[sdiy] Outputs and Impedances

Youssef Menebhi youssef.menebhi.79 at gmail.com
Fri Oct 26 04:22:31 CEST 2018


Sorry, but I just need to clarify the exceptions:
The idea is that the "inputs" that are being fed by the output of the
single op-amp will serve ultimately as outputs from the device.  So,
buffers are needed?
On Thu, Oct 25, 2018 at 10:15 PM <mskala at ansuz.sooke.bc.ca> wrote:
>
> On Thu, 25 Oct 2018, Youssef Menebhi wrote:
> > I have the output of an op-amp in a non-inverting configuration - and
> > I would like to spread its output to three different inputs.  One
> > input is a voltage divider feeding into a transformer, the other two
> > are just voltage dividers.  If I take three equal-sized resistors
> > (let's say 1k) out of the initial op-amp, will that evenly distribute
> > the signal? Or do I need additional buffer stages for each output?
>
> You shouldn't need the resistors.  Just connect the op amp output to all
> three inputs in parallel.  "Evenly distributing the signal" shouldn't be
> an issue; the op amp's output is intended to act as a pure voltage source
> (very low impedance) and as long as it's able to do that, the presence of
> other inputs in parallel should not affect the voltage seen by each input.
>
> Exceptions would be if the inputs have such low impedances that when
> connected in parallel they require more current than the op amp can
> supply; or if there's an issue of interfacing to the outside world, where
> someone might plug in something weird that screws up both the op amp
> output and the other inputs.  In those cases, you'd need additional
> buffering or protective circuitry.
>
> --
> Matthew Skala
> mskala at ansuz.sooke.bc.ca                 People before tribes.
> http://ansuz.sooke.bc.ca/


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