Small voltage across Vds of mosfet while turnt on

Thread Starter

jacky1997

Joined Oct 30, 2015
29
I'm trying to use a N-channel mosfet as a switch. When I have 3.3V on the gate of the mosfet, it lets current flow through the 100 Ohms resistor, but the voltage across the mosfet is above 10mV. The circuit i used is in the attachment. The tested mosfet is the IPP055N03L. It has a max VGS(TH) of 2.2V and a RdsON of around 6.2mOhms.

So my question is: Why is there still 10mV across the mosfet when it should be alot lower? The VGS is above the threshold voltage and the RdsON is so low.

According to the simulation the voltage across the VDS should be 60uV. And according to calculations it should be: 1V/100,0062Ohm*0.0062Ohm = 62uV
 

Thread Starter

jacky1997

Joined Oct 30, 2015
29
Never mind... I rebuild the circuit on a different spot on my breadboard and it works now. Still no idea what went wrong
 

Audioguru again

Joined Oct 21, 2019
1,488
The threshold Vgs of a mosfet is when its is barely turned on (almost turned off) with a current in it of only 0.25mA. For it to be fully turned on you look at the On-Resistance specs which show a resistance typically of 6.2 m-ohms when its Vgs is 4.5V.

Solderless breadboards cause all kinds of problems.
 
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