacturers should provide
numerical specs.
Specs from a responsible power supply manufacturer are quite
long. Abridged election from one responsible power supply
vendor whose supply could never sell for $25 retail - because
it includes essential functions:
Specification compliance: ATX 2.03 & ATX12V v1.1
Short circuit protection on all outputs
Over voltage protection
Over power protection
100% hi-pot test
Efficiency; 100-120VAC and full range: >65%
EMI/RFI compliance: CE, CISPR22 & FCC part 15 class B
Safety compliance: VDE, TUV, D, N, S, Fi, UL, C-UL & CB
Hold up time, full load: 16ms. typical
Does your power supply specifically, with numbers, make
these claims? Why not? Symptoms of a supply that does not
have these essential functions; which can create future
computer failures. Demonstrated are how those with minimal
education recommend and buy power supplies. Schematics from
Franc Zabkar only demonstrate that power supplies without
essential functions are being manufactured. Some computer
failures can be created by power supplies missing these
essential functions. Many computer assemblers may then invent
other suspects to blame. If a power supply failure coincides
with disk drive damage, then first look for a missing
overvoltage protection circuit.
Franc Zabkar wrote:
> The chip senses all the rails, including the negative ones, and shuts
> down the oscillator if there is a fault condition. No oscillator means
> no output. AFAICS, there is no need to crowbar the affected rail(s).
> Pins 3,4, and 6 provide the OV functions. Pin 5 is probably equivalent
> in function to the OPP (over power protection) pin of the SG6105.
> ...
>
> Crowbar SCRs/zeners were used in the old days with linear supplies,
> but these days most supplies are switchmode. The crowbar would protect
> the load from a shorted pass transistor by blowing a fuse, but IMO a
> switchmode supply doesn't really need such protection, unless there is
> a possibility that the OV sense circuitry itself could fail.
> ...
>
> The chip's datasheet states that the chip performs under- and
> overvoltage sensing/protection, as well as overpower and short circuit
> protection. The overpower pin (OPP) requires some inexpensive external
> components including a diode and some passives.
> ...
>
> True, but I suspect Intel is just playing it safe. I have no problem
> with a single-chip PSU, especially if the cost savings could be
> applied to properly rated parts, particularly the capacitors, diodes,
> and magnetics on the DC side.
> ...
Franc Zabkar
finger to keyboard and composed:
> Even in the very first IBM PC, power supply included that
>voltage monitoring function (that is now part of the single
>IC). A function completely different from the overvoltage
>protection circuit - which was also in that IBM PC. Some
>power supply controller failures can cause overvoltage.
>Totally unacceptable 30 years ago as today. The crowbar (or
>equivalent) is required today as it was 30 years ago on switch
>mode power supplies. Even the Intel spec (which is only for
>switch mode power supplies) says
>> The overvoltage sense circuitry and reference shall reside
>> in packages that are separate and distinct from the
>> regulator control circuitry and reference. No single point
>> fault shall be able to cause a sustained overvoltage
>> condition on any or all outputs. The supply shall provide
>> latch-mode overvoltage protection as defined below.
I understand that separating the two functions (OVS and OVP) gives
added security, but I can't see the need for a brute-force approach to
OVP. By this I mean that it is not necessary to clamp the output with
an expensive high-current zener or SCR - one can much more elegantly
achieve the same end, and still comply with Intel's spec, by turning
off the PWM controller, or by turning off its drive transistors. See
this DTK PSU which implements OVS, OVP and OPP with about $2 worth of
parts:
http://www.pavouk.comp.cz/hw/en_atxps.html
I have a 1000W minicomputer SMPS whose control module senses the
output and shuts off the oscillator in the event of an OV fault. There
are no expensive OVP parts, and this is in an SMPS that has 4 or 5
screw terminal capacitors the size of soft drink cans, stud mounted
diodes on massive heatsinks, four TO3 chopper transistors, and an AC
fan. The +5V cables (+5V @ 150A) are thick enough to start my car.
