As I understand, to prevent oscillations the minimum resistance is: Rg min(non-osc) = 2×√ Lg/Cg. (Lg = parasitic inductance, not every datasheet have it) Rg in the datasheet is pretty close to it, I think. The maximum - is a compromise inbetween the desired switching losses and VDS max of the MOSFET vs. dI\dT (the voltage surge when the FET is off). Note that the driver resistance and the MOSFET internal gate resistance are also counted. For example: IRLR120N Rg min = 2×√ 7,5nH/0,44nF = 8.2 Ohm. But these minimal 8.2 Ohm = the actual resistor + the driver resistance + the connections and PCB traces resistance + the internal MOSFET resistance.
Definitely makes a difference having that resistor. I managed to find the value using a potentiometer and oscilloscope. Correct value drastically reduces "ringing" and makes amplified signal cleaner and stronger. I used rpi pico as a 7mhz square wave source, act244 as a mosfet driver and two parallel 12v powered bs170s as amplifiers. The resistor value varied between 220 and 370 ohms depending on mosfet load.
@Vojislav Great comment. Gate resistance also depends on Vds and gate lead inductance. It's also very layout specific as a result - when testing on oscilloscope, did you use PCB or breadboard?
@@subhobroto I used a breadboad, and it is not a nice setup :) just proving a concept though. I expect the value to change once on a PCB, so some more experimentation and calculation will be needed.
This is important stuff that people often learn the hard way. If you have a pretty beefy mosfet, gate resistance too small; mosfet goes bang. Gate resistance too large; mosfet goes bang. In both cases, often something else goes bang, like the gate driver and possibly as far back as killing the controller before that. Things really go bang when the mosfet fails as a short and its in a H-bridge or something because then you can short your extra beefy power supply and all the magic smoke comes out.
There is another reason. To prevent a low power driver output to be blown up. The gate capacity can draw huge peak currents to charge the gate capacity when the FET is switched on. For sure with microprocessor outputs connecting to the gate it is advisable to use a resistor.
I don't think, who connects the MOSFET gate directly to the MCU pin? the G should connect to the MOSFET driver. And also with the drive, the resistor should be used, not for huge current but for noise and efficiency too.
A resistor to ground or Vdd is also wise if you want a fail-safe design. If the input to the FET gate is floating (which it is until the mosfet or driver is turned on (and running the appropriate code section), then it easily can float to turn on, partially on or off. If using a micro, it can be several ms or 100s of ms before the output pin is driven with a known state. Also, low resistor does not increase heat, fast switching does (since the average current does) and also a slowly rising and falling gate voltage will cause the fet to be in the linear (ie resistive) region too much of the time compared to the signal it is driving, that translates to efficiency losses and heat.
> A resistor to ground or Vdd is also wise if you want a fail-safe design. If the input to the FET gate is floating (which it is until the mosfet or driver is turned on (and running the appropriate code section), then it easily can float to turn on, partially on or off Indeed - one way this manifests itself is when the gate resistor blows, and the designer did not put in the pull down. The gate's now floating and cascading failure ensues. I have no clue why designers miss this failsafe detail
It took me far too long to figure out what you mean by "Dyabadeety" 😀 Also, shouldn't there be another resistor to ground to decrease depletion time in the transistor?
I will also often add a small value of resistance as close as possible to the output pin of the driver IC as well as at the gate. That helps soak up reactance in the circuit board trace, or, lead wire between the two devices. It can be a very low value, ~2.2-4.7 Ohms. I agree, the bulk of the total resistance should be at the MOSFET gate. An individual resistance should be used on each gate, if running several FET's in parallel.
With resistor value too small, some microcontrollers fail to convey the output logic state. The software drives a '1', sets the register latch but the output latch stays at '0'. Because 'pulled down' by the gate capacitance.
Thx for sharing, however the Miller effect has the most profound effect on switching speed. What size range of resistor are you talking about 1Ω, 10Ω, 100Ω 1KΩ. It takes amperes of current to push the output fast against the Miller capacitance. A sim or lab work would have been most helpful but you did get a click outta me.
I love your short content and the summarize. I would like to see real oscilloscope images Or simulation? I would assume this could be simulated if you add the other parasitic components
Power loss is the power (V x I) lost during switching and during steady state. The power is lost due to dynamics of Vds, ID and Rds(ON). Current flowing through the Rds(ON) value of the MOSFET causes I^2R power losses. Entire power lost is in terms of heat. For saving the MOSFET device from failing due to overheating, the power needs to be dissipated (thrown away). Power dissipation is regarding how effectively and how much, the MOSFET package is able to convey out the heat generated within the junction while the Id current is flowing. The power dissipation is entirely an ability of the MOSFET package. User can effectively dissipate (to the cooling medium - Air) the entire amount of power losses if one has effective heat sink in place. Hope this helps.
