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

**paulus.v** · 12-02-2017

Yes, my bad. There is one signal +/-10V and ground.

**paulus.v** · 12-02-2017

Now the question is how accurate will be the 0V, where the motor should stand still... Some chips have some sort of balance but don't understand what it is for.

**Doddy** · 12-02-2017

Yes some op amps allow you to set precisely the 0v offset voltage, but not the original op amp that you specified. These are used when precision is required, and it's unclear whether you will need this or not. If in doubt code an op amp that supports this and reference the data sheet for how to use it (a common use is a potentiometer between the balance pins with the wiper connected to -V, but that's not due for all opamps

**paulus.v** · 12-02-2017

Originally Posted by Doddy

Yes some op amps allow you to set precisely the 0v offset voltage, but not the original op amp that you specified. These are used when precision is required, and it's unclear whether you will need this or not. If in doubt code an op amp that supports this and reference the data sheet for how to use it (a common use is a potentiometer between the balance pins with the wiper connected to -V, but that's not due for all opamps

I have linked to a dozen op-amps in a previous post. Please point me out one of them if you have the time. I need a robust one.

The 0V is important as the positive voltage will turn the motor in one direction and the negative in the other so at 0V it should stand still. But I could filter out a "dead zone" from the drive settings if necessary.

**Doddy** · 13-02-2017

Originally Posted by paulus.v

I have linked to a dozen op-amps in a previous post. Please point me out one of them if you have the time. I need a robust one.

The 0V is important as the positive voltage will turn the motor in one direction and the negative in the other so at 0V it should stand still. But I could filter out a "dead zone" from the drive settings if necessary.

Chances are any of the op-amps would work well, particularly if you can set a dead-zone around zero.

If you insist on having a balance control then I'd look at the LF356, just from 5 minutes glancing at the datasheets - there's an example of how to connect the balance trim pot (I'd select a multi-turn pot for this); but I doubt that you really need it given the low gain you need.

**paulus.v** · 13-02-2017

Thanks a lot for your help, Doddy.

I'll go with LF356 just in case.

One more silly question. Should I connect the power supply ground with the controller output/ drive input ground?

**Doddy** · 13-02-2017

Originally Posted by paulus.v

One more silly question. Should I connect the power supply ground with the controller output/ drive input ground?

Yes. You need a common ground.

**paulus.v** · 13-02-2017

Originally Posted by Doddy

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

Should I put the capacitors between the power supply pos/neg and ground or between pos/neg and ground op-amp input?

**Doddy** · 13-02-2017

Hmmm, thought I'd replied to this but was by phone. Nevermind - caps are from pin7 (+V) to ground and from pin 4 (-V) to ground. Ignore the +/- signal inputs to the op-amp as far as capacitors.