A cryogenically cooled circuit (12), operating at temperatures at which inductors windings (L1) of the circuit exhibit superconducting characteristics, provides unique advantages in high performance, preferably high power circuits. Portions of the circuit (or the entire circuit), as opposed to, for example only the superconducting elements (i.e., inductor winding (216)), are refrigerated to cryogenic temperatures. Advantages in the characteristics of not only the superconducting based components but also the diodes, and gating elements such as MOSFET's (208-213), yield a uniquely advantageous circuit enabling the operation of, for example, a switching power supplies, frequency converters, and motor speed controllers with increased performance and efficiency. Size, component count, and stability are benefits attained by cryogenically cooling the entire circuit configuration. Cryogenically-cooled solid-state contacting switches may be utilized for connecting/disconnecting AC and/or DC power between the high performance circuit and a source/load.