> Since I admit I know little to nothing in the world of power supplies, can
> anyone tell me if there is any way I can turn a +12VDC power supply into a
> +-12VDC power supply? Maybe this is impossible, I don't need much current,
> just enough to run a keyboard circuit. Let me know... Thanks. -Nate
HA! One of my famous lectures coming on.
The ∗first day∗ I was in EE lab, I saw a little HP bench supply. It said "DC
output 0 - 20V".
There were 3 terminals on the front, marked +, -, and G. Whipping out
Electronotes #6
(this shows my age), I decided to build something.
Well, I carefully hooked everything up (it was a LFO, I think), power up,
and NOTHING.
I sat there for about 45 minutes doing my Stooge Larry imitation, looking at
each connection,
ohming-out each resistor (I was a little iffy on the color code). Yep, it
was all correct.
About this time the lab instructor wanders over, looked over my stuff and
sort of half laughed
and half sighed. He then pointed out that the HP was only outputting +15V. I
said "Look, it
has a minus terminal!". He calmly explaind it wasn't ∗really∗ minus, but
ground. I then
blurted out "What's this friggin' GROUND TERMINAL connected to?". Oh, that
was a ∗different∗
ground, the chassis ground. At this point, switching majors back to physical
chemistry looked
∗REAL∗ appealling.
The moral of the story: To get +-12V, you really need a 24V ∗total
potential∗ and you are
calling "ground" the middle point. What a "negative" voltage means is that
the ground is
∗above∗ it by 12V.
So, the only way is to use the +12 to drive a switching inverter IC. Look at
www.maxim-ic.com
there are many there. The hard part will be getting the -12V. -5V is more
common. Also
look at Linear Tech's website. Maxim and LT parts are available from
Digikey.
As a former boss said, "Ground only exists in the basement of Bell Labs"
which he liked to
shorten to "Ground is in New Jersey!" anytime anybody in the lab said
'Ground' out loud.
In telcom, you say "Earth potential".
One day, I shall relate another "Ground" story about my first "real job"
measurement, that
caused me to blow up (literally) a $4500 scope.
Paul S.
((Boss's other favorite expression: "No matter how hard you try, you can't
polish a turd."))