Determining proportion of faulty LEDs in a traffic light display

摘要

A method for determining a proportion of LEDs with open circuit failures in anarray of LEDs in a traffic light display, the array of LEDs being arranged as a pluralityof sections in parallel and in which each section includes a pair of LEDs in series,the method comprising the steps of:- (a) providing a fault sensing resistor whichconnects between each pair of LEDs in series and a common sensing point, (b) feedinga sensing signal of a predetermined frequency to the common sensing point, (c)providing a differential amplifier which connects to both the common sensingpoint and to a voltage divider circuit in series with the common sensing point,wherein the potential difference between the common sensing point and the voltagedivider circuit is dependent on the proportion of LEDs in the array having opencircuit failures, the potential difference being converted to a signal for determiningthe proportion of LEDs with open circuit failures by the differential amplifier.