You mentioned the gate voltage to switch it fully on will fall between 3.3v and 5v. Wouldn't this make it unsuitable for 3.3v logic where the 3.3v would be the maximum (and the actual may be a little lower)?
At about 13:00 or so could you have illustrated that the circuit could have been switched with just your hand touching the gate and the switching signal?
I'm familar with the n-Channel Mosfet. What I don't understand, is, what is the current draw from 5v on the gate. I usually use a 15k Ω resistor on the gate and source as a pulldown resistor. So when the momentary switch is released (off), then the voltage that was on the gate, will have to go thru the resistor, and threw the source to ground right? So does that mean that according to Ohm's law, that 0.00033 Amps (0.33mA) is seen by the microcontroller like the Arduino or the switch? I = E/R, 5vdc / 15000Ω = 0.000333A, which also means that the resistor has to be rated for at least.. P = E² / R, (5vdc * 5vdc) = 25 / 15000Ω = 0.001666 Watts, or 1.66mW Is that correct, or do I have it wrong? What does the momentary switch or microcontroller see when it is supplying voltage? It has nothing to do with the Rds(on) resistance right? I'm looking, and have on hand, the IRLB3034PBF, that I've purchased from Mouser Electronics. I'm fully aware of the Vgs(th), which is the voltage in order for the n-Channel Mosfet to turn on, or conduct and allow voltage and current to flow thu the Drain and source. Could you help? Great video. (+1 : 10)
Hello Mark II, My apologies it has taken so much time to respond, I was finish research for the summer and it has been a whirlwind, but enough excuses, lets get down to your question! If I understand your question correctly, you're asking about having a resistor in series with the gate and the switch (or micro-controller) of ~15k, and having a similar pull up/pull down resistor (as is I had in the video)? This is definitely a common circuit and it is a highly conservative and good circuit. Essentially what this series resistance is doing it limiting the current flow out of the I/O pin on your micro-controller (or switch) that goes into the gate. In this video I largely excluded this current and just said "it is small/negligible" since, it is, at least for many basic applications. The reason for this current is that when you put a block of semi-conductor together, it has intrinsic properties which are manifested in what are know as parasitics. So on the gate of the transistor you actually have a parasitic capacitance, resistance, and inductance. So when you apply a voltage to the gate of the transistor you are actually charging a small capacitor, which of course requires current, however for most transistors of this nature this capacitance is not very large, but it is always good to have a series resistance to limit current from your micro-controller. By the way, I can't remember if I mentioned it or not, but it is this capacitance that requires us to have the pull up/pull down resistor, since if we did not, this capacitor would charge and never discharge (or do so at an incredible slow rate), so we need to externally discharge it in order to put the transistor in the correct state. The micro-controller or switch would 'see' a small current caused by the charging of this capacitor when it is applying the voltage. And you are most correct, the Rds(on) is a very important characteristic, but it refers to the resistance the transistor has between the drain and source (this would be analogous to having a switch, closing it, and measuring the resistance of it. It wont be much, there definitely will be a bit of resistance, a few tenths of an ohm). The Rds(on) will determine the voltage drop across the resistor when it is fully on (for a given current) and from this, it will also tell you the power loss over the transistor for a given current. I hope that I understood you correctly and was able to answer your question, if not please feel free to let me know! Glad you liked the video, and thanks for taking the time to watch it!
good video, some other was saying the difrents between IRF AND IRL MOS FET Now i can see i should get a IRL MOS FET as in logic gate for the IRL520, IRL530, IRL540, IRL630, IRL640
Hi Bobby, for your circuit for the P channel FET, shouldn't the gate voltage be referenced to the Source voltage? In other words, when you show +3.3V on the gate to turn it on, don't you really mean Vs + 3.3V? And then to turn it off, you should apply Vs to the gate. Unlike the N channel circuit where the Source is connected to ground, in the P channel circuit, neither Drain nor Source are connected directly to ground so specifying the gate voltage with respect to ground doesn't make sense. Do you agree?
tzampini thank you for your comment and for keeping me honest! So just to start, you are very much correct, the gate voltage should be referenced to the source of the transistor. For this example however, this circuit will work (and so will the idea of referencing the voltage to ground) since the load is referenced to ground and is resistive, so we are switching the gate-source voltage between Vcc and 0. However if the load had a voltage drop across it when no current is flowing (inductor, capacitor, battery, etc) then the issue of referencing to the source does become important! In this case you need to deal with a gate driver, which applies a relative voltage between the gate and source, regardless of the voltage of the load (source) relative to ground. However this was an added level of complexity I did not want to get into in this video, but in general you are correct, and this is a good thing to consider! I hope this has helped clarify things, and thank you again for the question!
Agreed, Bobby. I actually was incorrect (I think) when I said the gate should be Vs + 3.3V to turn it on. Shouldn't it be Vs - 3.3V? For example, if the source had 50V on it, I believe 46.7V on the gate would turn it on (50 - 3.3). Am I correct?
