A circuit for complementing the AC mains supply voltage, particularly for resistive loads, comprising means (3) inserted between an AC power source and a resistive load (8) and adapted to prevent the reverse flow of a processed portion of the AC supply voltage towards the AC power source, and one or more capacitive means (3; 4a-4g) arranged ahead of the resistive load (8); the circuit has the particularity that the values of the one or more capacitive means are chosen, according to table 2, low enough to maintain the AC nature of said AC voltage and to complement, during discharge towards the resistive load (8), the AC supply voltage until a desired value thereof is reached.