Input circuit for providing a supply voltage

1. An input circuit for providing a supply voltage, the input circuit having an input side and an output side, and comprising:

a switching unit;

an electronic unit;

a monitoring unit;

an auxiliary connection; a first input on said input side, said output side serves the purpose of connecting to said electronic unit; and

a first path for monitoring the power or voltage between said first input and said switching unit, wherein:

said monitoring unit is provided in said first path;

the supply voltage can be transmitted via said first input to said output side of the input circuit;

said first input is connected to said output side of the input circuit via a first path;

in said first path, said switching unit is provided;

said monitoring unit is configured such that in the event of a current or voltage being introduced via said first input that exceeds a preset threshold value, said first path is interrupted via said switching unit;

there is a node on said first path arranged between said first input and said switching unit; and

the node serves the purpose of at least partly redirecting the electrical power that was introduced through said first input via said auxiliary connection in the event that said switching unit has interrupted said first path.

2. The input circuit according to claim 1 , wherein:

said auxiliary connection serves the purpose of connecting a switching power supply.

3. The input circuit according to claim 2 , wherein:

the input circuit has a second input on the input side, wherein said second input is connected to the output of the input circuit via a second path; and

the supply voltage for operating said electronic unit can be transmitted via said first and/or said second input to said output of the input circuit.

4. The input circuit according to claim 2 , wherein:

said second input serves the purpose of receiving at least part of the electrical power, which has been redirected by said node at said first path via said auxiliary connection and via said switching power supply.

5. The input circuit according to claim 1 , wherein:

said monitoring unit serves the purpose of piloting said switching unit.

6. The input circuit according to claim 1 , wherein:

said first input of the input circuit serves the purpose of connecting a mains voltage or some other kind of energy source for energy supply, such as, for example, a solar panel.

7. The input circuit according to claim 1 , wherein:

said second input of the input circuit serves the purpose of connecting a switching power supply or a battery unit.

8. A field device with an input circuit as defined in claim 1 .

9. The field device according to claim 8 , wherein:

the field device has a switching power supply, which is arranged between said node on said first path and said second input of said input circuit.

10. The field device according to claim 8 , wherein:

the field device has a battery unit, which is connected to the second input.

11. The field device according to claim 8 , wherein:

the connection for said first input of said input circuit is arranged outside of said node or on said node of the field device, in the form of a terminal.

12. The field device according to claim 1 , wherein:

the connection for said second input of said input circuit is arranged inside the said node of the field device.

13. The use of an input circuit as defined in claim 1 for providing a supply voltage for operating an electronic unit of a field device.

14. A method for providing an energy supply, which energy supply serves the purpose of operating an electronic unit of a field device, comprising the steps of:

providing an input circuit, which has a first input on an input side of the input circuit;

providing the electronic unit with an output on an output side; and

supplying the electronic unit with electrical power via the input circuit, wherein:

in the event of an energy supply having been connected to the first input, the electronic unit is supplied with the electrical power via a first path between the first input and the output; and

in the event of the electrical power introduced via the first input exceeding a preset threshold value, the first input is connected to an auxiliary connection of the input circuit.