be coupled to the 220 vac mains as conventionally available in a home the secondary winding of the transformer tsf 1 power supplies a diode bridge the output of which is filtered through the capacitor c 1 which has one end coupled to ground and the other end thereof or top end 10 coupled in addition to the mentioned output of the diode bridge to the cathode of a diode d 1 the anode of which is coupled to the terminal of a 12 v dc power supply which as stated can be a conventional battery of a motor vehicle the cathode of the diode d 1 is moreover coupled through a photodiode d 3 and two resistors r 3 and r 4 to the base electrode of a transistor tr having its emitter electrode coupled to ground the collector electrode of the transistor tr is coupled to a winding of a further transformer tsf 2 of the central tap type the other end of this winding is coupled through the capacitor c 2 to the common junction point 11 of the resistors r 3 and r 4 the collector electrode of the transistor tr is also coupled to the ground through a diode d 2 which is coupled with the shown polarity this collector electrode moreover is coupled through a further capacitor c 3 to the central tap of the winding of the transformer tsf 2 to the anode of the photodiode d 3 and the cathode of the diode d 1 the other winding indicated at 12 of the transformer tsf 3 is coupled to a voltage multiplier assembly overally indicated at the reference number 13 this assembly comprises in a known way a cell cascade consisting of respective diodes and capacitors each cell operating.