mofet question, VGSS, & datasheet N or P chanel

hp1729

Joined Nov 23, 2015
2,304
You catch the point.
There are two kinds of mosfets, the one is logical level as Vgs = 4.5V or 5V, this type will be very narrow for the linear area as 2V~4.5V or 2V to 5V, and another type is the Vgs =10V and the linear range as 2V~10V, when the Vgs≥10V then the mosfet will get into the full saturation status, that is the logic conception as the switch on, the Rds will be very low as IRF540N that the Rds(on)=40mΩ, when you want to using mosfet to control its Vgs then you should choosing the type Vgs=10V.

You can try the right part of the circuit that I linked, it just using the mosfet, if you want to try LM317 + mosfet then you you need to choosing the part of the linear area 2~10V.

IRF540N -- 33A, 100V, 0.040 Ohm, N-Channel, Power MOSFET.
Yes, there are those two types. We can also say there are N-type MOSFETs and P-type MOSFETs. There are also Depletion modes of the N and P types and Enhancement mode N and P types. In Depletion mode devices applying a voltage to the Gate decreases conduction from Source to Drain. Like J-FETs. In Enhancement mode devices applying a voltage on the Gate increases conduction between Source and Drain. The Enhancement mode N-MOSFET is probably the most popular. Like an NPN transistor a positive voltage (relative to the Source) turns the transistor on. The Enhancement mode P-MOSFET is similar to a PNP transistor. Moving the Gate negative (relative to the Source) turns it on.
 

hp1729

Joined Nov 23, 2015
2,304
NPN bjt:
C : +
B : +
E : --

N ch Mosfet:
D : +
G : +
S : --
A positive voltage on the base, relative to the emitter, turns the NPN on. A positive voltage on the gate, relative to the source, turns the N-MOSFET (Enh) on. Did I type something wrong?
 

ScottWang

Joined Aug 23, 2012
7,414
A positive voltage on the base, relative to the emitter, turns the NPN on. A positive voltage on the gate, relative to the source, turns the N-MOSFET (Enh) on. Did I type something wrong?
This times is right., the posted in #23 that you described was positive to Base(bjt) and relative to Source(mosfet), that was combined two type bjt and mosfet to one, it's quite strange.
 
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