Multiplexed d.c. electrical systems for automotive vehicles

Abstract

In a 'two-wire' multiplexed lighting system, a square wave voltage alternating between positive and negative polarities is delivered by the two wires to both right and left lamps. Each lamp includes a diode, and the diodes are oppositely pulled with respect to each other so that one of the lamps is energized by one polarity of the square wave while the other lamp is energized by the opposite polarity. The magnitude of each polarity relative to ground is twice the continuous D.C. voltage rating of each lamp so that the average voltage applied to each lamp can be equal to the load's maximum continuous rating to thereby provide full intensity illumination. The lamps provide different signaling functions, such as turn signal, emergency warning, brake lamp and running lamp signals by the operation of corresponding command switches acting through a control logic circuit, including multiplexing, configured to assign a priority to the commands such that the highest priority command will override any others and produce the corresponding operation of a lamps. In the 'three-wire' embodiment of a multiplexed vehicle lighting system, the two lamps have a common ground but each is supplied by its own individual wire. The control circuit further includes a novel circuit for performing the marker lamp function that is commonly used in large trucks and highway tractors.