Question of possible circuit
You could have an AC signal superimposed on a DC level - that's quite common in electronics but, if you wished to use that DC level without the clutter of an AC signal superimposed you could use a low pass LC filter like this: -

\$V_{IN}\$ would be your combined AC signal and DC level and \$V_{OUT}\$ would be largely free from AC artefacts but, never totally free of them. So, you have to be pragmatic and ask yourself how low an AC signal on the DC output (\$V_{OUT}\$) can I tolerate to achieve my goals. For instance, if the lowest frequency AC signal were 1 kHz then, if you used an inductance of 100 mH and a capacitance of 100 uF, you would find that the AC signal on \$V_{OUT}\$ due to the presence of 1 kHz on the input would be reduced by about 52 dB. Is this enough? Only you can say: -

Pictures from this Interactive LCR filter.