Question

what characteristic of an LED is critical to successful charlieplexing but not important for traditional multiplexing?

Answer 1

Charlieplexing:

It is a method of driving more number of LEDs with a small number of Outpin Pins when compared to the traditional multiplexing method. ie while applying charlieplexing method we can use n drive pins to connect n digits with n-1 segments. in simplified statement , n pins can be used to drive n^2 - n LEDs.

Important characteristic Needed For Charlieplexing:

Charlieplexing connection will put LED segments into reverse biased condition during a portion of the multiplexing time(ie between another LED turn on cathode drive and a current source which drives an oopen circuit). Also the maximum value of the reverse bias voltage that will be applied to an LED segment will be equal to the supply voltage. Hence it is most important to choose a LED with is capable of withstanding the reverse bias voltage ( which is at maximum equal to the applied supply voltage).

An LED capable to withstand a reverse bias voltage equal to supply voltage must be choosen for charlieplexing. wheres this characteristic of LED is not needed in traditional multiplexing method.