Mosfet gate voltage higher than drain.

Thread Starter

coinmaster

Joined Dec 24, 2015
502
Can I apply the gate voltage of a mosfet to a higher voltage than the drain voltage in order to raise the source voltage without causing problems?
 

R!f@@

Joined Apr 2, 2009
9,784
You will be causing problems.
And what makes you think you can raise Vs when you raise Vg


Read the data sheet of the MOSFET to see the max Vg
 

crutschow

Joined Mar 14, 2008
29,528
It there is a resistor from source to ground then the source voltage will start to rise with the gate voltage when the Vgs(th) of the MOSFET is reached.
That is a source-follower configuration.
The source voltage will then continue to rise with the gate voltage until the source voltage reaches the drain voltage, at which point further increase in the gate voltage will have little effect on the source voltage.
 

Thread Starter

coinmaster

Joined Dec 24, 2015
502
Yeah but at high current mosfets can have a GS difference of 6+ volts in a source follower so the gate voltage can be higher than the drain voltage and still have several volts between drain and source. But I've never heard of gate being driven beyond the drain and I don't know if it is bad or what can happen.
 

crutschow

Joined Mar 14, 2008
29,528
But I've never heard of gate being driven beyond the drain and I don't know if it is bad or what can happen.
Well, now you've heard of it, and nothing bad happens. :rolleyes:
The gate can be driven more postive/negative than the drain voltage and is done all the time when the MOSFET is used as a switch.
Vgd can go up to the Vgs maximum rating.
 
Top