I think drop sets are supposed to be from heavy to low in one set. Like 50lbs, then 40lbs, then 30lbs.. all within the same set rather than 50 - 50 - 50, 40 - 40 - 40, etc.
EX:
50lbs - 40 lbs - 30 lbs - etc.. usually 3 different levels is enough.. rest very little between the weight changes (10sec)
rest
repeat for however many sets.