Do the mosfets usually blow if the resistor is blown. My mosfets look good on my inverter but my resistor was blown. I didn't replace yet but wondering what else I should check
Please please please read the datasheet that comes with your mosfet driver before following this advice. The datasheet will nearly always tell you the prefered set up, drivers like Microchips MCP1415 specifically ask for it to share the same pad as the mosfet its driving with a diagram showing that the pins of both share the same copper fill area.
There's always a possibility that the MOSFET could short circuit and blow the computer being used to drive the device if there's no resistor, especially if the parts are chinesium. It's not uncommon for people to directly connect the gate directly to the output of a computer or microcontroller. A .25 cent optical isolator could be money well spent.
1M is too high, usually it's recommended between 10K and 100K. The gate source resistor is required when the MOSFET gate is driven by a microcontroller that can be in sleep state that will put all GPIO pins to high impedance state
@@dragoscucu3128making a circuit to drive a solenoid valve with up to 1 amp at 12 V (followed by pwm to keep the valve open with very little power), I discovered the logic level mosfet could remain high for minutes after disconnecting when messing with it, so I added a 100k resistor to ground in the circuit. I didn't know you're supposed to put a resistor between the controller and the gate as well.
@brainwater I think it depends on the driver's topology. If it is push-pull, you should turn the MOSFET off, but if it is open-collector the MOSFET gate capacitor will not discharge, then you need the resistor to GND. IMHO, it is better to put it from gate to GND instead of driver output to GND
The current flow can be huge. Because at turn on the gate capacitor is discharged, it looks like a short circuit to the gate driver. The ONLY current limit is the gate resistance.
Sir, I have a mosfet: Qg=200nC and tr=100ns, it mean's in theory I just need 2A to drive it but even I use a 4A out gate driver, it still not enough....why? the frequency is too fast?
sir can you please explain whats voltage over shoot mean in a mosfet and how to calculate the gate resistor value ,how does a high gate resistor value will increase power dissipation of a mosfet please explain
I thought the overshoot was because of stray inductance. In an inductor the current doesn't like to change suddenly so it will try to carry on pushing current, your pushing that current into a capacitor and when you do that the voltage rises. So thats why when you try to stop the current instantly it overshoots. The ringing is because the inductor will then steal that energy back from the capacitor; the reverse happens and then it flows back again, and they argue it out between them.
@@dr_jaymz Err ok, not sure what that reply has to do with my problem understanding the speech itself, if you make a video in English then it should be understandable by the majority of English speakers or it renders the content mute.
You don't need to calculate. The value depends on the driver. You can check the application circuit of any driver. you might get the resistor value there
Hi, will be videos of others topologies? For example, half bridge LLC Resonant? If what i don't know English, so if what - sorry for my literacy. I remember already leaving this question and you and you put a like on it.
When we change low current fet with high Current one we may. Decrease the value of gate. R. ...large current fet have large Gate capacitance withThe existing r the gate. Vdc raise Time is too large ...small r restore. The balance
It is simply the driver is driving a high impedance MOSFET input. A lot of ringing happens. A small resistor is needed to dampen this. We saw it with our circuit in the lab. Don't rememebr what it was, probably in the range of 22 to 56 or so Ohms.
No algorithm was given to indicate the best compromise value. In fact, I don't think there was any starting value suggested for the series gate resistance. Also a shunt gate resistance can help mitigate some performances....
I am sorry if this video disappointed you, but there is no proper calculations to calculate gate resistance, at least I didn’t find it, if you find any reference please let me know
@@FoolishEngineer Many youtubers make videos on mosfet gate resistance but do not tell about the calculation for gate resistor. I have destroyed more than 50 mosfet due to wrong resistance.
I learned that gate ringing can be a problem, though I don't believe it, but that's only because I need a second opinion, or even better, oscilloscope traces. Of course, I learned very little on how to mitigate the problem.
The best way to protect the gate is to keep the mosfets as far away from my workshop as possible.
They got us in the first half, not gona lie.
I named my cat Mosfet so ..
great content, but one thing is missing examples how to choose proper resistor in real application.
Yes
As I understand, to prevent oscillations the minimum resistance is: Rg min(non-osc) = 2×√ Lg/Cg. (Lg = parasitic inductance, not every datasheet have it)
Rg in the datasheet is pretty close to it, I think.
The maximum - is a compromise inbetween the desired switching losses and VDS max of the MOSFET vs. dI\dT (the voltage surge when the FET is off).
