Mosfets: How to know which one

I have a project that requires a RFP30N06LE. I went to our Makerspace draws and could only find a L7805CV.

Where do I begin trying to work out the differences?

I have looked at the datasheets and the L7805CV operates in my required voltage and amperage range. What I need to know is will it work in

I think you'll discover from the data sheets that the L7805 series devices are not mosfets at all but voltage regulators. The packages do look similar, though.

Anyway, the interesting basic characteristics from the data sheet for a mosfet are:

N or P Channel
Max Voltage
Max Current
RDS(on) in ohms (and at what voltage) A logic level mosfet will have a very small resistance when the gate is driven at 5 volts (N channel) or -5 (P channel)
Maybe package is interesting if you can't work with surface mounted devices.
Of course there are many other characteristics as well which could be relevant, depending on the application.

lol ok so now I know how lost a really am :slight_smile:

The draw with Mosfets labelled on the outside had these but I have just check again and they also have FQP13N10 and FQP17P10

So looking at RFP30N06LE I am guess that I am needing an N type. I will therefore compare the datasheets between what I am looking for and the FQP13N10.

Thanks for the pointers :smiley:

Just one more question. Should this work in the following

how would I determine what he resistor value should be?

Ok, to answer my own question it appears a 10K resistor will work. Also in case someone else is also learning about this, I found the following videos discussing mosfets beneficial:

While you're in learning mode, have a dig around this forum and eg stackexchange to read the views on the need for a gate resistor...

(It might be discussed in that vid, but I've not watched it yet.)

The FQP13N10 is not a logic level Mosfet. The RDS(on) characteristic implies that it needs 10 volts to drive its gate. An Arduino Uno can manage only 5 volts.

Thanks all, yes the 2nd video appears to explain all the main points; also points to a useful PDF that helps the newbie to bring it all together:

That link does not explain Vgs(th) properly.

Vgs(th) is the fet's turn on/off point.
At least 2-3 times that voltage is needed to fully switch the fet 'on'.
That makes a fet with a Vgs(th) of 2-4volt useless for 3.3volt logic and a bad choice for 5volt logic.

Logic level fets have a Vgs(th) of ~1.5-2.5volt.

Logic level MOSFETs have a Vthr typically stated as 0.5--1.0V
Non-logic level are 2--4V, anything in between you need to delve deeper into the datasheet.

Not the very wide spread in such voltages (1:2 factor) - there is a lot of device spread with gate voltages,
which is why its important to only trust the max Rds(on) figure in the datasheet - most of the
graphs are "typical" values only, ie mean values, not worst-case.