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'[EE:] Power Supplies'
2004\04\21@234737 by Robert B.

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I'm getting pretty sick of my LM317 adjustable power supply I cobbled
together when I first started with PICS, and am getting the urge for
something a bit more substantial (read "more than 100mA output.  I don't
have much $ to blow on a fancy lab bench supply, and I really only need
+5,+12 volts.  What do most of you guys use as a basic power supply for
cheap?

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2004\04\22@001303 by onio (Nino) Benci

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What you can do is upgrade the LM317 design for a more substantial one
using an LM338, adjustable with 5A capability. I have built 100's (yes
100's) of units using this device for student bench supplies and have
had less than a dozen returned with blown regulators. At full current
and max Vin to Vout differential you will need a substantial heatsink.

Good luck.

PS: Check out the NatSemi WWW site fo more app data.

Nino Benci.

Robert B. wrote:

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2004\04\22@001310 by Mike nicholas

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Couldnt you use an old computer power supply, as far as I know the outputs
are 5v and 12v.
----- Original Message -----
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To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Wednesday, April 21, 2004 8:48 PM
Subject: [EE:] Power Supplies


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2004\04\22@012801 by Robert B.

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I thought about that.. but i'm a little afraid to try it out since I don't
have a clue what's inside a PC power supply.  I have an old one for a P3
laying around somewhere with a burned out fan...


{Original Message removed}

2004\04\22@024353 by William Chops Westfield
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On Wednesday, Apr 21, 2004, at 21:29 US/Pacific, Robert B. wrote:

>>>  I don't have much $ to blow on a fancy lab bench supply

Just how much do you have to spend?  For between $50 and $100 you can
get a pretty nice bench supply, with meters.  I've found my bench
supply to be unexpectedly useful; having voltage and current meters is
like having an extra two DMMs that are always connected, and can keep
you
somewhat out of trouble.  (see that little pic circuit start to draw
an amp of current?  Something's wrong!)  Also charges batteries, runs
hot wire cutters, shows motor run characteristcs, tests LEDs, and zaps
NiCds..

www.bgmicro.com/prodinfo.asp?prodid=PWR1166
http://www.elexp.com/tst_3003.htm
http://www.elexp.com/tst_1802.htm

BillW

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2004\04\22@025426 by Robert B.

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Most of the bench supplies I've seen have been well over $100.  $50 I would
definitely go for.  For now I dug out an old atx power supply as someone
suggested and converted it to a $0.00 net +5/+12 supply.  I think I might
have cut off the - wires on accident, but oh well.  It doesn't have a fan so
it will probably melt someday and burn down my house.... all for saving a
measley $50.  Such is life.


{Original Message removed}

2004\04\22@031132 by William Chops Westfield

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On Wednesday, Apr 21, 2004, at 23:54 US/Pacific, Robert B. wrote:

> $50 I would definitely go for.
>

http://www.elexp.com/tst_1802.htm is $58 (plus postage/etc.  sigh.)

You have some leeway in your lm317 design.  Should be good for at least
500mA with a heatsink.

I'm starting to be a fan of wall warts of assorted types.  They can
usually be plucked out of the trash.  Some aren't regulated at all, but
others deliver the same sort of convenient voltages as a PC supply in a
much nicer package...

BillW

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2004\04\22@105346 by Herbert Graf

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> I'm getting pretty sick of my LM317 adjustable power supply I cobbled
> together when I first started with PICS, and am getting the urge for
> something a bit more substantial (read "more than 100mA output.  I don't
> have much $ to blow on a fancy lab bench supply, and I really only need
> +5,+12 volts.  What do most of you guys use as a basic power supply for
> cheap?

       I've done the same for the longest time, but finally settled and bought a
cheap bench power supply:

www.bgmicro.com/prodinfo.asp?sid=0410497685185185659563113&prodid=PWR
1166&page=3&cri=power+supply&stype=3&time_out=19:33

or
http://makeashorterlink.com/?B17025918

       It's a great little supply, and has done all I've needed it to do. Thanks,
TTYL


----------------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

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2004\04\22@114200 by Byron A Jeff

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On Thu, Apr 22, 2004 at 12:03:52AM -0700, Mike nicholas wrote:
> Couldnt you use an old computer power supply, as far as I know the outputs
> are 5v and 12v.

