Automatic bidirectional indicator driver

Abstract

A bidirectional indicator driver circuit having automatic current sensing for driving an indicator regardless of its orientation. A comparator is coupled to memory which has an output indicating a driving direction polarity. An output driver which drives one terminal of a plurality of LED diodes is coupled to the memory. Individual three state buffers are coupled to the second terminal of each of the respective LEDs. The comparator detects whether the output driver is driving current. If no current is being driven to the LEDs, the comparator causes the memory to toggle states, and toggles the level of the polarity signal. Because the polarity signal is coupled to one terminal of the LEDs, the change in polarity will automatically cause one or more of the LEDs to be forward biased and emit light. The driver circuit can correctly operate LEDs which are incorrectly inserted into a circuit board or multichip module, because the direction the LEDs is driven will be changed until one or more devices is forward biased and current begins to flow. A second embodiment is described for an output driver circuit which will correctly operate LEDs regardless of their orientation using a clock and a common output driver. An integrated circuit incorporating the invention as output driver circuitry is described for use in a system where LEDs are used as indicators. Other devices, systems and methods are also disclosed.