During the development process it is comfortable to test components with fixed conditions and high precision like constant voltage without disturbing influences in the power source. For this lab power supplies can be used because they are a very stable source in a wide range of environmental conditions. Some of these lab power supplies are programmable, either the main parameter itself or modelling special conditions like rising parameters over time or defined time-spans of electricity supply (like impulses). Figure 6 shows a programmable power supply from Hameg, which supports 4 separated and independent sources. Depending on the test procedures it is not always necessary to use a programmable power supply.