He said he looked at the "off" threshold voltage.

An IRL540 has a threshold voltage of 1V to 2V when it is almost turned off with a current of only 0.25mA. Its is spec'd to be turned on very well with a max on-resistance of only 0.058 ohms when its gate voltage is 5.0V.

If you read the entire post, it will be clear(?) that he had only looked at threshold voltage until I told him to look at the Rds(on) spec'ed voltage. He did, and was relieved to find that it was 4.5V.
At least, that's my take.

Chris? You can clarify this.

 

Many people are confused by the "threshold voltage" spec. It should not be listed or it should say it is when the Mosfet is almost turned off, not when it is turned on well.

 

Many people are confused by the "threshold voltage" spec. It should not be listed or it should say it is when the Mosfet is almost turned off, not when it is turned on well.

I agree that it confuses a lot of noobs, as it did our OP.

 

If you read the entire post, it will be clear(?) that he had only looked at threshold voltage until I told him to look at the Rds(on) spec'ed voltage. He did, and was relieved to find that it was 4.5V.
At least, that's my take.

Chris? You can clarify this.

Ron, you are right.. i was relieved
thing is.. and im gonna be honest, iv used mosfets occasionally.. but theres so many things on the datasheet so many parameters, but theres no concise.. definition, looking at wikipedia, the threshold voltage is some long winded explanation, and i get it, i think i got slightly confused originally.. that with a p-channel mosfet, pulling the voltage over the threshold voltage turns the device (i.e.: increasing Source-Gate) means it will turn on.. however getting somewhere to concisely say what each parameter means seems difficult..
i shall try my mosfet, and im pretty sure i need the inverter, im getting very confused lol.. and i shall report back.. i mentioned a mosfet switch the other day in an offtopic thread, i shall post findings in a blog because its a damned useful circuit to have for test equipment and things like this!

 

What is the part number of your MOSFET?

 

for the switch?
SI2303CDS-T1-GE3
links to farnell.
iv been soldering it in today =]

 

Solved.. it works, the on board USB host is now functional

 

Congrats! I hope you get a few extra FETs for the junkbox. They are handy (when they're on-hand that is!).

A FET in the hand is worth 3000 in the Farnell.

 

haha i found a packet of maybe.. 100+ FDV301N (SOT23) i will post some pictures etc when i get a chance, but now iv got the usb functional i can get the programming on that part done! woop.. now to stop procrastinating wish they marked me on it, id get a first class honour lol