A yarn feeder for textile applications, of storage type, comprising: - a body carrying a drum on which turns of yarn originating from a spool are wound; - a braking member associated with the drum arranged to act on the yarn as it leaves the drum under withdrawal by a textile machine, the braking member being of the type using magnets (30, 36, 38) and comprising - a first permanent magnet movable relative to the drum and at least one fixed second magnet (36, 38), - regulator means (38, 39) to vary the action exerted by the second magnet (36, 38) on the first magnet, - a control unit arranged to operate on said regulator means to control its intervention on said second magnet, - a tension sensor to measure the value of the tension in the yarn leaving the drum; characterised in that: - the first permanent magnet is shaped as a ring freely movable parallel to the axis of the drum and along it, and arranged to cooperate with a counteracting element rigid with the drum, the yarn being disposed, on undergoing braking, between said annular first magnet and said counteracting element, said annular first magnet having a diameter greater than that of the drum so as to be able to move along and parallel to this latter such as to assume a working first position in which the first permanent magnet presses the yarn exiting the drum against the counteracting element, and a second position in which this effect does not take place, the braking action taking place by squeezing the yarn between said first freely movable annular magnet and said counteracting element rigid with the drum in the direction of movement of the yarn exiting the drum, - the fixed second magnet (36; 38) enabling the first permanent magnet to be maintained in the first or in the second of its said positions; the control unit receiving the tension values measured by the tension sensor, comparing them with a predetermined tension value and intervening in real time on said regulator means (38; 39) such that they regulate the action exerted by the second magnet (36, 38) on the annular first magnet to obtain a braking action of this latter on the yarn such as to adjust the tension value to the predetermined value. - a body carrying a drum on which turns of yarn originating from a spool are wound; - a braking member associated with the drum arranged to act on the yarn as it leaves the drum under withdrawal by a textile machine, the braking member being of the type using magnets (30, 36, 38) and comprising - a first permanent magnet movable relative to the drum and at least one fixed second magnet (36, 38), - regulator means (38, 39) to vary the action exerted by the second magnet (36, 38) on the first magnet, - a control unit arranged to operate on said regulator means to control its intervention on said second magnet, - a tension sensor to measure the value of the tension in the yarn leaving the drum; - the first permanent magnet is shaped as a ring freely movable parallel to the axis of the drum and along it, and arranged to cooperate with a counteracting element rigid with the drum, the yarn being disposed, on undergoing braking, between said annular first magnet and said counteracting element, said annular first magnet having a diameter greater than that of the drum so as to be able to move along and parallel to this latter such as to assume a working first position in which the first permanent magnet presses the yarn exiting the drum against the counteracting element, and a second position in which this effect does not take place, the braking action taking place by squeezing the yarn between said first freely movable annular magnet and said counteracting element rigid with the drum in the direction of movement of the yarn exiting the drum, - the fixed second magnet (36; 38) enabling the first permanent magnet to be maintained in the first or in the second of its said positions; the control unit receiving the tension values measured by the tension sensor, comparing them with a predetermined tension value and intervening in real time on said regulator means (38; 39) such that they regulate the action exerted by the second magnet (36, 38) on the annular first magnet to obtain a braking action of this latter on the yarn such as to adjust the tension value to the predetermined value.