> Nothing new in this requirement. However when dumping
>product into a marketplace dominated by 'bean counter'
>mentalities, then profits are just too great. How to suspect
>a defective power supply? No long list of numerical
>specification and no specific listing of overvoltage
>protection? Then it is a power supply for the market of 'bean
>counting' computer assemblers.
Some TV sets use 130V protection zeners (eg R2M, R2KY, $1.85 retail)
on their 100-115V supply rails. These designs have no OVS. Ironically
it appears that the designers have chosen this sledgehammer approach
because it costs *less* than OVS. I'm not really comfortable with such
a design because its success depends on the failure mode of the
protection device. IME the zener always fails SC, and therefore
protects the TV, but if it fails OC (unlikely, but possible), then
there is no protection at all. Killing the oscillator would be much
safer. In fact, HV protection and beam current limiting is usually
implemented by shutting down the horizontal oscillator.
I guess a comparable analogy may be MOVs in "surge protected" power
boards. They may sacrificially absorb the first surge, but thereafter
they are useless.
> That schematic is further proof that many power supplies are
>missing essential functions.
Sorry, I don't see it. You state that the original IBM supplies had an
OVP circuit, but you don't elaborate. How exactly did they do this? I
have the original IBM AT Tech Ref Manual but it doesn't adequately
spell out the PSU spec. Can you recommend one upmarket PSU that
handles OVP by brute-forcing the output(s)?
> Some power supplies fail and
>then destroy computer peripherals.
True. I witnessed a discussion at aus.electronics where an SMPS failed
in such a manner that AC leaked into the DC side of the switchmode
transformer, causing catastrophic damage to the PC. I suggested that
an external crowbar circuit could provide protection against such
disasters but the responses were negative.
> A failure directly
>traceable to a human who buys on price rather than learn basic
>electrical principles. In a market where so many 'experts'
>don't even know how how electricity works, then many clone
>computers do have $25 power supplies.
What I find hard to comprehend is how even the upmarket ATX PSUs can
deliver their claimed power given the relative size of the components
in my 1000W SMPS. For example, when comparing the mains filter caps,
one is the size of a Coke can, the other is smaller than a C size
battery. Has technology really improved that much?
w_tom
failures and then shutdown accordingly. What happens when
controller's feedback fails? A feedback circuit that will be
discussed again below. Power supply controller outputs more
power trying to raise a voltage that never rises. IOW power
supply has output excessive and destructive voltages. Just
another reason why "separate and distinct" overvoltage
protection has been required 30 years ago as it still is
required today.
Neither you nor I care how a particular power supply meets
this 'well proven to be necessary' OVP function. We don't
even care if the function uses a simple and easily constructed
crowbar or uses something different. The point remains a power
supply must provide that defined function. Schematic from
electro-tech.narod.ru quite obviously violates the industry
requirement. It has no overvoltage protection. It
demonstrates how power supplies are sold for well under $60
retail. They forget to include essential functions such as
OVP. That supply from http://electro-tech.narod.ru is
designed to be dumped into a market driven by 'bean counter'
engineering.
Provided were numeric specs for a supply that does provide
the OVP circuit. Back to the original point. Properly
designed supply does not and can not sell for $25 retail. So
how do others sell power supplies for $25 retail? They forget
to include required and necessary functions such as
Overvoltage Protection.
Is this done by a crowbar circuit or by some other means?
Neither you nor I care. Industry standards demand that OVP
function exist for 'long proven' necessary reasons. Some
supplies do provide such functions. But these minimally
acceptable supplies cannot sell for $25 retail - again
repeating the bottom line point.
In the meantime, that DTK PSU from www.pavouk.comp.cz
violates another essential function. The power supply must
provide galvanic isolation of at least 1000 volts. Therefore
the "Feedback" circuit must contain an optocoupler or
something equivalent. The DTK PSU has no such isolation. It
violates another industry standard. And so another essential
function would be 'forgotten'.
Earlier a power supply controller would output overvoltage
because the feedback circuit failed. Controller never knew it
was outputting excessive voltage. What feedback components?