Note that the driver resistance and the MOSFET internal gate resistance are also counted. For example: IRLR120N Rg min = 2×√ 7,5nH/0,44nF = 8.2 Ohm.
But these minimal 8.2 Ohm = the actual resistor + the driver resistance + the connections and PCB traces resistance + the internal MOSFET resistance.
@@arthasmenethil5752 thanks a lot
Definitely makes a difference having that resistor. I managed to find the value using a potentiometer and oscilloscope. Correct value drastically reduces "ringing" and makes amplified signal cleaner and stronger. I used rpi pico as a 7mhz square wave source, act244 as a mosfet driver and two parallel 12v powered bs170s as amplifiers. The resistor value varied between 220 and 370 ohms depending on mosfet load.
@Vojislav Great comment. Gate resistance also depends on Vds and gate lead inductance. It's also very layout specific as a result - when testing on oscilloscope, did you use PCB or breadboard?
@@subhobroto I used a breadboad, and it is not a nice setup :) just proving a concept though. I expect the value to change once on a PCB, so some more experimentation and calculation will be needed.
@@batica81 Excited to hear - do you plan to get back to this project soon?
This is important stuff that people often learn the hard way. If you have a pretty beefy mosfet, gate resistance too small; mosfet goes bang. Gate resistance too large; mosfet goes bang. In both cases, often something else goes bang, like the gate driver and possibly as far back as killing the controller before that. Things really go bang when the mosfet fails as a short and its in a H-bridge or something because then you can short your extra beefy power supply and all the magic smoke comes out.
There is another reason. To prevent a low power driver output to be blown up. The gate capacity can draw huge peak currents to charge the gate capacity when the FET is switched on. For sure with microprocessor outputs connecting to the gate it is advisable to use a resistor.
That's right :)
I don't think, who connects the MOSFET gate directly to the MCU pin? the G should connect to the MOSFET driver. And also with the drive, the resistor should be used, not for huge current but for noise and efficiency too.
In short...no resistor ..heavy load and too much paracite inductance....too large r ...slow speed smeared drive waveform and failure
A resistor to ground or Vdd is also wise if you want a fail-safe design. If the input to the FET gate is floating (which it is until the mosfet or driver is turned on (and running the appropriate code section), then it easily can float to turn on, partially on or off. If using a micro, it can be several ms or 100s of ms before the output pin is driven with a known state. Also, low resistor does not increase heat, fast switching does (since the average current does) and also a slowly rising and falling gate voltage will cause the fet to be in the linear (ie resistive) region too much of the time compared to the signal it is driving, that translates to efficiency losses and heat.
> A resistor to ground or Vdd is also wise if you want a fail-safe design. If the input to the FET gate is floating (which it is until the mosfet or driver is turned on (and running the appropriate code section), then it easily can float to turn on, partially on or off
Indeed - one way this manifests itself is when the gate resistor blows, and the designer did not put in the pull down. The gate's now floating and cascading failure ensues. I have no clue why designers miss this failsafe detail
Excellent way to introduce any subject with graphical pattern.. 👍👍 This s the key of electronic. Thanks 🙏
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Try placing a ferrite bead around the gate wire to stop ringing..
It took me far too long to figure out what you mean by "Dyabadeety" 😀
Also, shouldn't there be another resistor to ground to decrease depletion time in the transistor?
You will need the resistor if there is no low side switch in the driver to discharge the input caps.
Good job on explanation, animation, and thank you for omitting the silly background music. I can understand you clearly.
Glad you enjoyed it!
I did learn something new today, will treasure it for life.
Nice job
Thank you!
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I will also often add a small value of resistance as close as possible to the output pin of the driver IC as well as at the gate. That helps soak up reactance in the circuit board trace, or, lead wire between the two devices. It can be a very low value, ~2.2-4.7 Ohms. I agree, the bulk of the total resistance should be at the MOSFET gate. An individual resistance should be used on each gate, if running several FET's in parallel.
Great video! 😁
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Would you please show us to calculate gate resistor without mosfet driver ic and also gate pull down resistor calculation.
One of the best video series about mosfet. Also very interesting.
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Good tips. I'll keep them in mind when I run into a MOSFET having those problems.
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wise men shall use the largest resistor that is acceptable for your design e.g., dissipation and switching time
With resistor value too small, some microcontrollers fail to convey the output logic state. The software drives a '1', sets the register latch but the output latch stays at '0'. Because 'pulled down' by the gate capacitance.
