A yarn feeder, comprising - a drum having a yarn wound thereon which is adapted to be unwound upon request from a downstream textile machine, and - a passive weft-braking device, which is arranged to exert a predetermined, uncontrolled braking action upon the yarn unwinding from the drum, characterized in that it also comprises - a controlled weft-braking device, which is arranged downstream of said passive weft-braking device and is provided with - a first series of comb-like arranged prongs, - a second series of comb-like arranged prongs, which are inserted in an alternated configuration between the prongs of the first series, said yarn being slidably inserted in a zig-zag arrangement between the two series of prongs (36, 40) for receiving a braking action by friction from them which changes in strength depending on the position of said second series of prongs with respect to said first series of prongs, and - a stepper motor, which is operatively connected via transmission means to move said second series of prongs with respect to said first series of prongs in such a way as to adjust the strength of said braking action by friction, - a tension sensor, which is arranged downstream of said controlled, weft-braking device for measuring the tension of the yarn unwinding from the drum and generating a corresponding tension signal, and - a control unit, which is connected to feedback control said motor based on said tension signal, in such a way as to substantially stabilize the tension of the yarn on a desired level. - a drum having a yarn wound thereon which is adapted to be unwound upon request from a downstream textile machine, and - a passive weft-braking device, which is arranged to exert a predetermined, uncontrolled braking action upon the yarn unwinding from the drum, characterized in that it also comprises - a controlled weft-braking device, which is arranged downstream of said passive weft-braking device and is provided with - a first series of comb-like arranged prongs, - a second series of comb-like arranged prongs, which are inserted in an alternated configuration between the prongs of the first series, said yarn being slidably inserted in a zig-zag arrangement between the two series of prongs (36, 40) for receiving a braking action by friction from them which changes in strength depending on the position of said second series of prongs with respect to said first series of prongs, and - a stepper motor, which is operatively connected via transmission means to move said second series of prongs with respect to said first series of prongs in such a way as to adjust the strength of said braking action by friction, - a first series of comb-like arranged prongs, - a second series of comb-like arranged prongs, which are inserted in an alternated configuration between the prongs of the first series, said yarn being slidably inserted in a zig-zag arrangement between the two series of prongs (36, 40) for receiving a braking action by friction from them which changes in strength depending on the position of said second series of prongs with respect to said first series of prongs, and - a stepper motor, which is operatively connected via transmission means to move said second series of prongs with respect to said first series of prongs in such a way as to adjust the strength of said braking action by friction, - a tension sensor, which is arranged downstream of said controlled, weft-braking device for measuring the tension of the yarn unwinding from the drum and generating a corresponding tension signal, and - a control unit, which is connected to feedback control said motor based on said tension signal, in such a way as to substantially stabilize the tension of the yarn on a desired level.