[sci.electronics] want help with power supply

rom@xor.Sun.COM (Achyutram Bhamidipaty) (07/06/89)

Hello everyone! 

I am the proud owner of a LH RESEARCH Little-MITE 
model LM34-1522 115 power supply.

So what, you say. Well I'll tell ya, it appears to be
a rather peculiar beast in that it has some connectors
that dont seem to make much sense to me.

The power supply has the following connectors on it:

label	my guess on its purpose
ac	hot ac
acc	ac common
gnd	earth ground
pf	????
on/off	???? This is NOT a switch, just a bind post
+s1	??
-s1	???
+s2	???
+v2	plus side of supply 2
-v2	minus of supply 2
-s2	???
+v3	plus side of supply 3
-v3	minus ''
+v4	plus supply 4
-v4	minus ''

I expected the +/- vn connections, but not the +/- sn connections
but they didn't teach us about the sn connections at school!!

So the question: what are the sn and pf connections?

Thanks for any help.
-Rom
rom@xor.sun.com

howard@tp2.Waterloo.NCR.COM (Howard F. Steel) (07/06/89)

In article <113785@sun.Eng.Sun.COM> rom@xor.Sun.COM (Achyutram Bhamidipaty)
writes:

>The power supply has the following connectors on it:
>
>label	my guess on its purpose
>pf	????

Power Fail signal; usually an active low signal that gives you a few msec
warning that the supply has dropped below a specific level. Allows your
processor time to clean-house before the power actually is gone.

>+s1	??
>-s1	???
>+s2	???
>-s2	???
>So the question: what are the sn and pf connections?

+/-s is the Sense Line. The + side is connected to the load at the same place
as the + side of the V out that corresponds to it and likewise for the -s;
like so:

------------			   	  -------------
Power	   |				  |
Supply	   -s2--------------------------\ |  LOAD
	   |				 |-
	   -V2__________________________/ |
	   |				  |
	   +s2--------------------------\ |
	   |				 |-
	   -V2__________________________/ |
___________|				  |____________

The sense line lets the power supply compensate for line losses by comparing
the voltage at the load to the output voltage. If the the load is heavy
the voltage drop in the lines leading to it could be significant and result in
low voltage situations. If the sense lines are not going to be used (if for 
example your load is small in comparison to the rated output of the supply,
or you don't particularly care if the voltage drops a bit with varying loads)
then connect the -sn terminal directly to the -Vn terminal at the power supply
(same for the + lines). Don't operate the supply with terminating the sense
lines.

-- 
Howard.Steel@Waterloo.NCR.COM  :-(  	I Think, Therefore I AM,
aka: Howard "The Duck" Steel   :-) 		I think

ga9@vax5.CIT.CORNELL.EDU (07/06/89)

In article <113785@sun.Eng.Sun.COM> rom@xor.Sun.COM (Achyutram Bhamidipaty) writes:
>I am the proud owner of a LH RESEARCH Little-MITE 
>model LM34-1522 115 power supply.
>
>So what, you say. Well I'll tell ya, it appears to be
>a rather peculiar beast in that it has some connectors
>that dont seem to make much sense to me.
                             ^^^^^ 8^)
>
>The power supply has the following connectors on it:
>
>label	my guess on its purpose
>ac	hot ac
>acc	ac common
>gnd	earth ground
>pf	????
Hmmm, don't know this one...

>on/off	???? This is NOT a switch, just a bind post
This is the INHIBIT, asserted LOW (GND). Short it to GND to
disable output of the supply.

>+s1	??
Positive Sense, Supply 1. Tie to Supply 1 positive destination
(ie: the backplane) or short to +V1.

>-s1	???
Negative Sense, Supply 1. Tie to Supply 1 negative (GND) destination
(ie: the backplane) or short to -V1.

>+s2	???
Positive Sense, Supply 2. Tie to Supply 2 positive destination
(ie: the backplane) or short to +V2.

>-s2	???
Negative Sense, Supply 2. Tie to Supply 2 negative (GND) destination
(ie: the backplane) or short to -V2.

>
>I expected the +/- vn connections, but not the +/- sn connections
>but they didn't teach us about the sn connections at school!!

>
>Thanks for any help.
"No problem!"

>-Rom
>rom@xor.sun.com

	************************************************************
	John Erickson, Professional Student
	Digital Equipment Corp. & Cornell University
	************************************************************

henry@utzoo.uucp (Henry Spencer) (07/06/89)

In article <113785@sun.Eng.Sun.COM> rom@xor.Sun.COM (Achyutram Bhamidipaty) writes:
>pf	????
>on/off	???? This is NOT a switch, just a bind post
>+s1	??
>-s1	???
>+s2	???
>+v2	plus side of supply 2
>-v2	minus of supply 2
>-s2	???
> ...
>I expected the +/- vn connections, but not the +/- sn connections
>but they didn't teach us about the sn connections at school!!
>So the question: what are the sn and pf connections?

