Image Number 2 for United States Patent #8115456.
A circuit is disclosed for a power supply unit for generating a DC voltage, the power supply unit having a current transformer, a rectifier, a series circuit including a first blocking diode and a charging capacitor, an electronic switch which is in parallel with the current transformer, a comparator, a voltage reference circuit for the comparator. In at least one embodiment, the circuit includes a circuit for monitoring the voltage across the charging capacitor. The comparator is used to control the electronic switch on the basis of the voltage across the charging capacitor in relation to the voltage which is generated by the voltage reference circuit and is applied to the comparator. In at least one embodiment, provision is made of a tap which is located between the rectifier and the first blocking diode and at which the circuit for monitoring the voltage across the charging capacitor is located. The circuit is in the form of an RC combination having a second blocking diode connected in series.