Charge-control analysis of the COMFET turn-off transient

A quasi-static charge-control analysis of the unique transient turn-off characteristic of the COMFET is developed. The analysis describes the transient behavior in terms of steady ON-state current components that flow in the constituent MOSFET and BJT in the basic COMFET structure. The effects of the expanding depletion region at the cathode and of minority-carrier injection into the anode are properly accounted for. Consequently, the physics underlying the turnoff time is clarified, and device design criteria for shortening it, without considerably degrading the ON-state current conduction capability, are suggested.