  We study the $\beta, N$ critical behaviour of non compact QED with $N$
species of light fermions, using a method we have proposed for unquenched
simulations. We find that there exist two phase transition lines: one, second
order, and the other, first order, that approaches asymptotically the $\beta=0$
axis. These two lines have different physical origin, the second one being
entirely due to fermions effects. We discuss the effect of the approximation
used, in terms of an expansion of the effective action in powers of $N$, and
conclude that the general features should not be affected by this
approximation.