Same optocoupler that is required with galvanic isolation.
Just another missing specification to sell at $25. Again the
point. Power supplies missing essential functions and
routinely dumped into the market because so many computer
assemblers don't even have basic electrical knowledge; never
learned about galvanic isolation, overvoltage protection,
feedback current limiting, or overpower protection.
When a computer assembler looks only at power and price,
then a game of specmanship is afoot. For example, a Dell or
HP power supply may claim only 250 watts. The 'bean counting'
computer assembler then claims that is woefully too small.
And yet if the same power supply was being marketed by others
to computer assemblers, then suddenly the same supply is rated
at 375 watts. Why? They don't list the output power. Rated
is maximum power that a power supply might consume. The 'bean
counting' computer assembler then declares the HP and Dell
supplies are undersized.
It gets even more interesting. A power supply must be
completely shorted out and still must not be damaged. And yet
here are power supplies, designed for a 'bean counter' market,
that self destruct even before reaching 100% load:
http://www6.tomshardware.com/howto/02q4/021021/index.html
First thing to look for in any power supply: if the supply
manufacturer does not provide a long list of numerical specs,
then bet it is a scam. More responsible power supply
manufacturers provide numerous numerical specs. One need not
even know what those specs mean. Just having written numerical
specs is a first requirement. Manufacturer commits; says to
the 1% who know technology that this supply does provide these
functions. However a manufacturer who is dumping inferior
supplies into a market of computer assemblers must disempower
the 1%. He must provide no written specifications. Then a
knowledgeable 1% cannot warn the other 99% of a defective
product.
Welcome to a world where so many power supplies don't
provide specs and are then recommended based only on the price
and watts.
#1 requirement for a power supply: it must provide a long
list of numeric specs. If that power supply does not
specifically state overvoltage protection, then another
essential function is missing.
We care less how he provides overvoltage protection. We
care more that he claims to provide OVP. That missing
function demonstrates why so many supplies sell for only $25
and $40 full retail.
Franc Zabkar wrote:
> On Mon, 11 Apr 2005 19:35:21 -0400, w_tom <w_t...@hotmail.com> put
> finger to keyboard and composed:
> ...
>
> I understand that separating the two functions (OVS and OVP) gives
> added security, but I can't see the need for a brute-force approach to
> OVP. By this I mean that it is not necessary to clamp the output with
> an expensive high-current zener or SCR - one can much more elegantly
> achieve the same end, and still comply with Intel's spec, by turning
> off the PWM controller, or by turning off its drive transistors. See
> this DTK PSU which implements OVS, OVP and OPP with about $2 worth of
> parts:
>
> http://www.pavouk.comp.cz/hw/en_atxps.html
>
> I have a 1000W minicomputer SMPS whose control module senses the
> output and shuts off the oscillator in the event of an OV fault. There
> are no expensive OVP parts, and this is in an SMPS that has 4 or 5
> screw terminal capacitors the size of soft drink cans, stud mounted
> diodes on massive heatsinks, four TO3 chopper transistors, and an AC
> fan. The +5V cables (+5V @ 150A) are thick enough to start my car.
> ...
>
> Some TV sets use 130V protection zeners (eg R2M, R2KY, $1.85 retail)
> on their 100-115V supply rails. These designs have no OVS. Ironically
> it appears that the designers have chosen this sledgehammer approach
> because it costs *less* than OVS. I'm not really comfortable with such
> a design because its success depends on the failure mode of the
> protection device. IME the zener always fails SC, and therefore
> protects the TV, but if it fails OC (unlikely, but possible), then
> there is no protection at all. Killing the oscillator would be much
> safer. In fact, HV protection and beam current limiting is usually
> implemented by shutting down the horizontal oscillator.
>
> I guess a comparable analogy may be MOVs in "surge protected" power
> boards. They may sacrificially absorb the first surge, but thereafter
> they are useless.
> ...
