Automation field device with auxiliary current input

An automation system, comprising:

• an automation field device, including:
• a first, a second, and a third connection pin for connecting a field device electronics to an external voltage source;
• and
• the field device electronics, which are designed such that they can be operated either in a two-conductor mode or in a three-conductor mode, wherein a current is to be fed to the field device electronics in the two-conductor mode via a two-wire line to be connected to the first and second connection pins, and the field device electronics have a first data and energy supply path, which leads the current internally from the first to the second connection pin, wherein the field device electronics have an energy supply unit, which is designed to provide an internal energy supply exclusively by means of the fed current in the two-conductor mode, wherein the field device electronics are to be fed an additional auxiliary current in the three-conductor mode by means of an additional single-wire line to be connected to the third connection pin and the field device electronics have a second energy supply path, which leads the additional auxiliary current internally from the first to the third connection pin, wherein the energy supply unit is also designed to provide the internal energy supply by means of the fed current and the fed additional auxiliary current, wherein the field device electronics are also designed to use the additionally fed auxiliary current for the internal energy supply only if the current fed by means of the two-wire line is not sufficient for the internal energy supply;
• a voltage source arranged outside the field device;
• a two-wire line that connects a positive pole of the voltage source to the first connection pin via a first wire and which connects a negative pole of the voltage source to the second connection pin via a second wire.