3 Simple MOSFET Drive Circuits

[@TheElectronicDilettante]

This is hands down the best circuit design and simulation video I’ve seen. Your ability to take us step by step through each circuit then compare the theory to practical application is amazing. I hope you continue to make videos like this. I’m still an old guy beginner in the EE and RF fields. I learned more in your 13 min video than from hours of videos trying to explain the same circuits. Thanks!!!

[@smartpowerelectronics8779]

Thank you 🙂

[@davidsussens4478]

This was absolutely brilliant! I really enjoyed your explaination on the push pull circuit, as well as the demonstration on the effects of the 220 pf capacitor on the BC557 base. Liked and Subscribed!

[@smartpowerelectronics8779]

Thanks David!!!

[@RexxSchneider]

@@smartpowerelectronics8779 It would have been interesting to see the effects of a corresponding 220pF capacitor in the first circuit. I wouldn't expect a great improvement because the mosfet input capacitance is still charging through a 1K resistor, giving a typical time constant around 2μs with an IRFZ44, but it is not an expensive addition and you would then be comparing the three circuits on a rather more equal footing.

[@kamals4905]

​@@smartpowerelectronics8779can you please explain, constant current with driving logic with transistor & MOSFET?

[@kensmith5694]

On the second two circuits there are some improvements you can make. If you split the 2K resistor to make it two 1K in series and run a capacitor to the output of your gate driver stage, you can get the switching times to be a bit faster. Adding an inductor in series with the 2K will also work but inductors cost more. The reason this works is because it causes the current in the lower 1K to not start changing until after most of the switching action is over. On your 3rd circuit a small schottky in place of the 1N4148 does two things for you. The 1N4148 has a recovery time so when the MOSFET is to be switched on, there is a brief delay before the upper NPN starts to do its thing. Also with the lower drop of a small schottky, the gate of the MOSFET is closer to ground.

[@bartios]

Isn't the delay from the 1N4148 kind of the reason it's there? I'm not an expert but I think he says something like that at 9:55

[@kensmith5694]

@@bartios The reason for the 1N4148 is so that when the lower transistor is off, the upper one gets turned on. The delay in which is on really is a matter of his wording to explain the action. He is taking the voltage on the collector of the lower transistor as rising at some speed.

[@smartpowerelectronics8779]

Thank you for your tip!

[@wojciechbajon]

@@smartpowerelectronics8779 So, we are waiting for update video with tests ;) BTW: Can you explain why you use BC transistor instead 2N?

[@tvdylan]

sounds like you know what your talking about ! the science of fast switching is quite meticulous here ! can you recommend a good fast gate driver that i can just buy already made ? : )

[@yxyk-fr]

I find this video surprisingly good, compared to all you see online ! To the point, accurate, useful... And I even learned something !

[@smartpowerelectronics8779]

Thank you yxyk-fr! Happy to hear you liked it!

[@yxyk-fr]

@@smartpowerelectronics8779 Well, now, you know what you have to do: more of these!

[@Spark-Hole]

"compare to all you" ... Dude this is the best in the world.

[@wernerviehhauser94]

I'm usually a fan of MOSFET driver ICs out of laziness, but this was really interesting

[@smartpowerelectronics8779]

Thank you, Werner! Yes, as a hobbyist an IC is easier and less prone to mistakes. These circuits are actually used in mass production in very high volumes because IC's are -believe it or not-more expensive than this bunch of smd parts...

[@clifforddicarlo9178]

Super thumbs-up! I especially like the summary chart where we can compare the three circuits side-by-side. Explain the 100 nf capacitor; what does SPICE show when the 100 nf capacitor is in/out of the circuit.

[@NortHeed]

I am an electronics designer, or at least I attempt to be smart in electronics which I have learned that I some times fail to be :-) I have to say that I realy likes your clean way of explaining things up to a level that I share your videos to other designers that I work with, where we like to share clever tricks with each other.

[@smartpowerelectronics8779]

Thank you for your kind words 🙂Good to hear that!

[@DaveEtchells]

Very interesting & useful! I didn’t know about the base drive bypass cap pulling charges out of the b-e junction for faster turnoff before, thanks!

[@oakspines7171]

Or use a diode, schottky prefered, in reverse and parallel to the resistor in place of the cap. This video is cool, throughout, and clear. Thanks.

[@davidgapp1457]

Excellent. Much appreciate the time and effort that went into making this video (and others). Concise, clear and absolutely fascinating - I have a degree in Electrical and Electronic Engineering from UCL in England, but still find this channel to be educational and insightful.

[@smartpowerelectronics8779]

Thanks David!

[@JeromeDemers]

Amazing video for only 13min! Simulation and real world example! I would love to see #4 using dedicated gate driver.

