A voltage sensor comprising: a mechanically integral piezoelectric transformer assembly having at least first and second outputs and at least one input, said mechanically integral piezoelectric transformer assembly generating a modulation carrier signal having a frequency equal to a mechanical resonance frequency of said mechanically integral piezoelectric transformer assembly; a modulation circuit having a first input coupled to the first output of said mechanically integral piezoelectric transformer assembly and receiving a modulation carrier signal, said modulation circuit receiving a source voltage signal and modulating the source voltage signal with the modulation carrier signal as to generate a modulation circuit output signal, said modulation circuit being connected to and transmitting the modulation circuit output signal to the at least one input of said mechanically integral piezoelectric transformer assembly, thereby forming an internal self-oscillating circuit including said modulation circuit and said piezoelectric transformer assembly; one or more demodulators coupled to the second output of said mechanically integral piezoelectric transformer assembly, wherein said mechanically integral piezoelectric transformer assembly outputs a piezoelectric transformer assembly signal that is proportional to the carrier modulated voltage source signal, characterized in that said first and second outputs are distinct galvanically isolated outputs, wherein said mechanically integral piezoelectric transformer assembly includes at least first and second distinct galvanically isolated subtransformers (102, 103) sharing a common primary side, the first subtransformer having its output coupled to said modulation circuit as to supply the carrier signal for the internal self-oscillation circuit, and the second subtransformer being coupled to one of said demodulators. a mechanically integral piezoelectric transformer assembly having at least first and second outputs and at least one input, said mechanically integral piezoelectric transformer assembly generating a modulation carrier signal having a frequency equal to a mechanical resonance frequency of said mechanically integral piezoelectric transformer assembly; a modulation circuit having a first input coupled to the first output of said mechanically integral piezoelectric transformer assembly and receiving a modulation carrier signal, said modulation circuit receiving a source voltage signal and modulating the source voltage signal with the modulation carrier signal as to generate a modulation circuit output signal, said modulation circuit being connected to and transmitting the modulation circuit output signal to the at least one input of said mechanically integral piezoelectric transformer assembly, thereby forming an internal self-oscillating circuit including said modulation circuit and said piezoelectric transformer assembly; one or more demodulators coupled to the second output of said mechanically integral piezoelectric transformer assembly, wherein said mechanically integral piezoelectric transformer assembly outputs a piezoelectric transformer assembly signal that is proportional to the carrier modulated voltage source signal, characterized in that said first and second outputs are distinct galvanically isolated outputs, wherein said mechanically integral piezoelectric transformer assembly includes at least first and second distinct galvanically isolated subtransformers (102, 103) sharing a common primary side, the first subtransformer having its output coupled to said modulation circuit as to supply the carrier signal for the internal self-oscillation circuit, and the second subtransformer being coupled to one of said demodulators.