Transient simulations of a 4H-SiC 3kV p(+)-n(-)-n(+) power diode have been performed using the drift-diffusion approximation. An additional equation has been added to describe the time evolution of the dopant gap level occupation. In this way, we accomplish a more general dynamic description of donor and acceptor occupation than the conventional steady-state model (i.e. merely including incomplete ionization in the case of relatively large ionization energies). The influence of variations in the donor and acceptor ionization energies has been studied as well as the effects of different sets of carrier capture coefficients characterizing these dopant levels. For the device under study (a pin diode), our calculations show that the turn-off process depends mainly on the donor energy position and less on the acceptor energy position. As a consequence, we show that a donor-type defect which is in the n-region and which is deeper than Nitrogen donor, can give rise to a turn-off behaviour which, for a proper description, needs the more accurate dynamic donor occupation model.