[sdiy] L7912ACV puts out -16.3 volts

[Theo]

I remember having "fun" with helping debug a PSU over email.
Sure he checked the polarity of the big elcos a hundred times, nothing wrong
there.
It was a real mystery till it turned out he used tantalum types for the 100n
caps 8(

Theo



From: Rob B <cyborgzero at home.com>



> 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
> >
> >
>
>