Re: Datasheets and pin ordering

Abstract Dissonance wrote:
"Abstract Dissonance" <Abstract.Dissonance.hotmail.com> wrote in message
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Abstract Dissonance wrote:
"Abstract Dissonance" <Abstract.Dissonance.hotmail.com> wrote in message
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I just blew a adj regulator cause in the data *** the pins are orders
reading left to right 1 3 2 ;/ WTF is that?

1 = In, 3 = GND, 2 = Out..

Why not just enumerate them like everyone learns in elementary school
as
1, 2, 3,

1 = In, 2 = GND and 3 = Out?

Another issue is how to know which one is the first pin? On the same
data
*** as above they show the "top down" view but that could mean 1, 2,
3
or 3, 2, 1 considering what you call top and bottom... they do say
"bottom" next to it though. Does this mean the bottom is the "side"
with
the leads comming out?

Another *** completely omits the "top" or "bottom" reference and I
guess
leaves it up to you to guess? (this is from a different regulator and
the
pins in and out pins are actually flipped as to the first
regulator(unless
I had the first one wrong but seemed to work in that it adjed the
voltage
approximately correct(except it went below the 1.25V limit down to .9V
for
some reason ;/)

Why can't they just make it plain and simple and label the pins on the
"front" view(which is obvious cause you put the text on it)?


Jon


heres the two sheets I'm talking about:


http://www.ortodoxism.ro/datasheets/stmicroelectronics/2168.pdf

http://www.datasheetcatalog.com/datasheets_pdf/S/7/8/L/S78L08.shtml



These look ok

http://www.tranzistoare.ro/datasheets/37/54063_DS.pdf

And this one looks the best(least ambiguous)

http://www.ortodoxism.ro/datasheets/motorola/MC7809.pdf



Is there any place I can get good datasheets instead of relying on luck
to
get the pins right? Whats the reason for this crap? Laziness,
stupidity, or
they really want you to screw up some components to get it right so they
can
make more money?

The motorola doc is the only one that seems like its any good. It seems
the
graphic design engineers don't realize that pin order is important?

Jon

A trip to the optician would seem in order, or maybe your monitor is no
good, or your just plain careless. Just as well its just a cheap
regulator.


hmm... maybe you would be right but since you don't seem to offer any
reason to why I am wrong makes me think that you are just BS'ing.

If you are going to say something like that then tell me why, on the 2
sheets I gave, where it tells you the pin order unambiguously else I have
to believe you

http://www.ortodoxism.ro/datasheets/auk/S78LXX.pdf

First page under Outline Dimensions...

given that data*** determine the pin order unambiguously. If you can't
then maybe there is something wrong with your eyes? If you assume the
graphic i the lower left corner is looking at the bottom then I feel that
is a big assumption(atleast for someone that is not used to looking at
these types of graphics).

Maybe there is some standard think similar to how DIP's have the little
circle or cutout in the corner to determine the first pin but I don't see
that here.

Anyways... like I said.. if you are going to say that *** then back it up
with some factual evidence instead of just trying to say something
personal else I gotta take your argument as crap.

(and use the damn data*** for the S78LXX that I gave and not some other
one where its obvious. My problem is not with determing the pin order but
with determing the pin order from that specific data***.).


I eagerly wait your response,
Jon


oh, nevermind... sorry... didn't know you were from aol.

Hi, Jon. Sorry, but Ich Bin Ein AOLer, too. Teenage daughters, you
know. They'd just die without AOL. :-(

A couple of things come to mind here. First, the two data sheets
you're talking about _do_ happen to be perfectly correct, even if the
first isn't as clear as possible.

The first says "BOTTOM VIEW" in caps right next to the drawing of the
part. It's customary when only giving one view on a drawing to specify
the view, which they have done. The business of "1, 3, 2" is a bit of
a "gotcha", and it's definitely not as clear as, say, the National
Semiconductor data***:

http://cache.national.com/ds/LM/LM317L.pdf

where they actually have arrows going from pin descriptions to pins on
the bottom view.

The second S78LXX data *** is perfect. They give the standard three
regular views, number the pins on the bottom view, and give the pin
numbers on the functional schematic. I would suppose you might not be
too familiar with technical drawing. That's not really critical, but
you might want to just wander through a high school technical drawing
book when you get a chance, and get up to speed. The pinout is just
bass-ackwards from the TO-220 pinout you're familiar with.

