  We provide new exact solutions to the Einstein-Maxwell system of equations
for matter configurations with anisotropy and charge. The spacetime is static
and spherically symmetric. A quadratic equation of state is utilised for the
matter distribution. By specifying a particular form for one of the
gravitational potentials and the electric field intensity we obtain new exact
solutions in isotropic coordinates. In our general class of models, an earlier
model with a linear equation of state is regained. For particular choices of
parameters we regain the masses of the stars PSR J1614-2230, 4U 1608-52, PSR
J1903+0327, EXO 1745-248 and SAX J1808.4-3658. A comprehensive physical
analysis for the star PSR J1903+0327 reveals that our model is reasonable.
