Your 1k resistor is not in the Mosfet circuit.
5V/100 ohms is a current of only 50mA. If the current is higher then a Mosfet that needs 10V of gate to source voltage to conduct well will work poorly.

the whole point of that circuit is to test a mosfet to see how well it conducts when it is in on state as the title says this is about logic level MOSFETS.

 

there are some from AO semi - e.g. the AO34xx series
http://www.aosmd.com/products/p-ch-mosfets
e.g. AO3401
http://www.aosmd.com/products/p-ch-mosfets/single/AO3401
for N channel
there are the likes of AO3400 etc
http://www.aosmd.com/products/lv-mosfets/single
http://www.aosmd.com/products/p-ch-mosfets/single/AO3400
http://www.aosmd.com/products/lv-mosfets/single/AO3400A

https://www.aliexpress.com/wholesale?catId=0&SearchText=ao3401
I think these won't take too much currents, despite the specs for it
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if the current needed is low e.g. < 100 mA, I think bipolar transistors e.g. NPN or PNP are easier to work with for logic circuits.
Vbe is typically 0.7v or less to turn on a bipolar transistor. At higher currents BJT probably becomes a problem as Vce is probably quite high.

 

It's rare that one would actually need a logic-level P-channel MOSFET, as it would imply that a large load connected between 5V and 0V was being switched.
A P-channel MOSFET is most often used to switch a load on a higher voltage supply, in which case it would not be a problem to use a standard MOSFET.
For instance, FQP27P06 can switch 20A - when would one need to switch a 20A load on the 5V supply?

Hi,

I think it is hard to make a general statement about how a transistor is going to be used. They are very versatile and it's hard to predict every design that can ever use one in some as of yet unknown application.
For example, a logic level logic system combined with a high current negative supply both with a common +5v supply, maybe.
It still makes sense to think about it though.

 

Now that I have had a chance to look at my stock. I have some VP 2206 P channel mosfets in in my stock. They are in a TO-92 case and would probably work well for my application but I will test it using the circuit in post 18.

​

 

So if I wanted to test one out I would use this scheme and then measure the voltage on the drain to calculate the IDS resistance?

View attachment 272044​

Hi Wendy,

That looks good and if you want a little higher quality test you could vary the gate voltage with maybe a potentiometer while measuring the output across the 100 Ohm'er. If you see the output go up to near max just as you reach 0v on the gate, it's probably not that good, but if you see the output go up at 1v or less that's going to tell us that this must be pretty good for a logic circuit drive.
If you intend to use it with a 50ma output then this is probably good enough, but it's always good to test at a level above what you intend to use in the application to account for parts variations and temperature variations and the like. For a 50ma output that would probably mean 60ma but if you go all the way up to 100ma (assuming the transistor can take it) then it should really be OK for a 50ma load.
That's unless you already intended to use it with a 25ma load and are testing at 50ma

Switching speed with a given max input current drive is also a good comprehensive test. MOSFETs require high current to switch fast between states. That means driving with a 1k resistor wont cut it in high speed applications you'd have to use a genuine MOSFET driver.