Advantage of the use of an added driver source lead in discrete Power MOSFETs

Among all the semiconductor devices, the transistors are by far the most important ones; almost all of them are three pin devices (MOSFET, BJT, IGBT) and on the contrary of the diodes they have a driving section which makes them more sensitive to issues related to the interaction between power to handle and input signal. Aim of the article is to illustrate the limitation that is related to a 3 pin device and depict the advantage of using a fourth driving source pin also known as Kelvin source besides the traditional power source. In a 3 pin device during every switching cycle, the stray inductance of the source wire bonding coupled together with the slope of the current being interrupted is generating a voltage signal always opposed to the driving signal Vgs. The effect of such opposing signal is to slow down the switching cycle and in turn to increase the cycle by cycle switching losses. The effect of such fourth driving source pin solution is the reduction of the overall power losses in the transistor which turns into a lower operation temperature.