@Foolish_Engineer can you post video for AMBA AXI protocol
Thx for sharing, however the Miller effect has the most profound effect on switching speed. What size range of resistor are you talking about 1Ω, 10Ω, 100Ω 1KΩ. It takes amperes of current to push the output fast against the Miller capacitance.
A sim or lab work would have been most helpful but you did get a click outta me.
Hi, your explanations are clear en helpful. Thanks.
You are welcome!
Another great video on a subject I'm interested in. Clear and easily understood .
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I love your short content and the summarize. I would like to see real oscilloscope images Or simulation? I would assume this could be simulated if you add the other parasitic components
Thank you so much for watching!! I will do it in future. I need to set up a lab for it.
hi. what's the difference between 'power dissipation' and 'power loss'?
Power loss is the power (V x I) lost during switching and during steady state. The power is lost due to dynamics of Vds, ID and Rds(ON). Current flowing through the Rds(ON) value of the MOSFET causes I^2R power losses. Entire power lost is in terms of heat. For saving the MOSFET device from failing due to overheating, the power needs to be dissipated (thrown away).
Power dissipation is regarding how effectively and how much, the MOSFET package is able to convey out the heat generated within the junction while the Id current is flowing. The power dissipation is entirely an ability of the MOSFET package. User can effectively dissipate (to the cooling medium - Air) the entire amount of power losses if one has effective heat sink in place. Hope this helps.
Do the mosfets usually blow if the resistor is blown. My mosfets look good on my inverter but my resistor was blown. I didn't replace yet but wondering what else I should check
Sir please ...Make a video on how to select the gate resistance with mathematical example....
Please please please read the datasheet that comes with your mosfet driver before following this advice. The datasheet will nearly always tell you the prefered set up, drivers like Microchips MCP1415 specifically ask for it to share the same pad as the mosfet its driving with a diagram showing that the pins of both share the same copper fill area.
If I just want to turn something on... and off some minutes later. Presumably a high resistance would be fine?
There's always a possibility that the MOSFET could short circuit and blow the computer being used to drive the device if there's no resistor, especially if the parts are chinesium. It's not uncommon for people to directly connect the gate directly to the output of a computer or microcontroller. A .25 cent optical isolator could be money well spent.
What softwares is this
It's often also a good idea to put a large resistor (1M for example) from the driver output to ground to remove capacitative coupling.
1M is too high, usually it's recommended between 10K and 100K. The gate source resistor is required when the MOSFET gate is driven by a microcontroller that can be in sleep state that will put all GPIO pins to high impedance state
@@dragoscucu3128making a circuit to drive a solenoid valve with up to 1 amp at 12 V (followed by pwm to keep the valve open with very little power), I discovered the logic level mosfet could remain high for minutes after disconnecting when messing with it, so I added a 100k resistor to ground in the circuit. I didn't know you're supposed to put a resistor between the controller and the gate as well.
@brainwater I think it depends on the driver's topology. If it is push-pull, you should turn the MOSFET off, but if it is open-collector the MOSFET gate capacitor will not discharge, then you need the resistor to GND. IMHO, it is better to put it from gate to GND instead of driver output to GND
Sir why we add push and pull resistance and zener diode with MOSFET and how they works please explain..
Please don't call me sir, I'll make a video on that too... Stay tuned!!
I emailed you but u didn't reply I have queries about power electronics
There negligible current flow to gate, how res will control the dv/dt of cgs
The current flow can be huge. Because at turn on the gate capacitor is discharged, it looks like a short circuit to the gate driver. The ONLY current limit is the gate resistance.
I think you mean 'negligible DC current'? DC isn't involved
Nice Video, thumbs up!
May I ask what program do you use for production of your videos (for animations etc. not cut program)?
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Sir, I have a mosfet: Qg=200nC and tr=100ns, it mean's in theory I just need 2A to drive it but even I use a 4A out gate driver, it still not enough....why? the frequency is too fast?
Probably due to Miller effect.
which driver can i use?
What I understand from this video is if your mosfet is damaged, increase the gate resistor. Is it true?
Well, what's the best circuit solution to overcome these limititations ?
Using proper resistor is the solution
can you explain what is overshoot di dv and dt
already explained in previous videos, you can check those
Informative video. Can one drive the gate with a current source instead of resistor?
No. MOSFET is a voltage controlled device
Hi friend thanks for the informative video
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@@FoolishEngineer I did thanks
sir can you please explain whats voltage over shoot mean in a mosfet and how to calculate the gate resistor value ,how does a high gate resistor value will increase power dissipation of a mosfet please explain
You can check my other videos based on MOSFETs. You'll surely get the answers
do u have any book recomendation on learning electrical engenering.. i m guy without any degree but have some idea on how things work
you can read datasheets & application notes for practical applications. But for basics you can use 'Electronic principles by ALBERT MALVINO'
Voltage overshoot ? "Due to higher G I T T ?" Subtitles say "dl/dt" .. I have no idea what the actual words are ?
