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Filtered PWM DAC to provide +/- 10v — Parallax Forums

Filtered PWM DAC to provide +/- 10v

MicksterMickster Posts: 2,729
edited 2011-10-08 07:56 in Propeller 1
I plan to have a single 24VDC supply from which the Prop will be powered through regulators, etc.

A +/-10v analog output is required to command an industry-standard servo-drive.

Question: It is common practice to utilize a dc-dc converter to provide a +/- 12v supply to the op-amps for this type of circuit. Does anyone know of a reason why a 'rail-splitter' (virtual ground) would not be suitable for this application.

Thanks and regards,

Mickster

Comments

  • LawsonLawson Posts: 870
    edited 2011-10-07 08:54
    Depends on how the grounds are connected with the prop and servo-drive. If the prop circuit is isolated from ground and/or the input to the servo-drive is isolated, the rail splitter will work fine. Otherwise you're likely to short the virtual ground to earth ground.

    I've found this V7812-500/102-1712-ND little point of load DC-DC converter useful for generating negative voltages. Most buck converter modules can be abused as inverting regulators, but this series lists this use in the datasheet! They also have low noise, and sink current almost as well as they source current.

    Lawson
  • RaymanRayman Posts: 14,865
    edited 2011-10-07 11:10
    That's an interesting problem. FWIW, here's what I'd try:
    Use Lawson's things to get +/- 12 V. Then, use regular regulators to get +/- 5V and +3.3 V.
    Use a digial pot, like DS1267 to give you an output signal between -5 and +5 volts.
    Then, use a regular opamp (powered by +/- 12 V) to double that to -10 to +10 volts...
  • LawsonLawson Posts: 870
    edited 2011-10-07 19:22
    You can also go strait from a filtered 0-3.3v duty output to +-10v with an op-amp. This is easiest if you over-amplify a bit with the op-amp and clip the output range in software. I've also used the complementary duty output to generate a differential +-3.3v voltage, which I then amplified with and op-amp configured as a differential input low pass filter. This was the most elegant solution if spare pins are available. I was able to get 12-14bits at 4Ksps with that setup.

    Lawson
  • RaymanRayman Posts: 14,865
    edited 2011-10-08 07:56
    That's not a bad idea actually. You could probably take care of any zero offset with software too...
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