at the same time also on the input gp 1 if the supply voltage drops below the value given by the voltage detector 16 then its output vout switches to low signal and thus deactivates the controller 9 and the latter deactivates the voltage regulator 10 fig2 shows a second exemplary embodiment of the invention that differs from the one in fig1 substantially by the sensor 7 and the controller 9 the sensor 7 here is a position sensor with a switch that opens or closes as a function of the position of the sensor it can be for example a switch activated by gravity or a mercury switch this switch is then advantageously connected directly to the plus pole of the current source 3 furthermore the controller 9 of the example of fig1 is omitted the contact 12 is then connected via the resistor r 1 and the diode 8 as well as the sensor 7 to the plus pole ven of the voltage regulator 10 this last cited connection can be direct for the case that a voltage monitoring 16 is also provided instead of the controller 9 of fig1 an and gate 9 u2032 is provided whose output is connected to the input ven.