A couple of caveats though. The primary one is that a substantial load is
required in order to get the supply into regulation. Tie (and heatsink) a 25W
8 ohm power resistor across the +5 supply line. That should force enough
current to stabilize the supply.

The other is that if it's a current ATX supply you'll have to figure out
how to switch it to get it to work. See the MB actually controls powering
up and down the supply, not the switch on the panel. Ideally you want to get
one that has an on/off switch on the supply itself.

BAJ

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2004\04\22@120654 by Rick C.

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Try going to a hamfest and picking up a good used three-output lab supply
with meters and current limiting. I picked one up for $5. Sometimes you can
get some real bargains on used stuff. With the summer season upon us in the
US, there's a hamfest (electronics flea market) almost every weekend within
driving distance. Who knows what else you can pick up. You can check the
ARRL website for a hamfest in your area.
Rick
http://www.arrl.org/hamfests.html

"Robert B." wrote:

> I'm getting pretty sick of my LM317 adjustable power supply I cobbled
> together when I first started with PICS, and am getting the urge for
> something a bit more substantial (read "more than 100mA output.  I don't
> have much $ to blow on a fancy lab bench supply, and I really only need
> +5,+12 volts.  What do most of you guys use as a basic power supply for
> cheap?
>
> -

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2004\04\22@121729 by Denny Esterline

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> A couple of caveats though. The primary one is that a substantial load is
> required in order to get the supply into regulation. Tie (and heatsink) a
25W
> 8 ohm power resistor across the +5 supply line. That should force enough
> current to stabilize the supply.
>

Right idea, wrong value. 8 ohms on a 5 volt rail will only pass 600mA,
about 3 watts. Generaly PC power supplies need about 30% of the rated load
on the lowest output voltage to produce regulation. The one I have here is
rated for 18 amps on the 5V rail so you would need about a 1 Ohm reistor
(or slightly less) to force it into regulation.

Newer ATX supplies need the draw on the the 3.3 volt rail. 0.5 to 1 ohm
should suffice here.

> The other is that if it's a current ATX supply you'll have to figure out
> how to switch it to get it to work. See the MB actually controls powering
> up and down the supply, not the switch on the panel. Ideally you want to
get
> one that has an on/off switch on the supply itself.
>
> BAJ

ATX is easy enough to power up. There should be one green wire, short it to
any black (ground) wire and the supply should power up just fine. (mine
does :o)

-Denny

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2004\04\22@121730 by hael Rigby-Jones

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{Quote hidden}

The last bit is easy, you simply ground the green wire going to the main
connector to switch the supply on.

Regards


Mike




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2004\04\22@182528 by llile

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I always build 'em, usually in desperation when the old one quits.

The last one I built I put in a canned 5V open frame power supply, rated
maybe 5 amps, and a 0-24V supply built up out of a 24V 2 amp transformer,
a PIC, a FET chopper arranged into a regulator.  The output is metered
with a DC digital voltmeter, and slew controls run the voltage up and
down.  The slew controls just adjust the digital setpoint of the PIC
regulator.

It is not very sophisticated but it has served well for a while.  I have
one half built that will do +70VDC, but haven;t needed it bad enough to
finish it yet.

I have a high current version at home that started out life as a battery
charger.  Makes a nice cheap chassis.

-- Lawrence Lile





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04/22/2004 09:52 AM
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       Subject:        Re: [EE:] Power Supplies


> I'm getting pretty sick of my LM317 adjustable power supply I cobbled
> together when I first started with PICS, and am getting the urge for
> something a bit more substantial (read "more than 100mA output.  I don't
> have much $ to blow on a fancy lab bench supply, and I really only need
> +5,+12 volts.  What do most of you guys use as a basic power supply for
> cheap?

       I've done the same for the longest time, but finally settled and
bought a
cheap bench power supply:

www.bgmicro.com/prodinfo.asp?sid=0410497685185185659563113&prodid=PWR
1166&page=3&cri=power+supply&stype=3&time_out=19:33

or
http://makeashorterlink.com/?B17025918

       It's a great little supply, and has done all I've needed it to do.
Thanks,
TTYL


----------------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

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2004\04\22@182945 by llile

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Ah yes, you must have meters!

Once I was working on a CB, and hit the transmit button, and noticed the
output power was suddenly 15 watts.  5 Watts is all that is legal, and it
had just measured 5 watts a few minutes before.  Puzzled, I looked over at
my DC power supply, and noted that the meter on the front was pegged at
over 50 volts!  Luckily I reached for the big switch with my right arm,
which shielded my face from the explosion that came out of the CB radio
about 5 seconds later.

