op-amp to drive +/-10V analog servo from old +/-5V controller

[paulus.v]

Hi all,

I am trying to control a +/-10V analog servo drive from a +/-5V controller output. The problem is that the servo is running only at half the speed.

My searching lead me to the use of a single supply rail-to-rail operational amplifier. But I'm not an electronist and couldn't find a ready to build solution/schematic.

Here is an IC, OP295, that I can get locally. Could I use it for my application?

Has anyone here done this before and could advise me further?

Any help will be really appreciated.

[Robin Hewitt]

If you want +-10v output then you will need a split rail op-amp and a plus-minus power supply. Is that a problem?

The circuit requires only 2 resistors and a couple of decoupling capacitors for luck.

[paulus.v]

Thanks for your reply!

My only problem is that I need to build it with the components that are available locally. I need this thing asap. No matter how expensive.

[Doddy]

If you can solder, and have suitably sized iron and solder, then together with a bit of vero board (or whatever breadboard solutions you can find locally) then it's a pretty straight-forward build. Have a look at http://electronics-course.com/non-inverting-amplifier for the schematic you need (Robin's answer is correct - you'll need a couple of resistors - choose any value 1k-10k for Rf and Rg (but they must be the same as each other) - see equation (8).

Robin is also correct with the split rail supply requirement - see if you can find a DC-DC converter with a suitable input voltage for what you have available and +/- 12V through +/-15V output.

[paulus.v]

Thanks Doddy!

Now it is a bit more clear.

Luckily I found out there is a +/-12V power output from the servo drive.

Do I need two op-amps one for positive and one for negative? Should I look for any characteristics of the chips as I found dozens of them... Do I need any capacitors in addiction to the identical value resistors?

[Doddy]

If you're driving a single servo (I don't know the interface to these, but I'm going off your post) - and the drive is +/-10v wrt a common ground, then you need only one non-inverting amplifier.

Capacitors - pick a couple of 100nF ceramic capacitors and locate them close to the op-amp, between positive&ground, and between negative&ground.

Regarding which op-amp - how quickly will the signal change?, the one you originally picked had, I think, a gain/bandwidth product of a pretty miserly 75kHz, but if the signal is just driving an axis then I that'd be absolutely fine. If it was driving a spindle then it should still okay given the low gain you're looking at.