Current Injection Gate Drive Circuit for Controlling the Turn-Off Characteristic of Low Voltage Power MOSFETs with High Current Ratings

In battery fed power trains with power converters like in lift trucks or electrical passenger cars the battery voltage varies substantially between charching and discharching and for full loaded and empty battery status. For gate drive circuit design and MOSFET selection the overvoltage at turn-off affected by the induced voltages at the stray inductances in the commutation path and the maximum dc link respectively battery voltage has to be taken into account for the adjustment of the maximum allowed current slope. At lower battery voltages this leads to a potential of higher current slopes than at high battery voltages and thus lower losses. To meet these requirements a novel method of controlling the turn-off characteristic of low voltage power MOSFETs with high current ratings is presented. The gate drive circuit with an adjustable current source is described with the focus on the necessary reduction of the overvoltage at turn-off. Experimental results of the proposed gate drive circuit for different control voltages and blocking voltages are presented.