Electronic device of the type operating without an external power supply, comprising an electric power supply circuit arranged for supplying said device, said electric power supply circuit being arranged for supplying energy for operation of said electronic device via a storage element (13, 24, C2, V3), said electric power supply circuit comprising at least one component, called a variable capacitor (11, 211, Cv, Cvar), having an electrical capacitance that varies under the effect of an alternating mechanical movement, said variable capacitor ∘ being arranged to receive said mechanical movement from the environment of said electronic device, ∘ and being connected to said storage device (13, 24, C2, V3) by means of a rectifier circuit (23, 23') to increase the electrical energy stored there; wherein said electric power supply circuit comprises: - a generating branch formed by at least the variable capacitor (211, Cv) and a biasing capacitor (212, C1) mounted in series, said generating branch being mounted in parallel with the rectifier circuit (23, 23') and with a storage branch comprising the storage element, between ∘ a node, called base node, that is located at the end of the generating branch on the variable capacitor (211, Cv) side and is maintained at a reference potential, ∘ a node, called output node, located at the end of the generating branch on the biasing capacitor (211, C1) side; - a charge return branch of a type able to conduct a unidirectional electric current: ∘ to the generating branch, by at least one first end connected to a node, called a biasing node, which is located in the generating branch between the variable capacitor (211, Cv, Cvar) and the biasing capacitor (212, C1); ∘ from the rectifier, by at least one second end receiving a part of the electrical energy produced by said power supply circuit, wherein the assembly formed by said generating branch, the rectifier circuit (23, 23'), the storage branch and the charge return branch constitutes an electric circuit the behaviour of which is passive and remains unchanged and permanent in its characteristics during at least one plurality of cycles of the variable capacitor (211, Cv, Cvar), thus carrying out at each cycle an additional charge of the biasing capacitor (212, C1) according to an operating mode that is self-synchronizing, i.e. it does not require any means for synchronization with respect to the mechanical movements during said plurality of cycles; and being characterized in that the electric power supply circuit comprises a circuit arranged to form a voltage multiplier circuit (MT, MT1, MT2, MT3, MT4) that is connected to the generating branch at a biasing node located between the variable capacitor (211, Cv, Cvar) and the biasing capacitor (212, C1), for applying a voltage there that is multiplied relative to the voltage that exists between - on the one hand the output node of said generating branch, and - on the other hand the base node or one of the ends of the storage branch (24, C2, V3). ∘ being arranged to receive said mechanical movement from the environment of said electronic device, ∘ and being connected to said storage device (13, 24, C2, V3) by means of a rectifier circuit (23, 23') to increase the electrical energy stored there; - a generating branch formed by at least the variable capacitor (211, Cv) and a biasing capacitor (212, C1) mounted in series, said generating branch being mounted in parallel with the rectifier circuit (23, 23') and with a storage branch comprising the storage element, between ∘ a node, called base node, that is located at the end of the generating branch on the variable capacitor (211, Cv) side and is maintained at a reference potential, ∘ a node, called output node, located at the end of the generating branch on the biasing capacitor (211, C1) side; ∘ a node, called base node, that is located at the end of the generating branch on the variable capacitor (211, Cv) side and is maintained at a reference potential, ∘ a node, called output node, located at the end of the generating branch on the biasing capacitor (211, C1) side; - a charge return branch of a type able to conduct a unidirectional electric current: ∘ to the generating branch, by at least one first end connected to a node, called a biasing node, which is located in the generating branch between the variable capacitor (211, Cv, Cvar) and the biasing capacitor (212, C1); ∘ from the rectifier, by at least one second end receiving a part of the electrical energy produced by said power supply circuit, ∘ to the generating branch, by at least one first end connected to a node, called a biasing node, which is located in the generating branch between the variable capacitor (211, Cv, Cvar) and the biasing capacitor (212, C1); ∘ from the rectifier, by at least one second end receiving a part of the electrical energy produced by said power supply circuit, - on the one hand the output node of said generating branch, and - on the other hand the base node or one of the ends of the storage branch (24, C2, V3).