[@janrodo4978]

This is what I was looking for for a long time. Thank you so much!

[@BernhardKlein-xx8du]

I learned a lot in this video for my hobby. Thanks for your effort and posting. I personally liked the driver idea with the 555 as well. Thank you.

[@smartpowerelectronics8779]

Than you Berhard! Electronics is a great hobby, started at 10 yours old with a flipflop blink light which I wanted for my electric train, now 56 made my job out of it, but still tinker around in my free time!

[@tvdylan]

ive just bought all the components needed to make your cascode circuit !! i couldnt resist !! to infinity and beyond ! : )

[@smartpowerelectronics8779]

Yeah, that circuit is fun, even though you do not save many parts compared to the 3-transistor circuit.

[@tvdylan]

@@smartpowerelectronics8779 yeah, its a nice little challenge for me ! and i chose the cascode circuit because you said its faster than light ! : P hehe. and sharp on/ off times is what im looking for !! the parts will arrive soon. and i have also bought the gate driver chip you suggested as well. i also had a new nano board arrive today ! so i can trigger the gate driver chip soon and also use my hall sensors now ! and this way i wont be over voltage'ing the gate ! good luck to me ! ha thanks !

[@pepe6666]

thanks this is a great breakown. super useful. gone into my references and i have subscribed :) the capacitor on the gate input was a new one for me.

[@hamidsk2573]

thanks for these valuable practical electronic lessons, it was beneficial, please make more of such videos in which every circuit is validated with real test

[@yurcchello]

after experimenting with first example i found params for better delay: resistor 2.2k -> 100, parallel (to 4.7 resistor) cap 1n. on delay - 200ns, off delay - 310ns. also tried with diode after 2.2k resistor, delays almost the same

[@jensschroder8214]

Excellent! I often have a 3.3V logic level and have difficulty driving a MOSFET with it. For the third circuit I would connect a 12V Zener diode to the collector of the BC547 and cathode of the 1N4148 to GND. This would limit the voltage to around 12V. The base of the upper transistor does not go above 12V and therefore neither does the emitter. The upper transistor would also not become saturated and would therefore switch off more quickly. But it is difficult to predict the current through the Zener diode.

[@kensmith5694]

I like your solution. The zener current is best predicted with a "if the current doesn't go elsewhere" sort of thinking. The current in the pull up resistor always has to go somewhere. Also: If you use two resistors in series as the pull up and run a small capacitor from the mid point over to the emitter of the upper transistor, you can use a much higher value resistor for the upper one. You only need much base drive to the upper transistor when you are in the process of turning on the MOSFET. The small capacitor stops the base drive from decreasing right at the time you dealing with the miller effect.

[@smartpowerelectronics8779]

Good tip, I expect that will work!

[@GWAIHIRKV]

That takes me back. Used Simetrix for many years. I think it was the very best simulator. Also used the cascode driver for switching PSU designs back in the mid 80’s and was still using it for motor PWM driving in the 2000’s. The only downside is the addition voltage drop of the diode. Maybe not a problem for home electronics but it was a problem in automotive design when high current draw could cause local ground shifts.

[@L2.Lagrange]

Great topic for a video! I'll definitely mess around with a few of these drivers. I use PWM and PWM drivers in a lot of my projects

[@Jim_One-wl4ke]

Another well presented video for us electronics learning & exploring enthusiasts. Thank you very much for making such a good video and sharing your knowledge ❤

[@manulectric]

Fantastic video and discussion. Would be great to compare the discrete bipolar circuits to a dedicated MOSFET driver IC.

[@soupflood]

Or compared to a 555 in buffer mode

[@tabeschektabeschek1852]

Great Video, Thank You!

[@TerryClarkAccordioncrazy]

Good analysis of an area of circuit design which is surprisingly difficult to optimize. The Miller capacitance also works against you and becomes a big issue with high voltage switching.

[@kensmith5694]

Yes, at higher voltages that is an additional reason to not even bother with the simple resistor pull up drive. Also: "super junction" MOSFETs are much better for high voltage. Even with 1000V on the drain, the gate acts as though the drain only went up to about 200V. For those who don't know: Internally a super junction MOSFET is a lot like a normal one but some P doped silicon extends further down into the bulk of the device. This P doped silicon looks like the gate of a great big JFET wired in cascode with the MOSFET. This spreads out the voltage gradient in the silicon making 1600V parts possible and also means that the full drain voltage happens at a place further from the gate.

[@germanGGGG72]

Thanks so much, …do you have any video with P-MOS output system?

[@Oleksandr2005]

Very nice! Can you also make simillar video instruction for H-bridge drive?

[@JessieKropp]

Thank you for the clear and concise explanations. Great examples! Any recommendations for a non-inverting mosfet drive circuit?