>
> Sorry, I don't see it. You state that the original IBM supplies had an
> OVP circuit, but you don't elaborate. How exactly did they do this? I
> have the original IBM AT Tech Ref Manual but it doesn't adequately
> spell out the PSU spec. Can you recommend one upmarket PSU that
> handles OVP by brute-forcing the output(s)?
> ...
>
> True. I witnessed a discussion at aus.electronics where an SMPS failed
> in such a manner that AC leaked into the DC side of the switchmode
> transformer, causing catastrophic damage to the PC. I suggested that
> an external crowbar circuit could provide protection against such
> disasters but the responses were negative.
> ...
Franc Zabkar
finger to keyboard and composed:
> You are assuming a power supply controller will see all
>failures and then shutdown accordingly.
I did write that "I understand that separating the two functions (OVS
and OVP) gives added security", so I understand that there are some
caveats with a single-chip approach.
> What happens when
>controller's feedback fails?
In most cases the OVS circuitry will detect an OV condition and shut
down the oscillator. I've actually seen such faults in other PSUs, eg
when optocouplers or feedback transformers or sense resistors go OC.
One potential problem with single-chip solutions is if the internal
reference voltage is shared by both the OVS logic and the PWM
regulator. In such cases a fault in the voltage reference may cause
catastrophic damage. Having said that, it may still be possible to
separate these two functions within the same IC. In any case the DTK
circuit I alluded to *does* separate these functions and *does* comply
with Intel's spec. And it does this at the cost of a few small-signal
transistors, diodes, and passives. In fact the BOM for the OV, PG, and
PWM circuits would cost about $1 or $2.
http://focus.ti.com/docs/prod/folders/print/tl494.html
$0.23 /1000
http://focus.ti.com/docs/prod/folders/print/lm393.html
$0.16 /1000
> Neither you nor I care how a particular power supply meets
>this 'well proven to be necessary' OVP function. We don't
>even care if the function uses a simple and easily constructed
>crowbar or uses something different. The point remains a power
>supply must provide that defined function. Schematic from
>electro-tech.narod.ru quite obviously violates the industry
>requirement. It has no overvoltage protection.
It *does* have OVP. It's just that the implementation does not appear
to rigidly follow Intel's spec. For example, if I interfere with the
+5V feedback by removing R62 from pin 14, the output voltages will
rise to a point where the OVS pins (3,4,6) will trigger a shutdown of
the oscillator.
> Provided were numeric specs for a supply that does provide
>the OVP circuit.
Specs can lie, or at least be deceiving. A high price does not
guarantee quality or spec compliance.
> Is this done by a crowbar circuit or by some other means?
>Neither you nor I care.
On the contrary, I do. At the very least, knowing how a certain
function is implemented can explain any differences in price. For
example, if each of the major rails were shunted by high current SCRs
or protection zeners, then one could expect to pay a much higher
price. OTOH, if OVS and OVP were implemented with 50c ICs, then one
would not expect such functions to impact noticeably on the overall
cost.
In the absence of specific examples from you, I'm left to examine
various PSUs at this website:
Unfortunately the site is in Japanese, but there is just enough info
to ascertain the inner workings of both low-end and high-end ATX PSUs.
For example, Antec's TruePower 550 is pictured and described here:
http://terasan.okiraku-pc.net/dengen/no57/
The ICs of interest are the UC3844 PWM regulator and the TPS3510 PSU
supervisor:
http://www.st.com/stonline/books/pdf/docs/4299.pdf
http://focus.ti.com/lit/ds/symlink/tps3510.pdf
The costs are:
http://focus.ti.com/docs/prod/folders/print/tps3510.html
$0.45 /1000
http://focus.ti.com/docs/prod/folders/print/uc3844.html
$0.80 /1000
The TPS3510 IC implements OVS, UVS, OVP, UVP, and PG. I suspect its
Fault Protection Output pin controls the UC3844 regulator. There
appear to be no other OVP parts.