May I ask you for guidance on a project? I am a student working on an electronics project. The board is a Teensyboard, so I/O pin voltage is 3.3v. It's meant to control a 3 ampere load for 2 seconds. I'm looking for a logic level MOSFET which can operate at such a low voltage, but I can't find one. Can you point me in the right direction for a solution?
I was just responding to Mohit above who was asking about the MOSFET I used. I used a (if I remember correctly) FQP30N06L, which is a mosfet designed to operate with low gate voltage (like that directly from a microcontroller, without a gate driver). This N Type MOSFET is rated for 32A (when heat is properly dissipated!) and 60V, and has a max Vgs(t) of 2.5V (this is the voltage which the device will be "fully" switched on, it is more complex than that, but if you are just using it as an "on/off switch" that is the main thing you need to worry about) which is low enough to be driven with 3.3v, and I have used this exact part with 3.3v drive before. Good luck on your project!
Hi Bobby thanks for your time if we use the digital pins to turn on and of the transistor can we have a load to him that takes about 1A of current without burning ar Arduino or Raspberry Pi?
This is the beauty of a transistor, that the gate current is (to a certain degree of abstraction) independent of the drain source current. So you can drive a gate of a mosfet with very very little current (
Hi Bobby, it would be very nice if I could use your help in choosing the right logic level MOSFET for my application, since I know very little about them. It's about a 1S LiPo battery cutoff circuit I already assembled as in this video ruclips.net/video/0q8uq5ntjvI/видео.html which I intend to use in RC airboat for a small and powerful gear pump for active cooling of the boat's ESC. I previously tested and run the pump from the power supply's regulated 4.2V max., where the pump's motor draws approx. 2.25A at that voltage. Connected the motor in parallel with the led, but as soon as I tapped the pushbutton, I could barely hear the hiss coming out the motor. It looks like the MOSFET used (IRF9520) in that circuit couldn't push that much current, since the Gate pin wasn't saturated enough at applied voltage. My question is which logic level MOSFET with the lowest possible VDS and higher current capability should I use?
It's the simple circuit that explains it all; after a well explained structure of a MOSFET. Thanking you
Yes it did help a lot, very nicely done, thank you
Thank you so much!!your video helped me clear my concepts before an important presentation!!!
excellent explanation ! i wish you can make more videos about how to pick a MOSFET for certain project
8 years later, this explains with the pulldown resistor why I was having trouble, thought I accidentally made some sort of near-touch-sensor lol
You mentioned the gate voltage to switch it fully on will fall between 3.3v and 5v. Wouldn't this make it unsuitable for 3.3v logic where the 3.3v would be the maximum (and the actual may be a little lower)?
At about 13:00 or so could you have illustrated that the circuit could have been switched with just your hand touching the gate and the switching signal?
I'm your new subscriber.
I'm familar with the n-Channel Mosfet. What I don't understand, is, what is the current draw from 5v on the gate. I usually use a 15k Ω resistor on the gate and source as a pulldown resistor. So when the momentary switch is released (off), then the voltage that was on the gate, will have to go thru the resistor, and threw the source to ground right?
So does that mean that according to Ohm's law, that 0.00033 Amps (0.33mA) is seen by the microcontroller like the Arduino or the switch?
I = E/R, 5vdc / 15000Ω = 0.000333A, which also means that the resistor has to be rated for at least..
P = E² / R, (5vdc * 5vdc) = 25 / 15000Ω = 0.001666 Watts, or 1.66mW
Is that correct, or do I have it wrong?
What does the momentary switch or microcontroller see when it is supplying voltage? It has nothing to do with the Rds(on) resistance right?
I'm looking, and have on hand, the IRLB3034PBF, that I've purchased from Mouser Electronics. I'm fully aware of the Vgs(th), which is the voltage in order for the n-Channel Mosfet to turn on, or conduct and allow voltage and current to flow thu the Drain and source. Could you help?
Great video. (+1 : 10)
Hello Mark II, My apologies it has taken so much time to respond, I was finish research for the summer and it has been a whirlwind, but enough excuses, lets get down to your question!
If I understand your question correctly, you're asking about having a resistor in series with the gate and the switch (or micro-controller) of ~15k, and having a similar pull up/pull down resistor (as is I had in the video)? This is definitely a common circuit and it is a highly conservative and good circuit. Essentially what this series resistance is doing it limiting the current flow out of the I/O pin on your micro-controller (or switch) that goes into the gate. In this video I largely excluded this current and just said "it is small/negligible" since, it is, at least for many basic applications. The reason for this current is that when you put a block of semi-conductor together, it has intrinsic properties which are manifested in what are know as parasitics. So on the gate of the transistor you actually have a parasitic capacitance, resistance, and inductance. So when you apply a voltage to the gate of the transistor you are actually charging a small capacitor, which of course requires current, however for most transistors of this nature this capacitance is not very large, but it is always good to have a series resistance to limit current from your micro-controller.
