Fault tolerant led display design

A zener diode is connected in parallel with sets of series-connected light emitting diodes with a reverse forward bias orientation. The threshold voltage of the zener diode is matched to equal, or be just slightly greater than, the forward voltage drops for the light emitting diodes at maximum current. During normal operation, therefore, the zener diode draws virtually no current. Upon failure of one of the light emitting diodes, the zener diode conducts without increase in the applied voltage, providing an alternate current path maintaining circuit integrity so that other sets of light emitting diodes connected in series within the circuit continue to illuminate.