Electric supply circuit and method for providing a supply voltage

The control circuit has power supply circuit (VS) that supplies power supply voltage with constant value so as to operate electronic system such as sensor and actuator. The power supply circuit is used to output primary value of supply voltage for electronic system when the supply voltage is derived from voltage source (EA). The power supply circuit is used to output the supply voltage with secondary constant value, for electronic system when the supply voltage is derived from voltage source (ES). Independent claims are included for the following: (1) radio unit; and (2) method for providing supply voltage.