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'[EE:] How do you create and understand circuits?(i'
2007\01\28@180504 by Alexandre Guimar„es

face picon face
Hi, dave

> Mostly, I agree.  I tend to put power and ground where I can show the
> bypass
> caps connected there, so that I'm conveying that information to the layout
> guy. In general, I'm more picky than most on bypassing, but I get better
> results. :)  Would you believe in connecting three points 0.2" apart with
> 0.1" trace, I can get a 2dB improvement in switcher output noise by
> connecting them in the right order, as opposed to a triangular "blob" that
> connects all three?

   Can you comment a little more on this ? Sounds quite interesting....

Best regards,
Alexandre Guimaraes

2007\01\28@185032 by peter green

flavicon
face

> Currently I turn on pinswappability in eagle and munge the PCB, but
> the schematic comes out ... extremely icky.  

my way arround this for interchangable pins is to draw the schematic then if there is an issue where i'd like to swap pins i just go back to the schmatic and make the change there then update the pcb file from the schematic (you can certianly do this in altium i dunno about other packages).



2007\01\28@185637 by David VanHorn

picon face
> Would you believe in connecting three points 0.2" apart with
> > 0.1" trace, I can get a 2dB improvement in switcher output noise by
> > connecting them in the right order, as opposed to a triangular "blob"
> that
> > connects all three?
>
>    Can you comment a little more on this ? Sounds quite interesting....


In this particular case, I was dealing with the output of a 300kHz switcher.
The node in queston connected the output diode, an electrolytic cap, and an
inductor, which fed the next stage.  I knew that routing it in the order of
diode-cap-inductor was best, and diode-inductor-cap would be worse, but I
was curious what the "blob" would be.  So, I waited till the boards came
back, and pulled the traces off one and made the blob with braid and
solder.  I checked the noise on the output of the supply with a spectrum
analyzer, on the same board, before and after.  2dB worse for the blob.

There was a small value cap right across the electrolytic terminals,
probably a 0.1, but I don't remember for sure.

2007\01\29@083035 by olin piclist

face picon face
Vasile Surducan wrote:
> And what's hapening if Q3 drain-source or Q3 internal diode is short
> circuiting....

I thought it would be good to let the beginners have a crack at it before
the experts start commenting.

But you're talking about a different part of the circuit and a different
issue altogether than circuit analysis.  A failure is a failure, and circuit
operation can not be guaranteed when a part fails.  This product isn't a
critical system, so it's OK for it to stop working correctly when something
breaks.

> Are you always believe into the OTG USB power supply as current
> limiting ?

No, I don't.  But it is it's own job to protect itself if my device draws
more power than it is supposed to.  That might mean current limiting, but
could also mean a polyfuse, a real fuse, or just be able to tolerate all the
current my device can draw.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2007\01\29@094805 by Wouter van Ooijen
face picon face
>  And what's hapening if Q3 drain-source or Q3 internal diode is short
> circuiting....
> :)
> Are you always believe into the OTG USB power supply as
> current limiting ?
> (like it should...)

if either shorts *and* USB is not current limited you have a two-fail
situation, one component failure and one design failure. If you want to
be robuust against that you should also consider more weird (but
single!) failures, like USB power is >48V, and/or has its polarity
reversed. You can't design against all combinations of failures...

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\01\29@103406 by Wouter van Ooijen

face picon face
> A good start might be to explain the sub-circuit of R2, D3,
> C2, and Q1 near
> the center of page 1.  What does it do?  Why is it needed?  
> Explain its
> detailed operation.  What does each part do?

That's a good example of a common pattern. Once you have identified all
the common patterns you can start to wonder why those patterns are
present, and why this particular pattern implementation was choosen
instead of a different implementation (which is also present on that
same page).

But IMHO a real beginner should not start with this level of complexity.
Start with a good textbook, and read read read it. H&H is the 'default'
choice, but their might be others and even better ones. Once you have
learned the common patterns you can start with a circuit like this page.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\01\29@110749 by Vasile Surducan

face picon face
On 1/29/07, Wouter van Ooijen <spam_OUTwouterTakeThisOuTspamvoti.nl> wrote:
> >  And what's hapening if Q3 drain-source or Q3 internal diode is short
> > circuiting....
> > :)
> > Are you always believe into the OTG USB power supply as
> > current limiting ?
> > (like it should...)
>
> if either shorts *and* USB is not current limited you have a two-fail
> situation, one component failure and one design failure. If you want to
> be robuust against that you should also consider more weird (but
> single!) failures, like USB power is >48V, and/or has its polarity
> reversed. You can't design against all combinations of failures...

