A device includes a first transistor connected between a first node and an output terminal and a first current source connected between the first node and a supply rail. A circuit includes a second current source connected between the supply rail and a second node, an operational amplifier having a non-inverting input configured to receive a potential set point, and a second transistor connected between the second node and an inverting input of the operational amplifier. An output of the operational amplifier is connected to a control terminal of the second transistor and further connected to a control terminal of the first transistor.