DC offset dual rail battery supply

Can someone please have a look at this diagram and advise if it is workable?

The object is to output two identical signals, one with a +12V shift above DC/GND, and the other a -12V shift.

IOW there is a 24V differential between the mid-points of the two waveforms, with respect to each other, centered on the GND reference of the input signal.

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Thank you,

David White

Reply to
David White
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no, you need some negative feedback, and for each op-amp you need to keep the inputs between the supply voltages. easiest way is probably this.

maybe this (view with a fixed-pitch font)

+24 | .--R-----. | | | | | +24 | | | |\| | R +12-R-+--|-\ | | | >--+-- +----------|+/ | |/| R 0V | | .--R-----. ----+ | | | | 0V | | | |\| | R -12-R-+--|-\ | | | >--+-- +----------|+/ | |/| R -24 | -24 where R are all resistors of the same value (eg: 10K)
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Reply to
Jasen Betts

Sorry. I can see I have confused the issue by using op amp symbols to represent the amps.

In practice, I intend to use two commercially supplied kits, based upon a 10W audio amp IC (mono's) in push/pull configuration. IOW the only ground reference is between the battery common and input signal.

Rather than the amp details, I really just wanted to know if the battery arrangement was OK.

Once again, sorry for the inaccuracy of my OP.

David White

Reply to
David White

yeah, that should work, if you're expecting DC performance you'll need some sort of level shifting like I drew else you can probably use capacitors instead,

most amplifiers don't like seeing a voltage that's not between the supply voltages.

but if you're using batteries another way to get what you want is this

--------------- +12 + |\| 12V battery | \ - amp >------| | / + |/| 12V battery -12 - ---------------

with the advantage of possibly much less energy lost in the amplifier.

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Reply to
Jasen Betts

OK. Students: Which parts in Jasen's drawing are redundant? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

You don't show where the amplifier power is coming in. If the amplifiers have capacitively coupled inputs and DC coupled outputs, if those DC outputs are centered between the supply rails, if they can sustain whatever standing current there's going to be between their outputs without either failing to work correctly or outright frying, if U1.1 is powered from +24V to ground, and if U1.2 is powered from ground to -24V, then, well, maybe it'll work.

But you really can't depend on any precision to this, and you certainly can't depend on DC coupling. (Nor, IMHO, is it safe to assume that the amplifiers will work as desired, or even survive, if you have standing current from one to another).

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Reply to
Tim Wescott

The diagram was meant to show that one amp is powered from +24 to +12 and the other -24 to -12.

I assume you noted this and had an objection. If so, can you please advise further? I don't understand why this would be a problem if the output signal is not referenced to the rails.

Yes, this is what I am interested in finding out.

While on the subject. What about eliminating one battery per rail, and offseting one leg with a spower diode?

That would reduce the standing current you refer to, and provide +12 and +0.5, and -12 and -0.5 rails respectively.

David

Reply to
David White

No, actually -- I noted that the amplifier power inputs seemed to be completely disconnected.

But now that you specify, note that an audio amplifier is probably going to hold the output at about half way between it's positive and negative supplies, so your standing voltages will be (very) approximately +18 and

-18, giving you 36V between the amplifier outputs.

Well, how is the output referenced in your particular amplifier? If it just comes out a honkin' big electrolytic (which, come to think of it, is probably the case) then all the messing around with power supplies isn't going to do you any good at all.

I think that, if you don't have schematics for the amplifiers in question and know what you're doing, a better way to go would be to just do the whole shebang with op-amps, possibly with transistor followers to provide power.

If you are always going to be having current flowing from the + output to the - output, and your frequencies aren't too high (f < 5kHz) you should be able to do this easily with fairly wimpy opamps and source or emitter followers.

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Reply to
Tim Wescott

ers

Why do you want to do that?

It'd be pretty simple to capacitiviely couple a signal into two different amps operated from different power supplies.... but why?

George H.

Reply to
George Herold

You may feel this is a frustrated practical app rather than the off-beat experiment it is ... but what about the diode idea described above?

As far as the way the audio amps are wired, abeit strangely, no one here seems to be saying it wouldn't work.

There is no ground reference at the output as such. After setting this up, I just want to see what happens when the outputs of one amp are connected to the other through a resistive load. And how this differs between single ended and push pull.

Of course, if it is less than instructive, I would rather not buy the parts.

David

Reply to
David White

Most of them, here's a better way:. all resistors 10K

.--------+-------------+---------- R | | | |\| _|_ + |------|+\ _ | | >---. ___ 24V ---R-+------------|-/ _|_ _ | | |/| /// | | R | | | `--------+-------------+-------- === 10n | _|_ ///

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Reply to
Jasen Betts

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