Switched-mode power supply

Abstract

A switched-mode power supply for converting a DC input voltage (Uzk) into an output voltage (Ua). The switched-mode power supply comprises a circuit (AST) for triggering at least one controlled switch (S) that periodically applies the input voltage to at least one primary winding (Wp) of a transformer (UET). An auxiliary voltage for the triggering circuit can be switched off with the aid of an auxiliary semiconductor switch (Ts) when the input voltage drops below a given minimum value, the auxiliary voltage consisting of a first auxiliary supply voltage (Uh) diverted from the input voltage and a second auxiliary supply voltage (Uhl) diverted from a secondary winding (Wh) of the transformer by means of rectification. The control electrode (G) of the auxiliary switch (Uhl) is connected to both a reference voltage output (R) of a reference voltage (Uref) that is internally generated in the triggering circuit (AST) and a divider point (Te) of an input voltage divider (Rs1,R1,R2) such that the control electrode (G) of the auxiliary switch (Ts) receives an additional voltage during operation of the triggering circuit so as to turn on the auxiliary switch (Ts).

Dependencies are inferred from the claim text.