System and method for controlling current flow in an ac adapter

Abstract

A surge modification circuit controls surge current flows which may occur when a computer and AC adapter are connected. The surge current flows are controlled using active circuitry since passive circuitry, which is in place continuously, sustains large uninterrupted heating power losses in the order of watts that are wasted over time. In one embodiment, a surge modification circuit in an AC adapter includes a control element that operates as a power analog switch with a slow transition time to reduce the steepness of a surge wavefront resulting from the connection of the output terminals of the AC adapter to a computer while the AC adapter is energized. In a second embodiment, a surge modification circuit in an AC adapter employs a pair of power converter control circuits including a main power converter control circuit for performing the power conversion and a sensing power converter control circuit for determining whether the AC Adapter is connected to a computer and informing the main power converter control circuit of the connection status so that the main power converter is disabled when the computer is not attached. In some embodiments, an optoelectronic coupler is advantageously used to communicate a message indicative of the status of a connection between the AC Adapter and the computer. The optoelectronic coupler transfers the status message using optical isolation to maintain a barrier of isolation supplied by the transformer between the computer, mutually isolating AC and DC power.