SWITCHED-MODE POWER SUPPLY

摘要

The switched-mode power supply has a transformer which contains a primary winding and at least one secondary winding (W6), a switching transistor in series with the primary winding, a driver stage for controlling the switching transistor, and a control circuit for controlling an output voltage. The control circuit in this case contains an oscillator which can be adjusted via a connection (4) and is coupled to a secondary winding (W6) in order to determine the time at which the switching transistor is switched on. A switching stage (T1, T2) is, in particular, arranged between the connection (4) and the secondary winding (W6) and passes on a supply voltage (VRef) to the connection (4) when a sudden voltage change occurs on the secondary winding (W6) at the time of an oscillation. In consequence, the switching transistor is switched on at a time at which the losses when switched on are low, thus considerably reducing the losses which occur in the switching transistor.