Capacitance Multiplier
A capacitance multiplier is designed to make a capacitor function like a capacitor that is much larger. Capacitor multipliers make low-frequency filter and long-duration timing circuits possible that would be impractical with actual capacitors. Another application is in DC power supplies where very low ripple voltage (under load) is of paramount importance, such as in class-A amplifiers.
\[C = C_1 * ( 1+ \frac{R_1}{R_2})\]Other topologies
The active circuit could also be built with transistor A passive equivalent circuit could also be built using autotransformers.
Notes: source