[@smartpowerelectronics8779]

Thank you JessieKropp!...well only one more Transistor at the input, but that causes extra delay. To prevent starup flash I choose a GPIO which has no other function and set it to high first thing in your setup(), works OK for ESP8266 and AVR arduino boards.

[@Scrogan]

I’d add a weak pull-up on that GPIO pin too.

[@Юстас-п6й]

Very clear and understandable. Thank you.

[@Thesturmgever]

Конечно лайк. Очень подробно и наглядно объяснили! 👍

[@zhangzq71]

Thank you for your explaination. What is simulation software are you using?

[@moukafaslouka4796]

It looks like Simplis

[@smartpowerelectronics8779]

Yes, Simplis (Simetrix), free version up to 140 nodes. @@moukafaslouka4796

[@Madmax23419]

Great video! Thumbs up!👍

[@ahmeterdoğan-p8i]

Mosfet sürmek için harika bilgiler.

[@shovnikpaul3297]

hi, great tutorial. I apologize if this is very basic knowledge I'm missing, but why can't we directly connect the MCU's GPIO pin to the gate of the MOSFET? MOSFETs have insulated gates so they won't draw any (or perhaps very little) current, right? much less than the base of a bipolar transistor for sure; so why go through the trouble of connecting a separate NPN for example in the first circuit? Thanks.

[@HansBaier]

Great! The simple circuit with the speedup cap would be interesting!

[@smartpowerelectronics8779]

Thanks HansBaier! The speedup cap will help, but not too much because the the switch on of the MOSFET is sooo long ~2600ns, a few 100 ns does not help too much. :-)

[@KrisKasprzak]

Great vid!

[@SoVath-TV-]

Finally I found it. It's helping me a lot . Thanks you ❤🎉🎉

[@MasterIvo]

#4 gate driver IC with logic input

[@smartpowerelectronics8779]

Haha, no no, that is too easy...but for sure they will outperform these circuits 🙂

[@cmc906]

Am I right with my guess that a bipolar transistor is used instead of a small mosfet like the BS170 because the driver transistor's switch time doesn't matter much compared to the power MOSFET's switch time?

[@smartpowerelectronics8779]

Yep and because you probably already have a npn lying around 😊

[@cmc906]

@@smartpowerelectronics8779 You're right, I did! I also had the IRFZ44N, it was like magic.

[@ehsanbahrani8936]

Thanks a lot

[@MM-no4eg]

why using 1% duty cycle? What will happen if w use 50% or more? Power losses will stay same? And will that going to allow us higher frequency (more 10Khz) to operate the first circuit?

[@smartpowerelectronics8779]

I actually use 99% duty cycle, so the load is 99% of the time on in the simulation. 99% results in the maximum loss (conduction + switching loss) For the first circuit the ELECTRICAL limit is the on/off time which is in the range of 2.5µsec, so you can go to 100kHz at 50% duty cycle, 5µsec on/off. Thermally 100kHz at 50%is NOT ok because the switching losses will be too high. Hence 10kHz is the maximum.

[@MM-no4eg]

@@smartpowerelectronics8779 Hi, thank you for the explanation, very helpful. One more question, is it possible to calculate the gate driver efficiency? And also can we use MOSFET instead of BJT in the level shifter?

[@gerardzi7930]

Very useful !

[@smartpowerelectronics8779]

Thank you Gerardzi!

[@jafinch78]

Great video! Thanks for all the detail. I was looking again at electronics design to repair some modules I invested in to charge my Prius HV batteries if needed from sitting to long. Possibly use as a battery tender as well. Anyways, this got me thinking some more about control of the H bridge of the other gen 2 and gen 3 inverter converter assemblies I got from the salvage yards since I couldn't believe they were so cheap, like $20 for some of them at one time when the 50% off sale and even then about $75US then at most before half priced. The gen 2 inverter converter assembly is more modularized and seems based on the specs can more easily make a universal pure since wave inverter for whatever rectified generator inputs within spec input range. Plus have the three phase option. Seems can also be controlled to make a multifunction welder and maybe also a plasma cutter. I was thinking for the offset balance control called for Aluminum TIG welding. So not there yet and carefully paranoid to be safe before I do any hands on being the capacitors alone really small in size can pack a punch and be lethal potentially. Looking forward to using the Elements design and simulation app. Thanks for all again!

[@kostiaspongo]

Perfect explanation!!!! Thanks.

[@smartpowerelectronics8779]

Thank you kostiapongo! Glad it was helpful!

[@2Fast4Mellow]

Stupid question: What would occur if we introduce a parallel capacitor to the resistor on the PWM signal line? In the second diagram, you've shown that the capacitor diminishes the switching delay, so couldn't we enhance the first diagram by including a basic capacitor? This would also ensure that the signal logic is consistent across all three diagrams...

