Patent ID: 8649192
Filing Date: 2014-02-11
Classification: H02M

Abstract:
1. A power-supply with galvanic isolation, comprising: a power-supply input having first and second input terminals, and a power-supply output having first and second output terminals, a transformer that has a primary winding, the primary winding having first and second primary winding terminals, wherein the first primary winding terminal is connected to the first input terminal; and a secondary winding separated galvanically from the primary winding, the secondary winding having first and second secondary winding terminals connected to the first and second power-supply output terminals and across an output capacitor, a diode having a cathode connected to the first input terminal via an input capacitor and an anode connected to the second primary winding terminal; a controlled semiconductor switch that has at least one control input, a first switch terminal, and a second switch terminal, wherein the first switch terminal is connected to the second primary winding terminal, and wherein the second switch terminal is connected to the second input terminal, such that the controlled semiconductor switch forms, with the primary winding, a series circuit that lies parallel to the power-supply input, a controllable control circuit for the semiconductor switch that delivers, for the semiconductor switch, to the at least one control input, a periodic control signal that is controlled such that the output voltage on the secondary winding is kept at a specified desired value independent of the load, and a voltage limiting circuit having first and second voltage limiting circuit terminals, the first voltage limiting circuit terminal being connected to the second primary winding terminal, and the second voltage limiting circuit terminal being connected to the anode of the diode, such that the voltage limiting circuit lies parallel to the primary winding on the input side so that the voltage limiting circuit receives a voltage of the primary winding, wherein an output signal of the voltage limiting circuit acts on the switch state of the semiconductor switch such that the semiconductor switch is moved to a stationary state in which it generates no alternating current on the primary winding when the voltage on the primary winding has exceeded a specified limiting value.