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Kurt Franzen

How a PI Controller converts input voltage signals to a current...

Craig Eckhoff  Follow

With a current driving power stage.
I mean, if you have a control system,
(1.) You have some error signal pickup, say position signal.
    - This can be either voltage or current. In optical disc, eg, error signal is derived
       from photocurrents, and they are currents.
   - The input signal is translated to voltage (if it was a current) with a transimpedance
     amplifier or something else.
(2.) You have a controller
   - Can be digital or analog. Nowadays more and more digital. Means
     input signal is converted by an A/D convertor to digital, control loop is
     executed in digital domain, output signal is converted to analog by means
     of an D/A convertor.
  - You can also do digital, integrated (I dont think this still exists), or with op-amps,
    or whatever.
(3.) You have an output stage.
   - Simplest form is class-B power amplifier, (take any power op-amp).
     Current drive means the op-amp senses the current through the actuator, and
    the feedback is such that the op-amp will equal the current to the input signal.
  - You can also have more complicated power stage, eg H-bridge PWM drive.
    This has higher efficiency, but I think this is most of the time voltage drive.
Best Regards,
Henri.

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