Uninterruptible power supply circuit comprising a buck-boost voltage converter

An uninterruptible power supply circuit configured to, in a first operating mode, supply power to a second AC electrical network from a first AC electrical network; and, in a second operating mode, supply power to the second AC electrical network from a DC voltage source. The circuit comprises a buck-boost voltage converter comprising two input terminals which are configured to, in the first operating mode, receive, between them, an AC voltage from the first network; and, in the second operating mode, receive a DC voltage from the DC voltage source; and two output terminals configured to, in the first and the second operating mode, receive, between then, an AC voltage from the second AC electrical network; the buck-boost voltage converter being configured to, in the first operating mode, perform an AC/AC conversion between the first AC electrical network and the second AC electrical network.