Transistor / MOSFET tutorial


In this tutorial I’m going to go over the
basics of a popular transistor and show you how you can use it to control different gadgets. What is a transistor? A transistor is a device that allows you to
use small changes in voltage to switch things on and off. They are kind of like a valve in your plumbing
system but instead of controlling the flow of water, you’re controlling the flow of electric current. To make things as simple as possible I’m only
going to talk about the easiest type of transistor to work with: The N-channel MOSFET. Basically they work like this: When the transistor is off, no current can flow.
So it’s as if one of the power wires on your gadget has been disconnected so obviously the gadget will stay off. When the transistor is on current can flow
and it’s like both of the power wires on your gadget are connected now so the gadget
will activate. So where can you get an N-channel MOSFET? Well there are many different types of N-channel
MOSFETs but they all work in pretty much the same way. You can get an N-channel FET from Radio Shack or you can scavenge them from from old computer hardware. They usually look like this. Google the part number on the transistor to
double check exactly what you’re working with. Here I have an IRFZ44. Anything else you need? Well in addition to the transistor, you’re going
to need a couple of other things. You’re going to need the gadget that you want to switch on and off.
And I’m going to use a car’s headlight as an example here. You’re going to need an external voltage supply that
your gadget would normally require. And in this case it would be the car’s twelve volt
battery. And finally you will need some sort of signal
that is either 0 volts or 5 volts. Basically a digital logic signal… and I’ll give you a few examples later. Okay so you’ve got all that? Let’s talk about
how you connect the transistor. N-channel MOSFETs always have 3 pins
called Gate, Drain, and Source. I know the names are kind of funny sounding
but you will have to memorize them. Gate Drain, and Source. Drain is the pin that current will drain into.
Source is the pin that current will flow out of. And Gate is the pin that will turn the transistor
on and off, kind of like how a water gate valve will control the flow of water. Connect up the transistor like this: The source is connected to your circuit ground. Connect the negative side of your load to the
drain of your transistor. Connect the positive side of your load to
the positive terminal of your external power supply. Now whether the transistor is off or on will
depend on whether the gate is at 0 volts or 5 volts. Here is the equivalent circuit when the gate is at 0V. The transistor stays off, so no current can
flow, so the headlights stays off. Here is the equivalent circuit when the gate
is at 5V. The transistor turns on and starts acting like a very low resistance current
path so current can flow. Current will flow from the power supply through
to your load, into the drain of the transistor, and then out from the source of your transistor into
ground. So when the transistor is on, your gadget will turn on too. Now let’s talk a little more about the signaling
voltages that are going to the gate. There are a lot of different ways to do it and
that’s why transistors are so much fun. Here is an example with a little mercury vibration
switch to turn on the transistor. When you hit the switch, the gates receives five
volts so the transistor turns on. Here’s an example with a computer’s parallel
port pins. When the parallel port outputs a 1 (which would
be five volts) The transistor turns on. And here’s another example with a 6 volt
solar cell. When the light shines on solar cell, the gate receives at least five volts, so the
transistor turns on. And there are hundreds of other ways you could
switch the transistor on so basically you can control anything with anything. Now I would like to clarify something for safety’s
sake. Over here on the gate side, you want
to keep the signaling voltages less than fifteen volts. 0-5V is fine, 0-12V is fine but if you try to signal things with a 0 to 30V signal
you will blow something up. However on the Drain side of things you have
a lot more freedom in the voltages you can use. The only limitation is what the transistor can
handle. This IRFZ44 is rated for up to 60V so it can switch 12V
loads, 50V loads, whatever I want all the way up to 60V DC. So I could switch LEDs on and off. I could
switch a string of low voltage christmas lights on or off. If you add a diode over here you can switch a motor
on and off, or switch a solenoid on and off, or switch a relay on and off. And once you have a relay being switched you can switch light bulbs on and off, you can switch toaster
ovens on and off and you can switch your refrigerator on and off. Basically if you can get a system that puts out a 0 to 5V signal, you can
attach a transistor to it and you’ll be able to switch any gadget on and off. Now remember, I just showed you the basics of
one type of transistor. There are many kinds of transistors out there with many different
operating modes. If you are interested in learning about other kinds of transistors, google “NPN transistor tutorial” “PNP transistor
tutorial” “P channel MOSFET tutorial” and “JFET tutorial.” That should be enough to give you a headache. But for now, you know how to use an N-channel
MOSFET and that is all you need to turn any DC powered device on or off.

100 thoughts on “Transistor / MOSFET tutorial

  1. This is the most neurotransmitter efficient tutorial I've seen for a long time. Straight to the point, clear and precise. Thanks!

