[sdiy] how to power my opamp?

[Czech Martin]

Depends.

If you have a mains psu, the classic +-15 V with regulators are common.
But I think you want some battery driven stuff.

A few op amps run as low as 5 V. Most need arround 10V, so a
9V cell is appropriate. Since op amps have symetrical design 
in terms of ground, you need to invent a "false" ground.
I.e. all points of the usual +-15V circuit that are connected to + are
connected to battery plus. Minus goes to battery minus. Ground
goes to false ground, which is the center tap of a resistive
divider 1:1, i.e. it delivers 4.5V.
Of course, this divider will eat power. So you want high resistance.
OTOH you draw currents from the false ground, so you want low resistance.
Some people use another op amp to buffer a high impedance
divider. Anyway, for ac the false ground should have low impedance,
so capacitors to plus and minus are adviseable.

Look at stomp box schematics with op amps.

For more headroom, higher gain, in general higher performance
a dual battery +-9V should be used, then the normal textbook
designs will work without problems.

Another issue of low volatge design is rail to rail swing at input
and output. The individual datasheets of op amps have to be reviewed.

The danger of input stage phase reversal (latch up) is 
may be a bit higher in low voltage circuits. Unfortunately
this is not too well described in most data sheets.


m.c.

-----Original Message-----
From: marcel 0101101 [mailto:analogic at mail.com]
Sent: Donnerstag, 14. August 2003 14:33
To: post thread
Subject: [sdiy] how to power my opamp?


hi,
i want to know what's the best (most common?) way to power an opamp(TL084)with 9V DC power supply (i need +9V and -9V).
i've heard about (input)biasing but i don't know how it works..

anyone??
-- 
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