An autarkic field device or an autarkic radio adapter for a field device, of automation technology fed with limited energy via an energy supply unit associated, or associable, with the field device or the radio adapter. Between the energy supply unit and an internal voltage source, whose voltage exceeds, or at times can exceed, the voltage of the energy supply unit, a barrier of at least one diode group having at least two diodes connected in parallel is arranged, which blocks flow of electrical current from the internal voltage source to the energy supply unit or to the connection terminals of the field device or of the radio adapter for the energy supply unit.