How to adjust output resistance with galvanic isolation?
A switched capacitor can be thought of as a device that converts a frequency into a conductance value (i.e., the inverse of resistance). Therefore, you might consider a circuit something like this:







simulate this circuit &ndash; Schematic created using CircuitLab

It can be shown through a simplified analysis that the voltage on \$C_{filt}\$ is:

$$V = \frac{I1 \cdot t}{C_{sw}}$$

where t is the switching period, or 1/frequency.

The ripple voltage is basically a function of the ratio between \$C_{sw}\$ and \$C_{filt}\$.

The switches could be nothing more than a pair of optoisolators, if you can find something that has the right output and timing characteristics.