Look. I've smoked both the TO-92 78LXX (plugged it in backwards) as
well as an LM317CT (circuit layout IN-ADJ-OUT-BOOM). When I did that
with the LM317, though, they were going for about 10 times as much in
today's dollars.

The problem with the drawings is that they aren't what you expect.
That can be a problem with datasheets. Very rarely, you'll find an
error. Sometimes, you'll find something that isn't very clear. That's
more common.

But you need some perspective here. You're a hobbyist, trying to get
up to speed on some pretty basic stuff. The semiconductor
manufacturers do know what they're doing. If they didn't, they'd be
out of business.

Even as a technician or engineer, the rule of thumb is to look for your
mistake first -- almost always, you'll save a lot of time that way.
And you really have to look at each data*** as an opportunity to
learn. Clear your mind, get a cup of coffee if it helps, and take the
time to really read and understand the information there. It will be
well worth the time. Then, if something isn't clear, see if the part
is second-sourced, and try to get another data***. If it's single
source, send an email to the app engineers at the manufacturer. They
do have people who are paid to help. Just neglect to mention that it's
a hobbyist one-off, and make sure to read the data*** first to avoid
looking foolish.

If it helps, I've found there's a slight correlation between the length
of a .pdf file and the clarity of the data*** (not including those
which have been scanned). And I find National Semiconductor datasheets
are generally (not always) put together with more care than most.
Either that, or I'm more accustomed to their way of describing things.
But I'll look there first if I can.

What I'd like to know, though, is what you're doing playing with TO-92
packages with your power supply, anyway. They're small, their thermal
resistance is around 160 to 180 degrees C per watt, and they aren't
really made for attaching a good heat sink. You're cranking current,
and you're going to need TO-220 or TO-3 packages here.

Let's assume your 25.2VCT transformer has an unregulated 34V, and
you're using your LM317 to put out 3.3V at .5A that means your power
dissipation will be

(34V - 3.3V) * .5A = 15.35 watts
[Note: Power in a pass element = volts dropped * amps passed]

Your little TO-92 package will glow like a nite lite. Isn't going to
happen.

If I could offer you a little free advice. Go to Surplus Sales of
Nebraska

http://www.surplussales.com/

and take a look at their Triple Deltron Power Supply (PS) 10656X, that
has two 12 - 16 vdc outputs @ 2.5 amps each and a 5 vdc output @ 8
amps. It costs $35 in single quantities. The two 12 - 16 vdc supplies
are adjustable, and all the power supplies have independent current
limit adjusts on board. If you mount this supply under your bench, you
can be set up with a mongo +5V and a +/-12V supply (as well as a 24V
supply for the industrial stuff, if you go from the +12 to the -12),
which should get you 80% of the way toward where you want to go. Just
use a 5 amp 3AG fuse (not slo-blo) in series, and mount that with an
industrial power switch in a jiffy box.

If you're dying for a variable supply too, get a 28VDC @ 1A linear open
frame ((PS) IHB28-1) for $25, set the on-board current limit for 1/2A,
and place an LM317CK in series to give you your 1.25V-to-24VDC variable
supply. Don't forget to put 10uF caps at the input and output of the
regulator. And also, get a good heat sink capable of dissipating more
than 15 watts without cooking the LM317CK IC.

Linear open frames are typically based on a standard LM723 circuit (not
shown in datasheets -- from what I understand, someone tried to
copyright the circuit a long time ago, without success). They have
very low ripple, great line and load regulation, and they're pretty
much indestructible, as long as you keep them fairly cool. It might
also be a good idea to run a couple of small muffin fans on the open
frame linears to help with heat dissipation. They also have remote
sensing, which means they can compensate for line drops to the load.

If you want, you can also put 0.1 ohm 1% resistors in line with each
V+out, if you put the V+sense on the other side of the resistor. You
can then use your DMM and a 4PDT break-before-make switch to read
current exactly with an autoranging DMM on whichever supply you choose
(100mV/amp, to the resolution of the meter you're using).

You'll have the electronics for the whole shebang for less than $75.
That way, you can spend your electronics time actually learning,
instead of preparing to learn. A good bench power supply is a
necessity for electronics, so you might as well just get something good
on the bench right now, and play when you have the toy. You're walking
into getting stuck in a chicken and egg problem.

Good luck
Chris

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