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Hello spec, back from vacation. THANX a bunch the open collector driver worked perfectly to gate the pFET and i got everything working.Can I suggest that...
spec
I've had that same question many times.Why do so many people look at the "Threshold Voltage" of a Mosfet and think that since it says 2V to 4V then it will conduct lots of current when its Vgs is only 3V??
Good news- hope you had a good vacation.Hello spec, back from vacation. THANX a bunch the open collector driver worked perfectly to gate the pFET and i got everything working.
The maximum gate threshold voltage of a MOSFET is a fundamentally important parameter, just like many other parameters: Rdss, Tjmax, RthJC, Cg, SOA, and so on.I've had that same question many times.
Even when you tell them otherwise, that they need to look at the voltage used to specify the Ron value, they still want to refer to Vth as a voltage of interest when using the MOSFET as a switch.
Apparently they think that Vth is some type of digital threshold, where anything above that fully turns the MOSFET on.
Oh well, I guess all we can do is keep preaching..
i figure every student reaches a point where they realise that when you're down to discrete components, there's really no such thing as purely digital electronics, unless you're using relays. my understanding (correct me if i'm wrong) is that Rds is a curve and that the Vgs is a key indicator of the shape and displacement of that curve.The maximum gate threshold voltage of a MOSFET is a fundamentally important parameter, just like many other parameters: Rdss, Tjmax, RthJC, Cg and so on.
spec
So true. It is rare that any data sheet is complete, and anyway you would need one hell of a load of work to take into account all the variables- which you would do in a worst-case safety-critical design.i figure every student reaches a point where they realise that when you're down to discrete components, there's really no such thing as purely digital electronics, unless you're using relays. my understanding (correct me if i'm wrong) is that Rds is a curve and that the Vgs is a key indicator of the shape and displacement of that curve.
isn't it true that sometimes you just gotta check the data sheet and extrapolate from insufficient information?
it is. i'm now getting the same circuit performance that i had when i had a 5v MCU.In the case of this thread, the OP had already stated that that his particular MOSFET was turning on OK with a relatively low gate voltage.
No argument there.The maximum gate threshold voltage of a MOSFET is a fundamentally important parameter, just like many other parameters: Rdss, Tjmax, RthJC, Cg, SOA, and so on
And no argument there either.No argument there.
But Vgs(th) max is not what should be used to determine the voltage needed to reliably use the MOSFET as a low on-resistance switch.