[@kensmith5694]

When you do this with a logic signal from a micro, the edges on the micro's pin get slower while the driven circuit gets faster.

[@smartpowerelectronics8779]

Your logic is right, The capacitor will speed up the 1st circuit too, but the switch on is sooooo slow that it would not make a big difference.

[@jozefnovak7750]

Super! Thank you very much!

[@PhG1961]

Waw, merkwaardige resultaten! Schitterende video!

[@smartpowerelectronics8779]

Dankjewel! I also did not expect that the bas-cap would have so much impact, maybe it is because I use BC547's which are not really suitable for switching applications (but every hobbyist has some lying around...) Gelukkig Nieuwjaar!

[@TonySwitzerland]

BRILLIANT ! Thank you.

[@smartpowerelectronics8779]

Thanks Tony!

[@Edmorbus]

Thanks for sharing and Happy New Year

[@smartpowerelectronics8779]

Thank you Edmorbus! Happy new year!

[@Enigma758]

Nice circuits! My only concern is that these are all negative true, so when power is first applied and the Arduino hasn't yet fully booted, there may be a momentary period where the output is on. Any thoughts on how to prevent that?

[@smartpowerelectronics8779]

You are right, so you need to check the starting conditions. You can also add a pull up resistor to the base of the transistor connected to the arduino to make sure it is high at startup.

[@mitsos_306]

Oh, sweet university memories...😂 Thank you for this great video!

[@Scrogan]

Folllow #3 with a totem-pole for even more current, up into the 10A range even. That’s better than most monolithic gate drivers, though there’s nothing stopping you from just putting a totem-pole (or ZXGD300_) after a monolithic gate driver.

[@smartpowerelectronics8779]

Thx ScroganY. You are absolutely right, the totem pole will not add much delay and can further boost the gate current. By the way BC547/557's are not the best switching bjts, I was surprised how well they stood up to the task ;-)

[@paulmeynell8866]

Just use a IRLZ44 it’s the upto 5v gate version. I run it straight off of the arduino pin and common ground. It only uses voltage to se itch on or of so no issues with current.

[@TheLordNemesis]

There is always a little current required to overcome the gate capacitance, but charging and discharging a few picofarads directly from the Arduino is usually fine, I've done it to around 30kHz without issues.

[@paulmeynell8866]

@@TheLordNemesis the video is very interesting,and your use of the simulator is excellent thank you

[@poptartmcjelly7054]

That cascode drive is smart but has big issues, especially when done in a pullup like this. 1. The output is high when no input is present, so your gate will be high until your MCU boots up. This can be fixed by connecting a pullup resistor to your gate driver input. Also that means it's inverted. 2. BJT's saturate and make high speed drive for dc-dc converters a pain. (high dead time, delay and all that) 3. The drive is non symmetrical, so you can have good turn off and bad turn on and vice versa. I've played with these gate drives a lot and push-pull is my go-to for now if i want predictable timings ;)

[@kensmith5694]

On #2 part of the fun of electronics is working out how to make that not matter in the design.

[@Graham_Langley]

Came up with that cascode cct for a commercial product back in 1981 and was rather pleased with it. Then a bit later I found it in a Philips publication that may have just predated it.

[@smartpowerelectronics8779]

Really!? Cool I used "real" cascode in CFL's at the company you just mentioned: a low voltage MOSFET switching off the emitter of a power bipolar which has its base connected to 12V with a resistor.

[@sachinkapatkar]

Please share the simulator used by you. Really nice explanation with simulation.

[@smartpowerelectronics8779]

Simetrix, free version. www.simetrix.co.uk/

[@michaelhawthorne8696]

Nice video and thanks for uploading. Just one question though. You say these circuits invert the logic signal.... but... If the input voltage is high with respects 0V then the MOSFET is off and the output voltage is high with respects to 0V too. Doesn't that mean the circuit Does not invert the signal? (In terms of Voltage)

[@RexxSchneider]

The signal driving the mosfet gate is inverted with respect to the MCU signal driving the first transistor. Of course, the mosfet will also invert the signal applied to its gate, which means its drain will go high when the input from the MCU goes high. The two stages together indeed do not invert the signal. It's hopefully obvious, though, that the drain is high when the mosfet is off, and therefore no current passes through the load.

[@LaboussoleNano]

Hello, thanks for your video can you explain the choice of the BJTs for this push pull, I am trying with BJTs that have Ic=10A and I can't get a good signal at the output. 2SCR582D3 for the NPN and 2SAR582D3 for the pnp. Thanks

[@TT-it9gg]

Thanks for the video. Instead of using mosfet driver, how about the 74F or HC series IC? Thanks!

[@saularanda7924]

In the Fast Push-Pull Circuit, are the push-pull transistors backward in their position?

