Differential amplifier 0 to 5v signal input with -10 to +10v output

Thread Starter

cj9

Joined Nov 23, 2011
3
Hi,

I'm trying to drive a galvanometer which needs a differential input. It's not well documented (galvo board), but I tried driving it with a differential input from a DRV134, which doesn't work properly. The output of the
I can't work out what's going on.

Instead I'm hoping to use an op amp to drive it by putting -10 to 10v on the +ve pin and tying the -ve pin to ground.

The only problem is that I can't find a working circuit anywhere that uses an op amp to convert 0-5v to -10-10v, could anyone help me with this please?

Thanks for your time.
 

nomurphy

Joined Aug 8, 2005
567
For DC: by using two op amps from the same input, one that is non-inverting and one that is inverting, both with a gain of 2; then the output of one will go from 0 to +10V while the other goes from 0 to -10V.

If you are dealing with a high enough AC frequency (audio), by cap coupling the 0V-5V input to an op amp it will become +/- 2.5V; with a gain of 4 the output will be +/-10V.
 

SgtWookie

Joined Jul 17, 2007
22,210
I did this schematic for someone awhile back.

It converts 0v to +5v, to -5v to +5v; and has both non-inverting and inverting output.
It depends on +V being 10v, as R1 and R2 are summed to be 5v; and that is summed with the feedback resistor R3.

You could change U1b to a noninverting configuration with a gain of 2 to get your desired output.
 

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Thread Starter

cj9

Joined Nov 23, 2011
3
Thank you for the schematic, it's very helpful. I'll build it up and see if it works!

Just a quick question - what's the selection switch for?
 

SgtWookie

Joined Jul 17, 2007
22,210
As shown, the selector switch connects the galvanometer to the noninverting output.
If it were at the other position, the inverting output would be connected; the red trace would then be at 5v when the input was 0v, and -5v when the input was at 5v.
 

Thread Starter

cj9

Joined Nov 23, 2011
3
I see. I have some LM324s on hand, they are designed to "eliminate the need for dual rail power supplies". This means they have ground rather than -ve voltage input. Could you tell me if this circuit can utilise the LM324? It would be helpful as they have 4 amps in each chip. Thanks!
 

t_n_k

Joined Mar 6, 2009
5,455
If you eliminate the negative supply by replacing it with ground then the op-amp output can't swing below ground. You need a ±10V swing.
 
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