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Can you explain further the RDS(on)Limited dotted line?

Latest Updated:09/02/2013


"The RDS(on)Limited dotted line shows the limits of the area in which characteristics cannot be obtained due to ON resistance" in the safe operating area in the forward direction of the power MOSFET (part name: 2SJ553). (FAQ 1007651) In order to increase device output current Id, must Vds be enlarged to some extent from this limiting line? I think that if I increase the gate voltage and lower the on-resistance, I can use up to the rated Id. Is this wrong?


For operation in this range, the area is theoretically limited by RDS(on)max, and ID = VDS/RDS(on). In the case of the 2SJ553, from the datasheet RDS(on)max is 0.037 Ω, and from the above formula ID = VDS/0.037. For example from the SOA diagram on page 3 of the datasheet, when VDS = -0.4 V, ID = -0.4/0.037 = -10.8 A. A general explanation is shown in the application note.
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Power MOSFETs for General Switching