[@Suavache]

Bài giảng rất tuyệt vời xin cảm ơn đã chia sẻ với khán giả

[@ruslankadylak2999]

Thank you for the great video. I have a question. Can these circuits be used to enfage/disengage an engine battery? And what MOSFET would be up for the job? Mind that when engaged, current should be able to flow in both directions: from the battery (engine is starting), to the battery (engine is charging the battery).

[@smartpowerelectronics8779]

For car 12V car battery applications I suggest a relay. The MOSFET can not handle a short circuit. If the current is limited you can use a MOSFET and circuit #1 is a good choice. If you use a relay --do not forget the flyback diode 🙂 electronics.stackexchange.com/questions/110574/how-to-choose-a-flyback-diode-for-a-relay

[@ruslankadylak2999]

@@smartpowerelectronics8779 Thank you very much for responding.

[@richardneal3841]

I like your presentation but may I suggest a 12v sorce as most, if not all, projects with the Ardunio and Rasberry PI are 9 to12 voll supplies and I want to learn how to control mosfets with those controllers. Thanks and I hope to see some examples... Rick

[@smartpowerelectronics8779]

Thank you richaredneal384! The circuit works with 12V, I used 24V because it is commonly used for LED flextapes and to show it is suitable for higher voltages 🙂

[@ChrisHalden007]

Great video. Thanks

[@alocin110]

Thank you for this very informative and practical circuit with critical analysis. I would like to know if inductive load can be triggered with high side switching. Here the MOSFET is used as Low Side Switching. Any idea? or can you kindly do a high side switching, meaning the source of MOSFET is connected to an inductive load and +24 feeds directly to the Drain of MOSFET. Thank you sho much for sharing your knowledge. I am a second year studen in Electric and Electronics Engineering.I am working on a higher frequency design, say from 45KHz to 2MHz. If there is a gate driver IC, please give some ideas of practical circuit. I searched couldn't find one except your video is very helpful and gives engineering details. Thank you so much.

[@smartpowerelectronics8779]

.I am working on a video for high side drive of N-MOS which would work for you, but it may take a few weeks before I publish. This pdf from TI may be helpful for you. /slua887a.pdf?ts=1705275507968&ref_url=https%253A%252F%252Fwww.bing.com%252F

[@ngakeo_anan]

Hello Mr T's. What is the simulator did you use to simulate in your video?

[@smartpowerelectronics8779]

www.simetrix.co.uk/ the free demo 🙂

[@tsmwebb]

Nice! The speedup cap is interesting. I wonder what the current and power on the io pin looks like.

[@smartpowerelectronics8779]

Thank you! The IO should be ok, the 220pF causes a minor extra loss of 0.5*C*V^2*freq ~ about 30µW? There is another solution called "baker Clamp" with a Schottky Diode over b-c but I did not try that.

[@kensmith5694]

@@smartpowerelectronics8779 I have done Baker Clamp circuits. They do get rid of the storage delay but they don't help on the miller. Also just a schottky means that you now have the added capacitance of the schottky in the miller effect. Baker clamps end up complicated in real life. Also if you have a TN0629-N3 in place of the lower NPN, you can save some parts.

[@59rashad]

Can the third gate driver circuit drive high side mosfet in half bridge configuration?

[@CoolDudeClem]

Do you have anything on driving a high side mosfet without resorting to having to use a p channel mosfet? I came up with one circuit, but it involves an extra 12 volts added on to the supply voltage, and having the transistors running at those high voltages.

[@kensmith5694]

If you want to drive the N channel, you are going to need those higher voltages. They do make chips that contain charge pumps for doing just that but if you want to go with common parts, there are tricks. If the switch is being driven with a duty cycle, you have a squarewave somewhere to drive a charge pump.

[@nelsonrod2]

Excuse me sir, what software are you using to simulate the designs?

[@elirosenberg6603]

Looks like Simplis from Simplis Technologies

[@smartpowerelectronics8779]

Simetrix Free demo: www.simetrix.co.uk/

[@derrickadusei7987]

great video . pls what is the name of your simulator

[@smartpowerelectronics8779]

@@derrickadusei7987 it is simetrix, simplis , the free version

[@mumbaiverve2307]

In the first circuit, the capacitor across the gate drive resistor would not make any difference ?

[@smartpowerelectronics8779]

yes, but only a very, because most of the delay is caused by the resistor charging the gate slowly. The 2 delays add up.

[@XYZ736-hdr]

Thanks, a great lesson! What program do you use to model circuits?

[@GluonToo]

It is probably the MPLAB Mindi Analog Simulator program from Microchip. A free version of this program exists, but it has limited capabilities.

[@XYZ736-hdr]

@@GluonToo Thank You

[@craigs5212]

Thanks for the video. What simulator are you using?

