I've done a bunch of reading and some testing with MOSFETs but there's something going on that I don't see in the datasheets and I don't see much mention of when I search..
I've been playing with 3 different MOSFETs here, all three are logic level power MOSFETs. I'm driving the gate of all three with +5v, which is far above their minimum "on" threshold levels. Source is connected to GND and Drain is connected to the load (LEDs mostly at this point.) Simple, right?
According to the datasheets I should be seeing resistances far under 1 ohm so I should be seeing virtually zero voltage drop, right? Well, that's not the case...
STS8DNH3LL - 0.018 Ohm 8A, SOIC-8. I'm seeing a 1.2-1.5 volt drop from S to G. (https://www.st.com/stonline/products/literature/ds/10590/sts8dnh3ll.pdf)
VNS3NV04D-E - 0.012 Ohm 3.5A, SOIC-8. I'm seeing a 0.8 volt drop from S to G. (https://www.st.com/stonline/books/pdf/docs/7396.pdf)
STD16NF06L - 0.060 Ohm, 24A, DPAK. I'm also seeing a 0.5 volt drop from S to G. (https://www.st.com/stonline/books/pdf/docs/11188.pdf)
Why the heck am I getting this voltage drop? The closest thing I can find in the datasheets is mention of the Vsd for the source-drain diode voltage - is this the drop I'm seeing?
Thanks,
Ray
I've been playing with 3 different MOSFETs here, all three are logic level power MOSFETs. I'm driving the gate of all three with +5v, which is far above their minimum "on" threshold levels. Source is connected to GND and Drain is connected to the load (LEDs mostly at this point.) Simple, right?
According to the datasheets I should be seeing resistances far under 1 ohm so I should be seeing virtually zero voltage drop, right? Well, that's not the case...
STS8DNH3LL - 0.018 Ohm 8A, SOIC-8. I'm seeing a 1.2-1.5 volt drop from S to G. (https://www.st.com/stonline/products/literature/ds/10590/sts8dnh3ll.pdf)
VNS3NV04D-E - 0.012 Ohm 3.5A, SOIC-8. I'm seeing a 0.8 volt drop from S to G. (https://www.st.com/stonline/books/pdf/docs/7396.pdf)
STD16NF06L - 0.060 Ohm, 24A, DPAK. I'm also seeing a 0.5 volt drop from S to G. (https://www.st.com/stonline/books/pdf/docs/11188.pdf)
Why the heck am I getting this voltage drop? The closest thing I can find in the datasheets is mention of the Vsd for the source-drain diode voltage - is this the drop I'm seeing?
Thanks,
Ray
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