  2. Hi! ca u show how to connect diode from drain flange to the positive line of the load using an airsoft motor? tnx. and Godbless!!

  3. Hi, I'm complete green idiotwith electronics…. I have one question, if you could help me. I know there are adjustable potentiometers, howether, I need potentiometer you can adjust not by hand, but but voltage. Hmmm, probably I'm writing tyrange things, so in short: I need to change voltage, similarly as adjustable potentiometers do, bu not by hand, byt by other potentiometers… For example: Potentiometer is set to 1 to 1 (just letting everything go as it is – (5V). But there is other potentiometer which is sending 0.5V to the "main potentiometer" and – yes, it's easy for now, but, I want to change potentiometer value to 0.5V, not by hand, but by voltage…. I'm sorry if you do not understand anything – I have no idea how electronics, even analog works. I prefer analog in this case. Instead of using my scewdriver, is it possible to set the potentiometer just by voltage sent to it? Is this possible?

  4. Yes, but can you swich the motor faster or slower, depending on the gates voltage??? Is there any type of transistor which can do it? This is all I need to be happy! 🙂

  5. Nice tutorial for beginners just what I needed to get a bit of reassurance and a confident start. Thanks and keep it up.

  6. This is to inform you that my IRFZ44 MOSFET is not working as you mentioned over here once I am giving it the +5v signal to its gate and the -5v signal to the circuit groung then it becomes on but after that when I am giving 0v to the gate then also it is not getting off it stays on until or unless I reverse the polarity of my 5v signaling source I mean -5v on the gate and +5v on the circuit ground so can you help me regarding this problem???

  7. why is the diode inside the schematic drawn backwards w.r.t. to the current? is it some electron vs. conventional current? seems hugely impractical, as normal diodes are drawn with conventional current in mind. don't see why this would be.

  8. Is it required for the source to be connected to the ground? Or could you have the mosfet between the load and positive rail?

  9. question. at minute 1.55 . Drain is input , Source is output. But why at 2.59 minture. when it has current 5v go to mosfet at gate. then the source has arrow go up to drain and light OPEN. am i understand correct. that 5v input go to gate . then the power wil go to Source and Output at drain. and ligth turn on.

    another question. why it has 12 v at drain

  10. I'm a little confused as to why the solid arrow inside the transistor points toward the +12V drain, yet the hollow arrow inside an LED points in the direction of conventional (+) current. It would have been so much easier to remember one convention for arrow notation…. Can anybody think of why they chose that more confusing notation?

  11. Is resistance of the Drain lower on the pin or the heatplate? I can't find that information in the datasheet, as the heatplate probably wasn't designed for it, but I thought maybe it had more direct connection to the die.

    Very good video.

  12. What does the diode do for a DC motor or any of the other things that require it? Shouldn’t they turn on and off without it, just like a light?

  13. I don't know if you can help me or not. I am trying to find a N-MOSFET IRF1342 but I cannot seem to find it. I am trying to make a MOSFET Trigger for a airsoft minigun that allow's it to fire continuously with out it over heating. Is there a substitution? How do I know what to look for?

    If you can help me I would greatly appreciate it.

  14. I had so much trouble getting these to work, but I made a simple motor controller. it was running below 1amp. I need to make a board which can handle 40 amp 48v …

  15. Hopefully someone can answer this: why can't a potentiometer be used with a resistor to vary the resistance of a load like an LED or fan as opposed to using a potentiometer with a mosfet? Assume the load is around 5A at 12VDC and uses a 100K pot and 3ohm resistor.

  16. Ok, but why would I use a transistor to turn something on and off if I can do it with a simple switch? What is the advantage of using a transistor? I am new to this, sorry for such a basic question.

  17. 4:05 made me to subscribe this channel.
    This is what i was searching.
    In a single video you had explained everything.

    Please provide direction of diode to be used with solenoid.

  18. many similar types of MOSFETs and their specs can be viewed at https://www.onsemi.com/PowerSolutions/parametrics/809/products

  19. Nice try but fail! Your description has an error….if you apply 5v to gate to turn it on, then remove the 5v from the gate & leave it hanging in space the device will remain on between D-S…until…you apply 0v to the gate to discharge the gate which will turn it off…

  20. That was awesome. Very easy to follow and super cool information. Thanks a million. I'm going be using transistors in an upcoming project and wanted to understand them a little better. This was great!

  21. Ground switching.

    gate=switch (0=ff, 5v=on).
    drain=conductor from load intended to be grounded.
    source=the actual connection to ground.

  22. I could use transistors to shut off power if my motor gets too hot
    i also found out how to make the int pins selection more useful

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