[@smartpowerelectronics8779]

Simetrix Free demo: www.simetrix.co.uk/

[@steveandamyalso]

@5:13 !!! Would you, please, study the current flowing through your push-pull BJTs? I am confident they will be cross-conducting! The simulation might not show the cross-conducting currents, but a real-world construction of this design will probably be heating up the push-pull BJTs a lot. There is no circuitry in the design that will guarantee the top BJT will turn off before the bottom BJT turns on and vice-versa. Furthermore, the level-shifting BJT will experience significant current spikes associated with attempting to sweep stored B-E charges of the two push-pull BJTs.

[@ChrisSmith-tc4df]

That push-pull arrangement of BJT’s is in a complementary emitter follower configuration that affords a >1V dead zone at the crossover thereby operating as a Class B amplifier as there’s no biasing circuitry to force (unnecessary) Class AB operation. I agree that a small resistance at the collector of the inverting level shifter BJT would limit the very brief switching current spike - especially with the delicate transistor chosen.

[@blackarrow8683]

This is class B. It has NO biasing therefore there will be 0 cross-conducting! Also, the 10 Ohm resistor already reduces the current spike, no need for other resistors.

[@SanjaySharma-pw6ww]

very nice video .

[@JB-fh1bb]

Can you go in to the 25kHz - 300kHz range? With the ESP32’s LED PWM circuit it’s finally possible to have truly flicker-free dimming even at low brightnesses but it’s difficult to match the other components in order to make it happen.

[@billglass5160]

Very interesting explanation. Can you please tell me what your simulator is and where I can obtain one. Thank You!

[@smartpowerelectronics8779]

simetrix, free version, max 140 nodes. www.simetrix.co.uk/ There are also real free simulators like LTSpice, but I happen to be a little familiar with this one.

[@billglass5160]

@@smartpowerelectronics8779 Thank You!

[@billglass5160]

I tried it. A great tool. Thanks again!

[@idus]

Is the drive circuit what triggers the mosfet gate or what the mosfet powers/drives?

[@smartpowerelectronics8779]

The drive circuit triggers the MOSFET Gate

[@tomapc]

Nicely explained.

[@smartpowerelectronics8779]

Thank you!

[@tomapc]

@@smartpowerelectronics8779 You are welcomed, always. I am not very good at explaining ...

[@edwardgilmour9013]

Please list what CAD software you're using?

[@smartpowerelectronics8779]

Hello Edward, I use Simetrix, free version

[@punpck]

10:00 are you sure this works in real life with real parts? I can't see where the base current of the upper NPN would flow because bottom NPN is switched off and there is no current going though a gate of a MOSFET (except charging the gate ofc) 🤔

[@ChrisSmith-tc4df]

You nailed it. Charge the gate and trail off to quiescence. There is an inverted version of this circuit where a PNP is used in this fashion to discharge the MOSFET’s gate and the inverter transistor is also PNP to drive the gate towards 12V. But that version doesn’t accomplish level shifting and would need another transistor or perhaps just a zener to spare the PIO from the nearly 12V at the upper PNP’s base.

[@smartpowerelectronics8779]

Correct, after the gate is charged there is no current! Actually I recommend circuit #2 because it is the same amount of components and a little faster.

[@ChrisSmith-tc4df]

@@smartpowerelectronics8779 The slow trailing off near the peak is why I suggested pulling up to 24V with a diode clamp to 12V. Then that transistor will remain saturated right up to when the diode clamps the base to the 12V rail.

[@ghlscitel6714]

One comment on the schematics for rather figurative reasons hinting at an engineering necessity: the emitter of the lower BC547 should be drawn with a line directly to the source of the iRFZ44. The idea behind it: The electric connection should also be as short as possible to minimize ground spike effects. Very nice solution though. Congrats!

[@Techn0man1ac]

Thanks

[@MartinRoth-sta]

Great video! But unfortunately, i was not able to find out where i can find this Elements circuit simulator. It seems, that all components are already included in the library. Does anybody know where to get. Thanks!

[@smartpowerelectronics8779]

www.simetrix.co.uk/ you can use the free demo version, it works "up to 140 nodes"

[@klausbrinck2137]

For me, the 2nd would be the most suitable, cause of the lowest on/off-delays. Other people, who don´t publicate their schematics, say, that their mosfets don´t survive for long (30-40kHz), so I thought, I´ll use an igbt instead of a mosfet. Is that a good idea, or would that mean, that your schematic isn´t suitable (in its basic principle, and not the exact values of resistors/caps/diodes themselves, I mean) ??????? The purpose is to use the pwm-signal to turn on-and-off a circuit with 60v, letting sparks spring over a gap, for ED-machining, edm... I know almost nothing about electronics, but I still can easily follow you, and I know, that those other makers also use some simple mosfet-drivers for their circuitries, but no-schematics, and low-resolution-videos don´t help figure out their driver-circuits... Thanks á priori for any answer

[@smartpowerelectronics8779]

For 60V MOSFET's should be fine. IGBT's are used for high voltage. I do not know the circuit you use, is it a transformer or an only a choke? The choke can make high voltages and destroy your MOSFET.

