A power-supply circuit includes a transformer with primary and secondary windings, and an energy accumulator on the secondary winding. A circuit monitors the secondary winding and generates a feedback signal that is transferred by a transmission circuit through the secondary winding by selectively transferring energy from the energy accumulator. The transmission circuit includes: a) an electronic switch having a control terminal; and b) a driver circuit for driving the electronic switch. The driver circuit includes a charge-accumulation capacitor connected to the control terminal, and a charge circuit configured to draw energy from the secondary winding and charge the charge-accumulation capacitor.