safe operating area of power transistor

Dear All,

i am a final student and working to design an inverter. for this purpose i have selected a power MOSFET IRF740. but i am very much confused about the safe operating area figure and saturation characteristics. Considering the FIARCHILD datasheet SOA curve (fig 4) says that Id=0.8A for VDS=1v but fig 6 says that Id= 2.5A for Vds=1V.

please advise about it.

Thanks in advance

One is the SOA region, outside of it the transistor won't run safely, and most likely be burnt or incure obvious parameter shift. The other one is the electrical I-V characteristic, and it is without the consideration of safely working.

Thanks for your reply,

confusion to me is about first region that indicates "Rds(on) LIMITS". what i understand is that for small value of Vds one can get the max current given by Ids=Vds/Rds(on). Rds(on) automatically limits the Ids so cannot enter this region of SOA curve and device is safe automatically. But Rds(on)=0.5 max as per datasheet. So this limit must allow more Ids.

Further when you calculate the boundry resistance of this region i.e Vds/Ids (1/0.8) from SOA curve it gives greater than unity. but for same Ids & Vds saturation characteristics curve gives approx 0.5 which is acceptable value of Rds(on) as per datasheet.

i am considering these curves as conflicting with each other.

Also consider the attaced datasheet of IRF740 from international rectifiers which shows curves as per my understanding.

please comment if i am missing something