Abstract: An apparatus for testing an electrical device, having a high side terminal and a low side terminal, includes a power source which is connected to the high side terminal. A voltage monitor is also connected to the high side terminal to determine the voltage that is input to the device. Additionally, a current monitor is connected to the low side terminal to determine the current that passes through the device. A processor is connected to the power source, to the voltage monitor, and to the current monitor. Using the voltage input to high side terminal, and the through current from the low side terminal, the processor computes algorithmic functions which are compared with a predetermined value to establish an error signal. The apparatus then uses this error signal to control the input voltage from the power source to the high side terminal of the device.