No you can't. But at least you should try.
USB power greater than 48V could be found only in software...
:)

Vasile

2007\01\29@115711 by Mark Rages

face picon face
On 1/29/07, Wouter van Ooijen <.....wouterKILLspamspam@spam@voti.nl> wrote:
> >  And what's hapening if Q3 drain-source or Q3 internal diode is short
> > circuiting....
> > :)
> > Are you always believe into the OTG USB power supply as
> > current limiting ?
> > (like it should...)
>
> if either shorts *and* USB is not current limited you have a two-fail
> situation, one component failure and one design failure. If you want to
> be robuust against that you should also consider more weird (but
> single!) failures, like USB power is >48V, and/or has its polarity
> reversed. You can't design against all combinations of failures...
>
> Wouter van Ooijen
>

USB power is not guaranteed to be current-limited.  On my computer, it
is tied directly to the +5V rail.  If you draw more than about 30
amperes, the computer will reset.

I have thought before that it would be nice for the PICkit 2 to have a
polyfuse.  This occured to me when I was changing that SOT23 diode.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2007\01\29@120548 by gacrowell

flavicon
face
> I want a schematic drawing utility where I can move the pins around
> after it's drawn.  Logical pin grouping is fine, but I'd also like
> to have some clue when I'm drawing a schematic just HOW BAD the
> resulting PCB layout is going to be (especially when dealing with
> pins basically interchangeable, like uC output pins...)

I create a lot of library parts for other people, and always waffle over
how best to organize symbol pins for the best schematic organization.  I
occasionally wind up creating and including 'alternate' symbols and let
the designer decide - in PCAD its easy to swap in an alternate.

But we are also slowly changing over to Altium Designer 6.  It has the
feature that allows symbol pin positions to be altered at the schematic
level.  In the demos, and, so far, in our limited practical experience
with it, it seems to work well.  

Gary Crowell, PE CID+
Micron Technology

2007\01\29@124323 by David VanHorn

picon face
>
>
> USB power is not guaranteed to be current-limited.  On my computer, it
> is tied directly to the +5V rail.  If you draw more than about 30
> amperes, the computer will reset.


Well, right you are!
http://www.ce-mag.com/archive/03/ARG/mikolajczak.html  (and other sources)

The USB specification states that current limiting, power switching, or both
may be required in a USB product, as shown in Table I. Where current
limiting is required, the UL 60950 specifications must be met. This means
that in the event of a short circuit or other fault condition, current
output must be limited to below 5 A within 60 seconds. The USB specification
also defines acceptable voltage output levels and limits total voltage drop
in the system.

2007\01\29@130459 by Mark Rages

face picon face
On 1/29/07, David VanHorn <dvanhornspamKILLspammicrobrix.com> wrote:
> >
> >
> > USB power is not guaranteed to be current-limited.  On my computer, it
> > is tied directly to the +5V rail.  If you draw more than about 30
> > amperes, the computer will reset.
>
>
> Well, right you are!
> http://www.ce-mag.com/archive/03/ARG/mikolajczak.html  (and other sources)
>

I think you mean "wrong you are."

Perhaps I should complain to my computer's manufacturer. (IBM, er,
Lenovo) Or maybe resetting the computer is their implementation of
current-limiting.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2007\01\29@134029 by David VanHorn

picon face
>
> > Well, right you are!
> > http://www.ce-mag.com/archive/03/ARG/mikolajczak.html  (and other
> sources)
> >
>
> I think you mean "wrong you are."
>
> Perhaps I should complain to my computer's manufacturer. (IBM, er,
> Lenovo) Or maybe resetting the computer is their implementation of
> current-limiting.


Well, I would think that the USB port should do the current limiting, but it
looks like the spec puts the burden on the device, not the bus.

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