The article presented a mathematical analysis of a double-circuit parametric circuit of ferroresonance nature at the fundamental frequency, performed by the harmonic balance method. The adjustment, current-voltage, and load characteristics of the circuit are given. The possibility of using this circuit in voltage regulators with direct current output is proved. Parametric sources of secondary power supply, in particular voltage stabilizers of ferromagnetic and ferroresonance nature, are used in autonomous vehicles (for example, in spacecraft, some types of intelligent transport systems) and in renewable energy sources due to their ability to operate in heavy environments (high and low temperatures, radiation, strong magnetic or electric fields).