[sdiy] L7912ACV puts out -16.3 volts

[Scott Gravenhorst]

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/>
>>
>
>
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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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