Pass transistor failed shorted, you know.


-- Lawrence Lile
Senior Project Engineer
Toastmaster, Inc.
Division of Salton, Inc.
573-446-5661 voice
573-446-5676 fax




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04/22/2004 01:44 AM
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On Wednesday, Apr 21, 2004, at 21:29 US/Pacific, Robert B. wrote:

>>>  I don't have much $ to blow on a fancy lab bench supply

Just how much do you have to spend?  For between $50 and $100 you can
get a pretty nice bench supply, with meters.  I've found my bench
supply to be unexpectedly useful; having voltage and current meters is
like having an extra two DMMs that are always connected, and can keep
you
somewhat out of trouble.  (see that little pic circuit start to draw
an amp of current?  Something's wrong!)  Also charges batteries, runs
hot wire cutters, shows motor run characteristcs, tests LEDs, and zaps
NiCds..

www.bgmicro.com/prodinfo.asp?prodid=PWR1166
http://www.elexp.com/tst_3003.htm
http://www.elexp.com/tst_1802.htm

BillW

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2004\04\22@220628 by David Bearrow

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This is how I built mine.

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

David Bearrow

At 10:42 AM 4/22/04, you wrote:
{Quote hidden}

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2004\04\23@031229 by Jesse Lackey

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Spend the $58 and get a current-limited supply.  That feature alone is
worth it.  I've saved many buggy boards by having the current limit trip
and not destroy a board while I figure out what's wrong.

The wall-warts I totally agree with.  I have a bin of them from misc
wherever - trash, flea markets, household electronic junk friends are
tossing, etc., and I use them all the time for one-offs I give to
clients.  You do have to watch the voltages out, but most circuits I
wind up making are 7805 @ < 200mA and its hard to go wrong.

J


William Chops Westfield wrote:
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2004\04\23@032719 by Robert B.

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Awe! But I really love the smell of melted silicon in the morning.  If all I
had to look forward to after a long bout of soldering was the click of a
current limiting power supply, I might just drop the hobby all together. :-D


{Original Message removed}

2004\04\23@033134 by Hulatt, Jon

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> -----Original Message-----
> From: Robert B. [piclistEraseMEspam.....NERDULATOR.NET]

> Awe! But I really love the smell of melted silicon in the
> morning.

IMHO you should add some GaAlAs LED's to it. When they go pop the Arsenic
stench really clears your head :)

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2004\04\24@040250 by Peter L. Peres

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> Awe! But I really love the smell of melted silicon in the morning.  If
> all I had to look forward to after a long bout of soldering was the
> click of a current limiting power supply, I might just drop the hobby
> all together.  :-D

You can always set the limit high and troubleshoot by observing the smoke
source if that's your personal style ...

Peter

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2004\04\24@040912 by Andre Thomas

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Incidently, I did this with an amplifier which was in my car... Kept on
blowing fuses so I replaced the fuse with a piece of copper wire to see
where the smoke comes from.... Replaced some mosfets and now everything
is working perfectly again :)

-----Original Message-----
From: pic microcontroller discussion list
[RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU] On Behalf Of Peter L. Peres

You can always set the limit high and troubleshoot by observing the
smoke source if that's your personal style ...

Peter

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2004\04\24@101012 by Jake Anderson

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we had a proto board that halfway through building developed a short, part
had to be out that day of course. After 3 people looked at it for half an
hour we were still no closer to finding it. Wound up pulling the valuablle
chips and connecting a 12V SLA battery across 5V and gnd, found the fault, a
tantalum cap and failed got a few choice holes burnt into the desk (i'm not
joking these are serious holes) and blew a 5v regulator (understandablly I
think, I really should have removed that too). A note to all who try this
method AIM AWAY FROM FACE. Seriously that ammount of energy and things go
pop with a bang.

{Original Message removed}

2004\04\24@111308 by Russell McMahon

face
flavicon
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> we had a proto board that halfway through building developed a short, part
> had to be out that day of course. After 3 people looked at it for half an
> hour we were still no closer to finding it. Wound up pulling the valuablle
> chips and connecting a 12V SLA battery across 5V and gnd, found the fault,
a
> tantalum cap and failed

Electronics lessons to learn the hard way.

