Abstract: The power supply unit comprises a switched-mode power supply which has a transformer (TR1) with a primary winding (W1) and a multitude of secondary windings (W2, W3), a switching transistor (T1) which is coupled to the primary winding (W1) and a control circuit by means of which an output voltage (U2) from the switched-mode power supply can be stabilized on the flyback converter principle. The power supply also comprises a switching regulator (7) which is connected to a secondary winding (W3) which supplies a positive voltage (U3) when the switching transistor (T1) is in the switched-on phase. The output voltage (U4) which is produced by the switching regulator is used in particular for operation of a low-noise converter (LNB). In one preferred embodiment, the switched-mode regulator (7) is a step-down converter, and the secondary winding (W3) supplies a rectified output voltage (U4) via a rectifier means (D4), the value of which output voltage (U4) is preferably in a range from 25 to 50 volts.

Abstract: The protection circuit for a power supply unit comprises a switching stage, at which at least two output voltages to be monitored are connected, these voltages being isolated from one another by means of resistors. Arranged here in the connection path of the output voltages is a diode, which turns on and thereby triggers the switching stage in the event of a fault, when there is a drop in one of the output voltages. In this way, the switching stage provides information which acts on a control loop of the power supply unit, so that the power supply unit switches off. The protection circuit also includes a passive network with a resistor and a capacitor, which prescribes a time constant, after which the protection circuit permits renewed starting of the power supply unit. The switching stage may be realized, for example, by a transistor stage, which provides the information signal for the event of a fault for the power supply unit when turning on occurs.

Abstract: The protection circuit for a switch has an energy-storage means, which is connected to a control input of the switch and which is charged with a delay via resistance means when a control voltage is present and is discharged via switching means when the control voltage is low or absent, and has a switching stage which is connected to a supply voltage, is switched on when a specific threshold voltage is present across the energy-storage means and in this way reduces the supply voltage. In one exemplary embodiment, when the switching stage is switched on, the charge which is dissipated from the supply voltage is at least partially routed to the energy-storage means via a diode which is connected in parallel with the said energy-storage means, so that the phase during which the switching stage is switched on is lengthened and the energy-storage means, in this case a capacitor, is completely discharged.

Abstract: The protection circuit for a power supply unit comprises a switching stage, at which at least two output voltages to be monitored are connected, these voltages being isolated from one another by means of resistors. Arranged here in the connection path of the output voltages is a diode, which turns on and thereby triggers the switching stage in the event of a fault, when there is a drop in one of the output voltages. In this way, the switching stage provides information which acts on a control loop of the power supply unit, so that the power supply unit switches off. The protection circuit also includes a passive network with a resistor and a capacitor, which prescribes a time constant, after which the protection circuit permits renewed starting of the power supply unit. The switching stage may be realized, for example, by a transistor stage, which provides the information signal for the event of a fault for the power supply unit when turning on occurs.