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Navraj
Guest
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 Posted:
Wed Nov 16, 2005 12:05 am Post subject:
MOSFET question: Drive voltage vs. Vgs(th) |
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Can anyone tell me the difference between the drive voltage and the
gate-to-source threshold voltage (Vgs,th) of a MOSFET, if any?
I was under the impression that these refer to the same voltage - the
voltage that is needed to turn the MOSFET 'on'.
However, if you look at the following datasheet for a Fairchild
MOSFET...
http://www.fairchildsemi.com/ds/FD%2FFDG311N.pdf
you'll see that the title says "2.5V Specified", which I understand
refers to the drive voltage. However, under the "On Characteristics,"
you'll see Vgs(th) min. = 0.4V and Vgs(th) max. = 1.5V. Why isn't
Vgs(th) max. = 2.5V, as the title suggests? Is there a difference
between Vgs(th) and the "specified voltage"?
Thanks!
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Tim Williams
Guest
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| Posted:
Wed Nov 16, 2005 1:35 am Post subject:
Re: MOSFET question: Drive voltage vs. Vgs(th) |
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"Navraj" <accolade@gmail.com> wrote in message
news:1132077937.913437.171630@o13g2000cwo.googlegroups.com...
| Quote: | Can anyone tell me the difference between the drive voltage and the
gate-to-source threshold voltage (Vgs,th) of a MOSFET, if any?
|
Threshold is where it begins to conduct. This varies a hell of a lot
between FETs so a much better idea is to "turn on" to a few extra volts,
which also affords you a lower ON resistance if you'll inspect the Ids vs.
Vds, Vgs graph (if printed), or R(on) vs. Vg graph.
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms |
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John Larkin
Guest
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| Posted:
Wed Nov 16, 2005 9:35 am Post subject:
Re: MOSFET question: Drive voltage vs. Vgs(th) |
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On 15 Nov 2005 10:05:37 -0800, "Navraj" <accolade@gmail.com> wrote:
| Quote: | Can anyone tell me the difference between the drive voltage and the
gate-to-source threshold voltage (Vgs,th) of a MOSFET, if any?
|
Threshold is the voltage where it barely begins to conduct. Drive is
the voltage you elect to use in a given situation. If you want it to
conduct hard, drive it way past threshold.
John
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