An adapter circuit for connecting a switching circuit of an airport visual aid is equipped with an LED as a light source and a secondary-side coil (secondary side) of a supply transformer, wherein at least one switch element is provided for selectively making or breaking the connection and wherein at least one trigger circuit is provided for actuating the switch element when a specified voltage level is exceeded, wherein the switch element is provided between the trigger circuit and the secondary side of the supply transformer and/or the trigger circuit is connected to the switch contact and to the switching circuit of the LED airport visual aid.