For a guess...  pf is probably a power-fail warning signal, meant to warn
your system that the AC power has failed and the DC outputs are therefore
about to fail.  on/off may be for remote control.  As for the sn connections,
those are probably sensing leads.  Consider:  if you have a fairly long
cable running from the supply to the equipment it is supplying, there may
well be some voltage drop in the cable -- it does have a non-zero resistance,
after all.  So regulating the output voltage at the power-supply end of the
cable won't get it precisely right at the other end.  Worse, the voltage at
the other end will *change* if current demand changes, since the voltage
drop in the cable will be proportional to current drawn.  What to do?  Run
a separate pair of sensing wires.  The sensing wires are connected to the
power wires at the destination end.  At the power-supply end, they go into
high-impedance sensing circuits.  Since virtually no current flows in the
sensing wires, there is essentially no voltage drop along them.  So the
sensing circuitry on the power-supply end gets to see what the voltage is
at the *destination* end of the power wires, and the power supply can
adjust its output so the right voltage is delivered at the destination.
This is pretty standard practice for high-output power supplies.  If your
cables are short or you don't care that much, just connect the sensing
terminals to the output terminals at the supply.
-- 
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

myers@hpfcdj.HP.COM (Bob Myers) (07/07/89)

>ac	hot ac
           "line"
>acc	ac common
           "common"
>gnd	earth ground
           yep - "safety" or "green wire" ground

>pf	????
           This is probably a logic output - "power fail" - indicating to
           the equipment being powered that the supply has detected the loss
           of the AC line and will be shutting itself down VERY soon (say
           about 1-10 msec from the assertion of this signal - actual time
           depends on how long the caps can keep the supply going, but around
           1-10 msec is typical.)

>on/off	???? This is NOT a switch, just a bind post

           Probably a logic input - a "remote" on/off, permitting the supply
           to be shut down/turned on via a TTL line.  If the supply does not
           function when this pin is left unconnected, try grounding it.
           (You may wish to trace it out first, to verify that it runs to
            an appropriate-looking input.)

>+s1	??
>-s1	???

           The "s" inputs are most likely for remote sensing of the output
           voltages; +/- s1 would correspond to output 1, and so forth.
           Remote sensing is used in many supplies so that the voltage being
           regulated is actually that across the load, and not that at the
           output terminals of the supply.  This eliminates potential (pardon
           the pun) problems caused by voltage drops in the wires between the
           supply and the load.  Simply hook these terminals up across the 
           load, so that the voltage to be regulated appears across the 
           terminals in the proper polarity.  Heavy wire is not required for
           this, as the current drawn by the sense terminals will be very
           small.

           Not all of the outputs will necessarily have remote sensing
           capabilities; this is typically used only on those outputs which
           are expected to have a fairly heavy load.  Outputs without
           sensing are either regulated separately, with the voltage being
           monitored at the supply terminals, or (and more typically) use
           some simple linear regulation and actually track the main output
           to some degree, as this is the only output which is actually 
           monitored by the regulation circuitry.

           Hope this helps.


Bob M.

rusty@cadnetix.COM (Rusty Carruth) (07/07/89)

In article <113785@sun.Eng.Sun.COM> rom@xor.Sun.COM (Achyutram Bhamidipaty) writes:
...
>a rather peculiar beast in that it has some connectors
>that dont seem to make much sense to me.
>
>The power supply has the following connectors on it:
>
>label	my guess on its purpose
...
>pf	????
>on/off	???? This is NOT a switch, just a bind post
>+s1	??
...
>+v3	plus side of supply 3
...
PF - Power Fail  May be either in or out, my guess is an output which
        goes low or high some number of ms before you lose voltage.

Sn - voltage sense, for remote voltage sensing.  Helps you regulate 
        out at the object being supplied with voltage rather than at
	the power supply output terminals.

ON/off may be a remote control for thepower supply.

just a guess, hope this helps.

---------- 
Rusty Carruth  UUCP:{uunet,boulder}!cadnetix!rusty  DOMAIN: rusty@cadnetix.com
Daisy/Cadnetix Corp. (303) 444-8075\  5775 Flatiron Pkwy. \ Boulder, Co 80301
Radio: N7IKQ    'home': P.O.B. 461 \  Lafayette, CO 80026

barry@hprmokg.HP.COM (Barry Fowler) (07/07/89)

pf is probably Power Fail, a signal issued when a comparator detects that
the power output is about to be interrupted in ?-milliseconds.

As for sn, I don't know (possible "sense" for a voltage or current
sense??)

michael@xanadu.COM (Michael McClary) (08/05/89)

In article <10040006@hprmokg.hp.com> barry@hprmokg.HP.COM (Barry Fowler) writes:
>pf is probably Power Fail, a signal issued when a comparator detects that
>the power output is about to be interrupted in ?-milliseconds.

In an Intel supply I've used, the power failure signal was an open-collector.
Add pullups and such as appropriate for your logic family.