A synchronous rectifier circuit operates as a high-efficiency DC/DC converter for mixed step-up/step-down applications, and includes an input terminal receiving a voltage signal, a second input terminal node connected to an external inductor, and an output terminal. A power switch may be connected between the second input terminal node and the output terminal to generate on its output a voltage at one terminal of the inductor. A driver circuit is provided for driving the power switch, and a comparator senses the potential difference between the output and input terminals and produces an enable signal for the driver circuit. The comparator may be a wide pass-band comparator forcing prompt triggering of the regulation loop in the rectifier.