103.    ***NEVER*** use tantalum capacitors in other than low energy high
impedance circuits if the voltage may exceed the capacitors rating for any
period of time. Here the word "any" assumes the normal meaning. eg a 1 uS
pulse is included in the period "any of the time".

A power supply rail is never a low energy high impedance circuit.

104.    *** NEVER *** listen to people trying to assure you that rule 103 is
bunkum.

105    Tantalum capacitors belong to the common class of electronic
components which contain crisis detectors. These allow them to detect when
the worst possible time to fail will be and to act accordingly.

__________________

Tantalum capacitors are great fun. I have seen one, in sequence:

- smell terrible
- emit smoke
- emit a jet of flame
- shriek loudly
- explode
- short the power supply rail.

Solid aluminium capacitors (NOT common Al electrolytics) are much more
boring. Apart from having about the same capacitance for size as Tantalum
caps, they lack all the interesting features.

YMMV but only in terms of what combination and sequence of events will
happen to you.



       RM

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2004\04\24@200453 by Jake Anderson

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I was just following the spec sheet for the $160 A/D chip I figure if they
feel they can charge $160 for a chip they know a bit more about stuff than
little old me lol.

All the rest of my power supply caps were electrolytic or ceramic.

{Original Message removed}

2004\04\25@195827 by Russell McMahon

face
flavicon
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> > Electronics lessons to learn the hard way.
> >
> > 103.    ***NEVER*** use tantalum capacitors in other than low energy
high
> > impedance circuits if the voltage may exceed the capacitors rating for
any
> > period of time. Here the word "any" assumes the normal meaning. eg a 1
uS
> > pulse is included in the period "any of the time".
> >
> > A power supply rail is never a low energy high impedance circuit.
> >
> > 104.    *** NEVER *** listen to people trying to assure you that
> > rule 103 is
> > bunkum.
> >
> > 105    Tantalum capacitors belong to the common class of electronic
> > components which contain crisis detectors. These allow them to detect
when
> > the worst possible time to fail will be and to act accordingly.
> >


Comment on this from my friend Ken who has extensive manufacturing
experience.


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2004\04\25@195827 by Russell McMahon

face
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>> 103.    ***NEVER*** use tantalum capacitors in other than low energy high
>> impedance circuits if the voltage may exceed the capacitors rating for
any
>> period of time. Here the word "any" assumes the normal meaning. eg a 1 uS
>> pulse is included in the period "any of the time".
>>
>> A power supply rail is never a low energy high impedance circuit.

> I was just following the spec sheet for the $160 A/D chip I figure if they
> feel they can charge $160 for a chip they know a bit more about stuff than
> little old me lol.
>
> All the rest of my power supply caps were electrolytic or ceramic.

I suspect that your results speak for themselves.
People who make $160 ICs probably also use laboratory grade supplies for
testing and tend to assume that you do too. Unless they specify the purity
of the supply that feeds the tantalum capacitor you have a grey area.

Tantalums often fail when applied voltage is SLIGHTLY above rated voltage.
If there is enough energy available in the line they are connected to (and
power supply lines usually qualify nicely for this) then they will make a
very hard short circuit, sometimes but not always preceded by smell, smoke,
flame and explosion. This is a very predictable feature of Tantalum
capacitors but they still seem to often be specified in this sort of
application. If you can GUARANTEE that the supply to them will NEVER exceed
their specification then they are a very nice capacitor - low impedance &
compact. Excellent filter capacitors. But even better over-voltage crowbars
:-). Solid Aluminium capacitors (not electrolytic) (available from Philips
and others) have similar performance but lack the bad features.




       Russell McMahon

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2004\04\25@211245 by William Chops Westfield

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On Sunday, Apr 25, 2004, at 16:16 US/Pacific, Russell McMahon wrote:

>>> 103.    ***NEVER*** use tantalum capacitors in other than low energy
>>> high impedance circuits if the voltage may exceed the capacitors
>>> rating for any period of time. Here the word "any" assumes the
>>> normal meaning. eg a 1 uS pulse is included in the period "any of
>>> the time".
>>>
>>> A power supply rail is never a low energy high impedance circuit.

But Mommy... EVERYBODY does it!

(Hmm.  Can you tell the difference between Solid Al and Solid Ta SMT
caps just by looking at them?)