[@LaboussoleNano]

Is it mandatory using bjt pushpull for high switching like 200kHz?

[@smartpowerelectronics8779]

Yes, for 200kHz I would add the push-pulls

[@LaboussoleNano]

@@smartpowerelectronics8779 Thanks for replying

[@setevarmer]

Can i change the IRFZ44 for a PNP Mosfet ? making it PNP normaly open, and switch highsize ? or does the circuit need modification ?

[@smartpowerelectronics8779]

No, a PMOS will not work you will need another circuit for it. I have another video that shows how to switch an NMOS at the high side though.

[@eglintonflats]

Have you ever tried LTspice to simulate circuits?

[@ChrisSmith-tc4df]

I wonder how a 2N7002 N-channel MOSFET would fare in place of the inverting level shifter transistor in Circuit #2. Its base could be directly connected to the uC PIO pin. Might need a small series resistance in the drain to limit the peak pulse current.

[@kensmith5694]

There are better options than the 2N700x series. There are MOSFETs with quite a low VGS(th) smaller input capacitance and a lower on resistance but your thought is a sound one. A small MOSFET can save you parts in the circuit.

[@ChrisSmith-tc4df]

@@kensmith5694 The Toshiba T2N7002BX is a quite reasonably priced enhanced version, but I doubt that anyone has that lying around.

[@smartpowerelectronics8779]

Thank you for your tip! Using a small signal MOSFET for the first transistor will speed up the circuit. I would recommend a pull down resistor on the gate to make sure it is off.

[@ChrisSmith-tc4df]

@@smartpowerelectronics8779 Coupling the small MOSFET with the active pull-up transistor in your 3rd circuit might further speed things up while reducing the continuous power draw from the passive pull-up. Then decide whether complimentary emitter following buffering is necessary to get the desired slew rate.

[@ChrisSmith-tc4df]

@@smartpowerelectronics8779​​⁠ Could also a small MOSFET for the active pull-up transistor as in your 3rd circuit. A further optimization is to use a gate pull-up resistor to 24V, but then clamp that gate to 12V with a diode. As the gate can then rise to one diode forward voltage above 12V, this hides a portion of that MOSFET’s higher VGS compared to the favorable VBE of an NPN BJT. This optimization could also improve a BJT as the base current wouldn’t diminish as much as it approaches 12V.

[@schetenwapper6591]

Goede informatie!

[@bruceclothier8238]

Should you not have a resistor between the base of the BC547 and ground. Does this not turn the transistor off much faster?

[@kensmith5694]

Adding that resistor can help a bit but the speed up capacitor does more.

[@bruceclothier8238]

@@kensmith5694 Yes, of course, but I learned that you always clamp the base to ground. Leaving the base connection floating isnt good practise.

[@kensmith5694]

@@bruceclothier8238 The chip's pin pulls all the way to ground when low. The base is not floating.

[@bruceclothier8238]

@@kensmith5694 OK

[@HamzaKhwayre]

شكرا لكم

[@shrawankhatri6083]

How much voltage the mosfet will be able to deliver at 1% duty cycle at 10khz can ve able to detect that voltage or not.

[@tvdylan]

so ive got my hall sensor triggering my arduino and then arduino into a gate driver chip and then gate driver chip into a mosfet. but the coils are being turned on for wayy to long and its over heating the coils very quickly and not even getitng up to speed, very un smooth, i have a 100 ohms resistor between gate and driver output and10k across gate/source. and a 4k7 ohm reisstor between arduino out and gate driver logic input. can you suggest what im doing wrong here ??

[@RicardodeSena]

Great!!! Thanks.

[@smartpowerelectronics8779]

You're welcome! Happy New Year!

[@tvdylan]

the cascode circuit: Is the 100nf cap connected to the arduino ground ? and im slightly confused about the 12v arrow, where do i get the 12 volts ? i understand if my source voltage is 24 volts for my main load then i have 24 volts for my mosfet drain/source but im not sure what the 12 volts is ?

[@smartpowerelectronics8779]

Hi TVDylan, Yes the 100nF is connected to the Arduino ground. The 12V you need to make from the 24V or any other high voltage you have in your circuit. For example, from 24V use a 2k2 resistor and a 12V zener diode, or a 7812/LM317 voltage regulator as you wish. Most MOSFETs do not allow more than 20V on the gate, so 24V is too much.