By the way, I can't remember if I mentioned it or not, but it is this capacitance that requires us to have the pull up/pull down resistor, since if we did not, this capacitor would charge and never discharge (or do so at an incredible slow rate), so we need to externally discharge it in order to put the transistor in the correct state.
The micro-controller or switch would 'see' a small current caused by the charging of this capacitor when it is applying the voltage. And you are most correct, the Rds(on) is a very important characteristic, but it refers to the resistance the transistor has between the drain and source (this would be analogous to having a switch, closing it, and measuring the resistance of it. It wont be much, there definitely will be a bit of resistance, a few tenths of an ohm). The Rds(on) will determine the voltage drop across the resistor when it is fully on (for a given current) and from this, it will also tell you the power loss over the transistor for a given current.
I hope that I understood you correctly and was able to answer your question, if not please feel free to let me know!
Glad you liked the video, and thanks for taking the time to watch it!
good video, some other was saying the difrents between IRF AND IRL MOS FET Now i can see i should get a IRL MOS FET as in logic gate for the IRL520, IRL530, IRL540, IRL630, IRL640
Hi Bobby, for your circuit for the P channel FET, shouldn't the gate voltage be referenced to the Source voltage? In other words, when you show +3.3V on the gate to turn it on, don't you really mean Vs + 3.3V? And then to turn it off, you should apply Vs to the gate. Unlike the N channel circuit where the Source is connected to ground, in the P channel circuit, neither Drain nor Source are connected directly to ground so specifying the gate voltage with respect to ground doesn't make sense. Do you agree?
tzampini thank you for your comment and for keeping me honest! So just to start, you are very much correct, the gate voltage should be referenced to the source of the transistor. For this example however, this circuit will work (and so will the idea of referencing the voltage to ground) since the load is referenced to ground and is resistive, so we are switching the gate-source voltage between Vcc and 0. However if the load had a voltage drop across it when no current is flowing (inductor, capacitor, battery, etc) then the issue of referencing to the source does become important! In this case you need to deal with a gate driver, which applies a relative voltage between the gate and source, regardless of the voltage of the load (source) relative to ground. However this was an added level of complexity I did not want to get into in this video, but in general you are correct, and this is a good thing to consider!
I hope this has helped clarify things, and thank you again for the question!
Agreed, Bobby. I actually was incorrect (I think) when I said the gate should be Vs + 3.3V to turn it on. Shouldn't it be Vs - 3.3V? For example, if the source had 50V on it, I believe 46.7V on the gate would turn it on (50 - 3.3). Am I correct?
Great video!
May I ask you for guidance on a project?
I am a student working on an electronics project. The board is a Teensyboard, so I/O pin voltage is 3.3v. It's meant to control a 3 ampere load for 2 seconds.
I'm looking for a logic level MOSFET which can operate at such a low voltage, but I can't find one.
Can you point me in the right direction for a solution?
I was just responding to Mohit above who was asking about the MOSFET I used. I used a (if I remember correctly) FQP30N06L, which is a mosfet designed to operate with low gate voltage (like that directly from a microcontroller, without a gate driver). This N Type MOSFET is rated for 32A (when heat is properly dissipated!) and 60V, and has a max Vgs(t) of 2.5V (this is the voltage which the device will be "fully" switched on, it is more complex than that, but if you are just using it as an "on/off switch" that is the main thing you need to worry about) which is low enough to be driven with 3.3v, and I have used this exact part with 3.3v drive before.
Good luck on your project!
Hi Bobby thanks for your time if we use the digital pins to turn on and of the transistor can we have a load to him that takes about 1A of current without burning ar Arduino or Raspberry Pi?
This is the beauty of a transistor, that the gate current is (to a certain degree of abstraction) independent of the drain source current. So you can drive a gate of a mosfet with very very little current (
Great video Bobby.
Most handsome youtuber doing EE tutorial. lol
Thanks! I try to use it as a skill to distract from any technical mistakes I might make haha
Erm...ForrestKnight has his fans too...
ruclips.net/video/D1qnuKSfPOg/видео.html
binary, or bipolar?
snaprollinpitts if I said binary, that was my slip up, BJT is a bipolar junction transistor
Hi Bobby, it would be very nice if I could use your help in choosing the right logic level MOSFET for my application, since I know very little about them. It's about a 1S LiPo battery cutoff circuit I already assembled as in this video ruclips.net/video/0q8uq5ntjvI/видео.html which I intend to use in RC airboat for a small and powerful gear pump for active cooling of the boat's ESC. I previously tested and run the pump from the power supply's regulated 4.2V max., where the pump's motor draws approx. 2.25A at that voltage. Connected the motor in parallel with the led, but as soon as I tapped the pushbutton, I could barely hear the hiss coming out the motor. It looks like the MOSFET used (IRF9520) in that circuit couldn't push that much current, since the Gate pin wasn't saturated enough at applied voltage. My question is which logic level MOSFET with the lowest possible VDS and higher current capability should I use?
Total Dunce!