A radiation-hardened DC-DC converter capable of operating at cryogenic temperatures in high radiation environments. The radiation-hardened DC-DC converter can include an input side, the input side producing a high frequency AC voltage; a transformer; and an output side, the output side including a magnetic amplifier, wherein the pre-regulated high frequency AC voltage is fed to the magnetic amplifier through the transformer allowing the magnetic amplifier to provide a pulse width modulation function for voltage regulation.