Let 0<α<1 and β>1. We show that every x∈[0,1] has an expansion of the form where hi=hi(x)∈{0,α/β}, and pi=pi(x)∈{0,1}. We study the dynamical system underlying this expansion and give the density of the invariant measure that is equivalent to the Lebesgue measure. We prove that the system is weakly Bernoulli, and we give a version of the natural extension. For special values of α, we give the relationship of this expansion with the greedy β-expansion.