Patent ID: 7622828

Claim:
A system for interfacing, comprising: a first controller; a second controller having an input connected to an output of the first controller for receiving a control signal from the first controller; and an interface device connected to the output of the first controller; and wherein: the first controller needs a first current at the output to operate; the second controller needs a second current at the input to operate; the first current has a minimum value; the second current has a maximum value; the minimum value of the first current is greater than the maximum value of the second current; the interface device uses an amount of current approximately equivalent to a difference between the first current and the second current; wherein the interface device comprises: a conditioning circuit having an input connected to the output of the first controller; and a supply circuit having an output connected to the input of the conditioning circuit; wherein: the first controller comprises an input for connection to a voltage supply; the supply circuit comprises an input for connection to the voltage supply; the first controller has a first voltage drop between the input and the output; the supply circuit has a second voltage drop between the input and the output; the second voltage drop is greater than the first voltage drop; the first voltage drop appears upon the first current occurring at the output of the first controller; and the second voltage drop appears upon a third current occurring at the output of the supply circuit; the system further comprising: a first current control device connected in series between the output of the first controller and the input of the conditioning circuit for restricting current flow in one direction from the first controller to the conditioning circuit; and a second current control device connected in series between the output of the supply circuit and the input of the conditioning circuit for restricting current flow in one direction from the supply circuit to the conditioning circuit.