During the development of a high speed automotive injector drive circuit we needed to quantify the losses in the power MOSFET devices during the switch-on, hold and switch-off events. This oscilloscope plot shows the energy loss in a power MOSFET during switch-off at a rate controlled to minimise EMI. The device voltage and current are measured directly on channels 1 and 2 and the oscilloscope's powerful math functions are used to calculate the instantaneous power and then, by integration, the energy loss during the switching event. The energy loss in this case is 787µJ, clearly shown on the plot. and this can be converted to power loss at any engine speed.

Plots such as these form part of the documentation for design reviews with our customers. If required, the plots can be e-mailed quickly to the customer for rapid evaluation.