Circuit arrangement for limiting the current in a timed DC voltage converter

The described circuit arrangement for limiting the current is intended for a timed d.c. current converter in which there is voltage separation between the primary and the secondary sides and in which the switching-on times of a switching transistor in the primary circuit are changed by a pulse width modulator. By changing the switching-on times of the switching transistor, the output voltage is regulated to its required value and the current in the primary circuit is kept below a critical value. In order to limit the current in the primary circuit, the decreasing voltage across a measurement resistance is compared with a threshold voltage. If in such a d.c. voltage converter the switching-on times of the switching transistor must continuously be shortened because of an increasing load at the output and consequently an increasing current in the primary circuit, then the voltage at the output decreases with increasing output current. In order to obtain a limitation of the output current even in this case, the threshold voltage is then reduced by means of a voltage-separating component (0) when the output voltage (Ua) drops below a predetermined fraction of its required value.