Parametrical investigation of turn-off loss generation shows exponential dependency on the applied voltage and almost linear dependency on the switching frequency. The lowest losses had occurred during investigation of Qspeed structure LQA12T300. It has very low losses in whole range of investigated parameters, whereby its dependency on switching frequency can be almost neglected. Second diode which has showed best performance is second type of Qspeed diode QH12TZ600. Standard Schottky diode MBR20200CT together with both SiC structures SDT10S30 and SDT12S60 are showing similar performace. The only disadvantage of MBR20200CT is that its reverse voltage can be only up to 200 V. On the other side, SDT12S60 shows higher dependency on switching frequency against other structures, what can be caused due to higher value of internal capacitances, which are influencing turn-off process of diode. Diode LQA12T300C are the highest performance 300 V diodes available. Manufacturer declares soft switching of this diode with dramatically reduced overshoot and EMI. With such structure, the elimination of snubber circuit can be easily done. All these facts are confirmed by best performance from all of the investigated structures. Also QH12TZ600 is diode, which is suited for applications with switching frequencies above 80 kHz what is perfectly confirmed also by these experiments.
In next chapter we are evaluating behavior of each diode in dedicated applications, i.e. in selected topologies of switched mode power supplies.