We have studied the nonlinear dynamical properties of a simple periodicallydriven rate equation model describing electrical conduction in extrinsic photoconductors. Extensive numerical simulations analysed using phase portraits, Poincart sections, approximate one-dimensional mappings, and nonlinear phase diagrams show a range of nonlinear dynamical behavior including chaotic oscillation, transitions to intermittently chaotic oscillation, and phase locking behavior for large drive amplitudes. In addition, we have fully explored the strong dependence of observed nonlinear dynamical behavior on parameter variation in the model. © 1986 IOP Publishing Ltd.