Ferredoxin is an electron receptor used in both Cyclic and Non cyclic photophosphorylation. It "picks up" excited electrons produced from chlorophyll, when exposed to sunlight. The ferredoxin then passes on the electron to a series of enzymes known as "carrier" enzymes, which will eventually return the electron to the chlorophyll, where it may be used again.
The main action of ferredoxin is to convert ADP (adenosine diphosphate) to ATP (adenosine triphosphate) this is done by the excited electrons "giving up" their energy to add on the inorganic phosphate unit. This energy will be used during the course of the light-independent reaction (stage) of photosynthesis, to produce glucose.