[@tvdylan]

@@smartpowerelectronics8779 i see, thank you !! i can do that ! and..so if mysource is 24 volts, two batterries in series, can i connect inbetween the two batterries for the 12 volts ? : )

[@VitalySarychev]

А разве в схеме с двумя bc547, верхний транзистор не сгорит? Если у него большой h21e, то ему кабзда.

[@smartpowerelectronics8779]

No, the 4148 will prevent it burning out, even with unbalanced Hfe ;-)

[@mikejones-vd3fg]

Ahh so thats why you need to drive them, I only used a mosfet in a battery capacity tester that switched on and off once every few hours, I had no idea you'd need more voltage / current to switch them fast. I was going to say why cant you just drive them directly from the arduino, now i know, would have been interesting to see the performance anyhow. I coincidentaly salvaged some "logic level gate drive" mosfets today (D30NF06L) and was trying to make sense of of the difference before seeing this video.

[@PainterVierax]

Well it's a good practice to not use the signal directly from the microcontroller. The output mosfets of those little guys are not meant to drive more than a few milliamps (this is even worse with the most recent ones) and it's better to fry a cheap and easy to replace discrete component than having to deal with a fried pin (or a fried microcontroller). This also ensure your transistor is completely saturated and way outside of the linear range. And putting some darlington circuit with a small signal transistor driving a larger one allows better efficiency. Finally, BJTs are a good security measure even when driving low current since they gracefully go in safe failure instead of short circuit.

[@tvdylan]

i have another question for you master of mosfets ! now i have my mosfet, 600V CoolMOSª P7 Power Transistor IPA60R08, im not using gate driver yet, but i have my pulse motor that the mosfet is triggering a coil on and off for. the voltage for the gate/source is coming from a trigger coil. the magnets spin passed it and create a voltage etc. And the coil is getting a bit hot, is there a solution to keep my coil COOLER? the coil is significantly hot. the mosfet is a bit warm, but only a little bit, with a small heat sink. but its normally cool when i run the pulse motor at 12 volts. i would like to figure out how to keep things cool at 24 volts. because i get a much better output @ 24 volts input. what i am doing is charging battery's on the output of my motor with the energy pulses that occur when the coil turns ON and off. the transient spikes. do you have any ideas about keeping my motor coil cool in this situation ? its always been a challenge for me. would my coils stay cooler with a higher power rating of mosfet? or is this not how things work ? and do you think the ON time of the mosfet is too long and is perhaps whats causing the excess heat ? the mosfet says 4volts is the max gate voltage, but my trigger coil generates a higher voltage than that, 7 - 17 volts is this naughty to give the mosfet gate a higher voltage than the datasheet says is its maximum? should i be limiting the voltage to the recommended maximum voltage for the gate ? i plan to replace the trigger coil, with a hall sensor and gate driver soon ! thanks for your help so far ! : )

[@smartpowerelectronics8779]

I am not sure why the motor coil gets hot, reducing the on time will for sure help. A MOSFET will die very quickly if the gate-source voltage exceeds its maximum, there is some margin but not much, if you exceed, it is gone instantly. Is the trigger coil a seperate coil? Or part of the motor? Sorry I am not a motor expert ;-)

[@tvdylan]

@@smartpowerelectronics8779 i see ! my data sheet says the maximum voltage is 4volts of Vgs. but i have more than 8 volts and its still working. its a little warm, but it is pushing 1.5 amps through the drain/source. so i thought maybe thats normal. and yes ! its a sperate trigger coil. so it produces more and more volts the faster the motor spins ! so it will be good to replace the trigger coil with a lovely hall sensor / arduino / gate driver situation !! : ) i tried connecting my two motor coils in series and that makes them cooler, which is most likely because i am halfing the current draw on each coil. but then this makes motor slower, so i put the two coils bakc in parrallel and this is faster for better output. but coils are a bit warm now. but soon i can test the shorter on/off times ! i can make a video when i have succeeded with my hall sensor ! thank you !

[@lit2021]

Why complicate? IRFZ44N has a low threshold voltage of 4V at which the MOSFET will start conducting. Hence it is commonly used with microcontrollers to drive with 5V.

[@smartpowerelectronics8779]

You are right, it starts to conduct at 4V, but to fully switch it on you will need a higher gate voltage 8...12V. Also your micro controller cannot provide enough current to switch it very fast. So you can use it with 5V as a general switch but not too fast and not with high current.

[@wahyu_zx]

Can the third circuit run at a voltage of 3v - 8.4v with a battery as a voltage source

[@smartpowerelectronics8779]

No it can not, the IR2104 locks out below 8 Volt. You can search for another lower voltage IC

[@wahyu_zx]

​@@smartpowerelectronics8779What I mean is cascode drive, not ir2104