Abstract: A switched-mode power supply is disclosed, which includes a transformer with a primary winding and a secondary winding. A switch is coupled in series with the primary winding and configured to repeatedly interrupt a current through the primary winding. An inductor is located differently with reference to magnetic fields that the primary and secondary windings are configured to induce. A connection exists between the inductor and a circuit that contains one of the primary and secondary windings. The connection is configured to connect from the inductor to the circuit a first voltage that has a waveform representative of and a polarity opposite to a second voltage induced in the switched-mode power supply by leakage flux of the transformer at a switching moment of the switch.

Abstract: A switched-mode power supply comprises a transformer with a primary winding and a secondary winding. A switch is coupled in series with the primary winding and configured to repeatedly interrupt a current through the primary winding. An inductor is located differently with reference to magnetic fields that the primary and secondary windings are configured to induce. A connection exists between the inductor and a circuit that contains one of the primary and secondary windings. The connection is configured to connect from the inductor to the circuit a first voltage that has a waveform representative of and a polarity opposite to a second voltage induced in the switched-mode power supply by leakage flux of the transformer at a switching moment of the switch.

Abstract: The invention relates to a method and arrangement for detecting a situation in which an electrical device is connected to another electrical device. The electrical device comprises a first, second, and third electrical contact terminal (101, 102, 103). Non-zero voltage is arranged between the second and third electrical contact terminal. The other electrical device comprises counterparts (104, 105, 106) for the first, second, and third electrical contact terminal. There is a galvanic coupling (107) between the counterparts for the first and second electrical contact terminal. The arrangement comprises a resistor (108) between the first and second electrical contact terminal and a detector (112) for detecting the situation in which the electrical device is connected to the other electrical device on the basis of a change of an electrical quantity associated with the resistor. The first electrical contact terminal can be e.g. a metal shield on a USB-connector.

Abstract: The invention relates to a method and arrangement for detecting a situation in which an electrical device is connected to another electrical device. The electrical device comprises a first, second, and third electrical contact terminal (101, 102, 103). Non-zero voltage is arranged between the second and third electrical contact terminal. The other electrical device comprises counterparts (104, 105, 106) for the first, second, and third electrical contact terminal. There is a galvanic coupling (107) between the counterparts for the first and second electrical contact terminal. The arrangement comprises a resistor (108) between the first and second electrical contact terminal and a detector (112) for detecting the situation in which the electrical device is connected to the other electrical device on the basis of a change of an electrical quantity associated with the resistor. The first electrical contact terminal can be e.g. a metal shield on a USB-connector.

Abstract: A power supply converts an input voltage to an output voltage. A primary cur-rent path comprises a primary coil (105, 601), a primary switch (104, T1) and a resistive path portion (109, 301, 302, 401, 402, 501, R4, T3, R15). A pulse forming circuit (108) is adapted to deliver switching pulses to the primary switch (104, T1). As a part of the pulse forming circuit there is a cut-off switch (201, T2) adapted to end a switching pulse as a response to a voltage drop over the resistive path portion (109, 301, 302, 401, 402, 501, R4, T3, R15) reaching a threshold value. An electrically controllable resistance (301, 302, 401, 402, 501, T3, R15) constitutes a part of the resistive path portion and is responsive by its resistance value to a value of an input voltage coupled to the power supply.

Abstract: An output current limiting coupling for a switched-mode power supply is arranged to produce a feedback signal on the basis of the output current of the switched-mode power supply and to transmit it from the secondary side of the switched-mode power supply to its primary side by means of an opto-isolator (3). The coupling may include the following parts implemented with passive components: a bias voltage coupling (25, 26, 27, 28; 30, 31, 32, 33; 42, 43, 44, 45, 46) for forming a certain first potential to the first electrode of the light-emitting diode (3a) contained in the opto-isolator, and an input coupling (24) for producing a second potential formed on the basis of the output current to the second electrode of the light-emitting diode contained in the opto-isolator. The coupling is suitable for switched-mode power supplies regardless of whether the lighting of the light-emitting diode of the opto-isolator indicates a low or high value of the output current.