What is the relationship between N MOSFET VGS(th) and tube conduction?

yhye2world

What is the relationship between N MOSFET VGS(th) and tube conduction? [Copy link]

 

As shown in the figure below, some parameters of AOT290L/AOB290L (N MOSET). Among them, the value of VGS(th) is: Min, 2.9V; Typ, 3.5V; Max, 4.1V. Question: My understanding of the relationship between the VGS(th) parameter and the conduction of the tube is as follows. I don’t know if it is correct. Please give me some advice (pat): 1. When VGS(th)≥4.1V, all MOSFETs of this specification are turned on; 2. When 2.9V≤VGS(th)<4.1V, MOSFETs of this specification may be turned on (or not); 3. When VGS(th)<2.9V, all MOSFETs of this specification are not turned on. Thank you! Attached picture

whuer

It can be understood that the higher the VGS, the smaller the RDS (ON)

asimilar

whuer posted on 2017-8-10 02:41 You can understand that the higher the VGS, the smaller the RDS(ON)

This is simply misleading. Who told you that the higher the VGS, the smaller the RDS(ON)? Take a good look at the specification yourself

asimilar

No problem

maychang

VGS(th is the voltage between the gate and the source when the tube starts to conduct. Note that the test condition is a drain current of 250uA, which is a very small value and is far from the maximum value allowed for the drain current of the tube. After the tube starts to conduct, as the voltage between the gate and the source increases, the tube becomes more and more conductive, and the drain current continues to rise.

maychang

whuer posted on 2017-8-10 02:41 It can be understood that the higher the VGS, the smaller the RDS (ON)

You can't say "the higher the VGS, the smaller the RDS (ON)", you can only say "the higher the VGS, the smaller the RDS". RDS and RDS (ON) have different meanings. The former changes with VGS, while the latter basically does not change with VGS (it can be said to be the minimum value of RDS change).

elec32156

I also understand that the larger the Vgs, the smaller the Rds(on). Rds(on) is the channel resistance from D to S after Vgs reaches Vgs(th). The larger the Vgs, the wider the channel, and the smaller the Rds(on). Is there anything I misunderstood? Please enlighten me! Thank you.

yhye2world

Thank you all, heroes and seniors!

maychang

elec32156 posted on 2017-8-10 12:12 I also understand that the larger the Vgs, the smaller the Rds(on). Rds(on) is the channel resistance from D to S of the tube after Vgs reaches Vgs(th). The larger the vgs, the greater the resistance between the drain and source of the MOS tube.

This is not the case. After the gate-to-source voltage reaches Vgs(th), the resistance between the drain and source of the MOS tube is quite large (as can be seen from the drain current of only 250uA), and the resistance is strongly nonlinear. As Vgs continues to increase, the resistance between the drain and the source continues to decrease. After Vgs reaches a certain value, the resistance between the drain and the source decreases very slowly and almost stops decreasing. The resistance between the drain and the source at this time is called Rds(on).

asimilar

asimilar Posted on 2017-8-10 08:30 This is simply misleading. Who told you that the higher the VGS, the smaller the RDS(ON)? Take a good look at the specification sheet yourself

Sorry, I am a bit extreme here. It does not take into account that the MOS tube works in the amplification state. The amplification state shows impedance characteristics, that is, when the Vgs input voltage is lower than the Vgs (th) voltage, as the VGS voltage increases, the RDS(on) becomes smaller and smaller. When it is higher than a certain value (this value is greater than Vgs (th)), as the Vgs voltage increases until the Vgs (max) value, the RDS(on) does not change significantly. Generally, the drive level is selected according to the recommended test Vgs

elec32156

maychang posted on 2017-8-11 20:18 That's not the case. After the gate-to-source voltage reaches Vgs(th), the resistance between the drain and source of the MOS tube is quite large (since the drain current is only 25 ...

Thank you, senior! This can be understood as the resistance of the MOSFET channel when it is close to being fully opened. Previously, we always understood that "on" was the initial "conduction" of the MOSFET, but in fact it is equivalent to the RDS when the channel is "saturated".

maychang

elec32156 posted on 2017-8-14 12:47 Thank you, senior! This can be understood as the resistance of the MOSFET channel when it is close to being fully opened. Before, I always understood it as "on"...

Yes.