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 an array of LEDs in a traffic light display, the array of LEDs being arranged as a plurality of 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 which connects between each pair of LEDs in series and a common sensing point, (b) feeding a sensing signal of a predetermined frequency to the common sensing point, (c) providing a differential amplifier which connects to both the common sensing point and to a voltage divider circuit in series with the common sensing point, wherein the potential difference between the common sensing point and the voltage divider circuit is dependent on the proportion of LEDs in the array having open circuit failures, the potential difference being converted to a signal for determining the proportion of LEDs with open circuit failures by the differential amplifier.