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I'm working on a project using a micro to control two industrial servo drives. These drives take analog inputs of -10 to +10v. My plan is to use a dual-rail opamp circuit that takes a pwm input from the micro (0-5v) and outputs -10 to 10v. My question for the community is about how to provide the dual-rail supply to the opamp. I believe I could theoretically get, say a 24v supply, use resistor divider circuit to set 12v as ref point/gnd and then get +12 and -12v at 24 and 0v, respectively. However, I am concerned about this method when there is more going on. It is my understanding that with this method I would have to:

  • supply power to my 5v micro using 17v and ground it at 12v
  • supply all power demands to the servo drive with this offset and do the same for its grounds

If these assumptions are correct, then I do not think this method will work. I have a bunch of additional inputs and outputs that require power that might make this complicated (but maybe not--I would be happy if someone could convince me otherwise). I have been looking for dual rail supplies to purchase, but haven't had much luck. I also considered using a pc power supply unit, but the current ratings on the -12v line seem too low. I would appreciate any guidance on where to move from here!

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    \$\begingroup\$ You have a lot of words there but no specifications for current. That would be a good thing to fix. \$\endgroup\$ – Spehro Pefhany Sep 9 '20 at 15:52
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    \$\begingroup\$ Get a small 5V to +/-10V converter module (or more likely +/-12V). I tend to use the ISA or ISE series. ISA0512. Or whatever you want your primary power source to be 5V, 12V or whatever. \$\endgroup\$ – DKNguyen Sep 9 '20 at 16:01
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It is often simpler and easier to use a DC-DC converter for these situations. You would power the converter with your 5 V and it outputs dual rails for your opamp.

Dual 10 V outputs may be hard to find. If you can use 12 V rails, there are hundreds of choices.

You don't specify your current specs, but something like this might start you in the right direction: Digi-Key Link

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  • \$\begingroup\$ So the idea being I use one of these DC-DC converters to power my opamp? I don't have any direct information about the current requirements on the analog input to the drive, but I'm starting to think it would be quite low. The datasheet for the drive says the format of analog inputs is: "Differential input, ±10V range, >10kΩ, 10% of peak per volt scale". And on the limited input circuit diagram, the analog input is going into some opamp circuit. \$\endgroup\$ – e6r339b Sep 9 '20 at 16:14
  • \$\begingroup\$ Yes, it's for the opamp. This creates the possibility of the opamp's output to go to nearly 12 V, so if that is a problem for whatever you have it connected to, you should deal with that. \$\endgroup\$ – evildemonic Sep 9 '20 at 16:27
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There’s a lot of ways to make a low-current +/-10V op-amp supply. This is well within the range of a flying-cap converter for example.

The bigger (literally) question is, what’s making your servo supply? And that said, have you considered a full H-bridge drive, powering your servo with +20V instead of a split rail? That might be more economical. And since your drive signal is differential anyway, seems like you can do that.

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    \$\begingroup\$ I am using specific linear servo stages with specific industrial servo drives for feedback control. There is no substitution here. \$\endgroup\$ – e6r339b Sep 9 '20 at 16:37
  • \$\begingroup\$ Datasheet link? \$\endgroup\$ – hacktastical Sep 10 '20 at 2:18
  • \$\begingroup\$ teknic.com/files/product_info/E2-3L_r1.5.pdf \$\endgroup\$ – e6r339b Sep 16 '20 at 21:58
  • \$\begingroup\$ The range specifies the allowed swing of +/- 10V differential. That means that the difference between the two can be 10V in either polarity. It doesn't mean that the signals themselves need to be +/- 10V. In fact, if you were to use bipolar drive, then you'd want +5/-5 to -5/+5 swing on the signals. \$\endgroup\$ – hacktastical Sep 16 '20 at 23:09

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