BillW

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2004\04\25@212323 by Jake Anderson

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I was using a 35V 2.2uf cap from +5 to gnd running after a 7805 powered from
a +12 SLA. The 7805 has whatever caps the manufacturer recomends across
input and output (an electrolytic and ceramic). After we found that short
and replaced it, its been working fine for several tens of hours now (its
test equipment (acceleromiter) so it dosent get much use). Its running on a
16 bit A/D chip and there are another 2 caps on the chips 2.5 volt ref
lines. Crrently it looks like we are getting around 0 counts of noise from
the chip and 6 from the feeder circutry which is pretty good for 2 bigass
veroboard boards with a 20mhz pic nearby isnt it?
(Frst A/D project ;->)

Would the solid Al caps be good to use for bypass caps?
Is there some nice page that talks about the different kinds of caps in
something like a "caps for dummies" style with examples of use perhaps?



{Original Message removed}

2004\04\25@221930 by Gaston Gagnon

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Jake Anderson wrote:

<...>

> Is there some nice page that talks about the different kinds of caps in
> something like a "caps for dummies" style with examples of use perhaps?
>

Capacitors on bypassing.
http://www.glencoe.com/ps/ee/williamson/bypass.html#introduction

Picking Capacitors.
http://www.capacitors.com/picking_capacitors/pickcap.htm

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2004\04\25@230438 by Russell McMahon

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flavicon
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> (Hmm.  Can you tell the difference between Solid Al and Solid Ta SMT
> caps just by looking at them?)

Sure - Tantalum caps have holes, smoke marks, spattered metal, occupy a
large volume of space in a sparse manner, and smell bad :-)

Probably no, otherwise.


       RM

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2004\04\26@072749 by Alan B. Pearce

face picon face
>Spend the $58 and get a current-limited supply.  That feature alone is
>worth it.  I've saved many buggy boards by having the current limit trip
>and not destroy a board while I figure out what's wrong.

Agreed. Especially when the object you power up is someone else's. First
realisation of this came when the 8086 was the "new chip on the block" and
the local distributor had just received his demo kit. he did not have time
to build it, and I wanted to play with it, so was allowed use of it over
Christmas if I built it. When powered on the supply went into current limit.
A quick check showed no solder splashes or anything else untoward. A quick
probe around with a meter with a lot of digits showed that one of the
ceramic bypass capacitors was shorted. I found it by measuring across each
one, and looking for the lowest voltage.

Another experience was the absolute opposite of this. A new computer had
arrived, and was left running a memory test to soak test for a bit. Next
thing I got a panic call from the customer that it was on fire. again one of
the ceramic bypass capacitors on the memory board had gone short circuit,
and the 300 amp 5V supply just kept on going, as the Eveready advert says.
The result was a sizable hole burnt into the circuit board, that required
some work to patch it up - we could not send it back as it had been
purchased as a minimum memory configuration and then we had fully populated
the board ourselves, but it was one of the original components that died.

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2004\04\26@073827 by Jake Anderson

flavicon
face
ya know I'm thining i should stay away from these caps completley ;->

-----Original Message-----
From: pic microcontroller discussion list
[EraseMEPICLISTspamEraseMEMITVMA.MIT.EDU]On Behalf Of Alan B. Pearce
Sent: Monday, April 26, 2004 9:29 PM
To: @spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU
Subject: Re: [EE:] Power Supplies

<Snip>

Another experience was the absolute opposite of this. A new computer had
arrived, and was left running a memory test to soak test for a bit. Next
thing I got a panic call from the customer that it was on fire. again one of
the ceramic bypass capacitors on the memory board had gone short circuit,
and the 300 amp 5V supply just kept on going, as the Eveready advert says.
The result was a sizable hole burnt into the circuit board, that required
some work to patch it up - we could not send it back as it had been
purchased as a minimum memory configuration and then we had fully populated
the board ourselves, but it was one of the original components that died.

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2004\04\26@110300 by Shawn Wilton

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face
You're going to stay away from Ceramic capacitors?  Hrm, good luck to
you on that one... :-P


Shawn Wilton
Junior in CpE
MicroBiologist

Phone: (503) 881-2707
Email: spamBeGoneshawnspamKILLspamblack9.net

http://black9.net

Jake Anderson wrote:
> ya know I'm thining i should stay away from these caps completley ;->
>
> {Original Message removed}

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