[sdiy] L7912ACV puts out -16.3 volts

Mon Aug 27 04:15:18 CEST 2001

Could suspect bad/leaky caps perhaps...

App notes... Prolly a must to troubleshoot this type of thing too... Perhaps
the load is very capacitive? I wouldn't suspect this as a problem, but you
never know till you are knee deep..

Rob

aim : cybrgzr0 <--last thing is a number
----- Original Message -----
From: Scott Gravenhorst <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, August 26, 2001 6:12 PM
Subject: Re: [sdiy] L7912ACV puts out -16.3 volts

> This has not been my experience.  I have many in operation
> and they are all within factory spec. for years.  I have
> 6 in two FatMan synths and another 4 in mods for one of them.
> I have another 10 or more in various other things.
>
> "Dr Strangelove" <phdinfunk at hotmail.com> wrote:
> >People have said, on the EFM list, that 78xx and 79xx series voltage
> >regulators just plain suck.  I've used 7815 and 7915 regulators in a
power
> >supply from a Paia kit.  I built the thing exactly right and it puts out
> >something more like a +/- approx 18v (+/- .5v error).  Whats really
strange
> >is that when I FIRST built it it put out close to 15v pos and negative.
It
> >has "drifted" over time and is close to 18 volts top and bottom.  I
always
> >just assumed that this was anticipated in these types of regulators.
> >
> >         -=<Jonathan Pratt>=-
> >       (Phdinfunk at hotmail.com)
> >
> >
> >
> >
> >>From: sasami at blaze.net.au (Ken Stone)
> >>To: synth-diy at dropmix.xs4all.nl
> >>Subject: Re: [sdiy] L7912ACV puts out -16.3 volts
> >>Date: Mon, 27 Aug 2001 09:16:29 +1000 (EST)
> >>
> >> >Nothing wrong with two bridges.
> >> >Description sounds like missing minimal load to me. (If there is
> >> >no blatant circuit error.)
> >> >Connect two 1k resistors from +12V to GND and from GND to -12V
> >> >and see if voltages will be right then.
> >> >
> >> >JH.
> >> >
> >> >-----Ursprüngliche Nachricht-----
> >> >Von: harry <harrybissell at prodigy.net>
> >> >An: Dave Krooshof <krooshof at xs4all.nl>
> >> >Cc: <synth-diy at dropmix.xs4all.nl>
> >> >Gesendet: Sonntag, 26. August 2001 06:15
> >> >Betreff: Re: [sdiy] L7912ACV puts out -16.3 volts
> >> >
> >> >
> >> >> Hi Dave: inline
> >> >>
> >> >> Dave Krooshof wrote:
> >> >>
> >> >> > Hello,
> >> >> >
> >> >> > I just made a powersupply that is supposed to put out -12 and +12
> >>volts.
> >> >> > The + side is OK, it gives 12.1 volts.
> >> >> > The - side is wrong, as it puts out 16.3 volts.
> >> >> >
> >> >> > The powersupply consists of a 230 volt to 2x 15 volt transformer.
> >> >> > It puts out 2x 18volts AC. *
> >> >> > The circuit has 2 diode rings (bridge cell in english?),
> >> >>
> >> >> two diode rings ?   (two full wave bridges i.e. 8 diodes ?)
> >> >> That isn't right. You should only need one bridge ... the center tap
> >> >> of the transformer goes to DC common. the positive output of the
bridge
> >> >> is the positive (raw) supply. The negative is the negative....
> >> >>
> >> >> > 2 elcos 1000µF,
> >> >> > 4 104 caps, a L7812CV and a L7912ACV for + and - voltage
regulators
> >> >> >
> >> >> > What has gone wrong?
> >> >> > - Was my 7912 off when I bought it?
> >> >> > - did I make a wrong connection that causes it to shift? (I
checked
> >>and
> >> >> > rechecked, but who knows...) The 7912 connects differently from
its
> >> >> > positive brother: 1=left=ground, 2=middle=in, 3=right=out.
> >> >> > - Has my over-enthousiastic trafo just fried my 7912?
> >> >>
> >> >> probably not.
> >> >>
> >> >> > - Is 18 volts to much for a 7912? I couldn't tell from the data
> >>sheet.
> >> >> > (which is here:
> >> >http://www.st.com/stonline/campaign/gold/linear/stpos.htm )
> >> >>
> >> >> no... up to 35V is OK. I think its a problem with the two bridges
> >>myself.
> >> >If
> >> >> you
> >> >> used two bridges you might use two positive regulators.... then thie
> >>them
> >> >in
> >> >> series.
> >> >>
> >> >> H^) harry
> >> >>
> >> >> >
> >> >> >
> >> >> > Thanks a lot in advance for the responses.
> >> >> >
> >> >> > Dave
> >> >> >
> >> >> > * Why the hack can't they make stuff like trafos that behave
> >> >> > according to the given specs? (or boxes that say what the inside
will
> >> >do)
> >> >> >
> >> >> > Pierce: War is hack.
> >> >> >
> >> >> > ----- >^v< ---------------------------------------
> >> >> > Dave Krooshof http://www.xs4all.nl/~krooshof
> >> >> > geluidstechnicus @ http://www.ahk.nl/the
> >> >> > webmaster: http://www.popronde.nl
> >> >> > -------------------------------------- >^v< -----
> >> >>
> >> >
> >> >
> >> >
> >>_______________________________________________________________________
> >>Ken Stone   sasami at blaze.net.au
> >>Modular Synth <http://www.blaze.net.au/~sasami/synth/>
> >>Catgirl Paradise <http://www.anime.net/~kens/>
> >>Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
> >>
> >
> >
> >_________________________________________________________________
> >Get your FREE download of MSN Explorer at
http://explorer.msn.com/intl.asp
> >
> >
>
> =========================================================
> - Government: The other religion.
> - The media's credibility should always be questioned.
>
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: www.teklab.com/~chordman
> -- NonFatMan: members.xoom.com/_XMCM/chordman/index.html
>
>