Adapter circuit

1. An adapter circuit for connecting a switching circuit of an airport visual aid that is equipped with an LED as a light source and a secondary-side coil of a supply transformer, said adapter circuit comprising:

at least one switch element for selectively making or breaking the connection;

at least one trigger circuit for actuating the switch element when a specified voltage level is exceeded;

wherein the switch element is at least one of:

located between the trigger circuit and the secondary-side coil of the supply transformer and

connected to the trigger circuit, and wherein the trigger circuit is also connected to the switching circuit of the LED airport visual aid,

wherein no current flows through the at least one trigger circuit when said at least one switch element is in an open state to break the connection.

2. The adapter circuit according to claim 1 , wherein a bistable relay with at least one switch contact and with a relay coil is provided for actuating the switch contact, wherein the switch contact acts as the switch element interacting with the trigger circuit, and wherein the connection of the switching circuit of the airport visual aid to the supply transformer is made in a closed state of the relay or is broken in an open state of the relay.

3. The adapter circuit according to claim 1 , wherein the trigger circuit comprises at least one rectifier diode connected to the switching circuit of the LED airport visual aid and a filter arrangement for filtering the current and voltage of the rectifier diode.

4. The adapter circuit according to claim 2 , wherein the bistable relay is constructed as a latching relay or as a locking relay or as a support relay.

5. The adapter circuit according to claim 2 , wherein the bistable relay has a control input for resetting the relay to the closed state.

6. The adapter circuit according to claim 2 , wherein the secondary-side coil of the supply transformer and the switching circuit of the LED airport visual aid are connected in an electrically conductive way via two cables, and further including two switch contacts, wherein one switch contact is allocated to each cable and wherein the two switch contacts can be actuated by means of a common relay coil.

7. The adapter circuit according to claim 2 , wherein at least one of the trigger circuit and the bistable relay are installed in a common housing with the switching circuit for the LED airport visual aid.

8. The adapter circuit according to claim 1 , wherein a filter arrangement includes a resistor and a capacitor connected in series with the resistor.

9. The adapter circuit according to claim 8 , wherein a relay coil is connected in parallel with the capacitor of the filter arrangement.