The influence of source impedance on the electrooptical switching behavior of LED's

Abstract

Electrooptical switching of LED's is shown to be well described by a very simple equivalent circuit, the decisive elements of which are the diffusion capacitance and the lead inductance. Theory and experimental data indicate that even small lead inductances diminish performance if the LED is driven by a low-impedance source. Using a switched current source instead is likely to give the fastest possible response. The application of a reverse current pulse to the LED will reduce the light-fall time below the value given by the diode time constant. Then the carrier storage time and the light-fall time are found to be identical, thus offering a simple method of determining the latter without use of a photodetector.