Another manufacturer, PC Power & Cooling, uses the TPS5510 supervisor
IC in its Turbo-Cool 450ATX:
http://terasan.info/dengen/no041/
http://focus.ti.com/lit/ds/symlink/tps5510.pdf
>Industry standards demand that OVP
>function exist for 'long proven' necessary reasons. Some
>supplies do provide such functions. But these minimally
>acceptable supplies cannot sell for $25 retail - again
>repeating the bottom line point.
That may be true, but if we were to use your definition of OVP, then
some, if not all, branded PSUs do not provide this function either.
> In the meantime, that DTK PSU from www.pavouk.comp.cz
>violates another essential function. The power supply must
>provide galvanic isolation of at least 1000 volts. Therefore
>the "Feedback" circuit must contain an optocoupler or
>something equivalent. The DTK PSU has no such isolation. It
>violates another industry standard. And so another essential
>function would be 'forgotten'.
The regulator and the feedback circuit exist on the same side of the
PSU, ie on the DC side. Therefore no "galvanic isolation" is required
between the two. In any case, isolation between the AC and DC sections
is provided by transformers, at least when high currents are involved.
AFAICS, cheap optocouplers are only used in the 5VSB circuit, if at
all. In the DTK case, no special feedback is required in the 5VSB
section because the 78L05 linear regulator doesn't require it. OTOH,
the LC-B250ATX uses an optically isolated TL431 voltage reference to
achieve the same end. The Antec Truepower PSUs appear to do it this
way, too. All three PSU designs are "galvanically isolated" where
needed.
> When a computer assembler looks only at power and price,
>then a game of specmanship is afoot.
That works both ways. Ignorant people assume that a higher price means
higher quality. They have never heard of "badge engineering". That's
where an up-market vendor/manufacturer rebadges a down-market product
and extracts a price premium by leveraging his reputation rather than
his technical expertise.
>For example, a Dell or
>HP power supply may claim only 250 watts. The 'bean counting'
>computer assembler then claims that is woefully too small.
>And yet if the same power supply was being marketed by others
>to computer assemblers, then suddenly the same supply is rated
>at 375 watts. Why? They don't list the output power. Rated
>is maximum power that a power supply might consume. The 'bean
>counting' computer assembler then declares the HP and Dell
>supplies are undersized.
I have to agree. In fact my own measurements lead me to believe that
typical Athlon and P4 systems will never draw more than 150W.
> It gets even more interesting. A power supply must be
>completely shorted out and still must not be damaged. And yet
>here are power supplies, designed for a 'bean counter' market,
>that self destruct even before reaching 100% load:
> http://www6.tomshardware.com/howto/02q4/021021/index.html
The first thing that caught my eye was this:
"We've ... now decided to tackle this volatile subject with testing of
21 different, high-end power supplies in the THG lab in Munich,
Germany. In spite of the high end-user retail prices, our lab
technicians were surprised by the test results. No fewer than 6 power
supplies struggled under full load: 3 of the candidates simply went up
in smoke, while the other 3 shut down prematurely."
It seems that price, specs and reputation are no guarantee of
performance. ;-)
This also caught my eye:
"Our attempt to test the Noise Magic power supply had disastrous
consequences. This is a modified Enermax unit fitted with a Papst fan.
It stopped working after one minute. When we tried to switch it back
on again after a suitable delay, it simply burned out."
I would have thought that even a badge engineered Enermax was not a
"bean counter's" PSU ;-)
Anyway, you have introduced a new subject, namely overload protection.
OVP is cheap to implement, but sensing current is more difficult than
sensing voltage, so I would expect that many manufacturers would take
shortcuts here. The aforementioned LC and DTK PSUs both sense a
voltage at the drive transformer, whereas other PSUs monitor the
current flow in the chopper transistor(s). I'm not sure that's the way
the Antec 550W PSU does it, but its UC3844 PWM controller *does* have
a current sense pin. The application circuit shows this pin connected
to a current transformer. My 1000W minicomputer PSU also uses a
current transformer in the chopper circuit to indirectly sense the
load current. I suspect that the OPP circuits in cheaper PSUs (such as
the LC and DTK) would be able to respond correctly to dead shorts, but
not necessarily to overloads.