I thought the overshoot was because of stray inductance. In an inductor the current doesn't like to change suddenly so it will try to carry on pushing current, your pushing that current into a capacitor and when you do that the voltage rises. So thats why when you try to stop the current instantly it overshoots. The ringing is because the inductor will then steal that energy back from the capacitor; the reverse happens and then it flows back again, and they argue it out between them.
@@dr_jaymz Err ok, not sure what that reply has to do with my problem understanding the speech itself, if you make a video in English then it should be understandable by the majority of English speakers or it renders the content mute.
The subtitles are correct. I say it as "di" "dt". It means the rate of change of the current vs time. Usually expressed as amps per second.
@@jonshouse1 - Ages ago when I was in college, students made the same argument about teaching assistants and even professors.
Hello bro I am learning so many things deeply from you
So what is your name or should I call you Guru ji only 😃😃
Thank you so much, just call me Foolish Engineer
But how do I calculate the gate resistance value
You don't need to calculate. The value depends on the driver. You can check the application circuit of any driver. you might get the resistor value there
Oraya rezistorden ziyade BYW27 VEYA 29 koruma diyodu koyulursa daha iyi olur
Hi, will be videos of others topologies? For example, half bridge LLC Resonant? If what i don't know English, so if what - sorry for my literacy. I remember already leaving this question and you and you put a like on it.
i'll make videos on those in future
When we change low current fet with high Current one we may. Decrease the value of gate. R. ...large current fet have large Gate capacitance withThe existing r the gate. Vdc raise Time is too large ...small r restore. The balance
It is simply the driver is driving a high impedance MOSFET input. A lot of ringing happens. A small resistor is needed to dampen this. We saw it with our circuit in the lab. Don't rememebr what it was, probably in the range of 22 to 56 or so Ohms.
What a great job.
thanks for your channel .unfortunatly i am in iran and we are under sanction and cant help with mony.😢😢😢thanks.
so, now I know why my circuit will burn but not how to avoid it :( Where are the formulas for min and max R?
you get that in the driver or MOSFET datasheet or application note of particular driver ASIC
Nice info, thanks :)
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how can i determine the resistor value on gate mosfet ? can you tell me , because its important to me to know it.
thankssss
Very nice 👍
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No algorithm was given to indicate the best compromise value. In fact, I don't think there was any starting value suggested for the series gate resistance. Also a shunt gate resistance can help mitigate some performances....
Wait for gate driver transformator
thank you!
Welcome!
Nice 6-minutes explanation but you never said HOW TO CALCULATE THE RESISTOR VALUE !!
The video explains, WHY you need it. For calculations you can refer to this video. th-cam.com/video/BsAN09tsi2U/w-d-xo.html
❤❤❤
The subtitles are a bit messy. They have bad timings, and don't always match what's being said.
Not matching means he went to the extra effort to provide the subtitles rather than leaving it to TH-cam to decipher the speech.
I put a Resistor on my Gate and the chickens still get out. !!!
So Bruh? What gives? 🤪
haha!!
Please 🙏 make in hindi
North india needs Gates
😂😂
Thats it i wanted
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To keep the dogs out
Mort don't touch kings feet
Думаю автор понял за что дизлайк
You need an English class more than you need a resistor.
Give him credit for providing closed captioning should you click the CC.
This video would be much easier to follow if your accent wasn't impenetrable. As things stand, however, it's painful to listen to.
Apologies, if my accent is not pleasant to you
I have to dislike this vedio because you did not explain gate resistance calculation
And you explain only that things, which is normally known.
I am sorry if this video disappointed you, but there is no proper calculations to calculate gate resistance, at least I didn’t find it, if you find any reference please let me know
@@FoolishEngineer Many youtubers make videos on mosfet gate resistance but do not tell about the calculation for gate resistor.
I have destroyed more than 50 mosfet due to wrong resistance.
This is one of useless video ever i see !! 6 minute totally lost !!!
I learned that gate ringing can be a problem, though I don't believe it, but that's only because I need a second opinion, or even better, oscilloscope traces. Of course, I learned very little on how to mitigate the problem.
Crap.
Squilific !!!
Very nice video
Thank you so much for watching!! Please don't forget to subscribe to our channel
Nice 6-minutes explanation but you never said HOW TO CALCULATE THE RESISTOR VALUE !!
please check this video for calculation- th-cam.com/video/BsAN09tsi2U/w-d-xo.html