Possibilities of application of photodetectors based on photodiodes are very high, primarily because of their relatively low cost, small size and high speed response (among the highest in comparison to all other types of detectors). However, like all other types of photodetectors, photodiodes have certain limitations and disadvantages, too. If the photodiode is powered by the constant voltage, its response (current) is practically identical to the technical information provided by the manufacturer even if it has previously been subjected to the radiation (in that case the current is only a bit weaker). On the other hand, if the voltage is not constant and the photodiode is located in the areas with strong gamma radiation, then its response varies from the one that is expected. Therefore, the improvement of the electrical properties of photodetectors based on photodiodes is very important. The aim of this study was to research the behavior of photodiodes in nonideal conditions (variable voltage power supply and the environment with strong gamma radiation).