[sdiy] Outputs and Impedances

mskala at ansuz.sooke.bc.ca mskala at ansuz.sooke.bc.ca
Fri Oct 26 04:16:50 CEST 2018

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.

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