1 is strongly dependent on the selected duty factor of the primary input voltage if the capacitance of capacitor c 4 which is in parallel with the series connection of diodes d 1 and d 2 and with capacitors c 2 and c 3 is large enough here about 40 to 60 times larger than each of capacitors c 2 and c 3 then a voltage which is substantially independent of or only slightly dependent on the duty factor of the primary input voltage can be tapped across c 4 at points p 1 and p 3 in the present configuration a slight dependence can probably not be entirely avoided the voltage that can be tapped across points p 1 and p 3 i e across capacitor c 4 is further used as a supply voltage for comparator ic 1 so that the present invention may provide that all electronic components here for example ic 1 ultimately obtain a supply voltage from the primary input voltage it can be seen that the voltage applied to the lower input of comparator ic 1 is the central potential between ohmic resistors r 1 and r 2 so that if resistors r 1 and r 2 are identical the voltage applied is half the voltage that can be tapped across capacitor c 4 this voltage may provide a reference voltage with which the signal voltage that can be tapped at point p 2 may be compared in the example chosen here resistors r 1 and r 2 can have the same ohmic resistance as mentioned earlier so that the voltage across c 4 is ultimately reduced by half however it.